Dewatering tests

Electrokinetics. Electrokinetics is a tested technology that has been used for over half a century to dewater and stabilize soils, and has recently been investigated for in situ use at hazardous waste sites (23). Primarily used for metals removal, the technology utilizes an electrical field to generate a flow and concentration gradient in porous and semiporous soils. 

Finally, selective separation and dewatering of one suspended substance in a slurry containing different minerals or precipitates is possible by selectively adsorbing a magnetic material (usually hydrophobic) onto a soHd that is also naturally or chemically conditioned to a hydrophobic state. This process (Murex) was used on both sulfide ores and some oxides (145). More recently, hydrocarbon-based ferrofluids were tested and shown to selectively adsorb on coal from slurries of coal and mineral matter, allowing magnetic recovery (147). Copper and zinc sulfides were similarly recoverable as a dewatered product from waste-rock slurries (148). 

Generahzed correlations are available for each of the operations which make up the full filter cycle. This means that simulated operating conditions can be varied to obtain a maximum of information without requiring an excessive number of test runs. The minimum number of test runs required for a given feed will, of course, vary with the expertise of the experimenter and the number of operations performed during the filter cycle. If, for example, the operation invdves only the dewatering of a slurry which forms a cake of relatively low to moderate porosity, frequently sufficient data can be obtained in as little as six runs. For more difficult tests, more runs are usually advisable, and the novice certainly should make a larger number of runs as there is likely to be more data scatter. 

The following equations, which have been tested in centrifugal dewatering of granular solids, prove useful ... 

Corrective Action Application In Massachusetts, a municipal wastewater treatment plant receives a number of wastestreams containing heavy metals from local industries. When tested, the dewatered sludge failed the EP toxicity test. In order to permit landfill disposal of the sludge, solidification processes were examined. A soluble, silicate-based system, developed by Chemfix, was ultimately selected which produced a product whose leachate passed the EP toxicity test (Sullivan, 1984). 

Applications as soil conditioners (2) and in the dewatering of phosphate slimes (3) were among the first successful uses of synthetic polymeric flocculants. For this reason, several test methods based on permeability have been developed, including the re-filtration rate method of La Mer (3). 

Rapid loss from surface water (tj/2 on the order of hours), but probably due to photolysis [44, 70, 71] high removal in activated sludge treatment (-95% overall based on several studies) [45, 72-77], but 50% present in dewatered sludge in one study [45], so biodegradative removal may be less than overall removal, i.e., subsequent exposure possible via waste sludge BS-2 (water grab sample die-away tests)c ... 

Laboratory Flocculant Testing. The objective of laboratory testing of flocculants is lo determine which chemical composition and molecular weight will give the best cost performance. The usual method is lo simulate on a laboratory scale the formation of floes and then subject them to the same or similar types of forces as would be encountered in a full-scale dewatering device. 

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