Process for dewatering municipal and other sewage sludges

PCT No. PCT/HU85/00014 Sec. 371 Date Nov. 1, 1985 Sec. 102(e) Date Nov. 1, 1985 PCT Filed Mar. 6, 1985 PCT Pub. No. WO85/03927 PCT Pub. Date Sep. 12, 1985.The invention relates to a new process for dewatering the sludges arising from the aerobic and/or anaerobic decomposition of e.g. household sewages, by treating with chemical agents, which comprises adjusting the pH of the sludge to a value between 9 and 12 by adding at least one of a compound selected from the group consisting of calcium and magnesium hydroxide and calcium and magnesium oxide, then mixing 50 to 5000 g./m3, of formaldehyde and/or dimethylolurea to the sludge suitably in the form of an aqueous solution, then optionally adding a dusty or granular substance capable of adsorbing oils and fats in an amount of 0.5 to 15% by weight as calculated for the dry substance content of the sludge, and adding prior to the adjustment of the pH or after the optional treatment with said substance capable of adsorption to the sludge 20 to 500 g./m3. of a flocculating agent, suitably a nonionic or cationic polymer with a molecular weight suitably higher than 100,000, preferably higher than 2 millions to 3 millions, or a copolymeric electrolyte containing anionic and cationic groups, suitably in the form of an aqueous solution of 0.5 to 1% by weight, then letting settle, removing the water from above the sediment and subjecting the sediment to further dewatering in a manner known in the art, suitably by the means of filtration and/or centrifuging.