Microbiological assessment of sludge treatment at the 6[th] October wastewater treatment plant, Giza, Egypt

ABSTRACT

This study was carried out to assess the sludge treatment processes applied at the 6[th] October wastewater treatment plant [WWTP], Giza, Egypt. The applied processes included aerobic digestion followed by gravity thickening, filter-pressing and drying beds [in emergency cases]. Bacteriological, virological and parasitological evaluation was carried out. Results showed that aerobic digestion removed two log units of total and faecal coliforms and one log unit of Escherichia coli [E. coli] and feacal streptococci. The removal percentages of coliphage and enteroviruses after aerobic digestion were 97.0 and 58.3%, resectively. The salmonellae disappeared from sludge after aerobic digestion. Qualitative and quantitative decrease in helminth ova [Ascaris, Trichuris, Trichostrongylus, Taenia and Hymenoleois] was observed after aerobic digestion and thickening stages. An average decreae of 4 log units for total and faecal coliforms, 3 log units for each of faecal streptococci and coliphage and 2 log units for E. coli through sludge treatment process was observed. Enteroviruses, helminth ova and enteric protozoa were completely eliminated from sludge after 6 months in drying beds. The loads of faecal coliform, E coli, faecal streptococci and coliphage in the dried sludge were 6.5 x 10[2], 1.6 x10[2], 4.5 x 10[2], 4.56 x 10[2] cfu and 8.5 x 10[1] pfu/g, respectively. Microbiological quality of the final treated sludge complied with the regulations of Untied States Environmental Protection Agency