SEQUENTIAL ANAEROBIC-AEROBIC DIGESTION FOR ENHANCED VOLATILE SOLIDS REDUCTION AND NITROGEN REMOVAL

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°C) and thermophilic (55°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.