Identification of Key Parameters for Monitoring Changes in Natural Organic Matter Concentration in Response to Lake Recovery from Acidification
Lindsay Anderson, Amina Stoddart, Graham Gagnon, Colin Waddell, Alisha Knowles
Department of Civil and Resource Engineering, Dalhousie University; Halifax Water
In response to acid rain control programs, there has been substantial reductions in SO2 emissions; and SO4 deposition in surface waters has also decreased. Some UK and Scandinavian countries have experienced signs of recovery from acidification, as evidenced by increasing surface water pH and a rise in DOC levels by up to 0.15 mg/L/year (Monteith et al., 2007). Recently, lakes throughout Atlantic Canada have also shown signs of recovery from acidification (Anderson et al., 2017). Lake Major – a protected surface water supply located in Nova Scotia, Canada has experienced a 3.8x increase in color concentration over the past 16 years, corresponding with a similar increase in coagulant demand at the Lake Major Water Supply Plant (LMWSP) operated by Halifax Water (Anderson et al., 2017). This phenomenon has highlighted the need for more detailed water quality monitoring programs, particularly with respect to natural organic matter (NOM) concentration and composition. Accordingly, a NOM-focused water quality monitoring program was implemented at LMWSP to help better understand the impact of lake recovery from acidification on subsequent water treatment processes (e.g. coagulation).
The overall objective of this study was to identify key water quality parameters for monitoring responses to recovery from acidification. Through extending our detection metrics, our aim will be to better understand the interaction between NOM tools as rapid monitoring tools for the water industry.
Study Location — Lake Major serves as the main water supply for Dartmouth, Nova Scotia, Canada. It is characterized by low alkalinity and low turbidity, with moderate to high levels of color and organic matter. The NOM in Lake Major is >90% dissolved. The LMWSP is a 45 MLD conventional filtration plant with upflow clarification.
Technical Approach — Traditional and emerging NOM surrogates (e.g. photoelectrochemical oxygen demand (peCOD)) were used to monitor the changes in NOM concentration. The peCOD analyzer enables rapid detection of COD without the use of hazardous chemicals. An at-line peCOD monitoring unit was installed on the raw water intake at the LMWSP. It collected raw water samples at 2 hour intervals.
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