Solids Retention Time as a Control Parameter for Organic Nitrogen

Dissolved organic nitrogen (DON) and its biodegradability in treated wastewater have recently gained attention because DON potentially causes oxygen depletion and/or eutrophication in receiving waters. Laboratory scale chemostat experiments were conducted at 9 different solids retention times (SRT) between 0.3 and 13 days to examine whether SRT could be used to control DON, biodegradable DON (BDON), and DON biodegradability (BDON/DON) levels in treated wastewater. Results indicated no trend between effluent DON and SRTs. Effluent BDON was comparable for SRTs of 0.3 to 4 days and had a decreasing trend with SRT after that. Effluent DON biodegradability tended to decrease with SRT. During SRT longer 4 days, chemostat contributed to non-biodegradable DON (NBDON). Model calibration results indicated a decreasing trend for ammonification rate, and growth rates for ordinary heterotrophs, ammonia oxidizing bacteria and nitrite oxidizing bacteia with increasing SRT.