De Moor, Sofie

Meers, Erik

Michels, Evi

Velghe, Filip

Wierinck, Isabelle

English

Ghent University Academic Bibliography

Feasibility of grass co-digestion in an agricultural digesterSofie De Moor 1, Filip Velghe 2, Isabella Wierinck 2, Evi Michels 1, Willy Verbeke 3, Erik Meers 1,41 Laboratorium Analytical Chemistry and Applied Ecochemistry, Ghent University, Coupure Links 653, 9000 Ghent, Belgium2 Organic Waste Systems, Dok Noord 5, 9000 Ghent, Belgium3 Inverde, Koning Albert II-laan 20, 1000 Brussel, Belgium4 Biogas-E, Graaf Karel de Goedelaan 34, 8500 Kortrijk, BelgiumContact: Sofie.DeMoor@UGent.beIntroductionThe European Union has set a goal to reach a share of 20% renewable energy by 2020. First generation energy crops evoke ethical concerns because of thecompetition with food production. Low impact biomass are all types of biomass that do not entail competition with food production when used for theproduction of renewable energy. Examples of low impact biomass are: crop residues, organic waste streams (kitchen, garden, agriculture, industry…), biomassfrom marginal or residual land, greenery cuttings, but also grass. Grass is often an unwanted side product from maintenance of permanent grasslands orroadside verges. Vast quantities are available in all European countries, and are already used by some countries in the production of renewable energy. Asanaerobic digestion is already a well established process, anaerobic co-digestion of grass could be a good strategy for densely populated regions like Flanders,which has no capacity to enlarge its agricultural areal, to achieve the 2020 goal. In this study, the feasibility of using grass (from roadside verges or grassland)as a partial feedstock in an agricultural digester is investigated. 10 to 20% grass was added to test reactors and the influence on process parameters andresidue composition was studied.Conclusions• The use of up to 20% grass in the input mix of a typical Flemish agricultural digester does not cause any problems for the biology of the reactor, nor does itinfluence the gas yield or composition.• Viscosity of the reactor content increases, but this effect can be kept in an acceptable range by the addition of 100 mg/kg DM of the enzyme mixtureMethaPlus L100.• With respect to the composition of the residue, no influence of the grass in the input could be determined. The fertilizer value of the residue was notendangered.• No differences were found between the use of roadside grass and grass from grassland.Experimental set-up• 4 test reactors were run in parallel for 17 weeks.• Each reactor had a volume of 50 l with an active content of 20-25 kg.Temperature was kept constant at 37 ± 2°C.• Feeding was done semi-continuously, 3 times a week (25 kg/m.d).• This resulted in a retention time of 50 days.• Reactor 1 (R1) had an input mix of 30% pig manure, 30% maize silage and40% side streams and served as ‘blank’.• Side streams consisted of 50% Biomix, 25% Biograanmix, 12.5% glycerinand 12.5% rapeseed press cake.• In week 1 to 8, 10% of the maize input was replaced by grass in R2 to R4.• From week 10 to 17, 20% of grass was added.• The reactor feeds were composed of:• Studied parameters:• Biogas yield and composition• Residue properties and compositionFigure 1. Input mix evolution during 17 test weeksResults• All studied process parameters (pH, EC, FOS/TAC, VFA, ammonium,biogas production, CH4 % of the biogas) indicated a stable digestion.• Biogas production was higher than what was expected from batchtests for biogas potential of the input streams (Figure 2).• This result indicates a synergistic effect of the input streams (Figure 1).• No different trends for different input mixes were observed.• All reactors, including the blank needed addition of 0.4% 	. 	to avoid excess HS in the biogas.• The biogas composition (CH	and HS did not change because ofgrass addition.• 10% grass addition had no effect on the residue, while 20% grasscaused a significant increase of the viscosity, resulting in a highermixing energy demand and a lower mixing efficiency.• The enzyme mixture in R4 lowered the viscosity to an acceptablelevel, but it was still higher than the blank (21,5 vs 9,5).• The residue composition (nutrient and contaminant level) was notnegatively affected by the addition of grass in the feed.Figure 2. Biogas production of the different test reactors(batch tests for biogas potential of input streams given as horizontal lines)R1: no grassR2: roadside grassR3: grassland grassR4: grassland grass + enzyme mixture (MethaPlus L100), started in week 6

Feasibility of grass co-digestion in a typical Flemish agricultural digester: influence on process parameters and residue composition

https://biblio.ugent.be/publication/4157650/file/4157655

Feasibility of grass co-digestion in a typical Flemish agricultural digester: influence on process parameters and residue composition

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Ghent University Academic Bibliography