Evaluation of the biomethane yield from anaerobic co-digestion of nitrogenous substrates

Abstract

This paper examines three substrates for anaerobic co-digestion: abattoir waste; cheese waste and food waste. These substrates were assessed in detail for suitability for biomethane production. Biomethane potential (BMP) assays were carried out in mono and co-digestion for the three substrates and two mixes: T1 (40% abattoir waste; 50% cheese waste and 10% food waste on a wet weight basis) and T2 (30% abattoir waste; 40% cheese waste and 30% food waste). The C:N ratio of both mixes was below optimum. Low levels suggest that the production of free ammonia (NH3) in semi-continuous digestion was of primary concern. Both mixes were digested in a semi-continuous process for 25 weeks. The recommended operating condition for T1 was a loading rate of 3 kg VS mn(-3) day(-1) at a retention time of 23 days. The biomethane yield was 305 L CH4 kg(-1) volatile solids (VS) which was 87% of the BMP value and equivalent to 61% biodegradability. For T2 (with the higher C:N ratio) a higher loading rate of 4kg VS mn(-3) day(-1) at a lower retention time of 15 days was recommended. The biomethane yield was 439 L CH4 kg(-1) VS (99% of the BMP value and 84% biodegradibility). At these conditions, levels of total ammonical nitrogen (TAN) were 4109 and 4831 mg L(-1) for T1 and T2, respectively. These values are on the large side according to the literature. The temperature was reduced to 35 degrees C to minimize toxicity associated with TAN. Ratios of volatile acids to bicarbonate were typically in the range of 0.2-0.3 suggesting stable operation.

Investigation of the optimal percentage of green seaweed that may be co-digested with dairy slurry to produce gaseous biofuel

“…All samples were conducted in triplicate. A detailed description of the BMP assay is given by Allen et al (2013b). An ultimate analysis was carried out on each substrate to determine theoretical methane yields using the Buswell equation (Symons and Buswell, 1933).…”

Co-generation of biohydrogen and biomethane through two-stage batch co-fermentation of macro- and micro-algal biomass

“…The high C/N ratios in some macro-algae can lead to volatile fatty acid (VFA) accumulation and lack of nitrogen resource for the microorganisms . In contrast the low C/N ratios in many micro-algae species can cause high ammonia levels which inhibit the anaerobic fermentation process (Allen et al, 2013b). Thus, mixing carbon-rich macro-algae and nitrogen-rich micro-algae at a suitable C/N ratio as co-substrates will theoretically improve the fermentation performance (Xia et al, 2015a).…”

Methods for determination of biomethane potential of feedstocks: a review

“…The chemical composition of FW is presented in Table 2. FW composition is also determined by whether the waste has been segregated on the basis of source or is from a co-mingled source, separated at materials recovery facility (Allen et al, 2013). FW is easily biodegradable and has high methane potential yield (Strong et al, 2016).…”

“…This is based on energy value of the feedstock that is estimated from its elemental composition. For example, given the CH 4 energy value of 37.78 MJm -3 , the theoretical maximum CH 4 value was estimated at 560 L CH 4 . energy (f e ) and which fraction is used for synthesis of cellular material (f s ) (Labatut et al, 2011).…”

“…The amount of CH 4 and CO 2 of the biogas that ends up in the headspace of closed vials is measured by means of gas chromatography (GC) (EC, 2002).…”