Eco-friendly and low-cost Enhanced Pond and Wetland (EPW) system for the treatment of secondary wastewater effluent
2018
Park, Jason B.K. | Craggs, Rupert J. | Tanner, Chris C.
To demonstrate the feasibility of Enhanced Pond and Wetland (EPW) system for the treatment of Biological Trickling Filter (BTF) effluent, pilot-scale EPW systems were installed and operated in New Zealand climate conditions. The system consisted of: two High Rate Algal Ponds (HRAPs) followed by gravity Algal Harvesters (AHs), two Surface Flow Constructed Wetlands (SFCWs), and a Woodchip Denitrification Filter (WDF). The wastewater treatment performance of each treatment component was monitored fortnightly over six months (late autumn to winter) in terms of TSS, total and soluble BOD₅, nutrients (N and P) and E.coli removal. Algal biomass production, algal harvest efficiency, and algal dominance in the HRAPs were also determined. The pilot-scale system maintained low final effluent TSS and BOD₅ concentrations below 5 and 8 mg L⁻¹ respectively, and achieved high removal of nitrogen (NH₄-N: ∼95%; NO₃-N: 77%), phosphorus (DRP: ∼65%) and E. coli (at least 3-log E. coli removal) throughout the experimental period. Particularly in autumn, the HRAPs achieved almost complete removal of both NH₄-N (5.0 to <0.3 mg L⁻¹) and NO₃-N (3.4 to <0.2 mg L⁻¹) mainly through algal assimilation. Furthermore, when sunlight U.V radiation was high, ∼4-log E. coli removal (10⁴ to <2 cfu/100 ml) was achieved in the HRAPs mainly through sunlight disinfection. The HRAPs had algal biomass productivity of 7.2 and 4.1 g m⁻² d⁻¹ in autumn and winter respectively, and the algal biomass was efficiently removed in AHs by gravity sedimentation (∼80% TSS removal after 6.5 h settling) through bio-flocculation under nitrogen limiting conditions (<0.5 mg L⁻¹). Overall, the Enhanced Pond and Wetland system can efficiently treat secondary wastewater effluent from a domestic wastewater treatment plant and produce a high quality final effluent with minimum energy inputs.
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