Use of biodegradable dissolved organic carbon to assess treatment process performance in relation to solids retention time

A biodegradable dissolved organic carbon (BDOC) method has been developed and used to analyze secondary- and advanced-treated wastewater effluents and to investigate correlations between residual organic content and the solids retention time (SRT). Conventional biochemical oxygen demand (BOD) bottles and a 28-day incubation period were used. Secondary wastewater effluents from Hawaii were found to contain between 9.0 and 14.0 mg/L of dissolved organic carbon (DOC), of which 23 to 35% was biodegradable in the 28-day BDOC test (from a survey of nine treatment plants). Bench-scale, continuous-flow activated-sludge biological reactors treating synthetic wastewater were operated at SRTs between 2 and 15 days, and effluent BDOCs were determined. A good BDOC prediction equation was developed that incorporates the initial DOC, the DOC remaining after 5 days, and the SRT of the system from which the sample originated. This equation can be used to determine the BDOC value using data that can be obtained during a conventional 5-day BOD test. The determined equation was found to be appropriate for some of the full-scale wastewater effluent survey data.