Мікробоценози стічних вод Львова на різних етапах очищення

Abstract

The aim of this work was to investigate some physiological groups of microorganisms which are components of wastewater microbiocenoses. Microorganisms were grown in Petri dishes containing 20–30 ml agar selective medium and in 25 ml tubes at a temperature +30 ºC. The selective media were: wort agar for microscopic fungi and yeasts, Hutchinson medium for the cellulose-destroying microorganisms, starch-ammonium medium for microorganisms that can utilize mineral nitrogen forms, Postgate B medium for sulfate-reducing bacteria, Vinogradsky medium for nitrifying bacteria, Ashby medium for the nitrogen-fixing bacteria, Chapek medium for the actinomycetes. 1 mM Cr (VI) (104 mg/l) in the form of К2Cr2О7 was added to the medium. The number of colonies was determined by the Koch method. We studied wastewater microbocenoses of Lviv city at various stages of purification. We showed that the quantitative and qualitative composition of microorganisms differed significantly in primary and secondary clarifiers, the aerotank and sludge at different stages of sewage treatment. In the initial stages of purification, in the primary sump, bacteria that reached the treatment plant with sewage were found. Nitrifying bacteria (7.1 × 106colony forming units (CFU)/ml), nitrogen-fixing bacteria (9.0 × 106CFU/ml), and fungi (3.4 × 106 CFU/ml) dominated. The qualitative composition of microorganisms in primary clarifiers and the aerotank was similar, but their number in the aerotank was significantly higher than in the primary sump: 1.5 × 107 CFU/ml of nitrifying bacteria, 1.4 × 107CFU/ml of nitrogen-fixing bacteria, 6.7 × 106CFU/ml of fungi. The ratio of different physiological groups of microorganisms in the active sludge changed significantly. The predominant microorganisms were those that assimilate mineral forms of nitrogen (65%), their number was 1.6 × 108CFU/ml. In the secondary clarifier, the largest group was cellulose-destroying microorganisms (6.0 × 105CFU/ml). However, their numbers in the secondary sump were lower compared to their numbers in the aerotank and sludge (1.5–3.9 × 106CFU/ml). Among the representatives of various physiological groups of bacteria a significant number of chromium-resistant strains was detected. The largest number of chromium-resistant strains was detected in the active sludge and aerotank, which is probably due to the recirculation of microorganisms in the wastewater treatment. The highest percentage of Cr (VI) resistant microorganisms was among sulphate-reducing bacteria. An increase in the percentage of chromium-resistant microorganisms occurred together with the lowering of the total number of microorganisms of a certain physiological group. These microorganisms could prove useful for the development of biotechnological methods wastewater treatment to eliminate chromium compounds, which are highly toxic to living organisms.