Bioavailability of Organic Nitrogen from Treated Wastewater

EPA requested guidance from STAC regarding the bioavailability of organic nitrogen (ON) released through wastewater treatment plant effluents (effluent organic nitrogen or EON) and the appropriateness of a proposed assay for assessing its bioavailability. According to Virginia law, dischargers can argue cases before a nutrient control board to increase their discharge allowances or caps based on their assessment of EON bioavailability. A facility in Virginia employed a bioassay similar to a biochemical oxygen demand (BOD) assay in an attempt to demonstrate that a large fraction of their EON was biologically unavailable. In the short term, EPA requested guidance on: 1) whether EON is bioavailable in the proximate and ultimate receiving waters, and 2) whether the assay employed by the Virginia facility is appropriate for assessing EON bioavailability. In the longer term, the EPA has sought guidance on developing appropriate assays of EON bioavailability. To address this request, STAC formed an ad hoc committee of experts, including wastewater engineers, biogeochemists, and estuarine ecologists, who prepared the accompanying report on their findings.