Removal of bacterial indicators and pathogens from domestic wastewater by the multi-soil-layering (MSL) system

This paper presents the performance and behavior of a multi-soil-layering (MSL) system to remove fecal contamination bacteria indicators and pathogens from domestic wastewater. The experimental setup was performed using a laboratory-scale MSL system (depth 30 × width 36 × height 65 cm). The MSL system was composed of soil mixture blocks (SMB) arranged in a brick-like pattern and surrounded by permeable gravel layers (PL). The SMB comprised sandy soil, charcoal, sawdust and metal iron at a dry weight ratio of 7:1:1:1. The hydraulic loading rate was 200 L m−2 day−1. Bacteriological analyses comprised total bacterial count at 22 and 37°C, fecal coliforms, total coliforms, Escherichia coli, streptococci, intestinal enterococci and pathogenic bacteria: Clostridium sp., Staphylococcus sp., Pseudomonas sp. and Salmonella sp. The best removal efficiency was achieved for Staphylococcus sp. by 1.42 log unit, while the lowest removal efficiency was found for E. coli by 1.01 log unit. The mean removal efficiencies of total suspended solids (SS), biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorous (TP) were 93, 86, 81, 78 and 80%, respectively. Based on these results, the MSL system could efficiently remove organic matter, phosphorus and nitrogen. However, the performance to reduce bacterial indicators and pathogens was still moderate.