Nutrient Removal from Modeling Effluent of Secondary Treatment Process by Unvegetated Vertical Flow Constructed Wetlands

Abstract

Two types of unvegetated vertical flow constructed wetlands (UVFCWs) with zeolite and volcanic rock as composite substrates were constructed and the treatment performance for nutrient removal from modeling effluent of secondary treatment process was evaluated. The concentration of COD, NH4-N, NO3-N, NO2-N and DO were detected at five shorter hydraulic retention times (HRT). At carbon nitrogen ratio of 4:1, HRT of 0.25-4 days and a hydraulic loading (HL) of 0.995-1.592 m m d, the average COD concentration decreased from 60 mg L in the influent to 30 mg L in the effluent; the average NH4-N (ammonia) concentration decreased from 15 mg L to 2 mg L, thus meeting the Class-IV surface water standards in China. At the experimental conditions, HRT had little effect on the removal of COD, but had obvious influence on the removal of NH4-N. The concentrations of the NH4-N, NO3-N and NO2-N in the effluents of different depth of the reactor were all in low values, and the concentration of DO were almost unchangeable. The high efficiency of nitrification, denitrification and annamox process in the zeolite and volcanic rock composite substrates system is account for the good performance of UVFCWs. Keywords-vertical flow constructed wetlands; effluent of secondary treatment; COD removal; nitrogen removal; HRT.