Rational use of water resources is one of the urgent problems for arid regions of Kazakhstan. The biocenosis of activated sludge of urban sewage treatment plants in Zhanaozen periodically encounters stressful situations associated with violation of the operating mode of equipment or emergency discharges of toxicants into the sewage treatment plant system. It has been established that with sharp fluctuations in the physicochemical parameters of aqueous solutions, protozoal organisms are primarily eliminated from the composition of activated sludge. This pattern was noted with an increase in the content of ammonium nitrogen, phosphorus, monoethanolamine and pH fluctuations in wastewater. Under the conditions of a 10-month period of active insolation in Western Kazakhstan, the species diversity of the algoflora of activated sludge correlates with the duration of daylight hours, while it was found that diatoms predominate in the autumn-winter period of the year, blue-green and green algae predominate in the spring-summer period.