Comparison of household greywater sources and rainwater remediation on Mediterranean climate topsoils

Abstract Reuse of greywater for irrigation has surged due to increasing urban freshwater scarcity. Greywater sources differ in ease and cost of reuse, with limited studies on the effects of irrigation with different sources on soil properties and subsequent rainwater remediation. Thus, this study compared the effect of four major household greywater sources (shower (SH), dishwasher (DW) and liquid and powdered laundry detergent (LLD and PLD)) on soil properties and rainwater remediation potential of two contrasting (albic Planosol (bleached) and Lixisol (rhodic)) topsoils under Mediterranean climate conditions. Summer irrigation with the greywater and tap water sources was simulated (370 mm) followed by winter rainfall simulation (370 mm). Soil chemical, physical and microbial properties were determined after each simulation. Irrigation with SH and LLD greywaters was least harmful to soil chemistry; however, LLD decreased soil infiltration rate by 48–53%, and SH resulted in hydrophobic crusting. Irrigation with PLD and DW greywater was most damaging, resulting in alkalisation, sodification and salinisation accompanied by soil structural degradation, decreasing infiltration by 85–100%. All treatments reduced soil bacterial diversity and species richness. Rain simulation was only able to reduce sodicity and salinity associated with PLD and DW application on the rhodic soil, as the clay fraction was more stable, permitting some infiltration. Therefore, PLD and DW greywaters should not be used directly for irrigation, especially on bleached soils, as this can halt rainwater percolation. Furthermore, use of less chemically harmful SH or LLD liquid greywaters could result in undesirable soil physical problems in the long term.