Results of COD concentrations presented in Fig. 3 show
that the removal efficiency of COD ranged from 60.87%
to 90.07% with average 80.05%. The lowest effluent
concentration of COD was 20 mg/L in April. The highest
effluent concentration of COD was 47 mg/L in January,
resulting from the water temperature being lowest at that
time. The degradation effect for the combined wastewater
was good, and the outflow water quality was steady. COD
at the outlet was able to meet the grade IV (20–30 mg/L)
standard of environmental quality standards of surface
water (GB3838-2002), and was better than the grade I-A
(< 50 mg/L) discharge standard of pollutants for municipal
wastewater treatment plants (GB18918-2002).