Study And Pilot-scale Project Design Of Ecological Pond And Constructed Wetland Combination System Treating Polluted Shahe Reservoir Water

The water environment of Shahe Reservoir located in Beijing is greatly destroyed due to human activities.The main source water of Shahe Reservoir water is derived from the south and north Shahe Rivers and the nearby reclaimed water plant.The poor fluidity,self-purification ability and water ecosystem,resulted serious nitrogen and phosphorus pollution of Shahe reservoir.In this study,the experimental device with the pre-ecological pond,constructed wetland and post ecological pond as the core was constructed.The zeolite and slag were used as the substrate of constructed wetland.The calamus,canna and spirulina were planted in the ecological pond,constructed wetland combination system.The system was operated continuously from May to November under open air conditions.This study explored the influence of hydraulic residence time(HRT)of pre-ecological pond on the pollutants removal of overall combined system and that of each unit.Meanwhile,the appropriate natural material was selected as supplementary slow-release carbon sources to study its effect on denitrification of the combined system..The results indicated that preposition ecological pond HRT has obvious influence on the treatment effect of composite system.Algae in pre-ecological pond would proliferate when HRT is greater than 0.5 day,resulting in better absorption on nitrogen(N)and phosphorus(P)but higher ecological risk in the meantime.However,this would lead to instability of effluent quality and blockage problems in constructed wetland.Considering the removal performance of the combined system on each pollutant,the optimal HRT for pre-ecological pond was determined as 0.5 d,which corresponded to higher removal efficiency of chemical oxygen demand(COD),total phosphorus(TP)and ammonia nitrogen(NH4+-N)(83.5%,73.7%and 96.0%)and lower Nitrate nitrogen(NO3--N)and total nitrogen(TN)removal(57.6%and 68.4).Through the experiment of carbon source selection,wood blocks were introduced into the system as natural slow-release carbon source with the release rate of 0.2 mg/(g·d),resulting in a significant improvement of the denitrification ability.The removal rates of COD,TP,NH4+-N,NO3--N and TN were 72.8%,57.6%,93.9%,85.0%and 88.4%individually.The effluent quality achieved the IV class standard(Chinese environmental quality standards for surface water).A pilot-scale project on treatment of Shahe Reservoir water was designed in this paper,with the design flow of 30 m3/d and the total project cost of ? 98,128.