The industrial wastewater treatment plant discussed in this paper generates sludge containing heavy metals, including lead. Occasionally, the concentration of lead in the Toxic Characteristics Leaching Procedure (TCLP) extract from the sludge exceeded the U.S. Environmental Protection Agency (EPA) regulatory limit of 5 mg/l and resulted in the solid waste exhibiting the characteristics of toxicity. The technical and economic feasibility of a process for conditioning the lead-containing sludge was investigated. The results revealed that the lead-laden sludge could be made non-hazardous by chemical conditioning. The lead reduction efficiency of triple super phosphate (TSP) is higher than that of either calcium carbonate or magnesium hydroxide. The laboratory and pilot-scale tests indicated that the conditioning system consistently reduced the lead in the TCLP extract below the regulatory limit of 5 mg/l. The economic feasibility evaluation demonstrated that more than US$450,000 could be saved annually by conditioning the sludge with TSP and disposing it as a non-hazardous material in a landfill. The results obtained from the laboratory as well as from the pilot-scale operation are described and discussed in this paper.

Calcium carbonate, lead, magnesium hydroxide, sludge conditioning, triple super phosphate
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