Comparison between biological and chemical treatment of wastewater containing nitrogen and phosphorus

Abstract

The present work compared chemical and biological treatment methods to achieve the most efficient treatment for the reduction or elimination of phosphorus and nitrogen from mixed industrial-domestic wastewaters. Batch chemical precipitation by ferric chloride and aluminum sulfate (alum) and a continuous biological suspended growth system were investigated as well as the optimum operating conditions. Concerning chemical treatment, Alum generally achieved a higher removal efficiency percentage for the investigated pollutants compared with FeCl(3) at their optimum pH and dose, especially with chemical oxygen demand (COD). FeCl(3) treatment achieved success only with phosphorus removal, while none of the COD, 5-day biochemical oxygen demand (BOD(5)), total nitrogen (TN) and N-NH(3) achieved acceptable treatment and remained above the maximum permissible limits (MPL). Thus, for such wastewaters, alum is more efficient than FeCl(3). Biological treatment exhibited higher efficiencies, particularly towards nitrogen. TN removal increased by increasing the flow rate to 30-60 l/day. N-NH(3) removal was effective at the slowest flow rate and decreased with increasing flow rate, while an opposite trend was recorded for N-NO(3). At all flow rates, phosphorus levels were below the accepted MPL for discharging into natural systems. Moreover, there was a general trend for the proposed biological treatment to achieve a high removal efficiency for BOD(5) and COD, bringing them to acceptable levels to be released into watercourses safely, especially at the slowest flow rates. Thus, integration between the proposed chemical and biological treatment is highly recommended, producing high-quality effluents acceptable by the environmental law.