Study on indicators for on-line monitoring and diagnosis of anaerobic digestion process of piggery wastewater

•The response of state indicators to different types of load disturbances were studied.•Only H2, H2S, propionate, TVFAs and biogas yield showed positive response to the load disturbances.•A combination of H2∕H2S was chosen as the indicators.

To avoid the instability and failure of anaerobic digestion, a process of monitoring and controlling is strongly required. State indicators including biogas yield, methane content, hydrogen (H2), hydrogen sulphide (H2S), pH, total volatile fatty acids (TVFAs) and individual volatile fatty acids were studied under different types of load disturbances in order to find the most effective indicator(s). During load disturbances, biogas yield increased quickly in response to the easily degradable compounds while slowly to the complex compounds. Relatively stable methane content (55.8%-66.0%) and pH (6.6-7.2) were observed. H2 increased more than 200 times, 6 times and 15 times respectively for glucose, peptone and lipids. While H2S increased from 1000 ppm to 3500 ppm, 3500 ppm and 4221 ppm respectively for glucose, peptone and lipid. Not all individual VFAs except propionate made obvious response to the load shocks which rose from 6.5 mmol/L to 49.8 mmol/L, 17.1 mmol/L and 28.1 mmol/L respectively for glucose, peptone and lipids. A combination of H2∕H2S was chosen to monitor this kind of digester dealing with piggery wastewater.