The observed temperatures in each basin during the sampling period were 15–35 °C, and the observed air temperatures were 3.2–12 °C. Measurements of the removed BOD5 and TN were 96.9–1771 mg L−1 and 12.05–1550 mg L−1, respectively. BOD5 value of the sludge thickener is 12 times higher than that of the secondary settling basin, More BOD is required to decompose the organic compounds considering residence time of the sludge thickeners. The A2O process is also used for treating wastewater with excessive phosphorus and nitrogen to decrease eutrophication and improve the water quality. Anaerobic digestion is used to treat sewage sludge containing primary and secondary settling sludge, which produces gases and liquid by fermentations and generates approximately 65,000 ton CH4/day which is reused to supply energy in the WWTP