CHEMICAL FIXATION OF SEWAGE-SLUDGE DERIVED ASH

Los Angeles processes sewage sludge by dehydration and combustion at its Hyperion Treatment Plant. The ash product is usually classified as hazardous because of its heavy metal content, and four readily-available fixing agents have been evaluated for possible use as stabilizers. The ash leachability was assessed before and after fixation using the California Waste Extraction Test. The leaching characteristics of dewatered wet-cake sludge were also measured. While the fixing agents were found to decrease the leachability of ash considerably, ash and dewatered wet-cake mixtures also immobilize metals to some extent. Chemical binding with fixing agents (i.e., wet-cake, Portland cement alone, cement/silicate and cement/citrate mixtures) stabilizes the ash.