"Grade A"tail water standard improvement based on constructed wetlands with different substrates
In response to issues such as low denitrification efficiency and unclear hydraulic load of key param-eters in the upgrading and reconstruction of tail water in wastewater treatment plants by constructed wetlands,three groups of constructed wetlands with gravel(wetland A),zeolite(wetland B)and zeolite+pyrite(wet-land C)as substrates were constructed.By changing the hydraulic retention time(HRT),the restriction fac-tors and optimum operation hydraulic load of upgrading the"Grade A tail water"of municipal sewage treatment plants to"Quasi-Class Ⅳ water quality"were studied in constructed wetlands with different sub-strates.The results indicate that total nitrogen(TN)is the most critical factor limiting tailwater elevation,and the optimal operating hydraulic load for wetlands A and B is 0.30 m/d.Only wetland C can stably meet the re-quirement of TN≤1.50 mg/L for Class Ⅳ water quality lakes and reservoirs under hydraulic load≤1.80 m/d.Taking into account the nitrogen and phosphorus removal efficiency and economic land use,it is concluded that 0.90 m/d is the optimal operating hydraulic load for wetland C to elevate the tail water to Class Ⅳ water quality.This provides important reference value for the actual engineering design,operation,management,and application of pyrite in the tail water artificial wetland.
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