Examination of Digester Gas Production on an Hourly and Minute Time Scale

Digester gas production profiles at several water reclamation plants (WRPs) were examined during a digester gas piping upgrade study for the Metropolitan Water Reclamation District of Greater Chicago (MWRD). The digester gas production rate data retrieved from this study had time intervals on the order of minutes between observations. The goal of this analysis was to better understand the fluctuations in digester gas production rates that occur within one day and within one shift at the various WRPs. The results of this analysis brought to light a finely evolved digester ecosystem that is highly adapted to regular batch feeding intervals. Discussion is provided on patterns observed from the data, including the effects of batch feeding multiple digesters, and timing and amplitude of gas peaking. Using observed trends from the data, digester gas production models were developed to help determine future gas profiles and recommend operational strategies to limit peaking. With a better understanding on how digesters react on a short term scale, WRPs may be able to start managing their biogas before it even becomes biogas.