This paper presents the results of studies on the structure of the ciliate population in a freshwater lake. The classification of the ciliated communities based on the analysis of the distribution of ciliate population density in the lake along the oxygen gradients, taking into account their oxygen preferences, was proposed. It was shown that the distribution of ciliated protozoa in the space of a reservoir is determined not by such spatial units as the water column, bottom, and periphytal, but by the oxygen gradients. Four types of habitats with different oxygen regimes were distinguished: With stably high oxygen concentration, stably low oxygen concentration, stably oxygen-free conditions, and conditions with a high amplitude of diurnal oxygen variations. The location of these habitats in the space of the lake and their seasonal changes were determined. On the basis of the quantitative development of ciliate populations, zones of optima and tolerance ranges of some ciliate species in the oxygen gradient were established. The oxygen preferences were established for the species from four distinguished assemblages: Microoxyphilic, oxyphilic, euryoxyphilic, and anoxyphilic (anaerobic). The presence or the absence of a certain type of assemblage in the reservoirs depends solely on the parameters of the oxygen gradients. The diversity of the ciliated protozoa in water bodies also depends on the stability and diversity of the oxygen gradients.

The spatial distribution of ciliate assemblages was studied in a shallow floodplain lake with a sharp division of space by oxygen conditions. The surface zone occupied by the “carpet” of Lemna trisulca and L. minor was characterized by a large daily amplitude of oxygen content with periodic exceeding of 100% of saturation; the underlying water layer was characterized by microaerobic conditions throughout most of the year, with seasonal deviations towards oxygen-free conditions (in winter and mid-summer) or increased oxygen content (before freezing and after ice melt); stable oxygen-free conditions were maintained in the bottom layer of water and at the bottom of the lake. There were 111 species of ciliated protozoa recorded in the lake. The ciliated protozoa were clearly structured and formed three almost non-overlapping assemblages in terms of species composition, which retained their isolation during all seasons of the year. On the basis of the analysis performed using the R indicspecies package, species of ciliated protozoa were identified as indicators of conditions with different oxygen regimes, which are determined by the level of organic pollution and the distribution of photosynthetic organisms.

The representation of Peritricha ciliates was studied in the activated sludge of two wastewater treatment plants (WWTP), one of which operates using a technology that includes alternating aerobic, anoxic and anaerobic conditions in bioreactors (Lublin, Poland), and the other – only aerobic...

Laboratory-scale sequencing batch reactors (SBR) with activated sludge were used for co-treatment of municipal wastewater and two drilling fluids the polymer-potassium (DF1) and polymer (DF2) types. The influence of two doses of each types of drilling fluids, 1% and 3% of total added wastewater...