In this paper, biological treatability study results of a pilot-scale aerated lagoon treating white-waters from a mechanical groundwood-based pulp and paper mill, and long-term operating experiences on two full-scale aerated lagoon systems are presented. Biological treatability study was conducted in a 200 1 semi-pilot aerated lagoon. The results have shown that five-day Biochemical Oxygen Demand (BOD5) values are less than 50 mg/l for a hydraulic retention time of 5 days. BOD removal rate constant (K) was found as 1.01 per day for 20°C. Bioassay tests were also conducted to evaluate the toxic impacts of white-waters on receiving waters and 96 hours median tolerance level TL(96), was found as 84% for species Lapistes reticularis. Long-term operating results from two full-scale wastewater treatment plants for paper mill effluents are also presented.

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