1995-2009: What Have We Learned About Effluent Biotreatment in Relation to Environmental Protection?

Since 1995, most mills in Canada have biotreatment in order to meet effluent regulatory limits for toxicity, biochemical oxygen demand, and total suspended solids. With occasional exceptions, the limits have been met. However, questions remain about effluent biotreatment regarding environmental protection, such as the reproductive capacity of fish. To address these concerns, a series of before-after studies were undertaken during the past decade. These included i) comparisons of effluents before and after biotreatment by means of fish (vitellogenin activity and egg production) and Ceriodaphnia (young production) tests done in the laboratory and ii) comparisons of fish communities in a river before and after the installation of effluent biotreatment at two mill sites. In all laboratory tests and with respect to all endpoints examined in these tests, the effects of the effluents after biotreatment were less or nonexistent when compared with the effects of the effluents before biotreatment. The assessment of the fish communities based on various metrics (e.g., percent piscivores, percent fish with anomalies) indicated improved conditions after the installation of biotreatment. Taken overall, the results indicated that biotreatment has improved effluent quality and this has resulted in clear improvements for the receiving environment.