Treatment of Domestic Wastewater in Small-Scale Sand Filters Fortified with Gypsum, Biotite, and Peat

Sand filtration is a low-cost and easy solution for household wastewater treatment in areas lacking a centralized sewage system. However, there are only a few studies about the treatment efficiencies of nutrients and enteric microorganisms and their removal or filter mass reuse potential. Sand columns with different phosphorus adsorbents, gypsum, biotite, and peat were tested in laboratory-scale filters at 4 °C to assess their performance in variable conditions and their possibility to increase the efficiency of sand filters. The columns were fed with real municipal wastewater with variable wastewater flow and phosphate load at different stages of the experiments. Phosphate and total nitrogen concentrations were low in the effluent of all columns, and they were mostly rather similar. Waste gypsum was found to greatly increase the conductivity of the effluent. The numbers of enteric microorganisms in the effluents were low, and the used filter masses achieved good hygienic quality after the tests. Phosphate, ammonium, and nitrate concentrations were low in the used masses, evidently since the columns had operated only for 21–30 weeks. Sand filtration proved to be an effective method for wastewater treatment, but changing conditions should be considered when designing these filters. The masses have reuse potential as soil improvement.