Two Decades Constructed Wetland Experience in Treating Municipal Effluent for Power Plant Cooling at the Shand Power Station, SaskPower Part IV: The Effect of Seasonal Changes in Temperature, Rainfall

Emmanuel K. Quagraine, Bruce Duncan



This paper is fourth in series of publications on 20-year period constructed wetland (CW) operating experience at SaskPower’sShand Power Station and highlights the influence of season-related parameters such as temperature, rainfall and nutrient concentrations on ammonia-N (TAN) and NO3--N removal. The influent quality to the CW was influenced by temperature and rainfall. Theirimpacts in reducing TAN and NO3--N content in the wastewater were found to be concentration dependent. The effect of temperature and rainfall were estimated as ~5 % TAN and 4 % NO3--N reductionof the (at 0oC) background concentrationsper degree rise, and 1% TAN and 1% NO3--N reduction of (at zero rainfall) background concentrationsper mm depth of rainfall, respectively. The seasonal variation of the influent concentrations subsequently affected the effectiveness of the CW in removing TAN and NO3--N. Correlation and non-linear regression analyses were used to quantify effects of substrate concentration, temperature, rainfall and composite parameters promoting plant growth on removal efficiencies of TAN and NO3--N. Plant uptake was commonly the dominant means in removing these substrates. Temperature contribution toNO3--N reduction was more consistent at average of2.9 ±1.2% per degree rise. Its effect on TAN removal was however more variable and seems to show in two main groups: one group covering the early stages of operation till 1999 where significant variations were observed with essentially no temperature effect or negative effect exhibited commonly; and the second typified from 2000 to 2008 with average TAN reduction of 2.6 ± 0.9%per degree rise.Rainfall effect on TAN removal seemed to be only important after the initial stages of operation. On the whole, whether polishing lagoon or conventional treated effluent and irrespective of the operating season, the CW produced wastewater suitable for condenser cooling through the 2-decades period; even for systems such as this power plant where copper corrosion is of concern.