Low-cost wastewater treatment system with nutrient removal for decentralized wastewater treatment

Abstract

The aim of the present study was to investigate alternative low-cost and low-maintenance wastewater treatment methods for on-site wastewater treatment plants. The experiment with three filters (0.6 m, 0.8 m and 1.0 m in diameter and with 2.1 m packing height) feeding three different flowrates (0.25 m3/d, 0.5 m3/d and 0.75 m3/d) of presettled wastewater was carried out over a period of 4 months and at wastewater temperature of 11.2–20.5 ºC. Suspended solids, organic matter removal and nitrification occurred in the upper part of the filters filled with the stonewool medium and acting as a trickling filter, while the lower part of the filters was filled with woodchippings (submerged in two filters and not submerged in the third filter) and was used for post-denitrification. Besides, in order to enhance phosphorus removal iron filings were added in the upper part of the stonewool layer. Nitrification efficiency and total Kjeldahl nitrogen removal (TKN) efficiency in the filters were dependent on a flowrate. The highest values (>94 % for nitrification and >89 % for TKN) in all the filters were observed at 0.25 m3/d flowrate. Denitrification efficiency was higher than 92 % in the filters with the submerged woodchippings, while in the filter with non-submerged woodchippings denitrification efficiency reached only 57 %. On the other hand, BOD7 and SS removal was poorer in the filters with the submerged woodchippings (71–85 % for BOD7 and 87–88 % for SS) than in the filter with nonsubmerged woodchippings (95 % for BOD7 and 95 % for SS). Phosphorus removal process was unstable in all the filters during the experimental period. The highest phosphate phosphorus removal efficiency (mean value of 38 %) and total phosphorus removal efficiency (mean value of 50 %) were achieved in the largest filter.