The effects of soil type and effluent pre-treatment on soil aquifer treatment

Abstract

A matrix of three different levels of effluent pre-treatment and four different soil types was used in a study on the effects of soil type and effluent pre-treatment on Soil Aquifer Treatment (SAT). The objective of the study was to assess the feasibility of SAT for the recharge of groundwater and indirect potable reuse. The soils represented a wide range of hydrological and physicochemical characteristics from a proposed recharge site in Phoenix, Arizona, USA. Effluents studied included denitrified and conventional secondary effluents. These effluents contain different levels of biological oxygen demand (BOD5), organic carbon, ammonia, and nitrate. Ten 2.6 m columns were operated under different wetting/drying cycles. For the effluents studied, resultsindicate that effluent pre-treatment does not impact organic carbon removal efficiencies. Under optimal wetting/drying cycle times, BOD5 can be removed efficiently although a residual organic carbon concentration of 5–6 mg/l persists. Ammonia is effectively nitrified under most conditions but denitrification does not readily occur even when denitrified effluent is applied. Soil Aquifer Treatment appears to be a robust treatment system for denitrified effluent producing total nitrogen concentrations less than 8 mg/l and organic carbon concentrations less than 6 mg/l.