Opportunities and constraints for effective treatment of domestic wastewater in rural onsite wastewater treatment systems operating in a foothill climate

This paper presents the results of a study of two innovative quasi-technical installations designed for high- quality treatment of domestic wastewater in rural areas. The installations are equipped with similar technological devices arranged in sequences consisting of: three-chamber flow septic tanks, biological sprayed beds filled with granular (10–20 mm) calcined clay materials, special slope biofilters with soil-grass beds and infiltration ponds as recipients. The sites are located at an altitude of more than 600 m a.s.l. in a foothill climate, in southern Poland. For both sites, the analysis showed a high elimination efficiency for pollutants expressed as biochemical oxygen demand over five days, chemical oxygen demand and total suspended solids. In the case of total nitrogen, the reduction rate was 79.4% for facility No. 1 and 84.3% for facility No. 2, respectively. A high level of ammoniacal nitrogen removal was achieved at both analysed sites, at 98.7% for facility No. 1 and 92.1% for facility No. 2. The PO4-P were removed at 88.0% at facility No. 1 and 69.1% at facility No. 2. The correlation analysis showed no significant relationship between the removal efficiency of the analysed pollutant indicators and the temperature of the treated wastewater, with the exception of total nitrogen. Thus, it is concluded that the climatic conditions did not affect the wastewater treatment processes. They are an effective alternative to treatment plants based on activated sludge technology and are recommended for use in rural areas with high environmental values, without sewage systems, which require special protection.