Efficiency of a new hybrid multi-soil-layering eco-friendly technology for removing pollutants from domestic wastewater under an arid climate

The goal of this research is to assess and track the efficacy of hybrid multi-soil-layering (MSL) plant in treating domestic wastewater for reuse in landscape irrigation. The investigated wastewater treatment plant is composed of a solar septic tank followed by a vertical flow MSL (VF-MSL) unit in series with a subsurface horizontal flow MSL (HSSF-MSL) unit. Wastewater samples were taken bimonthly from the plant's influent and effluent, respectively. The two-stage MSL units are composed of gravel layers alternated with soil-based layers, which are arranged in brick-like patterns, although they are operated under an HLR of 250 L m−2 day−1, which corresponds to 125 g COD/m2/d, 52 g TN/m2/d, and 2.70 g TP/m2/d. The mean removal efficiency was 75 %, 42 %, 67 %, and 47 %, respectively, for TSS, COD, NH4+, and TP for the VF-MSL system. Moreover, the VF-MSL combined with the HSSF-MSL system resulted in significant nitrogen removal as well as a significant reduction (p < 0.05) in organic matter and phosphorus with an abatement of 97 %, 79 %, 76 %, and 27 %, respectively, for TSS, COD, TP, and TN. For fecal bacteria indicators, the hybrid MSL system achieved high log removals, reaching 2.88 log units during two years of monitoring. Principal component analysis (PCA) was done on the positive correlation between COD, NH4+, TP removal, and summer seasons. Nonetheless, the winter season significantly influenced TN removal in the MSL system. The investigated hybrid multi-soil-layering plant has been shown to be effective in terms of water quality for the irrigation of green spaces in urban areas.