Potential utilisation methods for brewer’s spent grain: a review

biosorbent, biogas, circular economy, brewer’s spent grain, lignocellulose

Introduction

In 2021, the worldwide beer production was 186 GL (Statista Inc, 2023). About 20 kg of wet brewer’s spent grain (BSG) accrue for every 100 L of beer produced. This amount represents 85% (w/w) of beer-specific waste, and it is therefore the largest proportion by mass (Herfellner et al., 2006; Mussatto et al., 2006). Depending on the brewing style, gravity, and technology, this ratio can differ a little. Still, it results in a yearly production of about 7.2 Mt BSG in China, 3.9 Mt BSG in the United States, 3.4 Mt BSG in the European Union (EU), 2.8 Mt BSG in Brazil, 0.7 Mt BSG in Africa, or 37.8 Mt BSG worldwide (Barth & Meier, 2022; Maqhuzu et al., 2021; Mussatto et al., 2006; Sganzerla et al., 2021b; Stojceska & Ainsworth, 2008). BSG is a problematic waste with its high-moisture content of up to 80%(w/w) directly from production, microbial susceptibility, unsuitable pH value for aerobic stabilisation, and non-optimal C/N ratio for direct composting (Assandri et al., 2020). A brewery needs a fast distribution method for BSG to continue production. Therefore, it can be assumed that BSG is an abundant and cheap substrate with a renewable source that needs a valorisation and recycle process to counteract its low market value and evade an ecologically harmful disposal. Now BSG is mainly used as animal feed but due to its instability this is only feasible if a livestock farm is near the brewery and in need for the feed. In this review, possible valorisation applications will be presented and evaluated. For this review, those applications are divided into four main categories: biorefinery, functional materials, energy recovery, and nutritional. Under those categories, the usage of BSG to produce biogas, biosorbents, brick additives, food additives, or paper, as well as microbiological, chemical and physical degradation, fermentation, and alteration to form useful materials is discussed. The same dilemma hovers over those application as with any application involving the transformation of a food or feed source into a technical operating material, to feed a human, animal, or a technical process (Figure 1) (Andechs, 2021; Augustiner, 2022; Brauerei S. Riegele I. R. K., 2022; Lammsbräu, 2023; München, 2020).

Figure 1

Averaged resource flow from the sustainability reports of seven German breweries.

Constituents of BSG

BSG is an abundant and cheap material but with a heterogeneous content, non-degradable protein, fermentable sugar, microbial load, and high moisture of 70%–80%(w/w) out of process (Vieira et al., 2014; Westendorf & Wohlt, 2002). The pretreatment for further processing can be highly expensive or complicated, when the BSG needs to be dried or transported. Just in a few days without conservation, the self-decomposition starts (Klemes et al., 2008), and without drying, the BSG undergoes microbial and chemical degradation (Robertson et al., 2010). A relatively cheap way to dry the BSG is by pressing down to a moisture content of about 10%(w/w) (Ivanova et al., 2017). Alternatively, it has to be collected in a timely manner from the brewery for further processing. Table 1 and Figure 2 show the major components of air-dry BSG in %(w/w).

Table 1

Constituents of air-dry brewer’s spent grain in %(w/w) (Herfellner et al., 2006).

Constituent	Barley draff	Wheat draff	Fine	Medium	Coarse
Protein	20–22	20–22	31.19	25.28	23.22
Fat	16–18	15–18	n.a.	n.a.	n.a.
Starch	0.8–1.0	0.6–1.0	n.a.	n.a.	n.a.
Hemicellulose	25–30	35–40	62.40	66.20	75.30
Cellulose	18–20	14–16
Lignin	8–10	4–7
Ash	3–4	3–4	3.57	3.66	3.76
Moisture	n.a.	n.a.	7.6	6.8	6.7
	Herfellner et al. (2006)		Mussatto and Roberto (2006)

Constituent	Barley draff	Wheat draff	Fine	Medium	Coarse
Protein	20–22	20–22	31.19	25.28	23.22
Fat	16–18	15–18	n.a.	n.a.	n.a.
Starch	0.8–1.0	0.6–1.0	n.a.	n.a.	n.a.
Hemicellulose	25–30	35–40	62.40	66.20	75.30
Cellulose	18–20	14–16
Lignin	8–10	4–7
Ash	3–4	3–4	3.57	3.66	3.76
Moisture	n.a.	n.a.	7.6	6.8	6.7
	Herfellner et al. (2006)		Mussatto and Roberto (2006)

Table 1

Constituents of air-dry brewer’s spent grain in %(w/w) (Herfellner et al., 2006).

Constituent	Barley draff	Wheat draff	Fine	Medium	Coarse
Protein	20–22	20–22	31.19	25.28	23.22
Fat	16–18	15–18	n.a.	n.a.	n.a.
Starch	0.8–1.0	0.6–1.0	n.a.	n.a.	n.a.
Hemicellulose	25–30	35–40	62.40	66.20	75.30
Cellulose	18–20	14–16
Lignin	8–10	4–7
Ash	3–4	3–4	3.57	3.66	3.76
Moisture	n.a.	n.a.	7.6	6.8	6.7
	Herfellner et al. (2006)		Mussatto and Roberto (2006)

Constituent	Barley draff	Wheat draff	Fine	Medium	Coarse
Protein	20–22	20–22	31.19	25.28	23.22
Fat	16–18	15–18	n.a.	n.a.	n.a.
Starch	0.8–1.0	0.6–1.0	n.a.	n.a.	n.a.
Hemicellulose	25–30	35–40	62.40	66.20	75.30
Cellulose	18–20	14–16
Lignin	8–10	4–7
Ash	3–4	3–4	3.57	3.66	3.76
Moisture	n.a.	n.a.	7.6	6.8	6.7
	Herfellner et al. (2006)		Mussatto and Roberto (2006)

Figure 2

Constituents of BSG DW (Herfellner et al., 2006). BSG = brewer’s spent grain; DW = dry weight.

Lignocellulose

Cellulose, hemicellulose, and lignin are not stored separately in the cell wall. The cellulose is embedded into elementary fibrils enclosed by hemicellulose and lignin. This complex biological structure is called lignocellulose (LC) (Ludwig, 2014). Since every plant cell wall on earth has LC as an important main ingredient, it is the most abundant polymer on earth. Cellulose alone can occur in a crystalline or amorphous structure as well. It is a poly saccharide made of β-(1,4)-linked D-glucopyranose molecules condensed together to form a hemiacetal. Contrary to expectations because of the high content of hydroxyl functional groups, the cellulose molecule is not water soluble. The hydroxyl groups form strong hydrogen bonds with neighbouring oxygen atoms forming a chain with high-tensile strength (O’Connell et al., 2008). Hemicellulose is an amorphous polymer consisting of smaller chains with different kind of hexose and pentose sugars as well as their oxidised acid counterparts (Figure 3) (BLE, 2023). The amorphous structure makes the hemicellulose easier susceptible to chemical hydrolysis compared to crystalline cellulose (Figure 4) (Wyman et al., 2005). Lignin is manly composed of the three monolignols coniferyl alcohol, p-coumaryl alcohol, and sinapyl alcohol (Figure 5). The lignin polymer is covalently bound with hemicellulose. Those cross-links are the reason for the sturdiness and rigidity of wood and create impermeable cell wall against water and microbial attack. This high biochemical resistance of LC impedes further utilisation, and its structure and composition can be influenced by the plant itself, its biotic and abiotic stress, and even processing steps like the mashing conditions (Mussatto & Roberto, 2006; Vanholme et al., 2010).

Figure 3

Cumulated feed consumption for 2014–2022 in Germany (BLE, 2023).

Figure 4

β-(1 → 4)-linked D-glucose (ChemDraw).

Figure 5

Lignin monomers (ChemDraw) (Vanholme et al., 2010).

Biorefinery

A biorefinery valorises biological raw material with microorganisms into building-block chemicals, intermediates, polymers, energy, or a final product like a petroleum refinery. They are a key component in a circular and sustainable economy with their ability to upcycle and eliminate waste. The use of biological substrates to create chemical products reduces the dependency on fossil fuels and CO₂ emissions. Preferably biological waste should be the substrate to maintain sustainability and to not interfere with the food production (De Bhowmick et al., 2018; de Jong et al., 2012; FitzPatrick et al., 2010). In general terms, the discussed biogas plant in Biogas section is a biorefinery as well. For this review, the term biorefinery focuses on the production of chemicals and is treated separately to the energy production of a biogas plant.

The composition of BSG, comprising carbohydrate and proteinaceous fractions, complicates subsequent processing steps due to the intricate polymeric lignocellulosic matrix, which can be valorised into distinct components separate from the protein fraction. Simultaneously, this opens up opportunities for multipurpose applications. If the anaerobic digestion (AD) is intentionally left incomplete through manipulating pH, temperature, and loading rate, it is possible to inhibit the methanogenesis and produce the intermediate products: short-chained organic acids, alcohols, and other platform chemicals to produce biofuels, bioplastics, fertiliser, or polyhydroxyalkanoates from a highly acidic dark fermentation digestate (Kleerebezem et al., 2015; Ospina-Betancourth et al., 2022; Peces et al., 2021; Ramos-Suarez et al., 2021; Venkata Mohan et al., 2016). With chemical synthesis and preparation similar to the paper industry, it is possible to separate the LC and produce bioactive compounds, e.g., activated carbon, lactic acid, phenolic acid, and xylitol (Mussatto et al., 2013). Many authors showed that it is possible to use the carbohydrate-rich fraction of BSG as biomass fuel for a biorefinery to produce ascorbic, lactic, and methylidenebutanedioic acid, butane-2,3-diol, butanol, and ethanol. An enzymatic, alkaline, or acid hydrolysis, or steam explosion pretreatment is needed to break down the structural LC from BSG into fermentable and saccharifiable molecules (Akermann et al., 2020; Banjo et al., 2018; Fernández-Delgado et al., 2019; López-Linares et al., 2020; Plaza et al., 2022; Pinheiro et al., 2019; Ravindran et al., 2019; Radosavljević et al., 2020; Rojas-Chamorro et al., 2020; Wagner et al., 2022; Weiermüller et al., 2021) (Figure 6).

Figure 6

Exemplary fermentation products (ChemDraw).

For most technical applications, the high-water content and microbial susceptibility of BSG are disadvantages which are flipped in biotechnology. BSG can be used as a substrate for the production of enzymes and value-added products with many different kinds of bacteria and fungi from the Aspergillus, Fusarium, Lactobacillus, and Bifidobacterium genera without the need for drying (Xiros & Christakopoulos, 2012).

Functional materials

Biosorbents

Climate change will lead to higher temperature and prolonged periods of drought in the world and especially Germany (Boeing et al., 2022), which emphasises the need for water reprocessing treatments to reduce wastewater (WW) and gain clean water sources. Through industrial processes, water gets contaminated with various kinds of chemicals, metals, pharmaceuticals, pesticides, by-products, auxiliary, and operating materials. One important clean-up tool is the adsorption for the removal of metals where adsorbents are used to reduce the solute content from a liquid. One important aspect for the environment and human health is the removal of toxic metals from industrial WW. Synthetic adsorbents like activated carbon, zeolites, silica gel, or aluminium oxides are expensive, and their production is not sustainable. Biosorbent is the technical generic term for adsorbents made of biomaterials, with or without, chemical, mechanical, or biological modification. Biosorbents in the form of algae, bacteria, fungi, spent grains, forest biowaste, or other agricultural waste are most abundant, sustainable, and inexpensive but with less adsorption capacity and secondary components. See Table 2 for an overview of biomaterials used for biosorbents. The main active component in the adsorption process of biosorbents is LC. Since the native form of the biosorbent material is a rather inefficient adsorbent, two procedures have been established to enhance the performance: pretreatment and modification. The pretreatment process involves washing the biomaterial with an acidic or alkaline solution or subjecting it to comminution. These steps activate binding surface sites, expose additional adsorption sites, and enhance the effective surface area by reducing particle size. The modification step introduces additional binding sites through esterification with organic or mineral acids, halogenation, and polymer grafting into the material (Hokkanen et al., 2016).

Table 2

List of biosorbents.

Biomaterial	Reference
Almond, peanut, and hazelnut shell	Pehlivan et al. (2009), Taşar et al. (2014)
Apple peel	Rasheed et al. (2013)
Black gram husk	Saeed et al. (2005)
Banana and orange peel	Annadurai et al. (2003)
BSG	Low et al. (2000), Li et al. (2010), Mussatto et al. (2010)
Canola, potato, sunflower, and walnut shell	Feizi and Jalali (2015)
Citrus reticulata	Zubair et al. (2008)
Chaff	Han et al. (2006)
Coffee waste	Oliveira et al. (2008)
Corn cobs	Vaughan et al. (2001)
Forest biowaste	Kim et al. (2015)
Grape stalks	Villaescusa et al. (2004)
Green algae	Nuhoglu et al. (2002)
Lignin, isolated from black liquor	Guo et al. (2008)
Mango peel	Iqbal et al. (2009)
Orange, carrot waste	Khormaei et al. (2007), Nasernejad et al. (2005)
Peat	Ma and Tobin (2003)
Pine bark	González-Feijoo et al.(2024)
Pineapple fruit peel	Mishra et al. (2010)
Rice husk ash	Srivastava et al. (2009)
Rhodophyta	Li et al. (2011)
Rubber leaves	Ngah and Hanafiah (2009)
Saw dust	Kim et al. (2015), Rafatullah et al. (2012)
Straw, rice, and barley	Rocha et al. (2009), Thevannan et al. (2010)
Sugar beet pulp	Aksu and İşoğlu (2005), Reddad et al. (2002)
Sugarcane bagasse	Fan et al. (2020), Hoang et al. (2021)
SG Whiskey	Lu and Gibb (2008)
Tectona grandis leaves	Prasanna Kumar et al. (2006)
Thermal power plant ash	Tofan et al. (2008)
Wheat bran	Özer et al. (2004)
Xanthated nano banana peel	Pillai et al. (2013)

Biomaterial	Reference
Almond, peanut, and hazelnut shell	Pehlivan et al. (2009), Taşar et al. (2014)
Apple peel	Rasheed et al. (2013)
Black gram husk	Saeed et al. (2005)
Banana and orange peel	Annadurai et al. (2003)
BSG	Low et al. (2000), Li et al. (2010), Mussatto et al. (2010)
Canola, potato, sunflower, and walnut shell	Feizi and Jalali (2015)
Citrus reticulata	Zubair et al. (2008)
Chaff	Han et al. (2006)
Coffee waste	Oliveira et al. (2008)
Corn cobs	Vaughan et al. (2001)
Forest biowaste	Kim et al. (2015)
Grape stalks	Villaescusa et al. (2004)
Green algae	Nuhoglu et al. (2002)
Lignin, isolated from black liquor	Guo et al. (2008)
Mango peel	Iqbal et al. (2009)
Orange, carrot waste	Khormaei et al. (2007), Nasernejad et al. (2005)
Peat	Ma and Tobin (2003)
Pine bark	González-Feijoo et al.(2024)
Pineapple fruit peel	Mishra et al. (2010)
Rice husk ash	Srivastava et al. (2009)
Rhodophyta	Li et al. (2011)
Rubber leaves	Ngah and Hanafiah (2009)
Saw dust	Kim et al. (2015), Rafatullah et al. (2012)
Straw, rice, and barley	Rocha et al. (2009), Thevannan et al. (2010)
Sugar beet pulp	Aksu and İşoğlu (2005), Reddad et al. (2002)
Sugarcane bagasse	Fan et al. (2020), Hoang et al. (2021)
SG Whiskey	Lu and Gibb (2008)
Tectona grandis leaves	Prasanna Kumar et al. (2006)
Thermal power plant ash	Tofan et al. (2008)
Wheat bran	Özer et al. (2004)
Xanthated nano banana peel	Pillai et al. (2013)

Table 2

List of biosorbents.

Biomaterial	Reference
Almond, peanut, and hazelnut shell	Pehlivan et al. (2009), Taşar et al. (2014)
Apple peel	Rasheed et al. (2013)
Black gram husk	Saeed et al. (2005)
Banana and orange peel	Annadurai et al. (2003)
BSG	Low et al. (2000), Li et al. (2010), Mussatto et al. (2010)
Canola, potato, sunflower, and walnut shell	Feizi and Jalali (2015)
Citrus reticulata	Zubair et al. (2008)
Chaff	Han et al. (2006)
Coffee waste	Oliveira et al. (2008)
Corn cobs	Vaughan et al. (2001)
Forest biowaste	Kim et al. (2015)
Grape stalks	Villaescusa et al. (2004)
Green algae	Nuhoglu et al. (2002)
Lignin, isolated from black liquor	Guo et al. (2008)
Mango peel	Iqbal et al. (2009)
Orange, carrot waste	Khormaei et al. (2007), Nasernejad et al. (2005)
Peat	Ma and Tobin (2003)
Pine bark	González-Feijoo et al.(2024)
Pineapple fruit peel	Mishra et al. (2010)
Rice husk ash	Srivastava et al. (2009)
Rhodophyta	Li et al. (2011)
Rubber leaves	Ngah and Hanafiah (2009)
Saw dust	Kim et al. (2015), Rafatullah et al. (2012)
Straw, rice, and barley	Rocha et al. (2009), Thevannan et al. (2010)
Sugar beet pulp	Aksu and İşoğlu (2005), Reddad et al. (2002)
Sugarcane bagasse	Fan et al. (2020), Hoang et al. (2021)
SG Whiskey	Lu and Gibb (2008)
Tectona grandis leaves	Prasanna Kumar et al. (2006)
Thermal power plant ash	Tofan et al. (2008)
Wheat bran	Özer et al. (2004)
Xanthated nano banana peel	Pillai et al. (2013)

Biomaterial	Reference
Almond, peanut, and hazelnut shell	Pehlivan et al. (2009), Taşar et al. (2014)
Apple peel	Rasheed et al. (2013)
Black gram husk	Saeed et al. (2005)
Banana and orange peel	Annadurai et al. (2003)
BSG	Low et al. (2000), Li et al. (2010), Mussatto et al. (2010)
Canola, potato, sunflower, and walnut shell	Feizi and Jalali (2015)
Citrus reticulata	Zubair et al. (2008)
Chaff	Han et al. (2006)
Coffee waste	Oliveira et al. (2008)
Corn cobs	Vaughan et al. (2001)
Forest biowaste	Kim et al. (2015)
Grape stalks	Villaescusa et al. (2004)
Green algae	Nuhoglu et al. (2002)
Lignin, isolated from black liquor	Guo et al. (2008)
Mango peel	Iqbal et al. (2009)
Orange, carrot waste	Khormaei et al. (2007), Nasernejad et al. (2005)
Peat	Ma and Tobin (2003)
Pine bark	González-Feijoo et al.(2024)
Pineapple fruit peel	Mishra et al. (2010)
Rice husk ash	Srivastava et al. (2009)
Rhodophyta	Li et al. (2011)
Rubber leaves	Ngah and Hanafiah (2009)
Saw dust	Kim et al. (2015), Rafatullah et al. (2012)
Straw, rice, and barley	Rocha et al. (2009), Thevannan et al. (2010)
Sugar beet pulp	Aksu and İşoğlu (2005), Reddad et al. (2002)
Sugarcane bagasse	Fan et al. (2020), Hoang et al. (2021)
SG Whiskey	Lu and Gibb (2008)
Tectona grandis leaves	Prasanna Kumar et al. (2006)
Thermal power plant ash	Tofan et al. (2008)
Wheat bran	Özer et al. (2004)
Xanthated nano banana peel	Pillai et al. (2013)

BSG with its high LC content can therefore be used as a biosorbent, which is already proven by some researchers (Carrasco et al., 2022; Li et al., 2012; Wierzba & Kłos, 2019). While the adsorption capacity cannot keep up with the technical adsorption materials, the cost can compensate for it. Technical adsorption materials are expensive materials compared to BSG. Publicly available prices for common technical adsorption materials from Merck are as follows: aluminium oxide 90 active basic for 82€ kg⁻¹, silica gel for 107€ kg⁻¹, < 20 μm zeolite powder for 622€ kg⁻¹, and 4–12 mesh particle size activated carbon for 246€ kg⁻¹ (Merck, 2024). BSG right out of the brewing process is sold for 0.02–0.05€ kg⁻¹. The price varies greatly depending on whether the BSG is collected directly from the farmer or distributed via a specialised company (phone survey among German breweries). Prices are no constants but negotiable values so those numbers will change depending on the trading partners. Nevertheless, it will not be possible to close this gap and a valorisation factor of at least 1,000 between a technical adsorbents and BSG can be assumed.

Brick additive, packaging materials, and hydrothermal carbonisation

To increase the porosity in bricks and therefore improve their insulation properties, BSG or other high fibre products can be added to the brick firing as aggregates. The theoretical demand for such an aggregate would equal the total produced amount of BSG in Germany in 2005 (Russ et al., 2005; Weber, 2009). Other applications are the use of single constituents of BSG after a chemical or physical pretreatments and the separation for the productions of biomaterials (Qazanfarzadeh et al., 2023). Through artificial coalification under high pressure by direct steam injection, biochar can be made from BSG like from every other hydrocarbon biomass (Poerschmann et al., 2014). This process is called hydrothermal carbonisation (HTC). The biomass is injected with saturated steam at around 200 °C with pressures above 2 MPa for several hours. Through dehydration, decarboxylation, and polymerisation, the BSG biomass is converted into solid biochar with the associated properties (Funke & Ziegler, 2010; Kirtania, 2018). While the biomass of BSG itself is carbon neutral source, the HTC process is energy-intensive with corresponding emissions counteracting the sustainable and inexpensive approach.

The applications as brick additive, biomaterial, or biochar have in common that they are not exclusive for BSG and substitution with any other LC biomass is possible. The water content of BSG decreases the overall efficiency because of the energy demand of thermal drying and the production of problematic WW with press drying or chemical modification and separation of the different fractions of BSG for packaging. The protein fraction of BSG is too valuable as a nutritional source to be used as packaging material. Substitute cellulose products like saw dust are more suitable and easily available.

Energy recovery

Biogas

A brewery requires energy inputs, especially heat and electricity, for brewing, pasteurisation, fermentation, and refrigerated conditions. The supply of the required quantities of electricity and heat is responsible for greenhouse gas emissions and highly influence the operating cost. The production and consumption of self-produced biogas can reduce both and positively influence the environmentally friendly image of a brewery. Among several waste management technologies, AD is a promising method for converting wet wastes and solid residues into biogas for energy recovery on an industrial scale (Sganzerla et al., 2021a).

Biogas can be classified as any combustible gas produced by the fermentation of biomass. The main combustible contributors are methane (CH₄) and hydrogen (H₂). Beside that the biogas contains hydrogen sulphide (H₂S), carbon dioxide (CO₂), and ammonia (NH₃) as by-products. The needed purification adds cost to the gasification, as well as the possibility of selling surplus CH₄ into the natural gas grid. After a clean-up to food product specifications, CO₂ emerges as a valuable resource for the carbonisation in the food industry or the brewery itself. Only CH₄ and H₂ can be used as a fuel for the generation of thermal energy in heating and steam boilers. Hydrogen fuel cells or combined heat and power plants can be utilised to cogenerate usable heat and electricity to increase the efficiency (Kaparaju & Rintala, 2013). The fermentation residue contains mineralised nitrogen, phosphate, and potassium which can be utilised as fertiliser (Buller et al., 2021). The operating and clean-up costs of a biogas plant decrease exponential with its capacity in m³ h⁻¹. About 2–4 c kWh⁻¹ can be reached at over 200 Nm³ h⁻¹ biogas production depending on the kind of clean-up method: membrane, polyethylene glycol, pressure swing adsorption, amine, or pressure washing (Daniel-Gromke, 2019). It needs to exceed a threshold to break even with the purchasing prices of natural gas for a brewery which will be unattainable at current market prices for small breweries (about 100,000 hL year⁻¹, see Equation 1) which are the majority in Europe. It is possible to ferment BSG alone or co-ferment it with WW, sewage sludge, wine vinasse, rice straw, and municipal waste (Atelge et al., 2020; Kim et al., 2013; Tena et al., 2020; Tyagi et al., 2014). Mixing different kinds of waste helps to adjust the C/N ratio, maintaining the optimal pH value and sustaining an optimal microbial community (Perez-Esteban et al., 2022). This enables the pooling of waste from several smaller breweries, food industries, and municipal waste management, which cannot maintain an own biogas plant and would profit indirectly in form of electricity, thermal energy, or income.

Rough estimate of the biogas production potential

$$ \begin{align} 4\ \frac{\mathrm{kg}\ \mathrm{BSG}\ \mathrm{DW}}{\mathrm{h}\mathrm{L}\ \mathrm{Beer}}\times&\ \mathrm{100,000}\frac{\mathrm{h}\mathrm{L}\ \mathrm{Beer}}{\mathrm{year}} \nonumber \\ \times &\ 0.133\frac{{\mathrm{m}}_{\mathrm{N}}^3}{\mathrm{kg}\ \mathrm{BSG}\ \mathrm{DW}}:8760\frac{\mathrm{h}}{\mathrm{year}}=6\frac{{\mathrm{m}}_{\mathrm{N}}^3}{\mathrm{h}} \end{align} $$

(1)

Ruminal nitrogen balance (RNB) (Riemeier, 2004).

$$ \begin{equation} \mathrm{RNB}=\frac{\mathrm{XP}-\mathrm{nXP}}{6.25} \end{equation} $$

(2)

The fermentation process consists of four main stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis in which the complex organic matrix is decomposed into small molecules like H₂, CH₄, H₂S, CO₂, H₂O, and NH₃. Depending on the grade of incrustation and chemical nature of the plants organic matter, the decomposition will be retarded (Li et al., 2013; Lübken et al., 2010). The acid detergent lignin (ADL) and hemicellulose content of a plant can serve as predictors of biogas yield. Biogas yield exhibits a significant negative correlation with ADL content and a positive correlation with hemicellulose content. (Dandikas et al., 2014). LC is the most abundant renewable resource in the world, widely available and cheap, but its hydrolysis is usually incomplete due to its complex structure. The scientific literature describes several challenges in energy production by AD, especially incomplete conversion of recalcitrant high ADL materials such as BSG, which can be enhanced by chemical, mechanical, biological, or combined pretreatments (Buller et al., 2022; Dandikas et al., 2014; Hendriks & Zeeman, 2009; Kamusoko et al., 2019; Passos et al., 2015). In contrast to chemical processes, ultrasound does not produce waste but increases energy consumption, while biological pretreatment processes require more time. From a technical-economic point of view, the feasibility of a pretreatment method must be assessed on a case-by-case basis.

In a single-phase biogas reactor, all four stages of fermentation occur at the same time while bacteria and archaea metabolic pathways are intertwined with the substrates and products of the others (Angelidaki et al., 2009; Mittweg et al., 2012). Although the groups of microorganisms have a different optimal growth range, the microbiological steps are highly interdependent due to syntrophic and synergic effects (Bauer et al., 2008). High proteinaceous waste like BSG contains large amounts of nitrogen, which can poison the fermentation and generates high amounts of inorganic ammonia nitrogen (NH₃, NH₄⁺) (Sganzerla et al., 2022b).

In an anaerobic co-fermentation reactor, hydrogen yields of 9.55 ml H₂ g⁻¹ total volatile solids (TVS) can be reached with 17.5%(w/w) BSG in the substrate. With only WW, the yield is higher at 25.11 ml H₂ g⁻¹ TVS which is explained with an ammonia inhibition from the high nitrogen content in BSG. As fermentation by-products, short-chain organic acids are formed and acidify the sludge (Cieciura-Włoch et al., 2021). While acetic and butyric acid enhance the H₂ production, propionic acid can be detrimental (Lovato et al., 2018). As seen, the fermentation can be modulated to produce desired results in CH₄ and H₂ yields. What remains as a problem is the exponential scaling with size which makes a biogas plant unattainable for small breweries and the highly reluctant proteinaceous LC matrix of BSG with its incomplete hydrolysis and ammonia inhibition.

Combustion

BSG has 70%–80%(w/w) water out of production which needs to be reduced to at least 60%(w/w) for direct combustion. If an organic substance is burnt, all the containing liquid water is turned into water vapour. The energy quantity required for this is the enthalpy of vaporisation ΔH_vap and if not recovered reduces the heating value of the fuel. The reduction of the water content prior to combustion of the fuel is therefore a necessity but requires energy as well. The two main methods to reduce the water content are pressing and thermal drying. While pressing requires 0.019–0.100 kWh kg⁻¹ dry weight (DW), there is a practical limit of about 40%(w/w) DW and the presswater emerges as a waste product with high chemical oxygen demand (COD). Thermal drying of BSG is possible up to 91%(w/w) DW, and no waste is generated but it needs at least 0.661 kWh kg⁻¹ water as thermal energy (enthalpy of vaporisation for water) which makes it unfeasible. Pressed to 40%(w/w) DW BSG becomes a fuel comparable to firewood with a heating value of 4.9 to 5.3 kWh kg⁻¹ DW (Gil-Castell et al., 2022) but with problematic flue gas that contains carbon monoxide (CO), nitrogen oxides (NO_x), and sulphur oxides (SO_x) through the high nitrogen and sulphur content and incomplete combustion which needs further cleaning (Weger et al., 2017). Without clean-up, nitrogen and sulphur oxides react to the highly corrosive nitric and sulphuric acid with water vapour. The classification of BSG as fuel depends on the local legislation which induces dedicated emission standards. For most countries, the combustion of BSG exceeds the legal threshold for dust, CO, NO_x, and SO_x (BFJ, 2013). A comprehensive and therefore expensive flue gas purification would be mandatory. Calculating with 4 kg BSG DW hL⁻¹, it results in 22.36 kWh hL⁻¹ beer as heat energy before deducting the energy needed to reduce the water content.

Nutritional

Feed

The high fibre and protein content of BSG makes it an excellent source of feed, but the microbial load, pH value, and fermentable sugar contributes to a susceptibility to spoilage and degradation. If BSG is used as a feed without further processing, livestock in the proximity to the brewery is needed to distribute it in a timely manner.

Before the distribution of BSG as animal feed is allowed, various limits for contaminants must be fulfilled. Legal basis for the assessment of marketability of feed in Germany are the Food and Feed Code and the Feed regulation. In the EU, there are the regulations 68/2013, 178/2022, 215/186, 396/2005, 574/2011, 767/2009, 1275/2013, and 2019/1869, as well as the directive 2002/32/EG. The directive establishes the limits for undesirable substances in feed like toxic metals (As, Pb, Hg, Cd), mycotoxins, pesticides, PCB, polycyclic aromatic hydrocarbon, endosulfan, and dioxins, while the regulations updated the respective rejection limits. The regulation 178/2022 states that feed shall not have an adverse effect on human or animal health, which induces the control of Salmonella spec.

A European brewery which wants to sell their BSG as feed needs to be authorised as a feed manufacturer according to the regulation (EC) No 183/2005 of the European Parliament for feed hygiene and registered into a national data base.

Direct feeding

Analysed data for Germany from 2014 to 2022 showed that the mean feed source for livestock can be divided into three major groups: primary feeds, plant-based feed (PBF) by-products, and non-marketable feed. While the latter makes over half of all the feed. BSG must compete with other high-protein plant-based feed from food production and plays only a minor behind press cake from soybean oil production and dried flakes from sugar beets (BLE, 2023). Seasonal fluctuations in beer production and PBF are both going up in the summer which makes it harder for BSG to compete and reduces its market value due to oversupply.

Modern cows with milk yield over 30 kg day⁻¹ need a specialised diet with a balanced energy and protein ratio. The energy is expressed as net energy content for lactation, while the protein is divided into crude protein (XP), usable crude protein (nXP), and non-degradable feed protein (UPD). The latter effects the RNB. By varying the proportion of XP, nXP, and UPD in the feed, the supply of amino acids going into the small intestine is controlled. Deviations from the optimum supply have a detrimental effect on the milk yield (Alert, 2013).

BSG contains on average 35% UPD (Kirchgessner, 2011), which limits its applicability as feed. The recommended maximum dosage varies depending on the source between 7.5% and 20 kg BSG per day and cow (Jeroch et al., 2008; LFL, 2008). Calculating with 12 million cows in Germany (BMEL, 2020), these results in a potential maximal demand of 33–88 Mt BSG feed per year which exceeds the actual amount of BSG produced in Germany (80 million hL times 20 kg BSG hL⁻¹ equals 1.6 Mt BSG) by a factor of 20 to 55. This calculation will be different for every country because of the large deviation of beer consumption, cattle husbandry, and their geographical proximity. What stays is that the beer consumption would need to exceed the consumption of dairy products and cattle meat by far to get a surplus of usable BSG. The problem rather occurs through seasonal fluctuations which influence the need for BSG as feed antagonistic to the beer production. There is a surplus of green fodder in the summer, while the beer production and therefore the BSG production is at its peak, which results in less demand for BSG and could release usable BSG for valorisation processes.

Ensiling

If no direct distribution of the BSG as feed is possible, it needs a way to increase the shelf life and still obtain the usability as a feed source. This is possible through ensiling. Since the brewing process is specialised on extracting fermentable carbohydrates from the malt, the BSG is therefore low on it with about 10–12 g kg⁻¹ which is lower than the recommended quantity of 30 g kg⁻¹ fermentable carbohydrates for other PBF to ensure successful ensiling. Contrary to the resulting expectation of a failing ensiling, it is nevertheless successful. The author Weber (2009) explained it through two main mechanisms: the high amount of lactic acid bacteria and the low buffer capacity of the BSG. Lactic acid bacteria are part of the natural microflora of malt and increased through the malting process. After a heat-induced log reduction in the late mashing process, the amount of colony-forming units of lactic acid bacteria rises again after the cool down of the BSG, consisting of hetero- and homofermentative lactic acid bacteria which decompose the reluctant LC into fermentable sugars and, through the production of lactic acid (LA), reduce the pH value of the silage. The low buffer capacity with about 32 g LA kg⁻¹ BSG DW to reduce the pH value to 4.0 ensures a rapid drop in the pH value and prevents the ensiling process from turning into a rotting process. The low buffer capacity is a result of a low ammonia content, since the soluble nitrogen substrates are already extracted during the mashing process and a well-balanced acidic and alkaline salts content in the BSG (Table 4) (Weber, 2009).

BSG can either be ensiled after pressing or directly through a film tube silage in hermetic plastic bags. While the pressing increases the DW to 20%–30%(w/w), the feed value, and the ensilability, it produces a high COD presswater which needs further processing or disposal (Milew et al., 2022). The film tube silage enables a direct hermetic packaging directly from the brewery with minimal risk of contamination, no additional silo requirement on the farmer's premises, and less edge and surface losses (Steinhöfel, 2004; Weber, 2009). The hermetic sealed tubes conceal the silage effluent which is negative proportional to the DW of the silage substrate, so BSG contains a lot of it which needs to be removed after ensiling.

Food

BSG with the high LC content is rich in dietary fibres like arabinoxylan and β-glucan, protein, minerals, and polyphenols. Polyphenols like the hydroxycinnamic acid and ferulic acid function as a potent antioxidant while their content is influenced by the malting technique. Birsan et al. (2019) measured fourfold higher values in light malt than in dark malt. The high nitrogen content of BSG in the form of proteins and amino acids at 22%(w/w) accounts for a significant portion of BSG (Herfellner et al., 2006). The main protein fractions are albumin, globulin, glutelin, and hordein, which are associated with anti-inflammatory and antioxidative health benefits (Wen et al., 2019), and are high on the essential amino acid lysine in contrast to other cereals (Lynch et al., 2016). Calcium, magnesium, iron, and phosphorus are present in BSG in nutritionally relevant amounts as shown from Mussatto et al. and own measurements (Table 4, Mussatto et al., 2006). A food product enriched with BSG will gain all the health benefits associated with fibres, polyphenols, minerals, and essential amino acids. BSG can therefore be considered as an important ingredient for functional foods (Table 3) (Fărcaş, 2014; Lynch et al., 2016; Verni et al., 2020).

Table 3

Examples of foods enhanced with brewer’s spent grain.

Food product	Reference
Cereal bars	Stelick et al. (2021)
Cheese	Abd El-Moneim et al. (2018)
Chips	Garrett et al. (2021)
Cookies/biscuits	Fărcaș et al. (2021), Guo et al. (2014)
Edible mushrooms	Weber (2009)
Low alcohol beer	Canonico et al. (2023)
Muffins	Combest et al. (2020)
Pasta	Schettino et al. (2021), Nocente et al. (2019)
Yoghurt	Naibaho et al. (2022)

Food product	Reference
Cereal bars	Stelick et al. (2021)
Cheese	Abd El-Moneim et al. (2018)
Chips	Garrett et al. (2021)
Cookies/biscuits	Fărcaș et al. (2021), Guo et al. (2014)
Edible mushrooms	Weber (2009)
Low alcohol beer	Canonico et al. (2023)
Muffins	Combest et al. (2020)
Pasta	Schettino et al. (2021), Nocente et al. (2019)
Yoghurt	Naibaho et al. (2022)

Table 3

Examples of foods enhanced with brewer’s spent grain.

Food product	Reference
Cereal bars	Stelick et al. (2021)
Cheese	Abd El-Moneim et al. (2018)
Chips	Garrett et al. (2021)
Cookies/biscuits	Fărcaș et al. (2021), Guo et al. (2014)
Edible mushrooms	Weber (2009)
Low alcohol beer	Canonico et al. (2023)
Muffins	Combest et al. (2020)
Pasta	Schettino et al. (2021), Nocente et al. (2019)
Yoghurt	Naibaho et al. (2022)

Food product	Reference
Cereal bars	Stelick et al. (2021)
Cheese	Abd El-Moneim et al. (2018)
Chips	Garrett et al. (2021)
Cookies/biscuits	Fărcaș et al. (2021), Guo et al. (2014)
Edible mushrooms	Weber (2009)
Low alcohol beer	Canonico et al. (2023)
Muffins	Combest et al. (2020)
Pasta	Schettino et al. (2021), Nocente et al. (2019)
Yoghurt	Naibaho et al. (2022)

Table 4

Metal content of brewer’s spent grain dry weight (own measurements).

	mg kg⁻¹		mg kg⁻¹		mg kg⁻¹
Phosphorus	3,272	Molybdenum	0.2	Cadmium	<0.04
Potassium	15.6	Silicon	241	Tin	<0.10
Nitrogen	41,600	Strontium	0.14	Nickel	<0.04
Calcium	39.5	Boron	0.44	Chromium	<0.04
Magnesium	29.5	Arsenic	<0.04	Manganese	0.9
Sodium	1.3	Antimony	<0.04	Zink	2.9
Iron	215	Selenium	<0.04	Barium	0.7
Copper	6.4	Lead	<0.04	Cobalt	<0.2

	mg kg⁻¹		mg kg⁻¹		mg kg⁻¹
Phosphorus	3,272	Molybdenum	0.2	Cadmium	<0.04
Potassium	15.6	Silicon	241	Tin	<0.10
Nitrogen	41,600	Strontium	0.14	Nickel	<0.04
Calcium	39.5	Boron	0.44	Chromium	<0.04
Magnesium	29.5	Arsenic	<0.04	Manganese	0.9
Sodium	1.3	Antimony	<0.04	Zink	2.9
Iron	215	Selenium	<0.04	Barium	0.7
Copper	6.4	Lead	<0.04	Cobalt	<0.2

Table 4

Metal content of brewer’s spent grain dry weight (own measurements).

	mg kg⁻¹		mg kg⁻¹		mg kg⁻¹
Phosphorus	3,272	Molybdenum	0.2	Cadmium	<0.04
Potassium	15.6	Silicon	241	Tin	<0.10
Nitrogen	41,600	Strontium	0.14	Nickel	<0.04
Calcium	39.5	Boron	0.44	Chromium	<0.04
Magnesium	29.5	Arsenic	<0.04	Manganese	0.9
Sodium	1.3	Antimony	<0.04	Zink	2.9
Iron	215	Selenium	<0.04	Barium	0.7
Copper	6.4	Lead	<0.04	Cobalt	<0.2

	mg kg⁻¹		mg kg⁻¹		mg kg⁻¹
Phosphorus	3,272	Molybdenum	0.2	Cadmium	<0.04
Potassium	15.6	Silicon	241	Tin	<0.10
Nitrogen	41,600	Strontium	0.14	Nickel	<0.04
Calcium	39.5	Boron	0.44	Chromium	<0.04
Magnesium	29.5	Arsenic	<0.04	Manganese	0.9
Sodium	1.3	Antimony	<0.04	Zink	2.9
Iron	215	Selenium	<0.04	Barium	0.7
Copper	6.4	Lead	<0.04	Cobalt	<0.2

Up to 10%(w/w) of wheat flour can be replaced by BSG without adversely alternating the physical properties of the final cereal product like pasta and bread and still profiting from the health benefits of BSG (Gupta et al., 2010). Those 10%(w/w) BSG will increase the protein content of the product by 50%(w/w), essential amino acids by 10%(w/w), and doubling the amount of fibre (Fărcaş, 2014). This fibre is the main component of BSG with a content of 36–52%(w/w) LC and responsible for the change in texture of BSG-enriched food products which tends to harden or become more viscous (Naibaho et al., 2022). The maximum amount of BSG enrichment can vary from 6%(w/w) in yoghurt to 50%(w/w) in cheese (Abd El-Moneim et al., 2018) while the added health beneficial ingredients correlate linear with it.

While lautering, the malt is not completely exhausted from fermentable sugars and free amino acids. Depending on the lautering process and the amount of rinse out, there could be enough fermentable material to produce low alcoholic beverages. The authors (Canonico et al., 2023) produced such a recycled wort containing glucose 0.67 g L⁻¹, sucrose 1.7 g L⁻¹, and maltose 9.7 g L⁻¹, and 47.11 mg N L⁻¹. Other authors used the fibre-rich BSG for yoghurt fermentation. The LC addition of BSG accelerates the fermentation process due to increased arabinoxylans, β-glucans, and prebiotic LC. After fermentation, the yoghurt showed increased viscosity and shear stress compared to a non-enriched yoghurt (Naibaho et al., 2022). While the susceptibility for microbial decomposition of BSG is a disadvantage for many technical and distributional purposes, the moisture, protein, and carbohydrate content make it a good cultivation medium for microorganisms, either for the production of edible mushrooms (Weber, 2009) or the biotechnology approaches to produce enzymes (Xiros & Christakopoulos, 2012).

Barley can be contaminated with mycotoxins from the Fusarium and Aspergillus genus, like deoxynivalenol, nivalenol, zearalenone, T-2, HT-2, fumonisins, aflatoxins, and ochratoxin A, which can be found throughout the entire production process from harvesting, over the malting and mashing process (Katharina Habler, 2016). Mycotoxins that are not extracted during the mashing process will be present in the BSG and every further step of the production chain (Saba et al., 2019). If BSG is to be sold as food, the legal thresholds for mycotoxins and other contaminants must be complied with.

Composting

It is possible to compost BSG, press cake, or fermentation digestate from a biogas plant directly if they are mixed with the right additives (Assandri et al., 2020; Rehl and Müller, 2011). While composting, the organic matter of BSG is broken down by microorganisms under aerobic and exothermic conditions. Through oxidative chemical and microbiological decomposition of the organic polymer matrix, humic substances originate from the BSG. After the final humification and mineralisation process, the original weight is reduced, organic pollutants are removed, and nutrients are enriched. Because of the low C/N ratio, high-moisture content and pH value, BSG cannot be composted directly and needs a carbon-rich source (e.g., straw, wood chips, sawdust) as well as manure to start the process (Assandri et al., 2020). Other authors described the direct usage of BSG mixed with mineral fertiliser (Assandri et al., 2020), composted material (Aboukila et al., 2018), with cow manure, or with worms to produce vermicompost (Saba et al., 2019). Own measurements with ICP-OES after a microwave-assisted nitric acid digestion of BSG obtained from the Bayerische Staatsbrauerei Weihenstephan in 2022 showed that it is rich in two of the three main components of mineral fertiliser nitrogen and phosphorus but not potassium. Correctly composted BSG with added carbon and some minerals could replace more expensive and not sustainable chemical fertiliser (Chrysargyris et al., 2013; Papamichalaki et al., 2014). Composting is an aerobic state and the fermentation gases are not used which lead to odour nuisance. The obtained fertiliser would need to be compared against the digestate from a biogas plant which has the same minerals but less biomass and a different C/N ratio.

Table 5

Energy yields in kWh kg⁻¹ brewer’s spent grain wet.

Source		Electrical	Heat	Combined
Waltenberger (2023)	Biogas	n.a.	n.a.	0.727
Sganzerla et al. (2022a)	Biogas	0.133	0.166	0.300
Buller et al. (2022)	Biogas	0.230	0.333	0.563
Dudek et al. (2019)	Biogas	n.a.	n.a.	0.536^a
Gil-Castell et al. (2022)	Combustion	n.a.	1.025	1.025^b
Wagner et al. (2022)	Bioethanol	n.a.	n.a.	1.634^c

Source		Electrical	Heat	Combined
Waltenberger (2023)	Biogas	n.a.	n.a.	0.727
Sganzerla et al. (2022a)	Biogas	0.133	0.166	0.300
Buller et al. (2022)	Biogas	0.230	0.333	0.563
Dudek et al. (2019)	Biogas	n.a.	n.a.	0.536^a
Gil-Castell et al. (2022)	Combustion	n.a.	1.025	1.025^b
Wagner et al. (2022)	Bioethanol	n.a.	n.a.	1.634^c

Energy content with the assumption of 50%(vol/vol) CH₄ in the biogas.

Energy required for drying is not deducted.

Heating value of the produced bioethanol, without deducted energy of production.

Table 5

Energy yields in kWh kg⁻¹ brewer’s spent grain wet.

Source		Electrical	Heat	Combined
Waltenberger (2023)	Biogas	n.a.	n.a.	0.727
Sganzerla et al. (2022a)	Biogas	0.133	0.166	0.300
Buller et al. (2022)	Biogas	0.230	0.333	0.563
Dudek et al. (2019)	Biogas	n.a.	n.a.	0.536^a
Gil-Castell et al. (2022)	Combustion	n.a.	1.025	1.025^b
Wagner et al. (2022)	Bioethanol	n.a.	n.a.	1.634^c

Source		Electrical	Heat	Combined
Waltenberger (2023)	Biogas	n.a.	n.a.	0.727
Sganzerla et al. (2022a)	Biogas	0.133	0.166	0.300
Buller et al. (2022)	Biogas	0.230	0.333	0.563
Dudek et al. (2019)	Biogas	n.a.	n.a.	0.536^a
Gil-Castell et al. (2022)	Combustion	n.a.	1.025	1.025^b
Wagner et al. (2022)	Bioethanol	n.a.	n.a.	1.634^c

Energy content with the assumption of 50%(vol/vol) CH₄ in the biogas.

Energy required for drying is not deducted.

Heating value of the produced bioethanol, without deducted energy of production.

Discussion

As shown by many scientific authors and compiled in this review, the potential utilisations methods for BSG are abundant. Separated into the fields of material production, energy recovery, and nutritional use, it is hard to find a comparative value, but it should be clear that a final disposal in a landfill must be avoided and BSG is integrated into a circular economy.

The high-water content of BSG and microbial susceptibility right out of production can be used as an advantage for the use in a biorefinery. From biofuels ethanol or 2–3-butanediol, bioplastic precursors polyhydroxyalkanoates, or biotechnological enzymes, BSG can be a suitable substrate. The cellulose fraction could potentially replace food waste. On the other hand, the highly reluctant LC biomatrix requires physicochemical pretreatments to increase the yields which further produces problematic WW and counteracts the sustainable approach. To extract and decrystallise the cellulose fraction from the protein, lignin, and hemicellulose fractions, a pretreatment like in the paper industry with alkaline, acidic, or ionic liquids would be needed. Those pretreatments saccharify the LC biomass to provide fermentable sugars for microorganism like Escherichia coli, Saccharomyces cerevisiae, and Zymomonas mobilis which generate problematic waste and would only use a fraction of the BSG (Fernández-Sandoval et al., 2019; Vargas-Tah et al., 2015; Wagner et al., 2022). The use of BSG as an aggregate in brick firing, for HTC, or as a packaging material are rather negligible. It is possible to use BSG for those processes, but it does not offer any advantage over other LC biomass by-products like straw and saw dust that can be used as substitutes. A biogas plant can ferment BSG into biogas to generate heat and electricity for the brewery, as well as digestate rich in minerals, phosphate, and nitrogen which can be sold as fertiliser. The Gösser-Brauerei AG achieves an annual biogas production of 2.2 Mm³ using 16,500 t of BSG, corresponding to a total energy content of 12 GWh (Waltenberger, 2023). This translates to approximately 0.133 m³ of biogas with 0.727 kWh of energy per kilogram of BSG, or 2.66 m³ of biogas with 14.54 kWh energy per hL beer. From the sustainability reports of seven different German breweries, an average energy consumption of 10.3 kWh hL⁻¹ electrical and 34.9 kWh hL⁻¹ thermal energy is deduced (Andechs, 2021; Augustiner, 2022; Brauerei S. Riegele I. R. K., 2022; Lammsbräu, 2023; München, 2020). Without differentiating between thermal and electrical energies, a potential of about 32% of the total energy usage could be covered. One must be careful when reading about energy numbers because some authors do not declare if their numbers are based on wet or DW of BSG and how much energy is useable rather than needed to prepare the BSG or maintain the production. In Table 5, different energy yields from biogas, direct combustion, and bioethanol are stated and they diverge strongly. Sganzerla et al. calculates a return on investment of 23.68% for a biogas plant if all the energy is used and the digestate sold as a fertiliser. Energy prizes are highly depending on the country, industry, and geopolitics. The energy demand of a brewery on the other side depends on its state of the art and utilisation. When a biogas plant pays off is very individual, but it would make a brewery in every case more energy independent, decrease its waste, and generate income. The main problem of a biogas plant is the exponential scaling of the clean-up and production cost. While most breweries in Europe are small to medium businesses, they do not reach a BSG mass flow to obtain competitive gas prices or do not have the place for a fermenter. If the BSG is instead directly combusted, the useful heat energy would be higher, but the generated emissions would not meet modern standards. If the water reduction is done energy efficiently by pressing, the presswater arises as a high COD WW.

When used in cereal food products, BSG competes with other cereal by-products high in fibre and protein-like oat and wheat bran which are well established and already dried with a good shelf-life. BSG offers neither health nor technological advantages over those but lacks the storage capability because of the high-moisture content and microbial susceptibility, and can only be added in small quantities. Dairy food products like cheese and yoghurt could benefit more from BSG with its prebiotic and rheological properties. When it comes to the utilisation as animal feed, BSG can be fed directly or ensiled for later use. The direct and silage feeding of BSG are already established and the predominant application. BSG is rich in protein, cheap, and a local biomass which needs no import from abroad and can replace press cake from the vegetable oil production. An issue arises from the simultaneous peak production of green fodder and BSG during the summer, leading to a temporary oversupply and a consequent reduction in market value. To get rid of the BSG to continue production, composting would be possible. Compared to the biogas plant, the technological prerequisites are low but the heat energy of the exothermic aerobic fermentation and emerging gases are not used but rather adversely affect the environment. Additionally supplements in the form of a high carbon biomass and manure are needed to start the composting process. The final product can be sold as a fertilizer comparable to the biogas plan digestate.

When used as a biosorbent, BSG has the highest valorisation potential and the redesign of the biowaste into a biosorbent can help to clean-up industrial WW in developing countries. The demand for adsorbents for water remediation worldwide is high. The most used adsorbent is activated carbon with a worldwide consumption of about 1.1 Mt yearly with a ratio of 85/15 between non-renewable coal base and renewable resources (Ragan & Megonnell, 2011), which is small compared to 7.6 MT BSG DW, respectively. Activated carbon is a highly expensive and non-renewable when made from coal and in need for high energy when made from biowaste (carbonisation). As shown in Functional materials and Biosorbents sections, it is possible to produce effective biosorbents from LC high biowaste like BSG. The mashing process in the brewery is already a good clean-up pretreatment, and the reduced lignin content of BSG compared to other plant-based biowaste improves its reactivity. The press and wash water that arises in the pretreatment process is high in COD and phosphate which both need to be recovered and could be combined with a biogas plant.

Conclusion

The world is in a high demand for sustainable biosorbents for the remediation of WW and its implementation would help to realise a circular economy when coal-based and non-biological technical adsorbents are replaced. LC-based materials offer a great potential for that application and have already been proven to be effective biosorbents. Through the brewing process, the BSG is mashed and extracted from small soluble molecules, thereby rendering it suitable for further processing steps to become a biosorbent, an advantage it holds over other forms of biowaste. In contrast to the other utilisation methods such as biogas, animal feed, and food, where BSG offers no significant benefits over existing plant-based biowaste already in use but rather poses additional technological or legal obstacles. The production of biosorbents from BSG is therefore seen as the most promising utilisation method.

Outlook

What needs to be studied is the life cycle of a BSG biosorbent. If the goal is to close the circle and obtain all resources in our economy, the disposal of a used and metal-loaded BSG biosorbent on a landfill would contradict the efforts made before. Depending on the adsorbed metal, the use case will differ. Fe and Mn could be recovered from ashes after incineration. Zn-enriched BSG would be a value-added feed. Pb, Cd, or other high toxic metal-enriched BSG biosorbents would need an exhausting regeneration before further use. If it were possible to regenerate the BSG biosorbents completely from any adsorbed contaminant, a reintroduction of the BSG biosorbent in every other utilisation method explained above would be possible again. To clarify the question of the life cycle assessment of a BSG biosorbent and its suitability for WW remediation, further studies are in progress.

Data availability

The data that support the findings of this study are available on request from the corresponding author.

Author contributions

Philipp Dancker (Conceptualization [lead], data curation [lead], investigation [equal], resources [lead], visualization [lead], writing—original draft [lead], writing—review & editing [equal]), Karl Glas (Conceptualization [equal], investigation [equal], supervision [equal], writing—review & editing [equal]), and Martina Gastl (Conceptualization [equal], investigation [equal], supervision [equal], validation [equal], writing—review & editing [equal]).

Funding

None declared.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this review.

References

Abd El-Moneim

R. A.

Shamsia

S. M.

El-Deeb

A. M.

, &

Ziena

H. M.

(

2018

Utilization of brewers spent grain (Bsg) in producing functional processed cheese “Block”

Journal of Food and Dairy Sciences

103

–

109

10.1016/j.jssas.2016.09.005

Aboukila

E. F.

Nassar

I. N.

Rashad

Hafez

, &

Norton

J. B.

(

2018

Reclamation of calcareous soil and improvement of squash growth using brewers’ spent grain and compost

Journal of the Saudi Society of Agricultural Sciences

390

–

397

10.1016/j.procbio.2005.02.004

Akermann

Weiermüller

Christmann

Guirande

Glaser

Knaus

, &

Ulber

(

2020

Brewers’ spent grain liquor as a feedstock for lactate production with Lactobacillus delbrueckii Subsp lactis

Engineering in Life Sciences

168

–

180

10.1002/elsc.201900143

Aksu

, &

İşoğlu

İ. A.

(

2005

Removal of copper(II) ions from aqueous solution by biosorption onto agricultural waste sugar beet pulp

Process Biochemistry

3031

–

3044

Alert

H.-J.

(

2013

Proteinabbau einheimischer Futtermittel Im Pansen

Landesamt Für Umwelt, Landwirtschaft Und Geologie

Andechs

(

2021

Umwelterklaerung Andechs

[online]

. https://www.andechs.de/fileadmin/kloster_andechs_dateien/pdf-downloads/uwerkl_2021_300dpi.pdf. Date accessed June 18, 2023.

Angelidaki

Alves

Bolzonella

Borzacconi

Campos

Guwy

Kalyuzhnyi

Jenicek

, &

Van Lier

(

2009

Defining the biomethane potential (Bmp) of solid organic wastes and energy crops: A proposed protocol for batch assays

Water Science and Technology

927

–

934

Annadurai

Juang

R.-S.

, &

Lee

(

2003

Adsorption of heavy metals from water using banana and orange peels

Water Science and Technology

185

–

190

10.2166/wst.2003.0049

Assandri

Pampuro

Zara

Cavallo

, &

Budroni

(

2020

Suitability of composting process for the disposal and valorization of brewer’s spent grain

Agriculture

10.1016/j.fuel.2020.117494

Atelge

M. R.

Atabani

A. E.

Banu

J. R.

Krisa

Kaya

Eskicioglu

Kumar

Lee

Yildiz

Y. Ş.

Unalan

Mohanasundaram

, &

Duman

(

2020

A critical review of pretreatment technologies to enhance anaerobic digestion and energy recovery

Fuel

270

117494

Augustiner.

2022

Umwelterklaerung Augustiner-Bräu Wagner kg

[online]

. https://www.augustiner-braeu.de/fileadmin/user_upload/03_verantwortung/umwelterklaerung_2022_augustiner-braeu_wagner_kg.pdf. Date accessed June 18, 2023.

Banjo

T. T.

Kareem

S. O.

Popoola

T. O.

, &

Akinloye

O. A.

(

2018

Microbial production of ascorbic acid from brewery spent grain (Bsg) by Aspergillus flavus and Aspergillus tamarii

Food and Applied Bioscience Journal

–

105

Barth

S. J.

, &

Meier

(

2022

Barthhaas report hops 2021/2022

Barthhaas Gmbh & Co. Kg

Bauer

Korthals

Gronauer

, &

Lebuhn

(

2008

Methanogens in biogas production from renewable resources—A novel molecular population analysis approach

Water Science and Technology

1433

–

1439

BFJ

(

2013

Verordnung Über die Verbrennung und die Mitverbrennung Von Abfällen—17

Bimschv

10.5194/hess-26-5137-2022

Birsan

R. I.

Wilde

Waldron

K. W.

, &

Rai

D. K.

(

2019

Recovery of polyphenols from brewer’s spent grains

Antioxidants

380

10.3390/antiox8090380

BLE

. (

2023

Feed volume from domestic production and imports

. Federal Office for Agriculture and Food. https://www.ble.de/de/bzl/daten-berichte/futter/futter_node.html. Date accessed May 25, 2023.

BMEL

. (

2020

Rinderhaltung In Deutschland

. Federal Ministry of Food and Agriculture

[online]

. https://www.bmel-statistik.de/landwirtschaft/tierhaltung/rinderhaltung. Date accessed August 20, 2023.

Boeing

Rakovec

Kumar

Samaniego

Schrön

Hildebrandt

Rebmann

Thober

Müller

Zacharias

Bogena

Schneider

Kiese

Attinger

, &

Marx

(

2022

High-resolution drought simulations and comparison to soil moisture observations in Germany

Hydrology and Earth System Sciences

5137

–

5161

10.1016/j.scitotenv.2020.142717

Brauerei S. Riegele I. R. K

. (

2022

Umwelterklaerung Riegele

[online]

. https://www.riegele.de/wp-content/uploads/2023/09/umwelterklaerung-2022_brauhaus-riegele.pdf. Date accessed June 18, 2023.

Buller

L. S.

Da Silva Romero

C. W.

Lamparelli

R. A. C.

Ferreira

S. F.

Bortoleto

A. P.

Mussatto

S. I.

, &

Forster-Carneiro

(

2021

A spatially explicit assessment of sugarcane vinasse as a sustainable by-product

Science of the Total Environment

765

142717

Buller

L. S.

Sganzerla

W. G.

Lima

M. N.

Muenchow

K. E.

Timko

M. T.

, &

Forster-Carneiro

(

2022

Ultrasonic pretreatment of brewers’ spent grains for anaerobic digestion: Biogas production for a sustainable industrial development

Journal of Cleaner Production

355

131802

10.1016/j.jclepro.2022.131802

10.1016/j.lwt.2023.115528

Canonico

Agarbati

Comitini

, &

Ciani

(

2023

Unravelling the potential of non-conventional yeasts and recycled brewers spent grains (Bsg) for non-alcoholic and low alcohol beer (Nablab)

Lwt

190

115528

10.3390/polysaccharides3020021

Carrasco

K. H.

Höfgen

E. G.

Brunner

Borchert

K. B. L.

Reis

Steinbach

Mayer

Schwarz

Glas

, &

Schwarz

(

2022

Removal of iron, manganese, cadmium, and nickel ions using brewers & spent grain

Polysaccharides

356

–

379

Chrysargyris

Saridakis

, &

Tzortzakis

(

2013

Use of municipal solid waste compost as growing medium component for melon seedlings production

Journal of Plant Biology & Soil Health

–

10.1016/j.biortech.2021.125622

Cieciura-Włoch

Borowski

, &

Domański

(

2021

Dark fermentative hydrogen production from hydrolyzed sugar beet pulp improved by nitrogen and phosphorus supplementation

Bioresource Technology

340

125622

Combest

Warren

, &

Patterson

(

2020

Upcycling brewers’ spent grain: The development of muffins and biomarker response after consuming muffins for 8-weeks In healthy adults from randomized-controlled trial

Current Developments in Nutrition

Nzaa052_014

10.1016/j.biortech.2014.10.019

Dandikas

Heuwinkel

Lichti

Drewes

J. E.

, &

Koch

(

2014

Correlation between biogas yield and chemical composition of energy crops

Bioresource Technology

174

316

–

320

Daniel-Gromke

(

2019

Effiziente Mikro-Biogasaufbereitungsanlagen (Emikrobgaa); Teilvorhaben 2: Potenzialabschätzung Und Betriebswirtschaftliche Bewertung Für Mikrobgaa—Akronym: Emikrobgaa

Fachagentur Nachwachsende Rohstoffe

–

171

10.1016/j.biortech.2017.09.163

De Bhowmick

Sarmah

A. K.

, &

Sen

(

2018

Lignocellulosic biorefinery as a model for sustainable development of biofuels and value added products

Bioresource Technology

247

1144

–

1154

De Jong

Higson

Walsh

, &

Wellisch

(

2012

Bio-based chemicals value added products from biorefineries

IEA Bioenergy

–

10.1016/j.biortech.2020.123128

Dudek

Świechowski

Manczarski

Koziel

J. A.

, &

Białowiec

(

2019

The effect of biochar addition on the biogas production kinetics from the anaerobic digestion of brewers’ spent grain

Energies

1518

Fan

Zhou

Zhang

Feng

Huang

, &

Qin

(

2020

Preparation of sugarcane bagasse succinate/alginate porous gel beads via a self-assembly strategy: Improving the structural stability and adsorption efficiency for heavy metal ions

Bioresource Technology

306

123128

Fărcaş

(

2014

Brewers’ spent grain–a new potential ingredient for functional foods

Journal of Agroalimentary Processes and Technologies

137

–

141

10.1016/j.jtice.2015.03.027

Fărcaș

A. C.

Socaci

S. A.

Chiș

M. S.

Pop

O. L.

Fogarasi

Păucean

Igual

, &

Michiu

(

2021

Reintegration of brewers spent grains In the food chain: Nutritional, functional and sensorial aspects

Plants

2504

10.3390/plants10112504

Feizi

, &

Jalali

(

2015

Removal of heavy metals from aqueous solutions using sunflower, potato, canola and walnut shell residues

Journal of the Taiwan Institute of Chemical Engineers

125

–

136

10.1016/j.indcrop.2018.12.087

Fernández-Delgado

Plaza

P. E.

Coca

García-Cubero

M. T.

González-Benito

, &

Lucas

(

2019

Comparison of mild alkaline and oxidative pretreatment methods for biobutanol production from brewer’s spent grains

Industrial Crops and Products

130

409

–

419

10.1016/j.biortech.2010.06.125

Fernández-Sandoval

M. T.

Galíndez-Mayer

Bolívar

Gosset

Ramírez

O. T.

, &

Martinez

(

2019

Xylose–glucose co-fermentation to ethanol by Escherichia coli strain MS04 using single- and two-stage continuous cultures under micro-aerated conditions

Microbial Cell Factories

–

Fitzpatrick

Champagne

Cunningham

M. F.

, &

Whitney

R. A.

(

2010

A biorefinery processing perspective: Treatment of lignocellulosic materials for the production of value-added products

Bioresource Technology

101

8915

–

8922

Funke

, &

Ziegler

(

2010

Hydrothermal carbonization of biomass: A summary and discussion of chemical mechanisms for process engineering

Biofuels, Bioproducts and Biorefining

160

–

177

Garrett

Bellmer

Mcglynn

, &

Rayas-Duarte

(

2021

Development of new chip products from brewer’s spent grain

Journal of Food Quality

2021

–

Gil-Castell

Mascia

Primaz

Vásqez-Garay

Baschetti

M. G.

, &

Ribes-Greus

(

2022

Brewer’s spent grains as biofuels In combustion-based energy recovery processes: Evaluation of thermo-oxidative decomposition

Fuel

312

122955

10.1016/j.fuel.2021.122955

10.1016/j.envres.2024.118455

González-Feijoo

Santás-Miguel

Arenas-Lago

Álvarez-Rodríguez

Núñez-Delgado

Arias-Estévez

, &

Pérez-Rodríguez

(

2024

Effectiveness of cork and pine bark powders as biosorbents for potentially toxic elements present in aqueous solution

Environmental Research

250

118455

Guo

Zhang

Z. A.

Zhang

, &

Jin

(

2014

Optimization of Brewer's spent grain-enriched biscuits processing formula

Journal of Food Process Engineering

122

–

130

Guo

Zhang

, &

Shan

X.-Q.

(

2008

Adsorption of metal ions on lignin

Journal of Hazardous Materials

151

134

–

142

10.1016/j.jhazmat.2007.05.065

Gupta

Abu-Ghannam

, &

Gallaghar

(

2010

Barley for brewing: Characteristic changes during malting, brewing and applications of its by-products

Comprehensive Reviews in Food Science and Food Safety

318

–

328

10.1111/j.1541-4337.2010.00112.x

Han

Zhang

Zou

Xiao

Shi

, &

Liu

(

2006

Biosorption of copper(II) and lead(II) from aqueous solution by chaff in a fixed-bed column

Journal of Hazardous Materials

133

262

–

268

10.1016/j.jhazmat.2005.10.019

Hendriks

A. T.

, &

Zeeman

(

2009

Pretreatments to enhance the digestibility of lignocellulosic biomass

Bioresource Technology

100

–

10.1016/j.biortech.2008.05.027

Herfellner

Bochmann

, &

Meyer-Pittroff

(

2006

Wirtschaftlich Sinnvolle Verfahren? Die Verwertung Von Biertrebern–Derzeitiger Stand Und Neue Ansätze Zur Energetischen Nutzung

Brauindustrie

–

10.1007/s11356-020-07623-9

Hoang

M. T.

Pham

T. D.

Pham

T. T.

Nguyen

M. K.

D. T. T.

Nguyen

T. H.

Bartling

, &

Van Der Bruggen

(

2021

Esterification of sugarcane bagasse by citric acid for Pb²⁺ adsorption: Effect of different chemical pretreatment methods

Environmental Science and Pollution Research

11869

–

11881

Hokkanen

Bhatnagar

, &

Sillanpaa

(

2016

A review on modification methods to cellulose-based adsorbents to improve adsorption capacity

Water Research

156

–

173

10.1016/j.watres.2016.01.008

Iqbal

Saeed

, &

Kalim

(

2009

Characterization of adsorptive capacity and investigation of mechanism of Cu²⁺, Ni²⁺ and Zn²⁺ adsorption on mango peel waste from constituted metal solution and genuine electroplating effluent

Separation Science and Technology

3770

–

3791

10.1080/01496390903182305

Ivanova

Denkova

Kostov

Petrova

Bakalov

Ruscova

, &

Penov

(

2017

Extrusion of brewers' spent grains and application In the production of functional food. Characteristics of spent grains and optimization of extrusion

Journal of the Institute of Brewing

123

544

–

552

Jeroch

Drochner

, &

Simon

(

2008

Ernährung Landwirtschaftlicher Nutztiere: Ernährungsphysiologie, Futtermittelkunde, Fütterung

Utb

Kamusoko

Jingura

R. M.

Parawira

, &

Sanyika

W. T.

(

2019

Comparison of pretreatment methods that enhance biomethane production from crop residues—a systematic review

Biofuel Research Journal

1080

–

1089

10.18331/BRJ2019.6.4.4

Kaparaju

, &

Rintala

(

2013

). 17—generation of heat and power from biogas for stationary applications: Boilers, gas engines and turbines, combined heat and power (Chp) plants and fuel cells. In

Wellinger

Murphy

Baxter

(Eds.),

The biogas handbook

Woodhead Publishing

10.1007/s00216-015-9110-7

Katharina Habler

M. R.

(

2016

Multi-mycotoxin stable isotope dilution LC-MS/MS method for fusarium toxins in cereals

Analytical and Bioanalytical Chemistry

408

307

–

317

Khormaei

Nasernejad

Edrisi

, &

Eslamzadeh

(

2007

Copper biosorption from aqueous solutions by sour orange residue

Journal of Hazardous Materials

149

269

–

274

10.1016/j.jhazmat.2007.03.074

Kim

Liu

Noh

J.-W.

Yang

Shimizu

Lee

D.-Y.

, &

Zhang

(

2013

Hydrogen and methane production from untreated rice straw and raw sewage sludge under thermophilic anaerobic conditions

International Journal of Hydrogen Energy

8648

–

8656

10.1016/j.ijhydene.2013.04.079

10.1016/j.biortech.2014.10.092

Kim

Park

, &

Park

(

2015

A new efficient forest biowaste as biosorbent for removal of cationic heavy metals

Bioresource Technology

175

629

–

632

Kirchgessner

(

2011

Tierernährung, 13. Aufl

(p.

643

Dlg Verlag Gmbh

Kirtania

(

2018

). Chapter 4—thermochemical conversion processes for waste biorefinery. In

Bhaskar

Pandey

S. V.

Mohan

D.-J.

Lee

S. K.

Khanal

(Eds.),

Waste biorefinery

Elsevier

10.1007/s11157-015-9374-6

Kleerebezem

Joosse

Rozendal

, &

Van Loosdrecht

M. C.

(

2015

Anaerobic digestion without biogas?

Reviews in Environmental Science and Bio/Technology

787

–

801

10.1016/j.cej.2012.04.102

Klemes

Smith

, &

Kim

J.-K.

(

2008

Handbook of water and energy management in food processing

Elsevier

Lammsbräu

(

2023

Umweltbericht Neumarkter Lammsbräu

. https://www.lammsbraeu.de/verantwortung/nachhaltigkeitsreporting. Date accessed June 18, 2023.

LFL

(

2008

Biertreber—Futterwert, Konservierung und Erfolgreicher Einsatz Beim Wiederkäuer

. http://www.lfl.bayern.de/ite/rind/082223/index.php. Date accessed June 21, 2023.

Chai

, &

Qin

(

2012

Cadmium(II) adsorption on esterified spent grain: Equilibrium modeling and possible mechanisms

Chemical Engineering Journal

197

173

–

180

10.1016/j.biortech.2010.01.003

Chai

Wang

Yang

Yan

, &

Wang

(

2010

Fast esterification of spent grain for enhanced heavy metal ions adsorption

Bioresource Technology

101

3796

–

3799

Helmreich

, &

Horn

(

2011

Biosorption of Cu(II) ions from aqueous solution by red alga (Palmaria palmata) and beer draff

Materials Sciences and Applications

10.1016/j.biortech.2013.09.063

Zhang

Liu

Chen

, &

Liu

(

2013

Comparison of methane production potential, biodegradability, and kinetics of different organic substrates

Bioresource Technology

149

565

–

569

López-Linares

J. C.

Lucas

García-Cubero

M. T.

Jiménez

J. J.

, &

Coca

(

2020

A biorefinery based on brewer’s spent grains: Arabinoxylans recovery by microwave assisted pretreatment integrated with butanol production

Industrial Crops and Products

158

113044

10.1016/j.indcrop.2020.113044

10.1016/j.bej.2018.07.007

Lovato

Albanez

Stracieri

Ruggero

L. S.

Ratusznei

S. M.

, &

Rodrigues

J. A. D.

(

2018

Hydrogen production by co-digesting cheese whey and glycerin in an Ansbbr: Temperature effect

Biochemical Engineering Journal

138

–

10.1016/s0032-9592(00)00177-1

Low

K. S.

Lee

C. K.

, & Liew, S. C. (

2000

Sorption of cadmium and lead from aqueous solutions by spent grain

Process Biochemistry

–

10.1016/j.biortech.2007.04.024

, &

Gibb

S. W.

(

2008

Copper removal from wastewater using spent-grain as biosorbent

Bioresource Technology

1509

–

1517

Lübken

Gehring

, &

Wichern

(

2010

Microbiological fermentation of lignocellulosic biomass: Current state and prospects of mathematical modeling

Applied Microbiology and Biotechnology

1643

–

1652

Ludwig

(

2014

Entwicklung Von Verfahren und Prozessmodellen Zur Fraktionierung Von lignocellulose

Fraunhofer Verlag

10.1016/S0043-1354(03)00290-2

Lynch

K. M.

Steffen

E. J.

, &

Arendt

E. K.

(

2016

Brewers' spent grain: A review with an emphasis on food and health

Journal of the Institute of Brewing

122

553

–

568

, &

Tobin

J. M.

(

2003

Development of multimetal binding model and application to binary metal biosorption onto peat biomass

Water Research

3967

–

3977

Maqhuzu

A. B.

Yoshikawa

, &

Takahashi

(

2021

Prospective utilization of Brewers' spent grains (Bsg) for energy and food In Africa and its global warming potential

Sustainable Production and Consumption

146

–

159

10.1016/j.spc.2020.09.022

10.1097/CORR.0000000000003276

Merck

2024

https://www.sigmaaldrich.com/de/en/product/sigma/96096/sigald/242233/mm/101076/aldrich/717185

. Date accessed March 20, 2024.

Milew

Manke

Grimm

Haseneder

Herdegen

, &

Braeuer

A. S.

(

2022

Application, characterisation and economic assessment of brewers’ spent grain and liquor

Journal of the Institute of Brewing

128

–

108

Mishra

Balomajumder

, &

Agarwal

V. K.

(

2010

Biosorption of Zn(II) onto the surface of non-living biomasses: A comparative study of adsorbent particle size and removal capacity of three different biomasses

Water, Air, & Soil Pollution

211

489

–

500

10.1007/s11270-009-0317-0

Mittweg

Oechsner

Hahn

Lemmer

, &

Reinhardt-Hanisch

(

2012

Repeatability of a laboratory batch method to determine the specific biogas and methane yields

Engineering in Life Sciences

270

–

278

10.1002/elsc.201100181

10.1016/j.jcs.2005.06.001

München

S. H. I.

2020

Umwelterklaerung Hofbräu

[online]

. https://www.hofbraeu-muenchen.de/sites/www.hofbraeu-muenchen.de/files/pdf/umwelterklaerung_hofbraeu_muenchen_2021.pdf. Date accessed June 18, 2023.

Mussatto

S. I.

Dragone

, &

Roberto

I. C.

(

2006

Brewers' spent grain: Generation, characteristics and potential applications

Journal of Cereal Science

–

10.1016/j.biortech.2009.11.025

Mussatto

S. I.

Fernandes

Rocha

G. J. M.

Órfão

J. J. M.

Teixeira

J. A.

, &

Roberto

I. C.

(

2010

Production, characterization and application of activated carbon from brewer’s spent grain lignin

Bioresource Technology

101

2450

–

2457

Mussatto

S. I.

Moncada

Roberto

I. C.

, &

Cardona

C. A.

(

2013

Techno-economic analysis for Brewer’s spent grains use on a biorefinery concept: The Brazilian case

Bioresource Technology

148

302

–

310

10.1016/j.biortech.2013.08.046

Mussatto

S. I.

, &

Roberto

I. C.

(

2006

Chemical characterization and liberation of pentose sugars from brewer's spent grain

Journal of Chemical Technology & Biotechnology

268

–

274

Naibaho

Butula

Jonuzi

Korzeniowska

Laaksonen

Föste

Kütt

M.-L.

, &

Yang

(

2022

Potential of brewers’ spent grain In yogurt fermentation and evaluation of its impact in rheological behaviour, consistency, microstructural properties and acidity profile during the refrigerated storage

Food Hydrocolloids

125

107412

10.1016/j.foodhyd.2021.107412

10.1016/j.procbio.2004.06.010

Nasernejad

Zadeh

T. E.

Pour

B. B.

Bygi

M. E.

, &

Zamani

(

2005

Camparison for biosorption modeling of heavy metals (Cr(III), Cu(II), Zn(II)) adsorption from wastewater by carrot residues

Process Biochemistry

1319

–

1322

10.1016/j.lwt.2019.108421

Ngah

W. S. W.

, &

Hanafiah

M. A. K. M.

(

2009

Surface modification of rubber (Hevea brasiliensis) leaves for the adsorption of copper ions: Kinetic, thermodynamic and binding mechanisms

Journal of Chemical Technology & Biotechnology

192

–

201

Nocente

Taddei

Galassi

, &

Gazza

(

2019

Upcycling of brewers’ spent grain by production of dry pasta with higher nutritional potential

LWT

114

108421

10.1016/S0960-8524(02)00098-6

Nuhoglu

Malkoc

Gürses

, &

Canpolat

(

2002

The removal of Cu(II) from aqueous solutions by Ulothrix zonata

Bioresource Technology

331

–

333

O’connell

D. W.

Birkinshaw

, &

O’dwyer

T. F.

(

2008

Heavy metal adsorbents prepared from the modification of cellulose: A review

Bioresource Technology

6709

–

6724

10.1016/j.biortech.2008.01.036

Oliveira

W. E.

Franca

A. S.

Oliveira

L. S.

, &

Rocha

S. D.

(

2008

Untreated coffee husks as biosorbents for the removal of heavy metals from aqueous solutions

Journal of Hazardous Materials

152

1073

–

1081

10.1016/j.jhazmat.2007.07.085

Ospina-Betancourth

Echeverri

Rodriguez-Gonzalez

Wist

Combariza

M. Y.

, &

Sanabria

(

2022

Enhancement of Pha production by a mixed microbial culture using Vfa obtained from the fermentation of wastewater from yeast industry

Fermentation

180

10.3390/fermentation8040180

10.1016/j.procbio.2003.11.008

Özer

, &

Özer

(

2004

The adsorption of copper(II) ions on to dehydrated wheat bran (Dwb): Determination of the equilibrium and thermodynamic parameters

Process Biochemistry

2183

–

2191

10.4067/S0718-58392014000400012

Papamichalaki

Papadaki

, &

Tzortzakis

(

2014

Substitution of peat with municipal solid waste compost In watermelon seedling production combined with fertigation

Chilean Journal of Agricultural Research

452

–

459

10.1016/j.cej.2015.05.065

Passos

Carretero

, &

Ferrer

(

2015

Comparing pretreatment methods for improving microalgae anaerobic digestion: Thermal, hydrothermal, microwave and ultrasound

Chemical Engineering Journal

279

667

–

672

10.1016/j.nbt.2020.07.005

Peces

Astals

Jensen

P. D.

, &

Clarke

W. P.

(

2021

Transition of microbial communities and degradation pathways In anaerobic digestion at decreasing retention time

New Biotechnology

–

Pehlivan

Altun

Cetin

, &

Bhanger

M. I.

(

2009

Lead sorption by waste biomass of hazelnut and almond shell

Journal of Hazardous Materials

167

1203

–

1208

10.1016/j.jhazmat.2009.01.126

Perez-Esteban

Vinardell

Vidal-Antich

Peña-Picola

Chimenos

J. M.

Peces

Dosta

, &

Astals

(

2022

Potential of anaerobic co-fermentation In wastewater treatments plants: A review

Science of the Total Environment

813

152498

10.1016/j.scitotenv.2021.152498

Pillai

S. S.

Deepa

Abraham

Girija

Geetha

Jacob

, &

Koshy

(

2013

Biosorption of Cd(II) from aqueous solution using xanthated nano banana cellulose: Equilibrium and kinetic studies

Ecotoxicology and Environmental Safety

352

–

360

10.1016/j.ecoenv.2013.09.003

Pinheiro

Coelho

Romaní

, &

Domingues

(

2019

Intensifying ethanol production from brewer’s spent grain waste: Use of whole slurry at high solid loadings

New Biotechnology

–

10.1016/j.nbt.2019.06.005

Plaza

P. E.

Coca

Yagüe

S. L.

Gutiérrez

Rochón

, &

García-Cubero

M. T.

(

2022

Bioprocess intensification for acetone-butanol-ethanol fermentation from brewer's spent grain: Fed-batch strategies coupled with in-situ gas stripping

Biomass and Bioenergy

156

106327

10.1016/j.biombioe.2021.106327

10.1016/j.biortech.2014.04.052

Poerschmann

Weiner

Wedwitschka

Baskyr

Koehler

, &

Kopinke

F. D.

(

2014

Characterization of biocoals and dissolved organic matter phases obtained upon hydrothermal carbonization of brewer’s spent grain

Bioresource Technology

164

162

–

169

Prasanna Kumar

King

, &

Prasad

V. S. R. K.

(

2006

Equilibrium and kinetic studies for the biosorption system of copper(II) ion from aqueous solution using Tectona grandis L.F. leaves powder

Journal of Hazardous Materials

137

1211

–

1217

10.1016/j.jhazmat.2006.04.006

Qazanfarzadeh

Ganesan

A. R.

Mariniello

Conterno

, &

Kumaravel

(

2023

Valorization of brewer's spent grain for sustainable food packaging

Journal of Cleaner Production

385

135726

10.1016/j.jclepro.2022.135726

10.1007/s00226-010-0374-y

Radosavljević

Pejin

Pribić

Kocić-Tanackov

Mladenović

Djukić-Vuković

, &

Mojović

(

2020

Brewing and malting technology by-products as raw materials In L-(+)-lactic acid fermentation

Journal of Chemical Technology & Biotechnology

339

–

347

Rafatullah

Sulaiman

Hashim

, &

Ahmad

(

2012

Removal of cadmium(II) from aqueous solutions by adsorption using Meranti wood

Wood Science and Technology

221

–

241

Ragan

, &

Megonnell

(

2011

Activated carbon from renewable resources—lignin

Cellulose Chemistry and Technology

527

10.1007/s11157-021-09566-0

Ramos-Suarez

Zhang

, &

Outram

(

2021

Current perspectives on acidogenic fermentation to produce volatile fatty acids from waste

Reviews in Environmental Science and Bio/Technology

439

–

478

Rasheed

Farooq

, &

Rafique

(

2013

Kinetic study of metal removal using apple peels: Closed batch approximation model

International Journal of Chemical and Environmetal Engineering

281

–

285

10.1016/j.resconrec.2011.08.007

Ravindran

Sarangapani

Jaiswal

Cullen

P. J.

Bourke

, &

Jaiswal

A. K.

(

2019

Improving enzymatic hydrolysis of brewer spent grain with nonthermal plasma

Bioresource Technology

282

520

–

524

Reddad

Gerente

Andres

, &

Le Cloirec

(

2002

Adsorption of several metal ions onto a low-cost biosorbent: Kinetic and equilibrium studies

Environmental Science & Technology

2067

–

2073

Rehl

, &

Müller

(

2011

Life cycle assessment of biogas digestate processing technologies

Resources, Conservation and Recycling

–

104

Riemeier

(

2004

Einfluss Der Ruminalen Stickstoffbilanz (Rnb) Auf Die Pansenfermentation, Mikrobielle Proteinsynthese, Menge Des Am Dünndarm Anflutenden Nutzbaren proteins (Nxp) Sowie Die Stickstoffausscheidung

Bundesforschungsanstalt Für Landwirtschaft In Braunschweig

–

176

10.1016/j.lwt.2010.01.019

Robertson

J. A.

I'anson

K. J. A.

Treimo

Faulds

C. B.

Brocklehurst

T. F.

Eijsink

V. G. H.

, &

Waldron

K. W.

(

2010

Profiling brewers' spent grain for composition and microbial ecology at the site of production

LWT—Food Science and Technology

890

–

896

10.1016/j.jhazmat.2008.11.074

Rocha

C. G.

Zaia

D. A. M.

Da Silva Alfaya

R. V.

, &

Da Silva Alfaya

A. A.

(

2009

Use of rice straw as biosorbent for removal of Cu(II), Zn(II), Cd(II) and Hg(II) ions In industrial effluents

Journal of Hazardous Materials

166

383

–

388

Rojas-Chamorro

J. A.

Romero-García

J. M.

Cara

Romero

, &

Castro

(

2020

Improved ethanol production from the slurry of pretreated brewers’ spent grain through different co-fermentation strategies

Bioresource Technology

296

122367

Russ

Mörtel

, &

Meyer-Pittroff

(

2005

Application of spent grains to increase porosity in bricks

Construction and Building Materials

117

–

126

10.1016/j.conbuildmat.2004.05.014

10.1016/j.biortech.2019.122019

Saba

Zara

Bianco

Garau

Bononi

Deroma

Pais

, &

Budroni

(

2019

Comparative analysis of vermicompost quality produced from brewers’ spent grain and cow manure by the red earthworm Eisenia fetida

Bioresource Technology

293

122019

Saeed

Iqbal

, &

Akhtar

M. W.

(

2005

Removal and recovery of lead(II) from single and multimetal (Cd, Cu, Ni, Zn) solutions by crop milling waste (black gram husk)

Journal of Hazardous Materials

117

–

10.1016/j.jhazmat.2004.09.008

Schettino

Verni

Acin-Albiac

Vincentini

Krona

Knaapila

Cagno

R. D.

Gobbetti

Rizzello

C. G.

, &

Coda

(

2021

Bioprocessed brewers’ spent grain improves nutritional and antioxidant properties of pasta

Antioxidants

742

10.3390/antiox10050742

Sganzerla

W. G.

Ampese

L. C.

Mussatto

S. I.

, &

Forster-Carneiro

(

2021a

A bibliometric analysis on potential uses of brewer's spent grains In a biorefinery for the circular economy transition of the beer industry

Biofuels, Bioproducts and Biorefining

1965

–

1988

Sganzerla

W. G.

Buller

L. S.

Mussatto

S. I.

, &

Forster-Carneiro

(

2021b

Techno-economic assessment of bioenergy and fertilizer production by anaerobic digestion of brewer’s spent grains in a biorefinery concept

Journal of Cleaner Production

297

126600

10.3390/fermentation9010002

Sganzerla

W. G.

Costa

J. M.

Tena-Villares

Buller

L. S.

Mussatto

S. I.

, &

Forster-Carneiro

(

2022a

Dry anaerobic digestion of brewer’s spent grains toward a more sustainable brewery: Operational performance, kinetic analysis, and bioenergy potential

Fermentation

, 2.

Sganzerla

W. G.

Sillero

Forster-Carneiro

Solera

, &

Perez

(

2022b

Determination of anaerobic co-fermentation of brewery wastewater and brewer’s spent grains for bio-hydrogen production

Bioenergy Research

1073

–

1083

10.1016/j.cep.2008.05.001

Srivastava

V. C.

Mall

I. D.

, &

Mishra

I. M.

(

2009

Competitive adsorption of cadmium(II) and nickel(II) metal ions from aqueous solution onto rice husk ash

Chemical Engineering and Processing: Process Intensification

370

–

379

Statista Inc

. (

2023

Beer production worldwide from 1998 to 2021

[online]

. https://www.statista.com/statistics/270275/worldwide-beer-production/ Date accessed July 17, 2023.

Steinhöfel

(

2004

Biertreber Im Schlauch Siliert

Bauernzeitung

–

10.1016/j.foodchem.2008.02.074

Stelick

Sogari

Rodolfi

Dando

, &

Paciulli

(

2021

Impact of sustainability and nutritional messaging on Italian consumers’ purchase intent of cereal bars made with brewery spent grains

Journal of Food Science

531

–

539

10.1111/1750-3841.15601

Stojceska

, &

Ainsworth

(

2008

The effect of different enzymes on the quality of high-fibre enriched brewer’s spent grain breads

Food Chemistry

110

865

–

872

Taşar

Ş.

Kaya

, &

Özer

(

2014

Biosorption of lead(II) ions from aqueous solution by peanut shells: Equilibrium, thermodynamic and kinetic studies

Journal of Environmental Chemical Engineering

1018

–

1026

10.1016/j.jece.2014.03.015

10.1016/j.ijhydene.2020.04.075

Tena

Luque

Perez

, &

Solera

(

2020

Enhanced hydrogen production from sewage sludge by cofermentation with wine vinasse

International Journal of Hydrogen Energy

15977

–

15984

10.1016/j.biortech.2009.10.035

Thevannan

Mungroo

, &

Niu

C. H.

(

2010

Biosorption of nickel with barley straw

Bioresource Technology

101

1776

–

1780

Tofan

Paduraru

Bilba

, &

Rotariu

(

2008

Thermal power plants ash as sorbent for the removal of Cu(II) and Zn(II) ions from wastewaters

Journal of Hazardous Materials

156

–

10.1016/j.jhazmat.2007.11.098

Tyagi

V. K.

Campoy

R. A.

Álvarez-Gallego

, &

García

L. R.

(

2014

Enhancement in hydrogen production by thermophilic anaerobic co-digestion of organic fraction of municipal solid waste and sewage sludge—Optimization of treatment conditions

Bioresource Technology

164

408

–

415

10.1016/j.biortech.2014.05.013

Vanholme

Demedts

Morreel

Ralph

, &

Boerjan

(

2010

Lignin biosynthesis and structure

Plant Physiology

153

895

–

905

10.1104/pp.110.155119

Vargas-Tah

Moss-Acosta

C. L.

Trujillo-Martinez

Tiessen

Lozoya-Gloria

Orencio-Trejo

Gosset

, &

Martinez

(

2015

Non-severe thermochemical hydrolysis of stover from white corn and sequential enzymatic saccharification and fermentation to ethanol

Bioresource Technology

198

611

–

618

10.1016/j.biortech.2015.09.036

Vaughan

Seo

C. W.

, &

Marshall

W. E.

(

2001

Removal of selected metal ions from aqueous solution using modified corncobs

Bioresource Technology

133

–

139

10.1016/S0960-8524(01)00007-4

Venkata Mohan

Nikhil

G. N.

Chiranjeevi

Nagendranatha Reddy

Rohit

M. V.

Kumar

A. N.

, &

Sarkar

(

2016

Waste biorefinery models towards sustainable circular bioeconomy: Critical review and future perspectives

Bioresource Technology

215

–

10.1016/j.biortech.2016.03.130

Verni

Pontonio

Krona

Jacob

Pinto

Rinaldi

Verardo

Díaz-De-Cerio

Coda

, &

Rizzello

C. G.

(

2020

Bioprocessing of brewers’ spent grain enhances its antioxidant activity: Characterization of phenolic compounds and bioactive peptides

Frontiers in Microbiology

1831

Vieira

Rocha

M. A. M.

Coelho

Pinho

Saraiva

J. A.

Ferreira

I. M. P. L. V. O.

, &

Coimbra

M. A.

(

2014

Valuation of Brewer's spent grain using a fully recyclable integrated process for extraction of proteins and arabinoxylans

Industrial Crops and Products

136

–

143

10.1016/j.indcrop.2013.10.012

10.1016/j.watres.2003.10.040

Villaescusa

Fiol

Martı́nez

M. A.

Miralles

Poch

, &

Serarols

(

2004

Removal of copper and nickel ions from aqueous solutions by grape stalks wastes

Water Research

992

–

1002

Wagner

Sierra-Ibarra

Rojas

N. L.

, &

Martinez

(

2022

One-pot bioethanol production from brewery spent grain using the ethanologenic Escherichia coli MS04

Renewable Energy

189

717

–

725

10.1016/j.renene.2022.03.014

Waltenberger

(

2023

Biogas plant for Göss brewery

Brauwelt International

253

–

255

Weber

(

2009

Untersuchungen Zur Silierung Von Biertrebern

Logos Verlag Berlin GmbH

Weger

Jung

Stenzel

, &

Hornung

(

2017

Optimized energetic usage of brewers' spent grains

Chemical Engineering & Technology

306

–

312

10.1002/ceat.201600186

10.1016/j.biortech.2021.125262

Weiermüller

Akermann

Laudensack

Chodorski

Blank

L. M.

, &

Ulber

(

2021

Brewers’ spent grain as carbon source for itaconate production with engineered Ustilago maydis

Bioresource Technology

336

125262

Wen

Zhang

Duan

Zhang

, &

(

2019

A mini-review on brewer's spent grain protein: Isolation, physicochemical properties, application of protein, and functional properties of hydrolysates

Journal of Food Science

3330

–

3340

10.1111/1750-3841.14906

Westendorf

M. L.

, &

Wohlt

J. E.

(

2002

Brewing by-products: Their use as animal feeds

Veterinary Clinics: Food Animal Practice

233

–

252

10.1016/s0749-0720(02)00016-6

10.1016/j.jclepro.2019.03.286

Wierzba

, &

Kłos

(

2019

Heavy metal sorption In biosorbents—Using spent grain from the brewing industry

Journal of Cleaner Production

225

112

–

120

10.1007/s12649-012-9108-8

Wyman

Decker

Himmel

M. E.

Brady

J. W.

Skopec

C. E.

, &

Viikari

(

2005

Hydrolysis of cellulose and hemicellulose

Polysaccharides: Structural diversity and functional versatility

1023

–

1062

Xiros

, &

Christakopoulos

(

2012

Biotechnological potential of brewers spent grain and its recent applications

Waste and Biomass Valorization

213

–

232

10.1007/s11270-008-9626-y

Zubair

Bhatti

H. N.

Hanif

M. A.

, &

Shafqat

(

2008

Kinetic and equilibrium modeling for Cr(III) and Cr(VI) removal from aqueous solutions by Citrus reticulata waste biomass

Water, Air, and Soil Pollution

191

305

–

318