Using Free Water Surface Constructed Wetland for the Mitigation of High PH Secondary Effluent From Municipal Wastewater Treatment Plant
Wastewater stabilization ponds (WSPs) are considered to be the most sustainable technology for small, rural and remote communities in North America. However, due to the configuration of WSPs and limited control over these systems, performance concerns during certain parts of the year may arise, as elevated temperature and extended hydraulic retention time (HRT) could stimulate excessive algal growth that results in sustained high pH levels in the system and effluent. Amherstview Water Pollution Control Plant (WPCP) in Amherstview, Ontario frequently experiences high pH effluent during the summer and is assessing the potential of a constructed wetland (CW) system to mitigate these operational issues. In order to design a CW, a bench-scale experiment was conducted to identify the best available substrates and operational conditions in the laboratory. A short-term assessment of four substrates followed by long-term monitoring of the two most promising substrates was undertaken under different HRTs and organic loading rates (OLRs). The results showed that peat exhibited the best pH attenuation capacity, and the pH attenuation performance could be substantially improved when the OLR was increased over 70 mg/L COD with a HRT longer than 4 days. The feasibility of this CW system was further tested in the field over the span of a year to investigate the nutrients removal efficiencies, as well as to evaluate the effects ofsubstrate and vegetation on the wetland system using authentic secondary effluents from the Amherstview WPCP. The results showed that all treatment systems could attenuate the pH level during both the start-up and operational periods, while significant nutrient removal performance could only be observed during the operational period. The results of the bench-scale and small-scale studies provided useful information for the design of the pilot-scale CW. The pilot-scale CW was successfully designed and established at the Amherstview WPCP. Overall, this newly designed free water surface (FWS) CW was highly effective at retaining phosphate (PO4-P) and total phosphorus (TP), and fairly effective at removing nitrate (NO3-N) and total nitrogen (TN). It is anticipated that the treatment performance of this CW could further improve when the CW becomes more mature.
URI for this recordhttp://hdl.handle.net/1974/23934
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