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Study on activated sludge flocs morphology and composition in a full-scale wastewater treatment plant in Poland

This work is a comprehensive study of a full-scale municipal wastewater treatment plant (WWTP) in the city of Zgierz (Poland) aiming at the estimation of the impact of seasonal changes of temperature on flocs morphology, biomass concentration, quantity of filamentous bacteria, content of polyhydroxybutyrate (PHB) and composition of microinvertebrates in the activated sludge system. Two short-term measurement campaigns, in winter and in summer, were carried out under dry weather conditions. It occurred that lower temperatures (11.1–14.6 °C) had hardly any effect on flocs size or concentration of activated sludge biomass in the full-scale activated sludge system treating municipal wastewater. They did not aggravate the biosynthesis of PHB either. However, decreasing temperature favored the growth of filamentous bacteria and led to the elevation of the sludge volume index (SVI). In spite of this, it did not induce any bulking events. Irrespective of the season, the groups of crawling ciliates, attached ciliates and testate amoebae, indicating good performance of the full-scale plant tested, were predominant.