Maintenance of the wastewater treatment plants and increasing the efficiency of existing aerobic biological reactors depend on the stability of activated sludge characteristics under varying wastewater parameters within significant limits and/or influence of some environmental factors. The steady microbial communities observed in biofilms and anaerobic granules of activated sludge can serve as successful samples of formation of the similar aerobic systems. The granular aerobic sludge obtained in the course of our researches is an ideal "plant" on treatment of biogenic pollution at both low and high concentrations. It demonstrates high ability for treatment and stability to adverse factors. To improve aerobic wastewater treatment characteristics, a possibility of using impact of stress conditions upon activated sludge has been studied. Under conditions of fractional hydrogen peroxide addition at diffused lighting, the granular aerobic activated sludge adapted to hydrogen peroxide has been obtained. This sludge has got good sedimentary properties and it differs from the control sample in the species diversity, improved treatment characteristics and also resistance to the stressor. It also endures an impact of one-time hydrogen peroxide addition up to 1.2-1.5 g H2O2/l. The conditions under which the steady aerobic granules of the diameter from 2 to 5 mm were formed with high treatment ability have been chosen. The granules were being stabilized at passages with hydrogen peroxide treatment and they endured up to 2.4-3.0 g/l of one-time H2O2 addition.

Toxic impact of silver and uranium salts on activated sludge of wastewater treatment facilities has been studied. Some dominating cultures (an active nitrogen fixer Agrobacterium tumifaciens (A.t) and micromyces such as Fusarium nivale, Fusarium oxysporum, and Penicillium glabrum) have been isolated and identified as a result of selection of the activated sludge microorganisms being steadiest under stressful conditions. For these cultures, the lethal doses of silver amounted 1, 600, 50, and 300 µg/l and the lethal doses of uranium were 120, 1,500, 1,000, and 1,000 mg/l, respectively. A.tumifaciens is shown to be more sensitive to heavy metals than micromyces. Synthetic granular activated sludge was formed on the basis of three cultures of the isolated micromyces steadiest against stress. Its granules were much more resistant to silver than the whole native activated sludge was. The concentration of silver causing 50 % inhibition of synthetic granular activated sludge growth reached 160-170 μg/l as far as for the native activated sludge it came only to 100-110 μg/l.

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