Effect of soil type on water quality improvement during soil aquifer treatment

Bench-scale soil column experiments were performed at The University of Arizona to examine the effects of soil type and infiltration rate on the removal of wastewater organics during soil aquifer treatment (SAT). The suitability of such waters for potable uses following a combination of above-ground treatments and SAT polishing was under investigation. SAT was simulated in 1-meter soil columns containing repacked homogenized soils ranging from poorly graded sands to silty sands. Soils were obtained from existing and potential effluent recharge sites in Arizona. All columns received chlorinated/dechlorinated secondary effluent, ponded to a 25-cm depth above the soil surface, under alternating wet/dry conditions. Treatment efficiencies in biologically active and inhibited columns were compared to determine the mechanism(s) of water quality improvements and the sustainability of SAT. Water quality parameters included: (i) non-purgable dissolved organic carbon and (ii) UV absorbance at 254 nm (used as a measure of disinfection-by-product precursors). Differences in through-column removal of non-purgable dissolved organic carbon were significant for columns containing sandy loam (56%), sand (48%) and silty sand (44%). Removal of UV-absorbing organics was not significantly different for columns containing sand and sandy loam (22 and 20%, respectively). There was no significant correlation between infiltration rate and removal efficiency of either organic parameter for both soils.