Clean Technologies and Environmental Policy (2018) 20:435–440
Biochemical methane potential of brewery by‑products
J. V. Oliveira
· M. M. Alves
· J. C. Costa
Received: 1 September 2017 / Accepted: 23 December 2017 / Published online: 6 January 2018
© Springer-Verlag GmbH Germany, part of Springer Nature 2018
Beer production generates by-products with high energy potential, namely trub (Tr, dead yeast from the fermentation) and
spent grain (SG, smashed barley grains). This work investigates the biochemical methane potential (BMP, volume of methane
produced per volatile solids of substrate—L kg
) of these by-products, performing batch anaerobic biodegradability assays.
Single substrates were evaluated as well as a mixture of Tr:SG (1:9, weight), in order to simulate the relative proportion
generated in breweries. Tr reached the highest BMP [(515 ± 4) L kg
], still, considering the total amount of by-product
available, the mixture of Tr:SG proved to be more rewarding in terms of volume of methane produced. The co-digestion of
Tr:SG with crude glycerol (cGly), which was chosen as a co-substrate to promote a synergetic eﬀect on their biodegradability,
was assessed by adding diﬀerent amounts of cGly, up to 33% (in weight). The assay with 10% of cGly achieved the highest
methane production [(573 ± 9) L kg
] and biodegradability [(94 ± 2) %], evidencing its potential for energy generation. The
co-digestion of these by-products presented a potential electricity production of 206 kWh per cubic meter of beer produced,
being capable of serving 80% of the brewer’s energy needs for heating.
Keywords Anaerobic digestion · Brewery by-products · Crude glycerol · Spent grain · Trub
Beer is one of the most consumed beverages in the world,
with an average consumption of 23 L per person per year.
Thus, the brewing industry is one of the leading economic
contributors to most countries in the world (Hay et al. 2017).
However, huge volumes of by-products and wastewater with
high content of degradable organic pollutants are produced.
Two important by-products are: (1) spent grain (SG), a
mixture of barley grain husk, pericarp and fragments of
endosperm, resulting from the mashing process (Pires et al.
2012), and (2) trub (Tr), also known as dead yeast or surplus
yeast, from the fermentation step (Ferreira et al. 2010). SG
and Tr may reach 30 and 3% of the volume of beer pro-
duced, respectively (Fillaudeau et al. 2006). Currently, waste
(water) management and disposal represent a signiﬁcant cost
for brewery industry and an important aspect of concern
for a sustainable brewery operation (Unterstein 2000). The
main use of brewery by-products regards animal nutrition,
but alternative options are worth to be investigated for valu-
ing (Fillaudeau et al. 2006).
Anaerobic digestion (AD) processes appear as a good
alternative to add value to these by-products, recovering,
in this way, energy in the form of biogas. Raw SG biometh-
ane potential can range from 271 L kg
of volatile solids
(VS) of substrate (Čater et al. 2015) to 387 L kg
substrate) (Bochmann et al. 2015), reaching 89% of chemi-
cal oxygen demand (COD) removal eﬃciency (Gonçalves
et al. 2015). Still, improvements can be achieved if some
pre-treatments were applied, such as enzymatic hydrolysis
(Wang et al. 2015). Regarding Tr, its treatment by AD pro-
cesses used to involve dilution with brewery wastewater (Yu
and Gu 1996; Xiangwen et al. 2008; Zupančič et al. 2012),
or application as a co-substrate with brewery spend grain
(Vitanza et al. 2016). No adverse eﬀects were found by co-
digesting yeast with wastewater, for concentrations up to
1.1% (v) on batch assays. Moreover, in a full-scale operation
using 0.7% yeast concentration, improvement in the biogas
production (38.5%) was detected (Zupančič et al. 2012).
Anaerobic co-digestion takes advantage of complementary
substrates for balancing the COD:N ratio, minimizing opera-
tional costs and increasing the methane yield of the blended
substrates (Wang et al. 2016).
* J. V. Oliveira
Centre of Biological Engineering, University of Minho,
Campus de Gualtar, 4710-057 Braga, Portugal