Effects of Anaerobic Digester Sludge Age on Odors from Dewatered Biosolids

Dewatered sludge cakes from bench scale anaerobic digesters operated at mesophilic temperatures and solids retention times (SRT) ranging from 10 days to 40 days were evaluated for their sulfur odor generation potential. Extracellular Polymeric Substances (EPS) extraction for digested sludge samples was also carried out. Static headspace sulfur gas analysis was successfully used to compare different sludge digestion SRTs for their odor potential. Higher volatile solids destruction was observed at higher SRTs and also the quantity of sulfur gases was found to decrease with an increase in the SRT of the anaerobic digesters. Results also showed that the cake solids concentration affected the odor generation from dewatered sludge cakes. Three different EPS extraction techniques were used to selectively extract materials bound to Fe, Al and Ca-Mg in sludge. It was found that Fe-associated proteins correlated well with sulfur gas production. As the Fe-associated protein content declined, the odor potential declined. Operating anaerobic digesters at higher SRTs seem to provide benefit with regard to odor generation. However, even after 40 days of anaerobic digestion, the odor potential remained high.