GB437469A - Improved process for treating sewage sludge - Google Patents

Abstract

A solution of formaldehyde is obtained from the gases given off from sewage sludge undergoing digestion and which contain methane and some carbon dioxide by partially burning the methane or by passing the gases into ozonized air, and then passing the gases through water.ALSO:The de-watering of sewage sludge by filtration, for use as fertilizer or prior to incineration, is promoted by previously elutriating the sludge with water, separating the sludge from the water by settlement or otherwise and treating the separated sludge with a coagulant, such as chlorinated copperas, ferric chloride, ferric sulphate or aluminium salts. A portion of the sludge only may be elutriated and this portion mixed with sludge that has not been elutriated, the mixture being then treated with coagulant. Sludge from raw sewage, digested sludge or activated sludge or mixtures of these different kinds of sludge may be treated in the way described. The sludge may be treated either before or during elutriation with de-ammonifying agents such as chlorine, hypochlorites, nitrous oxide or formaldehyde. In elutriating, the sludge and water may be agitated by means of air under pressure. Countercurrent elutriation using two or more decanting vessels may be performed. When ferric salt is used as coagulant, the water filtered from the sludge may be chlorinated and used for elutriating further sludge. A solution of formaldehyde for treating the sludge may be obtained from the gases, given off from sludge which is undergoing digestion and which contain methane and some carbon dioxide, by incompletely burning the methane or by passing the gases into ozonized air, and then passing the gases so treated through water.