The present study aimed the cost-effective removal of nitrogen and phosphorus nutrients, along with organic matter, from biologically pretreated domestic wastewater by chemical post-treatment. To achieve this objective, following the secondary settling biologically pretreated wastewater was subjected to chemical treatment by lime. And thereby we aimed to decrease phosphate, ammonium, and COD concentrations to low levels in the final effluent.
Sewage wastewater was fed into the activated sludge aeration column on a continuous-flow basis. Effluent was withdrawn from the side of the tank with a pump that helped operate the biological stage at a constant hydraulic retention rate under four different flowrate operations. The hydraulic retention time-controlled operation resulted in an almost constant sludge-age operation. This operation avoided nitrification, while the applied retention time was sufficient to convert nitrogen and phosphorus in the raw wastewater into ammonium and orthophosphate forms, respectively, in the biological stage. Following the secondary settling, lime was added to the supernatant and pH was increased to 10.5. Ammonia nitrogen was removed by air stripping, and removal of phosphate was achieved with chemical precipitation. Applied post chemical treatment by lime also helped decrease the supernatant organic matter content.