Oil and grease in soils irrigated with greywater and the potential effect on soil water repellency

Abstract

The reuse of greywater and other wastewaters are important considerations for effective
water management strategies. It is also imperative that the potential for detrimental
environmental effects be investigated. As part of ongoing research into the reuse of
greywater and oil-rich agro-wastewaters, the potential impact of oil and grease (O&G)
to soils irrigated with greywater (GW) was studied. Greywater streams were sampled
and analyzed for O&G content. Along with the greywater, soil profile samples were
collected from garden soils irrigated with these waters. The goal was to determine the
O&G content of these GW streams, verify ifeO&G was accumulating in the soil profiles,
and investigate the effect O&G can have on water movement through O&G
contaminated soils.
Untreated kitchen GW averaged 200 mg/L O&G, over an order of magnitude more than
other GW streams. GW-irrigated soils showed O&G accumulation of up to 200 mg/kg
within the first 20-cm of depth. GW with low O&G concentration (<! 0 mg/L) still
demonstrated long-tenn accumulation in the soil profile, with O&G concentration of
150 mg/kg. To detennine the potential effects that O&G accumulation may have on
water movement in soil, capillary rise and water drop penetration time (WDPT)
experiments were conducted. The results showed up to 60% decrease in capillary rise in
sand containing 250 mg/kg O&G. Interestingly, no additional reduction in capillary rise
was observed at concentrations above 250 mg/kg. WDPT was observed to increase
linearly (from nearly instantaneous to over 2 seconds) with increased O&G content, up
to 1000 mg/kg. This work demonstrated that O&G in GW used for irrigation can
accumulate in soil and may lead to a significant water repellency and reduction in the
soils ability to transmit water.