Demonstration of the Optium Level of Phosphorus Addition for Operation of Aeration Stabilization Basins, 1998 Environmental Conference Proceedings

Bruce A. Fenske, P.E.

Eder Associates

David W. Gabryel

Fletcher Paper Company

The Fletcher Paper Company (Fletcher) is subject to wastewater permitting by the Michigan Department of Environmental Quality (MDEQ). The NPDES permit issued to Fletcher in 1992 included limitations on BOD5 and total suspended solids. In order to comply with these limitations consistently, Fletcher upgraded its wastewater treatment system to provide secondary treatment using aeration stabilization basins (ASBs). If the secondary treatment provided by these ASBs is to work properly, phosphorus must be added to the mills wastewater, and the MDEQ regulates the discharge of phosphorus according to technology-based standards. These standards are designed to minimize the discharge of phosphorus to the Great Lakes and are part of an international agreement between the United States and Canada that was negotiated by the International Joint Commission.

In anticipation of receiving a phosphorus limitation when its NPDES permit was reissued, Fletcher undertook a 14-month study of phosphorus addition to its wastewater to determine the minimum amount of added phosphorus that the ASBs require to provide sufficient BOD5 removal to meet permit limitations. To ensure that its effluent limitation for phosphorus would not reduce the new treatment system’s ability to remove the maximum amount of BOD5 from the mills wastewater, Fletcher undertook the study, following approval by the MDEQ, to determine (1) the best nutrient addition rates and (2) the levels of phosphorus these rates would produce in the treated effluent.

This paper presents the results of the study of phosphorus use in the ASBs to meet categorical effluent limitations for BOD5 and total suspended solids established by the MDEQ. Like other paper mill wastewaters, Fletcher’s wastewater is nutrient-deficient, and the treatment system design provides for nutrient addition to assure proper growth of the biological organisms that remove BOD5. During the study, nutrient addition rates were varied according to a predetermined schedule, and the resulting BOD5 and total suspended solids levels were monitored to document the effect that nutrient levels had on treatment efficiency. Results of the study recommended a nutrient addition rate that supported optimal BOD5 removal and established an equilibrium effluent phosphorus concentration based on this optimal BOD5 removal rate. This equilibrium phosphorus concentration was adopted by the MDEQ as a less stringent phosphorus

limitation in Fletchers reissued NPDES permit.