Sludge chlorination process

A schematic of the sludge chlorination process (Purifax process) is shown in Fig. 5. The sludge is first pumped through a macerator to reduce the particle size for optimum chlorine exposure. It is then mixed with conditioned sludge ahead of the recirculation pump at a ratio of 3.8 gal of recirculated sludge for each gallon of raw sludge. 

Fig. 5. Schematic of a waste sludge chlorination process system (BIF).

Some of the important but expensive rare metals are usually extracted as by-products of other metal separation processes. Selenium and tellurium are recoverable from copper refinery slime by pressure leaching (M40), scandium from uranium plant iron sludge (R15), uranium from gold cyanida-tion residues (G3), silver from aqueous chlorination process for the treatment of slimes, and gravity concentrates from gold ores (V2). A host of other processes are in use. 

When chlorination process is used for treatment of sludge and septage, it can also be called chlorine stabilization process (3,5-8). 

The process equipment for sludge chlorination or stabilization is commercially available from BIT Corporation. 

Table 8 indicates the common process shortcomings and their respective solutions. Table 9 is a sludge chlorination trouble shooting guide. 

Applicability This process is applicable to liquid (pumpable) organic wastes and finely divided, fluidizable sludges. It may be particularly applicable to the processing of liquid wastes with a high chlorine, pesticide, PCB or dioxin content. Sludges must be capable of being fluidized by the addition of a liquid. Waste streams must be free of (or preprocessed to remove) solids, which prevent satisfactory atomization. 

Precipitation is nonselective in that compounds other than those targeted may be removed. Both precipitation and flocculation are nondestructive and generate a large volume of sludge which must be disposed of. Coagulation, flocculation, sedimentation, and filtration, are typically followed by chlorination in municipal wastewater treatment processes. 

On November 8, 2000, U.S. EPA listed as hazardous two wastes generated by the chlorinated aliphatics industry.18 The two wastes are wastewater treatment sludges from the production of ethylene dichloride or vinyl chloride monomer (EDC/VCM), and wastewater treatment sludges from the production of vinyl chloride monomer using mercuric chloride catalyst in an acetylene-based process. 

Wastewater treatment systems can be a significant source of cross-media pollutant transfer. For example, waterborne particulates and some chlorinated compounds settle or absorb onto treatment sludge and other compounds may volatilize during the wastewater treatment process. 

Besides fossil fuels, a process for conversion of sewage sludge was also suggested. Lastly, chlorination and/or the addition of heavy metals were suggested as a means of containing microorganisms. 

The precipitated mercurous chloride separates as a sludge. In the original process, some of this mercurous chloride was chlorinated to mercuric chloride for re-use. In a later version of the process, all the mercuric chloride is electrolytically converted to elemental mercury and chlorine. As of 1994 the electrolytic version had been installed in three plants. Developed by Boliden, Sweden, and Norzink, Norway, and now offered for license by Boliden Contech. 

Eurker PA, Clark CS, Elia VJ, et al. 1983. Worker exposure to chlorinated organic compounds from the activated-sludge wastewater treatment process. Am Ind Hyg Assoc J 44 109-112. 

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