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Zastosowanie ultradźwięków do odkażania osadów ściekowych

Nowak D.

Inżynieria i Ochrona Środowiska

2015

T. 18, nr 4

459--469

Szerokie możliwości stosowania technik ultradźwiękowych skłaniają do badań nad możliwościami zastosowania tego czynnika w różnych dziedzinach gospodarki. Destrukcyjne działanie ultradźwięków na układy biologiczne może być wykorzystane do pozbywania się niepożądanych mikroorganizmów z danego środowiska, np. osadów ściekowych, które jako nieodłączny produkt oczyszczania ścieków są koncentratem bardzo zróżnicowanej mikroflory patogennej. W artykule przedstawiono wyniki badań nad wpływem pola ultradźwiękowego na wybrane bakterie w osadzie przefermentowanym. W badaniach analizowano zmiany w liczebności bakterii mezofilowych, bakterii laktozo-dodatnich i laktozo-ujemnych oraz w odniesieniu do takich gatunków, jak Enterococcus faecalis oraz Clostridium perfringens. W badaniach zastosowano dezintegrator ultradźwiękowy o częstotliwości 22 kHz i amplitudzie 16 μm. Próby osadu poddano działaniu pola ultradźwiękowego w czasie 10 i 30 minut. Stopień unieszkodliwienia mikroorganizmów zależał od czasu nadźwiękawiania oraz był zróżnicowany w zależności od badanych bakterii.

Significant disproportion between technological development and the capacity of natural environment is one of the major causes of serious disturbances in shaping the biological equilibrium of ecosystems. One of the key issues to be solved in the aspect of sustainable development is efficient processing and utilizing of waste, including sewage sludge. The potential threat of these materials to the natural environment is mainly due to the presence of hazardous chemicals and unsafe sanitary state. The problems associated with the processing and safe managing of sewage sludge resulted in development of new methods or improvement of already existing methods for processing and hygienisation of sewage sludge. These methods include processes that facilitate anaerobic stabilization and ultrasonic dewatering of sewage sludge. The destructive effect of ultrasounds can be also applied to remove pathogenic microorganisms from sewage sludge. The article presents the results of the study on the potential of ultrasounds for the improvement of sanitary state of anaerobically fermented sewage sludge. The efficiency of ultrasonic field was evaluated based on the total number of mesophilic bacteria and the feacal indicators, i.e. the coliform index of Enterococcus faecalis, Clostridium perfringens and the number of lactose negative and positive rods. The samples of sewage sludge came from the Municipal Waste Water Treatment Plant and were taken after the completion of methane fermentation. Each sewage sludge sample was subjected to 4 series of tests that included bacteriological analyzes in the control and in the samples exposed to the ultrasonic field. Ultrasonication was applied to the volume of 100 ml of sewage sludge by the ultrasonic desintegrator UD-20 at the constant frequency of 22 kHz and the amplitude of 16 μm. The exposure time of sewage sludge samples to the ultrasonic field was 10 min and 30 min. The obtained results of microbiological analyzes indicate that the investigated sewage sludge is contaminated microbiologically and poses potential sanitary threat. Also, the obtained results confirmed the destructive effect of ultrasounds on the investigated groups of bacteria and diverse resistance of microorganisms towards ultrasounds. High resistance towards ultrasounds irrespective of the exposure time was observed for the endospores of Clostridium. Diverse resistance was observed between Gram-positive and Gram-negative bacteria. Gram-negative bacteria of Escherichia, Salmonella, Shigella were more sensitive to the ultrasonic field. The total degradation was obtained at shorter exposure time (i.e. 10 min) whereas gram positive bacteria from Enterococcus was observed even when the exposure time was extended to 30 min of ultrasonication. In case of mesophilic bacteria at the exposure time of 10 min the reduction was from 70.96% to 82.63%, and after extending the exposure time the mesophilic bacteria was destroyed in the range of 98.47% to 99.22%.