Combined biological-chemical detoxification of organics

A combined biological-chemical method for detoxifying a slurry of sludge of the municipal sewage or industrial organic type, which sludge contains excess-waste thermophilic bacteria, biodegradable organic material, sulfur, and toxic heavy metals in insoluble form, which comprises the sequential steps of:

• (a) introducing a sufficient quantity of the sludge slurry into an enclosed insulated reactor vessel to fill the same to about one-half of its volume;
• (b) aerating the slurry with ambient air by means of a self-aspirating aerator, and simultaneously cutting foam produced thereby, thereby to effect autoheating of the slurry by the thermophilic bacteria to a temperature maintained in the thermophilic range of from about 43.degree. C. to about 70.degree. C., said autoheating being achieved by conservation of the metabolic heat of oxidation of the biodegradable organic material in said insulated reactor vessel;
• (c) retaining said autoheated slurry in said reactor for a hydraulic retention time of 3 to 8 days sufficient to destroy the pathogenic bacteria and increase the oxidation reduction potential to a level greater than +500 mv, whereby the sulfur and heavy metals are converted to a desired higher oxidation state;
• (d) adding to said autoheated slurry a quantity of concentrated acid in an amount sufficient to acidify said slurry to a pH value ranging from 1.0 to 3.0 for an acidification period of 6 to 12 hours sufficient to solubilize the heavy metals while maintaining said oxidation reduction potential at a level greater than zero mv, and the temperature in the thermophilic range;
• and
• (e) dewatering the acidified slurry to remove the solubilized heavy metals therefrom, thereby to produce dewatered, detoxified acidic sludge and acidic, heavy-metal-containing water.