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Impact of solids retention time on dissolved organic nitrogen and its biodegradability in treated wastewater

Simsek, Halis, Kasi, Murthy, Ohm, Jae-Bom, Murthy, Sudhir, Khan, Eakalak
Water research 2016 v.92 pp. 44-51
biodegradability, dissolved organic nitrogen, eutrophication, oxygen, oxygen consumption, wastewater, water treatment
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 (SRTs) (0.3, 0.7, 2, 3, 4, 5, 7, 8, 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. Actual primary treated wastewater was used to feed the chemostat reactor. Results indicated that there was no trend between effluent DON and SRTs. The minimum and maximum effluent DON values were 4.75 mg/L (at 0.3-day SRT) and 8.08 mg/L (at 7-day SRT), respectively. Effluent BDON was comparable for SRTs of 0.3 to 4 days and had a decreasing trend with SRT after that. Effluent DON biodegradability (effluent BDON/effluent DON) ranging from 23% to 59% tended to decrease with SRT. This study indicates the benefit of high SRTs in term of producing effluent with less DON biodegrability which would lead to relatively less oxygen consumption and nutrient support in receiving waters.