Waste disposal treatment of calcium-containing organically loaded wastewaters

In a process for the treatment of calcium ion containing, organically loaded wastewater, wherein the wastewater has a pH of 10-12, contains 300-5,000 mg Ca.sup.++ per liter, and is from settling tanks containing the wastewater from the flushing and wash water cycle of a sugar manufacturing plant, which comprises subjecting said wastewater to an activated sludge process under aeration with an O.sub.2 -containing gas in an aeration tank, the improvement which comprises introducing a CO.sub.2 -containing gas having a concentration of at least 5% by volume of CO.sub.2 to lower and maintain the liquid present in the aeration tank at a pH of 6-8 and to precipitate therein said calcium ion as calcium carbonate, the components in the wastewater and the CO.sub.2 -introduction being such that the concentration of dry activated sludge matter is increased to above 8 kg/m.sup.3 and the proportion of organic substance therein, defined as the incineration loss, is maintained at 30-70% by weight, said improvement facilitating the separation of the activated slude solids and the bacterial action of the activated sludge process.