Composition of activated sludge microbial community used in the combined biological and chemical wastewater treatment
This article compares conventional (FeCl<sub>3</sub>, Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>) and innovative (Biokat P 500 и Nanofloc) reagents used in the combined biological and chemical wastewater treatment for coagulating medium components and microbial suspensions. In this study, we aimed to assess the effect of these reagents on the quantitative and species composition of microorganisms present in activated sludge. To that end, we modelled the processes of the combined biological and chemical wastewater treatment; cultivated samples of activated sludge and transferred them to selective media in order to establish the number of different physiological groups of microorganisms; as well as determined the taxonomic identity of bacterial colonies (nitrogen-fixing and phosphate-mobilizing bacteria). Changes in the biocoenosis of activated sludge were assessed for such agronomically important groups of microorganisms as diazotrophs, phosphate-mobilizing bacteria, actinobacteria, micromycetes, etc. It is established that combined biological and chemical wastewater treatment in most cases leads to a decrease in the number of these microorganisms. A notable decrease in the number of microorganisms in activated sludge samples containing a conventional reagent Al<sub>2</sub>(SO<sub>4</sub>)<sub>3 </sub>is experimentally confirmed. FeCl<sub>3</sub> is shown to be the second most effective reagent in this respect. It is demonstrated that Nanofloc, despite inhibiting many studied groups of microorganisms, contributes to an increase in the number of diazotrophs; whereas the use of Biokat P 500 leads to the least negative consequences in terms of the number and composition of microorganisms present in activated sludge. In the course of identifying predominant nitrogen-fixing and phosphate-mobilizing bacteria via proteomic analysis, it is established that the following bacterial cultures are present in the control sample: Klebsiella oxytoca, Pseudomonas putida, Acinetobacter johnsonii, Rhodococcus erythropolis. These microorganisms are known for playing a significant role in ecology and biotechnology. Following addition of FeCl<sub>3</sub> to the test samples, only one bacterial culture (K. oxytoca) was found to be predominant; whereas addition of innovative reagents resulted in two predominant bacterial cultures (Biokat P 500 - Enterobacter ludwigii and Aeromonas veronii; Nanofloc - Enterobacter cloacae and R. erythropolis). The presence of several dominant bacterial species, belonging to other groups than nitrogen-fixing or phosphate-mobilizing bacteria, may indicate the syntrophic nature of activated sludge communities.