Foaming Phenomenon in Bench‐Scale Anaerobic Digesters

Abstract

The Madison Metropolitan Sewerage District (The District) in Madison, Wisconsin has been experiencing seasonal foaming in their anaerobic biosolids digesters, which has occurred from mid‐November to late June for the past few years. The exact cause(s) of foaming is unknown. Previous research findings are unclear as to whether applications of advanced anaerobic digestion processes reduce the foaming potential of digesters. The object of this study was to investigate how configurations of thermophilic and acid phase‐thermophilic anaerobic digestion would affect foaming at the bench‐scale level compared to single stage mesophilic digestion for The District. Bench‐scale anaerobic digesters were fed with a 4 to 4.5% by dry weight of solids content blend of waste activated sludge (WAS) and primary sludge from The District. Foaming potential was monitored using Alka‐Seltzer and aeration foaming tests. The bench‐scale acid phase‐thermophilic digester had a higher foaming potential than the bench‐scale mesophilic digester. These results indicate that higher temperatures increase the foaming potential of the bench‐scale anaerobic digesters. The bench‐scale acid phase‐thermophilic digesters had a greater percent (approximately 5 to 10%) volatile solids destruction and a greater percent (approximately 5 to 10%) total solids destruction when compared to the bench‐scale mesophilic digester. Overall, for the full‐scale foaming experienced by The District, it appears that adding an acid phase or switching to thermophilic digestion would not alleviate The District's foaming issues.

Madison Metropolitan Sewerage District Foaming: A Case Study of the Effects of SRT, PAX-18, Microthrix Parvicella, and Extracellular Polymeric Substances

“…Similar results have been observed in other plants as well (Jenkins et al, 2003;Pagilla et al, 1998). It has been hypothesized that this is because the hydrophobic cell walls cause foaming in anaerobic digesters and destroying the cells only disperses them more evenly throughout the digester (Jenkins et al, 2003;Siebels and Long, 2012). Although PAX-14 has been shown to limit the growth of Microthrix parvicella in aeration basins, it also traps the organism in more dense flocs, which results in many of the organisms that would ordinarily be collected by scum skimmers instead ending up in the anaerobic digesters.…”

“…The primary purpose of this study was to determine if adding PAX to an activated sludge aeration basin would reduce foaming in the subsequent anaerobic digester receiving the PAX-containing WAS. In this study, PAX-18 (18% aluminum oxide content) was tested based on the recommendations of the manufacturer (Kemira, Atlanta, GA), Previous work using solids from the studied plant has indicated that non-viable organisms contribute to foaming in anaerobic digesters, and breaking the cells apart may actually increase foaming issues (Siebels and Long, 2012). Similar results have been observed in other plants as well (Jenkins et al, 2003;Pagilla et al, 1998).…”

“…Increases in filamentous organism densities may also be associated with the use of enhanced biological nutrient removal (Andreasen and Nielsen, 2000). Previous work by Siebels and Long (2012) suggested that the foaming problem at the studied facility resulted in part because of M. parvicella. Genetic analysis confirmed that M. parvicella was present in large numbers in both the digester foam and feed solids (Keadle et al, 2012).…”

Impacts of feed dilution and lower solids retention time on performance of thermal hydrolysis/anaerobic digestion

“…Foaming potential was measured using a similar approach to others (Ross & Ellis, 1992;Siebels & Long, 2013). A 100 ml sample of digestate was placed in a 1000-ml graduated cylinder with an aeration stone placed at the bottom of the graduated cylinder.…”

Anaerobic Processes

“…Alkalinity was a critical parameter in the digestion of thin stillage (Alkan-Ozkaynak and Karthikeyan, 2011). Foaming in different waste streams was assessed by Siebels and Long (2011), and bench-scale and acid-phase thermophilic treatment processes had a higher foaming potential than bench-scale mesophilic digestion. Shimada et al (2011b) assessed a two-phase acid-methane anaerobic digester to understand what bacteriological processes predominated, and found that the acid stage inhibited aceticlastic methanogens, and…”