Assessing the variability in biomethane production from the organic fraction of municipal solid waste in batch and continuous operation

• Eight organic waste streams were examined for biochemical methane potential (BMP).
• Commercial food waste produced 560 mL CH4 g VS−1 in continuous trials.
• Raising the loading rate to 4 kg VS m−3 day−1 led to a reduction in methane yield.
• The low C:N ratio led to levels of 7000 mg N L−1 at high loading rates.
• Free ammonia levels of 1000 mg N L−1 were encountered at a pH of 8.

This paper examines the variability in biomethane potential from the organic fraction of municipal solid waste depending on source of origin. Eight organic waste streams were examined for biochemical methane potential (BMP). Specific methane yields of between 274 and 368 mL CH4 g VS−1 for household waste and 491–535 mL CH4 g VS−1 for commercial waste were achieved. Inclusion of garden waste reduced methane yields. A continuous trial on commercial food waste produced an average of 560 ± 29 mL CH4 g VS−1 at a moderate organic loading rate (OLR) of 2 kg VS m−3 day−1 with a hydraulic retention time (HRT) of 30 days. Raising the OLR to 4 kg VS m−3 day−1 led to a reduction in specific methane yield. The low carbon to nitrogen (C:N) ratio of commercial food waste (14.4) led to process instability due to total ammonia nitrogen levels in excess of 7000 mg L−1 towards the end of the trial.