Abstract
The performances of single-pass vertically loaded fibrous peat biofilters treating septic tank wastewater from a single household (pe 6) and a small rural housing estate (pe ~100) are compared. Both systems achieved >90% BOD removal and consistently low suspended solids <11 mg L−1. Pathogen removal was generally >95% but inconsistent. Nitrification was linked to temperature with removal rates seasonal (50–98%) with no denitrification; this resulted in final effluents with either high NH4 or NO3 concentrations, both unsuitable for discharge to surface or ground waters. Phosphorus removal was generally poor. The filters responded poorly to sudden increases in hydraulic loading, causing a reduction in BOD removal in particular. Subsequent soil treatment of effluents after filtration caused a small decrease in both physicochemical and microbial quality. Single-pass vertical peat filters cannot meet the more stringent EU nutrient and microbial standards required for on-site treatment without tertiary treatment to ensure full compliance.
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