Removal of dissolved organic carbon and nitrogen during simulated soil aquifer treatment

• Phospholipid Fatty Acids analysis showed large concentration of microorganisms at the infiltration surface.
• Greater proportion of the overall removal occurs within the first few cm of the soil.
• DOC removal is achieved by aerobic and anaerobic bacterial biodegradation supported by fungi.
• Silt and clay reduced the microbial concentration in the soil column and reduced DOC removal.

Soil aquifer treatment was simulated in 1 m laboratory soil columns containing silica sand under saturated and unsaturated soil conditions to examine the effect of travel length through the unsaturated zone on the removal of wastewater organic matter, the effect of soil type on dissolved organic carbon removal and also the type of microorganisms involved in the removal process. Dissolved organic carbon removal and nitrification did enhance when the wastewater travelled a longer length through the unsaturated zone. A similar consortium of microorganisms was found to exist in both saturated and unsaturated columns. Microbial concentrations however were lowest in the soil column containing silt and clay in addition to silica sand. The presence of silt and clay was detrimental to DOC removal efficiency under saturated soil conditions due to their negative effect on the hydraulic performance of the soil column and microbial growth.