Control of Advanced Wastewater Treatment Costs Through Water Quality Modeling Techniques for a New Deink Pulp Mill, 1996 Environmental Conference Proceedings

Because a proposed deink pulp mill would discharge to a designated trout stream, very high standards were established for its effluent. The water quality model used by state officials to assess the impacts of wastewater on the creek used one set of permit limitations based on extreme low flows and high water temperatures that occurred infrequently in the stream. This model predicted that a treatment system using powdered activated carbon and costing the mill an estimated $1 million in O&M costs annually would be necessary. To save operating expenses by more accurately predicting conditions in the stream, a computer spread sheet-based water quality model was developed that used existing data and the Streeter-Phelps equation, but which also allowed the stream conditions to be modeled under a range of temperature and flow conditions. This model demonstrated that water quality standards could be met by adding powdered activated carbon an average of only three weeks per year, and the NPDES permit that was issued results in savings to the mill of over $900,000 per year. Mathematical water quality modeling can accurately characterize receiving waters under changing flow and temperature conditions, thereby incorporating flexibility into NPDES permits that can maintain water quality while saving dischargers unnecessary treatment costs.