Dynamika zmian mikroflory bakteryjnej w składowanych osadach ściekowych

Racjonalne wykorzystywanie osadów ściekowych obok trudności technicznych, stanowi ważny i niedostatecznie rozpoznany problem natury higienicznej. Należy pamiętać, że sanitarne właściwości osadów ściekowych mają charakter zmienny i są kształtowane przez wiele czynników, takich jak: standard życia i stan zdrowotny mieszkańców na danym terenie, rodzaj oczyszczalni ścieków oraz stosowane metody przeróbki osadów. Gospodarka osadowa znajduje się często na marginesie procesów oczyszczania ścieków. Niewielkie ilości osadów powstających w małych oczyszczalniach prowadzą często do pomijania lub bagatelizowania tego problemu przez projektantów i inwestorów.

The subject of the study was mechanically dewatered municipal sewage sludge, which was subjected to deposition process. At the beginning of the experiment, the total number of bacteria from the family Enterobacteriaceae and other gramnegative bacilli, streptococci and staphylococci and micrococci was determined in the tested material. The number of gram-negative bacilli at the beginning of the experiment was equal 6.6ź105 cfu/g, while at final stage of research the number of isolated bacteria was on the level of 6.6ź103 cfu/g. The number of streptococci in researches of sewage sludge ranged from 9.7ź105 cfu/g (first month of experiment) to 3.3ź103 cfu/g (last month of experiment). Micrococci and staphylococci in initial stage of research were isolated in number 1.6ź105 cfu in 1g of sewage sludge. The reduction of these bacteria during the storage of sewage sludge was observed, just like in case of Enterobacteriaceae and streptococci. The average number of micrococci and staphylococci was equal 7.3ź102 cfu/g in 7 month of experiment. Then the bacteriological composition of sludge was analysed at monthly intervals. The results of the study indicated that numerous Gram-negative bacilli, streptococci and staphylococci occur in raw sludge. Pathogenic species were identified among isolated microorganisms: Serratia odorifera, Citrobacter freundii, Klebsiella ozaenae, Proteus vulgaris Aerococcus viridans, Streptococcus sanguis oraz Gemella spp., Leuconostoc sp. Staphylococcus xylosus, S.lentus, S.hominis, S.caprae, S.epidermidis, S.aureus. The fact that the presence of Salmonella sp. was observed in all samples is very significant. It was stated that dying of pathogenic bacteria cells in sewage sludge during its deposition proceeds slowly. Consequently, their survival rate amounted to 13÷18 months. The results obtained indicate that municipal sewage sludge subjected only to deposition should not be used in agriculture for sanitary and hygienic reasons.