Foaming dynamics in full-scale WWTP anaerobic digesters
This paper presents data from a full-scale experience of foam monitoring and antifoam reagents dosing as well as microbial community structure. The association of foaming episodes with microbial population structure and operational parameters has improved our understanding of foaming episodes and their causes. During this long-term study (273 days), two foaming episodes occurred in the anaerobic digesters under study. Microbial community analysis showed that the first foaming episode correlated with the proliferation of ST-12K33 (midas_s_22), which could be related to variations in the hydraulic retention time, a decrease in inflow solids concentration, and a decrease in digesters total alkalinity. The second foaming episode coincide with a clear migration of Ca. Microthrix parvicella from the activated sludge (bulking episodes) to the anaerobic digesters. Laboratory experiments showed that an increase in anaerobic digestion temperature and sludge pre-treatments have a positive impact on foam biodegradability and, therefore, they could be used as foam mitigation strategies. Finally, a techno-economic analysis showed that foaming episodes had an over cost of about 250 € d-1 and dropped the WWTP energy self-sufficiency from 67 to 63%.