The article presents results of research aimed to determine optimum operational modes of ultrafiltration membranes used to purify biologically treated wastewater as a pretreatment for further reverse osmosis desalination to produce water for industrial use. Results of experimental investigations are presented that evaluated influence of working pressure on operational costs. Optimum values of working pressure are determined for ultrafiltration treatment of wastewater with suspended solids concentrations 20 and 50 mg/L. A special respect is attributed to reduction of ultrafiltration membrane flux due to pore plugging during filtration cycle. Characteristics of membrane backwashing process are determined aimed on flushing-off all particles that plug membrane pores. Prognostic techniques are developed to predict reduction of ultrafiltration membrane flux due to pore plugging and schedule to apply additional membrane backwashes after flux reduces by 25 per cent at high-pressure values is proposed. Additional operational costs values are determined that account for increase of required membrane area and wash water to remove particles that plug pores.