Managed Aquifer Recharge / Soil Aquifer Treatment
Managed Aquifer Recharge (MAR) is a natural water / wastewater treatment process, in which water is introduced into the groundwater via soil infiltration through spreading basins, vadose zone injection wells or direct injection methods (Sharma et al., 2012). Soil Aquifer Treatment (SAT) is a widely used MAR method, in which treated effluent is infiltrated through spreading recharge basins (Fox et al. 2005) (Figure 1). SAT aims to improve water quality regarding suspended solids, biodegradable materials, bacteria, viruses, and other microorganisms, while achieving significant reductions in nitrogen, phosphorus, and heavy metals concentrations (US EPA, 2012).
Land availability determines the type of SAT to be adopted. Spreading basins (Figure 3a: Types A and B) require availability of sufficient land and are applied in case of unconfined aquifers with unsaturated zones. These SAT types require high permeable soils within a reasonable depth of the non contaminated zone. The aquifer below the vadose zone should be sufficiently transmissive and not confined to form groundwater mounds beneath the basin for efficient recharge (Chol Deng Thon Abel, 2014).
When land availability or top soil suitability do not permit the use of surface spreading, effluent is applied via trenches or wells constructed directly into the unsaturated part of the aquifer (Figure 3a: Types C and D).
The operation of SAT systems involves wet and dry cycles to avoid clogging and optimize redox soil conditions (Amy & Drewes, 2007).
At the basin-soil interface, the combined effects of sedimentation, filtration, aeration, and microbial growth lead to the formation of a biologically active zone that may become impermeable. Wet and dry cycles which last several days prevent clogging; the basin-soil interface does not become impermeable (Fox, Abonshanp, & Alsamadi, 2005; Bouwer, 2002).
During dry cycles re-aeration takes place, increasing the redox potential and providing oxidative conditions for organic matter and NH4 removal. Ideally, SAT systems should comprise numerous basins so that some basins can be flooded while others are drying.
During groundwater recharge through the vadose zone and transport through the groundwater aquifer, water quality improvements occur. Sorption and biodegradation processes in the soil are mechanisms that can reduce or remove microbial and other contaminants from wastewater.
Table 1: Pollutant Removal in SAT Systems*
(Source: Sharma and Kennedy, 2017)
•Bacteria including indicators
•Giardia and Cryptosporidium
Bulk Organic matter (DOC/TOC)
PE=primary effluent, SE= secondary effluent, TE= tertiary effluent * SAT performance is site specific. ** Highly dependent on type of organic micropollutant, source water quality matrix and redox conditions
If you want to learn more about SAT in cNES click here ...
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