Factors controlling headspace pressure in a manual manometric BMP method can be used to produce a methane output comparable to AMPTS

The manual manometric biochemical methane potential (mBMP) test uses the increase in pressure to calculate the gas produced. This gas production may be affected by the headspace volume in the incubation bottle and by the overhead pressure measurement and release (OHPMR) frequency. The biogas and methane yields of cellulose, barley, silage and slurry were compared with three incubation bottle headspace volumes (50, 90 and 180ml; constant 70ml total medium) and four OHPMR frequencies (daily, each third day, weekly and solely at the end of experiment). The methane yields of barley, silage and slurry were compared with those from an automated volumetric method (AMPTS). Headspace volume and OHPMR frequency effects on biogas yield were mediated mainly through headspace pressure, with the latter having a negative effect on the biogas yield measured and relatively little effect on methane yield. Two mBMP treatments produced methane yields equivalent to AMPTS

Role of trace elements in single and two-stage digestion of food waste at high organic loading rates

This study investigated trace element deficiency and supplementation in mono-digestion of food waste. A single-stage system was contrasted to a two-stage system (hydrolysis followed by methanogenisis). Initial hydrolysis is beneficial as it releases hydrogen sulphide (H2S), while the prevailing pH prevents an associated H2S induced precipitation of trace elements (TE). Stable digestion took place without TE supplementation until an organic loading rate (OLR) of 2.0 g VS L−1 d−1; this was followed by severe instability at an OLR of 2.5 g VS L−1 d−1 in both systems. A major accumulation of volatile fatty acids (VFA) inhibited methanogenic activity. A gradual deterioration of pH, VFA/TIC (ratio of VFA to alkalinity) and specific methane yields provoked reactor failure. The benefit of enhanced TE availability in the two-stage system was not apparent due to the complete absence of essential TE in the feed stock. Supplementation of deficient TE (Co, Fe, Mo, Ni and Se) induced recovery, reflected by an immediate improvement of VFA/TIC and VFA concentrations in both systems. Specific methane yields were restored and maintained at initial levels. At a 16 day retention time, elevated loading rates as high as 5 g VS L−1 d−1 allowed stable digestion with TE supplementation