Defining full-scale Anaerobic Digestion Stability: The Case of Central Weber Sewer Improvement District

Abstract

A full-scale anaerobic digester receiving a mixture of primary and secondary sludge was monitored for one hundred days. A chemical oxygen demand (COD), volatile solids (VS), and mass balance were conducted to evaluate the stability of the digester and its capability of producing methane gas. The COD mass balance could account for nearly 90% of the methane gas produced while the VS mass balance showed that 91% of the organic matter removed resulted in biogas formation. Other parameters monitored included: pH, alkalinity, VFA, and propionic acid. The values of these parameters showed that steady state had occurred. At mesophilic temperature and at steady state performance, the anaerobic digester stability was defined as a constant rate of methane produced per substrate of ΔVS (average rate=0.40 L/g). This constant rate can be used as stability index to determine the anaerobic digestion stability in an easy and inexpensive way.

Performance of the Bio-electrochemical Anaerobic Digestion of Sewage Sludge at Different Hydraulic Retention Times

“…In the HRT range of 20 to 10 days, pH change due to the abrupt step change of HRT was not observed. Generally, pH in the anaerobic digester is determined by a combination of some state variables including alkalinity, carbon dioxide in biogas, and the VFA, which are affected by digester input parameters such as the characteristics of feed sludge and operational conditions. , In the bio-electrochemical digester, the alkalinity was stable at 4,860 mg/L (3,780–5,450 mg/L) as CaCO 3 (Figure b). The alkalinity was not affected by the HRTs ranging from 20 to 5 days, and the temporary drop due to the step change of HRT from 10 to 5 days was quickly recovered, similarly to the pH.…”

A high‐rate anaerobic biofilm reactor for biomethane recovery from source‐separated blackwater at ambient temperature

“…Generally, successful anaerobic digester operation possesses great ability to withstand the fluctuations of the inflow quality and shock loading to sustain process stability. In an anaerobic digester, pH level in the liquid phase and buffer capacity against pH fluctuation can be influenced by some state variables including carbon dioxide in biogas, alkalinity, the acid concentration, and operational conditions including temperature, HRT, OLR, and substrate characteristics(Demitry & McFarland, 2015; Song et al., 2016). The optimum pH range for anaerobic digestion has been proved to be 6.8–7.2 (Cioabla et al., 2012).…”