Domestic wastewater treatment with a novel process of chemically enhanced primary treatment using fly ash-based coagulants and constructed wetland

A novel integrated system of chemically enhanced primary treatment and constructed wetland was studied, aiming to provide an efficient domestic wastewater treatment method. In the coagulation pre-treatment, a composite coagulant was made from fly ash. This coagulant efficiently removes COD, suspended solids (SS) and total phosphorus (TP) from the wastewater. The removal efficacy depends on the dose of coagulant and pH of wastewater. At a dosage of 1 mL/L and pH of 6–7, the removal efficiencies of COD, SS and TP of domestic wastewater reached 64%, 93% and 91%, respectively. The operation of simulated subsurface-flow constructed wetland under different hydraulic loadings (0.03–0.10 m³/(m² d), corresponded to 5.61–18.7 g/(m² d)), which received effluents from the previous coagulation treatment, showed that COD might be further reduced 64%–77% with effluent COD values lower than 60 mg/L. However, the ammonium nitrogen was less effectively removed by limited oxygen transfer as a result of consumption through organic matter degradation. TP removal was compensated by the phosphorus release within the bed. Compared with single-stage, two-stage combinations of the subsurface horizontal flow beds are an alternative approach to improve the removal of ammonium nitrogen.