Journal of Water SustainabilityE.K. Quagraine, Volume / Journal 8, Issue of 1, MarchWater 2018,Sustainability 1-24 1 (2018) 1-24 1 © University of Technology Sydney & Xi’an University of Architecture and Technology Two Decades Constructed Wetland Experience in Treating Municipal Effluent for Power Plant Cooling at the Shand Power Station, SaskPower Part V: The Effect of Seasonal Changes in Temperature, Rainfall and Influent Concentration on Phosphate Removal Emmanuel K. Quagraine Saskatchewan Power Corporation, Shand Power Station, Estevan, Saskatchewan, S4A 2K9, Canada ABSTRACT The paper is part of publication series on 2-decade constructed wetland (CW) operation at SaskPower’s Shand Power 3- Station. It highlights influence of some climatological factors and PO4 -P load on its removal efficiency. Influent 3- PO4 -P was influenced by temperature and rainfall in concentration-dependent manner. The respective effects were 3- o estimated as ~3.3% PO4 -P reduction of the (at 0 C) background concentrations per degree rise and 0.7% NO3-N 3- reduction of (at zero rainfall) background concentrations per mm depth of rainfall. Rainfall effect in reducing PO4 - P is attributed to dilution and was typically noticed after one-month lag period. Its immediate impact was usually 3- adverse leading to ~2.3% increase of the WWTP output PO4 -P (at zero rainfall) and attributed to releases from 3- sediment perturbation. Seasonal variation of influent PO4 -P load subsequently affected effectiveness in its removal 3- by the CW. Regression analysis was used to estimate influent PO4 -P, temperature and rainfall effects on monthly 3- removal efficiency of PO4 -P. Temperature was the most consistent and statistically significant influencing factor (at 3- least, at 80% confidence level) across the years, causing release of PO4 -P. Its magnitude of effect was shown in 3- either of two main ways: primarily as 3.4 ± 0.9% or otherwise as 10.9 ± 0.3% PO4 -P release (over the inlet concen- tration) per degree rise in temperature. Rainfall effect was erratic both in direction (positive or negative) and in magnitude (extent) of influence. The influent concentration effect was consistent in direction (net removal) but variable in magnitude suggesting co-dependence on other variables. On the whole, except the first spring season 3- where effluent PO4 -P of only 0.09 mg/L was displayed with ~99% removal, the CW was incapable of producing 3- effluent PO4 -P of the ≤0.33 mg/L required to prevent Ca3(PO4)2 scale formation during condenser cooling process. Keywords: Wetlands; wastewater; temperature; rainfall; phosphate; cooling; scaling; regression 1. INTRODUCTION (MWW) (Cooper, 2012; USEPA, 2004; Veil, 2007; Vidic et al., 2009). However, the reuse of Steam electric power plants require vast treated MWW (usually to secondary standard) amount of water for cooling and hence is for industrial cooling raises three main currently one of the major beneficial sectors operational concerns: scaling, corrosion and taking advantage to reuse the abundant bio-fouling (Barcelo and Petrovic, 2011; resource of treated municipal wastewater Puckorious, 2015; Rebhun and Engel, 1988; *Corresponding to: [email protected] DOI: 10.11912/jws.2018.8.1.1-24 2 E.K. Quagraine / Journal of Water Sustainability 1 (2018) 1-24 Selby et al., 1996; Veil, 2007; Vidic et al., influent concentration on performance of the 2009). CW, but the focus was specifically on total - The relatively higher nutrients (nitrogen (N) ammonia-nitrogen (TAN) and nitrate (NO3 )- and phosphorous (P)) and organic matter con- nitrogen (N). In this present paper, we continue tents in MWW sources as compared to fresh the discussion on seasonal influence on the CW water sources such as surface and groundwater performance, but this time with phosphate 3- is one of the major reasons for these conse- (PO4 )-P as the specific nutrient focus. The 3- quence in industrial cooling applications. Con- paper also discusses seasonal PO4 -P varia- structed wetlands (CWs) have demonstrated tions in the effluent quality and the potential potential to further reduce these constituents in impact on reuse applications in thermoelectric treated MWW of various standards (Greenway, power plant condenser cooling. As earlier 2005; Kadlec and Wallace, 2009; Quagraine, discussed (Quagraine and Duncan, 2017), a 2017; Vymazal, 2010), and there is current good understanding of seasonal variations of interest to take advantage of various other nutrient levels in the CW effluent used for benefits inherent in CW technologies (includ- power plant cooling application is so critical in ing cooling, water harvesting, electricity making necessary adjustments in power plants’ harvesting, etc.) to further process municipal operation to minimize the potential risks wastewater (MWW) for power plant cooling associated with seasonal effluent quality. Why 3- (Apfelbaum et al., 2013; Bengston, 2010; Duke should we be concerned with PO4 ? First, as Energy, 2012; Quagraine, 2017). outlined in the third of the series (Quagraine et 3- al., 2017b), PO4 predominates the P fractions SaskPower’s Shand Power Station (SHPS) in Saskatchewan, Canada seems to be a pioneer in the MWW going into the SaskPower CW; in employing a CW on a commercial scale to constituting an annual average of 90% TP with 3- polish secondary treated MWW effluent for standard deviation of only 6.6%. PO4 occurs condenser cooling since 1994. Experience in relatively high but variable levels in treated gained over 2-decades is expected to help in MWW effluents (e.g. 0.6-51.0 mg/L in bridging knowledge gaps towards current and secondary treated MWW (SMWW) effluents future efforts in using CW technology as key from different USA locations (Vidic et al., component to address challenges around the 2009)) and is a critical constituent in dictating water-energy nexus. The present manuscript is scale formation and bio-fouling tendencies in the fifth in series of publications in sharing industrial cooling applications; whilst in con- such experience. The first reviewed the trast inhibiting corrosion due to the protective rationale to consider CW as polishing unit for layer of scales it forms on the metal surfaces. 3- power plant cooling and outlined several PO 4 content is indeed of concern in cooling benefits inherent in such reuse application water systems; it can form the tenacious nature (Quagraine, 2017). The second (Quagraine et of calcium phosphate (Ca3(PO4)2), and its al., 2017a) and third (Quagraine et al., 2017b) presence has the potential to nucleate or “seed” focused on the annual performances of the other mineral scales. For this reason, even SaskPower CW in removing various when polyphosphates (condensed phosphates) are added for corrosion protection in make-up contaminants for condenser cooling purpose. 3- Recognizing differences in annual and seasonal pipe-lines, total PO4 concentration in a cool- treatment performance data, the fourth paper ing tower (CT) make-up water from potable (Quagraine and Duncan, 2017) was dedicated water systems is advised to be kept below 0.5 to the effect of seasonal changes in parameters mg/L (Tierney, 2002); as also recommended by (Schimmoller, 2012) in reclaimed water for such as rainfall, temperature, plant growth and E.K. Quagraine / Journal of Water Sustainability 1 (2018) 1-24 3 CT-make up. Others however offer less strict limiting for cyanobacteria and algae growth, recommendations. For example, McNicholas not just in the environment but also in cooling 3- 3- (2002) recommends a maximum total PO4 of systems. Higher PO4 levels may result in 1 mg/L in CT make-up water. Odell (2015) excessive algae growth on CT fill material suggests (Ca3(PO4)2) scale formation to occur surfaces and other components within cooling in power plant cooling systems with reclaimed systems resulting in flow restrictions, high 3- make-up water of P ≥0.6 mg/L (i.e. PO4 chlorine demand, and high potential in equivalent of 1.84 mg/L). Such differences are biofouling heat transfer surfaces (Post et al., however rational, considering the different 2014; Veil, 2007). TP maximum limit of 1 3- cycles of concentrations (COCs) various CTs mg/L (PO4 equivalent of 3.1 mg/L) in operate. (Ca3(PO4)2) is reported to likely form reclaimed water for environmental reuse 3- when PO4 concentration in CTs exceeds 10 applications has been stipulated by North mg/L (Harfst, 2015). In an earlier EPRI Carolina, a state in USA (USEPA, 2012); thus, 3- guideline (1982), a PO4 limit of 5 mg/L was a stricter guideline is anticipated for industrial recommended for power plant CTs. However, cooling purposes considering the COCs some latter reports suggest a much higher limit expected in CTs and the favourable conditions 3- of 50 mg/L PO4 for refinery CTs (Eble and for biological growth in such systems. Feathers, 1993; EPRI, 2012; EPRI and CEC, Various types and sizes of CWs have 3- 3- 2003). Even so, PO4 concentration not demonstrated capability to remove PO4 (or exceeding 8 mg/L in recirculating CW of a CT total P, TP) from treated MWW effluents of in a Refinery Plant is of more recent different grades (i.e. primary, secondary-both recommendation (IOCL, 2016). With expected conventional and lagoon/stabilizing ponds, and make-up calcium (Ca) of <40 mg/L as CaCO3 tertiary) (Quagraine, 2017). In the third of the and an operating CT Ca maximum of 1000 series, the annual performance of the 3- mg/L as CaCO3 (i.e. COC up to 25) for this SaskPower CW in removing PO4 -P was refinery plant, the CT make-up water is discussed (Quagraine et al., 2017b). However, 3- expected to contain PO4 ≤0.32 mg/L. From nutrient removal by CWs commonly follows this brief review of the literature, it is fair to seasonal patterns, which may not necessarily expect CT make-up water from various sources reflect annual patterns.