Abstract
Wastewater reuse coupled to managed aquifer recharge (MAR) provides a means to store and reuse treated wastewater (TWW) year-round. Determining the fate of nutrients in the subsurface during MAR remains challenging for environmental regulation due to the interaction of the MAR source water with site specific aquifer conditions. To facilitate the understanding of natural treatment processes, this study uses operational monitoring data from a full-scale aquifer storage and recovery (ASR) scheme using TWW to assess nutrient (N and P) transformation and fate. Analysis of median water quality injected into and recovered from the ASR wells for two complete ASR cycles (June 2014 to March 2016) was used to describe the removal of nutrients in an anoxic carbonate aquifer. Total nitrogen (TN) removal was dominated by redox processes, with median removal of 40 to 60% for TN and nitrate (the dominant N species) and higher removal of ammonia (95%) and total Kjeldahl nitrogen (TKN) (70%). Total phosphorous (TP) removal was also observed (~ 90%) due to sorption (filterable reactive phosphorous median removal of ~ 80%). A 40% increase in median salinity was evident within each ASR cycle due to recovery of the entire volume of injected water each year (ambient groundwater is 200% higher in TDS, on average). A reduction in salinity of the recovered water could be achieved by leaving a residual of source water in the aquifer to create a buffer zone between the ambient groundwater and the fresher source water.
Highlights
Wastewater reuse coupled to managed aquifer recharge (MAR) provides a means to store and reuse treated wastewater (TWW) for agricultural production throughout the entire year
A summary of the ASR injectant and recovered water quality data and available ambient groundwater quality data is provided in Table 2 and Table 3
The ASR recovered water had a ~ 40% higher median TDS than that injected (TDS 1000–1100 mg/L; Fig. 3) and was typically lower in nutrients than that injected with median nitrogen Total nitrogen (TN) 5.9–8.4 mg/L and Total phosphorous (TP) 1.3 mg/L
Summary
Wastewater reuse coupled to managed aquifer recharge (MAR) provides a means to store and reuse treated wastewater (TWW) for agricultural production throughout the entire year. 65 Page 2 of 12 aquifers (Pyne, 2006) and requires creation of a buffer zone to separate the stored water from the surrounding brackish, ambient groundwater. Most wastewater treatment plants are designed to remove nutrients such as nitrogen and phosphorus prior to aquatic discharge as nitrogen and phosphorus are associated with eutrophication and water quality issues in receiving environments (Collins et al, 2010). Environmental regulations have evolved and generally require higher levels of treatment, especially nutrient removal prior to discharge. To date these regulations have not considered that in addition to providing storage, aquifers can serve as a treatment barrier providing improvements in water quality. Dillon et al (2008) reported nutrient and organic carbon removal from treated wastewater (Fox, 2002; Kim et al, 2004; Sharma et al, 2011; Abel et al, 2012; Vanderzalm et al, 2006, 2013, 2018) along with various other potential contaminants such as pathogens (Sidhu et al, 2015; Page et al, 2017), suspended solids and turbidity (Page et al, 2015) and trace organic chemicals (Patterson et al, 2011; Shareef et al, 2013)
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