However, since untreated effluents from our processes are typically deficient in nitrogen and phosphorus, the addition of these nutrients are required in order to achieve a high treatment efficiency rate. Consequently, each year, mills with high rate biotreatment systems are spending up to $1.5 million on supplemental nutrients which are necessary to provide treatment performance acceptable to comply with government regulations.
The discharge of excess residual amounts of phosphorous (P) in the final mill effluent to the receiving waters is a wasted expense as well an environmental concern for many mills. As such, there is a need for new strategies to minimize costs associated with P usage while minimizing its impact on the environment, and researchers from FPInnovations’ Resources Management team initiated a study to address this issue. In collaboration with two Quebec mills, phosphorus dosing was systematically reduced following a step-wise approach while closely monitoring treatment performance. The two mills were chosen based on their relatively high potential for reducing P addition and their having a sequential batch reactor (SBR) design, which is a modification of the conventional activated sludge process.
The ability of pulp and paper biotreatment systems to reduce their demand of supplemental phosphorus nutrients was demonstrated through two field studies. As a result, a phosphorus reduction of approximately 50 per cent was realized for each of the implementing mills. The floc structure of the mixed liquor suspended solids (MLSS) was improved as a result of P dose reduction, resulting in better settling sludge, while treatment performance was maintained. Substantial savings in effluent treatment costs were witnessed with the added benefits in terms of improved sludge settling.