Sand-filters used for wastewater treatment: Buildup and distribution of microorganisms

The work was conducted to find a solution for establishing a nonconventiona l wastewater treatment system suitable for the conditions of Egyptian villa ges in the delta where land is scarce and expensive by using sand-filters. Total viable bacteria (TVB) of heterotrophic aerobic bacteria were studied in two sand-filter systems used for primary settled sewage treatment. Filte r 1 consisted of two gravel layers separated by coarse sand (2.0-0.2 mm) mi xed with gravel (10-20 mm) with the ratio of 2:1, while filter 2 contained coarse sand only between gravel layers. No significant difference was found between TVB counts in the top and bottom layers of sand in case of filter 1, whereas counts were higher at the top layer of filter 2 than the bottom layer. Among the common genera encountered in the filter medium were Agroba cterium sp., Aeromonas sp. and Pseudomonas sp.. Counts of ammonium-oxidizer s and nitrite-oxidizers were low at the beginning of the experiment and sta rted to increase and reached a stable state in the filter by day 38 in the case of ammonium-oxidizers and day 52 for nitriteoxidizers. (C) 1999 Elsevi er Science Ltd. All rights reserved.