MUNICIPAL WASTEWATER AERATED FILTRATION USING A LOW-COST FILTRATION MEDIA

Abstract

The main objective of this research was to demonstrate that selected natural lava stones can be successfully used for lowcost aerobic biofiltration of municipal wastewater. To demonstrate the procedure a pilot filter was built using 6 mm lava stones as support material. The filter depth was 3.0 m. Using 24-hour samples, analysis of the wastewater could be made for COD, TSS, ammonia and nitrate nitrogen, pH, temperature and Kjeldahl nitrogen. Backwashing was performed every 72 hours. The results indicate that total and dissolved COD and TSS behaved in a similar way when compared with the organic load. The highest COD removal rate (80 %) was observed with the lowest organic load of 0.8 kgCOD/m3•d and the lowest removal (60 %) was obtained with the highest organic load of 2.6 kgCOD/m3•d. The highest total and dissolved COD removal values were 81 and 84 %, respectively. For TSS the best removal value was 95 % with a best average removal of 89 %. Up to 75 % ammonia removal was achieved at the lowest organic load of 0.8 kgCOD/m3•d and decreased to 36 % with a higher organic load of 2.6 kgCOD/m3•d. The mean cellular retention time (MCRT) showed values from 1 to 6 days with an average of 3.2 days proving that the MCRT depends on the backwashing frequency more than on any other factor involved. Caused by abrasion during the backwashing procedure, the bed volume decreased in about 5 % after 300 days of operation.

Key-words: Biological aerated filter, filter media, nitrification, tezontle