Results of experimental studies of deliquefaction of excess activated sludge from municipal wastewater treatment facilities in chamber-membrane filter presses were presented. To condition the sludge, fly ash from thermal power plants was added as a mineral additive. Experimental studies have shown high efficiency of deliquefaction of the excess activated sludge with addition of fly ash. Increase in the dose of fly ash has led to an overall increase in filtration capacity and a decrease in moisture content in the filter cake. It was found that in the case of adding fly ash in an amount of 2 wt. % of the initial sludge, deliquefaction efficiency did not increase significantly. In this case, filtering time was reduced only by 15 % and specific capacity increased by 12 %. In the case of increasing the proportion of fly ash to 6 wt. % of initial sludge, a more intensive acceleration of the process was observed. Filtering duration was reduced from 100 to 10 min, specific capacity increased from 87 to 400 l/m2∙hr.Experimental studies have shown that addition of fly ash to sediments of municipal wastewater treatment facilities as a mineral component provides the possibility of deliquefaction of the suspensions obtained using a chamber-membrane filter press. With optimal doses of 4–5 wt. % of the mass of initial sludge, filter capacity is expected to be 350–400 l/m2∙hr. The resulting filter cake had moisture content of about 60 %, a dense, dry structure making it possible to transport it in bulk.