Sludges, waste reduction methods

MF may be used to remove these heavy metals provided pretreatment chemicals are added to precipitate the metals to particles of filterable size. The chemical pretreatment step is crucial since it will affect the performance of the membrane and the resultant sludge volume as well as the contaminant removal efficiency. Reduction/oxidation, absorption/oxidation, and/or catalytic reactions are utilized along with pH adjustment to provide the optimum precipitation. Although conventional methods of waste water treatment may use a similar pretreatment chemistry, the final solid/liquid separation by gravity settling is usually not as effective as membrane filtration. 

Modern methods of waste-water treatment depend on macromole-cular additives used as coagulants to intensify sedimentation processesy to increase concentration of solid particlesr and to improve separation processes as well. The hydraulic transport of sludge forms a part of the waste-water treatment technology. Sludge is pumped not only between individual treatment processes but also out of the water-treatment plant to the sedimentation fields which are often distant. Even in this case the application of drag reduction is advisable from the point of view of saving electric energy. 

In addition to the effluent limitations and the processes shown in Table 24 the degree of reduction in heavy metals waste loadings should consider the sludge handling and disposal methods used for the metal finishing wastewaters. Some processes (e.g., anaerobic digestion) concentrate these metals, and this can lead to process failure unless adequate pretreatment is provided. Dewatering operations discussed in Chapter 7 should be referred to. 

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