Enhancing pollutant removal efficiency in urban domestic wastewater treatment through the hybrid multi-soil-layering (MSL) system: A case study in Morocco

This paper evaluates the performance and potential of a full-scale hybrid multi-soil-layering (MSL) system for the treatment of domestic wastewater for landscape irrigation reuse. The system integrates a solar septic tank and sequential vertical flow MSL and horizontal flow MSL components with alternating layers of gravel and soil-based material. It operates at a hydraulic loading rate of 250 L/m2/day. Results show significant removal of pollutants and pathogens, including total suspended solids (TSS) (97%), chemical oxygen demand (COD) (88.57%), total phosphorus (TP) (79.93%), and total nitrogen (TN) (88.49%), along with significant reductions in fecal bacteria indicators (4.21 log for fecal coliforms and 3.90 log for fecal streptococci) and the pathogen Staphylococcus sp. (2.43 log). The principal component analysis confirms the effectiveness of the system in reducing the concentrations of NH4, COD, TP, PO4, fecal coliforms, fecal streptococci, and fecal staphylococci, thus supporting the reliability of the study. This work highlights the promising potential of the hybrid MSL technology for the treatment of domestic wastewater, especially in arid regions such as North Africa and the Middle East, to support efforts to protect the environment and facilitate the reuse of wastewater for landscape irrigation and agriculture. HIGHLIGHTS High removal of TSS (97%), COD (88.57), TN (88.49), TP (79.93) achieved by MSL system.; Significant removal rates of fecal coliforms (4.21 log) and fecal streptococci (3.90 log).; Principal component analysis showed a positive correlation between COD, NH4+, TP removal, and pathogens.; Treated water met Moroccan and FAO guidelines for safe irrigation.; MSL sustainably reduces the environmental impact and health hazards of wastewater.;