Effect of packing substrates on the purification of municipal wastewater treatment plant effluent

The effluents of municipal wastewater treatment plant (WWTP) contain excessive nitrogen and phosphorus compared with the concentration in rivers or lakes. To reduce the pollutant load placed on aqueous environments, constructed wetland (CW) technology has been widely applied to advanced wastewater treatment. Packing substrates in CW could remove various pollutants. Steel slag, yellow earth, kaolin, volcanic rock, anthracite, and ceramsite could effectively remove phosphorus (P); volcanic rock, ceramsite, zeolite, yellow earth, manganese sand, and activated carbon have an affinity for ammonia nitrogen (NH4+-N). After 24 h reactions with the WWTP standard 1B synthetic wastewater, four packing substrates, i.e., volcanic rock and anthracite (1:1), volcanic rock and yellow earth (2:1), zeolite and yellow earth (2:1), and manganese sand and activated carbon (1:3), could remove over 56% and 30% of NH4+-N and phosphorus respectively. In addition, anthracite and volcanic rock (1:3), anthracite and activated carbon (1:40), anthracite and manganese sand (1:5), and anthracite and zeolite (1:4) effectively purified NH4+-N and phosphorus in secondary WWTP effluent, with removal efficiency exceeding 39% and 27%, respectively. A sequential experiment was performed to optimize packing substrates ratios in CW with volcanic rock and anthracite, ceramsite and yellow earth, and manganese sand and activated carbon. When the quantity of the substrate was doubled, most packing substrates adsorb more than 50% phosphorus and NH4+-N of the standard 1B WWTP synthetic wastewater. Considering the removal efficiency of packing substrates on phosphorus and NH4+-N, it is suggested that manganese sand and activated carbon (1:3), volcanic rock and anthracite (2:1), and yellow earth are appropriate substrates for CW in WWTP effluent advanced treatment.