Sequential Anaerobic-Aerobic Digestion for Enhanced Volatile Solids Reduction and Nitrogen Removal

Abstract

Sequential anaerobic -aerobic digestion has been studied for use in wastewater treatment, but has had limited use for digestion of waste solids. Recent studies suggest that some solids in sludge are degraded only during anaerobic digestion and some only during aerobic digestion. Therefore, dual digestion (anaerobic/aerobic) would be expected to provide volatile solids reduction beyond that achieved by either anaerobic or aerobic digestion alone. In this investigation, dual digestion was compared to single stage anaerobic digestion using both mesophilic (35 0 C) and thermophilic (55 0 C) digestion. The results showed that dual digestion was able to achieve up to 65% VS reduction, compared to 46 and 52% by mesophilic and thermophilic digestion, respectively alone. Aerobic digestion times of 3, 6 and 9 days were studied and increased VS reduction was observed for all aerobic detention times. This study also showed that more than 50% total nitrogen and 80 % ammonia can be removed from the anaerobic effluent after digesting it aerobically.

Effect of Secondary Aerobic Digestion on Properties of Anaerobic Digested Biosolids

“…Gas production, percentage gas distribution, pH, DO, digester temperature, chemical oxygen demand (COD), TKN, ammonia, selected dissolved ions and volatile fatty acids (VFA) were conducted and results are discussed elsewhere (Kumar et al, 2006).…”

Performance of sequential anaerobic/aerobic digestion applied to municipal sewage sludge

“…In the literature (Kumar et al, 2006a(Kumar et al, , 2006b low SRTs are suggested for the aerobic phase that can be considered to be a finishing step to complete the removal process initiated in the anaerobic one. Instead, if it is desired to reduce the nitrate load recycled to the WWTP with the supernatant from the digester, the optimal SRT should be high enough to ensure efficient nitrification and simultaneous denitrification.…”

“…The basic motivation behind this approach arises from the different reaction environments (anaerobic and aerobic) provided to attain optimal biodegradability conditions for the different volatile solid (VS) sludge fractions. This point is well addressed in Kumar et al (2006aKumar et al ( , 2006b reporting a simple classification for the sludge constituent fractions in terms of VS degradability:…”

“…Recently multiestep digestion has received increased interest and previous studies have demonstrated the potential of this approach to improve the performance of conventional digestion processing (Kumar et al, 2006a(Kumar et al, , 2006bParravicini et al, 2008;Zupancic and Ros, 2008). Kumar et al (2006a) observed that an aerobic digestion stage downstream from the anaerobic digestion unit improved the overall process performance both in terms of VS removal efficiency and dewatering properties of the biosolids.…”

Sequential Anaerobic/Aerobic Digestion for Enhanced Carbon/Nitrogen Removal and Cake Odor Reduction

“…This represents an additional opportunity for water resource recovery facilities to reduce their ammonia discharge. Other advantages of sequential AN/AERO digestion are the improved digestate dewaterability (Kumar et al, 2006b), enhanced pathogen destruction and reduction in odorcausing volatile sulphur compounds (Banjade, 2008).…”