Case Study of Anaerobic Digester Foaming: Effects of Mixing in Full-Scale Digesters

Abstract

Full-scale anaerobic digesters (AD`s) in three different wastewater treatment plants (WWTPs) were compared to study the effects of feeding and mixing on biogas production, total solids (TS) and temperature variation inside the digesters. In the three studies, mixing frequency was significantly reduced in both egg-shaped and cylindrical digesters. Total solids and temperature monitoring along the depth of the digesters illustrated that reducing mixing frequency by up to 75% did not significantly impact digester performance. This study demonstrates that significant energy savings can be accomplished by optimizing digester mixing without compromising performance. Reduced mixing has resulted in significant energy savings to the utilities that participated in the study.

A full-scale study of mixing and foaming in egg-shaped anaerobic digesters

“…As mentioned in Section 4.1, G. amarae counts in the ML correlated closely to mixed liquor temperature and to historical observations of foaming periods in the digesters at Oceanside WPCP (Miot et al, 2013). To confirm the existence of G. amarae, FISH analysis were carried out on samples of ML and digester sludge at different phases of the study, as described in Section 3.3.3.…”

“…Previous plant evaluations, reports and observations correlated the presence of G. amarae in the ML with foaming in these digesters (Miot et al, 2013). G. amarae growth in the ML was directly correlated to the ML temperature, which in turn was shown to correspond with the ambient temperature (Miot et al, 2013).…”

“…Previous research has directly correlated the presence of foam in the digesters at Oceanside WPCP to the presence of G. amarae in the ML feed to the digesters (Miot et al, 2013). In this study, Gram staining and FISH techniques were used to determine if filamentous bacteria, such as G. amarae, were present in digester sludge samples.…”

“…However, a method was developed to analyze past data dating back to 2005 (Miot et al, 2013). This method consisted of analyzing and scoring a set of parameters, the values of which were likely to be impacted by the presence of foam in the gas handling system.…”

“…This method consisted of analyzing and scoring a set of parameters, the values of which were likely to be impacted by the presence of foam in the gas handling system. These parameters included gas production flow rate (DQ > 100), gas pressure differential (DP > 10), and ML G. amarae concentration (10 6 intersections/mg VSS) (Miot et al, 2013).…”