A Survey on Efficiency of Natural Wastewater Treatment Systems and Activated Sludge for Municipal Wastewater Treatment

Consumption of dissolved oxygen by organic substances in water resources result in undesirable environment for living organisms. The aim of this study was to evaluate the efficiency of natural wastewater treatment systems and activated sludge for municipal wastewater treatment.

This one year-cross-sectional study was conducted on wastewater treatment plants in Kermanshah province. During the study, sampling of raw sewage and effluent of treatment plant was carried out and the efficiency of treatment plant was evaluated by measuring TSS, BOD5 and COD. All the sampling and testing procedures were adopted from the standard method.

The results showed that the annual average of BOD5 in effluent for Wetland, stabilization pond, extended aeration and conventional activated sludge was 55, 25, 21 and 23 mg/l respectively. Also the annual average was 143, 43, 40 and 40 mg/lfor COD, and 47, 101, 40 and 33 mg/l for TSS, respectively. For COD removal the conventional activated sludge (86.97%) and Wetland (61.6%) were the most efficient and least efficient systems. For BOD5 removal the stabilization pond (85.18%) and Wetland (72.01%) were the most efficient and least efficient systems. The BOD5 / COD ratio in influent were respectively 0.56, 0.62, 0.59 and 0.55 in these systems.

In all of the mentioned wastewater treatment systems, the effluent parameters comply with the Iran environmental protection agency standards and it can be reused or discharged to water bodies. Also it can be concluded that, for above-mentioned parameters the removal efficiency of natural systems was more than activated sludge.