PERFORMANCE OF INTERMITTENTLY OPERATED SAND FILTERS: A COMPARABLE STUDY, TREATING WASTEWATERS OF DIFFERENT ORIGINS

摘要

The purpose of this research was to determine the efficiency of sand filters to remove several common pollutants, found in most wastewaters. In order to achieve this objective, Plexiglas columns of 1m height were used. The columns were filled with river sand and loaded with real or synthetic wastewaters, corresponding to different origins, following an intermittent feeding schedule. The effect of addition of inoculum to the synthetic wastewaters was also examined and the results were compared with the uninoculated columns. The inoculum consisted of 20 ml addition of activated sludge from the aeration tank of a large-scale wastewater treatment plant. Samples of the inlet and outlet of these columns were analyzed for common parameters (TSS, COD, NH_4-N, NO_2-N, NO_3-N, TN, PO_4-P and pH). At the end of each experimental serie, sand samples from different column heights were obtained and observed, using a Scanning Electron Microscope (SEM). The SEM micrographs demonstrated the existence of microorganisms through out the column depth. The analysis of effluent show significant reduction of COD (more than 50% for the majority of wastewaters that were used) and PO_4-P (more than 40%), as compared with the initial loading. Ammonification occurred and by increasing the number of loadings, nitrification was subsequently observed. Denitrification was not found to take place, due to the lack of anoxic conditions.