The review examines the microbiological aspects of the biological phosphorus removal from wastewater. The history of the development of biotechnology and the discovery of the physiological group of phosphate-accumulating organisms (PAOs), which biologically remove phosphorus via the phosphate uptake and storage in the form of intracellular polyphosphates, is briefly described. PAOs are characterized by a cyclic type of metabolism that occurs when the anaerobic/aerobic conditions cyclically change. Under anaerobic conditions, PAOs uptake and store organic compounds through the energy of degradation of intracellular polyphosphates. When anaerobic conditions change to aerobic or an alternative electron acceptor appears, PAOs uptake phosphates and synthesize intracellular polyphosphates using the intracellular polymeric sources of carbon and energy accumulated under anaerobic conditions. The main representatives of the PAOs, their metabolic models, and physiological characteristics are described. The basic principles of the implementation of biotechnology used in the practice of wastewater treatment for phosphorus and other nutrients are considered.

The work deals with more efficient procedures for the isolation and cultivation of “nonculturable” microorganisms (NM) from environmental sources. The techniques for NM cultivation in situ and under laboratory conditions are discussed. A new approach is considered, viz., cultivation under cyclically varying conditions with the cycle duration comparable to the duration of the cell cycle. Cyclic cultivation implies sequential changes of several cultivation phases with different growth conditions. An established sequence of growth phases provides for the competitiveness of the target microorganisms and for accumulation of their biomass. Cultivation of phosphate-accumulating bacteria, nonculturable microorganisms which have not been previously isolated in pure culture, in an SBR reactor is discussed as an example of cyclic cultures.

Anammox is one of the most important processes in the global nitrogen cycle and the basis for an efficient technology of nitrogen removal from wastewater. The effect of the presence of sulfide in wastewater on the transformation of nitrogen compounds by the anammox community has been insufficiently studied. The present work dealt with the effect of sulfide on nitrogen removal efficiency and the dynamics of nitrogen species in a laboratory sequencing batch bioreactor modeling the functioning of the anammox community carrying out ammonium oxidation via nitritation and anammox and nitrite oxidation. The 16S rRNA gene profiling of the community of the anammox-activated sludge attached to the stationary carrier revealed members of the key physiological groups: ammonium oxidizers of the genus Nitrosomonas, nitrite oxidizers of the genus Nitrosospira, and anammox bacteria of the genera Candidatus Brocadia and Ca. Jettenia, as well as members of other bacterial genera. Nitrate removal was not sensitive to sulfide at concentrations up to 50 mg S/L and decreased by 17% at 100 mg/L. The threshold of sulfide sensitivity for group I nitrifiers was ~50 mg/L, while anammox bacteria were resistant to sulfide concentrations of up to 100 mg S/L in the incoming water. Group II nitrifiers were probably the most sulfide-sensitive components of the community. A drastic increase in the abundance of members of the family Hydrogenophilaceae at elevated sulfide concentrations, together with the precipitation of elemental sulfur, may indicate sulfide oxidation either by molecular oxygen or via nitrate reduction; this finding requires further investigation. This is the first report on the different effects of sulfide on the growth rate of members of the nitrifying genus Nitrosomonas, increasing/decreasing or not affecting it for different phylotypes at elevated sulfide concentrations.

The transition process caused by an abruptly increased ammonium load (2.5-fold) on the microbial community of a sequential batch reactor carrying out nitrogen removal from the water via nitritation-anammox was studied. The community developed in the bioreactor at incoming ammonium concentration of 200 mg N/L removed 76.5% of the inflowing nitrogen and was satisfactorily described by the BioWin mathematical simulator with corrected coefficients. Abrupt increase of nitrogen load from 200 to 500 mg N/L resulted in ammonium concentration at the reactor outlet increasing from 27 to 280–290 mg N/L, with nitrogen removal efficiency dropping to 40%. The calculation using the BioWin simulator showed that the efficiency of the nitritation-anammox process should increase in the course of a month and stabilize at the level close to the original one (76.5%). However, experimental data did not support this calculation: no increase in efficiency was observed during this period. Changes in the structural and functional characteristics of the biofilms and aggregates, which were not accounted for in the model, were probably responsible for discrepancies between the experimental and calculated data.

Changes in the structure and properties of a microbial community of a sequencing batch reactor (SBR) enriched with phosphate-accumulating microorganisms (PAO) after a pH shift to more acidic values (pH 6.7‒7.1) were studied in. The relative abundance of Ca. Accumulibacter decreased from 43.6 to 13.9%, while abundance of potential PAO belonging to the genera Dechloromonas and Thauera increased. The overall share of PAO changed insignificantly (40‒43%). The share of glycogen-accumulating microorganisms (GAO), the main competitors of PAO, remained low throughout the experiment: abundance of the Competibacter 16S rRNA gene fragments before and after the pH shift was 2‒4%. While decrease in pH resulted in a drop in the amount of phosphates released during the anaerobic phase, the amount of phosphorus in the biomass (15‒17%) remained high, as well as phosphorus removal (92‒94%).

For ammonium removal from wastewater, anammox technologies are among the most efficient and rapidly developing ones. Due to the low growth rate of anammox bacteria and their sensitivity to various inhibitors, technologies using attached biocenosis carriers (ABCs) provide for reliable operation. The goal of the present work was to investigate a new ABC type, ETEK biochips based on a nonwoven fibrous material. The work involved the techniques of materials science (design of a new ABC type) and physical modeling of the anammox process (in a laboratory bioreactor), as well as electron microscopy and molecular profiling of activated sludge communities. Comparison of the ETEK biochips with the ABCs of foamed polyethylene BF33 and Mutag revealed more rapid accumulation (5-fold) of the activated sludge biomass on ETEK biochips upon reactor launching, as well as comparable buoyancy and reactor productivity regarding N removal. The specific rate of nitrogen removal obtained with ETEK biochips considerably exceeded that for foamed polyethylene with a filler: 1.5–3 times higher per chip and 1.5 times higher per activated sludge biomass unit. The studied ABC shared the same issue of floating to the surface due to the active formation of gas (N₂). The algorithm for calculating the downward flows in bioreactors with rapidly surfacing ABC is proposed, and a new hydrodynamic type of a bioreactor (with hybrid hydrodynamics) is described, a moving bed–sequencing batch reactor (MB-SBR).