Accumulation of oil and grease in soils irrigated with greywater and their potential role in soil water repellency

The potential impact of oil and grease (O and G) to soils irrigated with greywater (GW) was investigated. Greywater streams were sampled and analyzed for O and G content, along with corresponding GW-irrigated soils. Untreated kitchen GW averaged 200 mg L^{- 1} O and G, over an order of magnitude more than other GW streams. GW-irrigated soils showed O and G accumulation of up to 200 mg kg^{- l} within the first 20-cm of depth. To determine the potential effects of such O and G accumulation 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 when sand containing 250 mg kg^{- 1} O and G was used. Interestingly, no additional reduction in capillary rise was observed at concentrations above 250 mg kg^{- 1}. WDPT was observed to increase linearly with increased O and G content, up to 1000 mg kg^{- 1}. This work demonstrated that O and G in GW used for irrigation can accumulate in soil and may lead to a significant reduction in the soils ability to transmit water.