Environment aqueous waste removal

In aqueous waste-removal operations, the solute is often an undesirable species to be removed from wastewater. After solute recovery, the rich streams, with solute in low concentrations, are disposed of, returned to the environment, recycled, or reused. Clearly, when returned to the environment, these streams must meet the latest federal, state, or local regida-tions. When recycled or reused, solute concentrations must be sufficiently low to meet the requirements of sinks elsewhere in the process. 

Relatively pure solid NaOH is recovered from the aqueous solution, and the regenerated mercury is then pumped back to the electrolysis cell. This process, called the chlor-alkali process, has often resulted in significant mercury contamination of the environment the waste solutions from this process are now carefully treated to remove mercury. 

For the bulk production of CPs, the chemical method is used. It is essentially a scaleup of the procedures used in the laboratory. In the case of PANi, benzidine is a byproduct formed during oxidation of aniline and is a carcinogen. Consequently, it must be removed by extraction or copolymerization during oxidation. In addition, the aqueous waste must be either treated before release into the environment or recycled. 

Eary, L.E., and D. Rai. 1988. Chromate removal from aqueous wastes by reduction with ferrous ion. Environ. Sci. Technol. 22 972-977. 

Biologically friendly ionic surfactants can be added to the wastewater at concentrations above the threshold value beyond which the surfactants self-assemble to form micelles. The resulting micelles can trap the hydrocarbon wastes since the hydrocarbon solutes prefer the hydrocarbon interior of the micelle over the aqueous environment outside. In addition, ionic wastes in the water adsorb to the polar heads of the surfactants (see Fig. 8.1). The resulting waste-laden micelles can then be removed more easily using ultrafiltration methods. Such a process, known as micellar-enhanced ultrafiltration (MEUF), can be made continuous, scalable, cost effective, and environmentally friendly (through the use of biodegradable surfactants). 

While cassava is an important crop across a wide range of tropical environment, cassava peels are an agricultural waste from the foodprocessing industry. Activated carbon prepared from cassava peel was used as an adsorbent in removal of dyes and metal ions from aqueous solutions. The material impregnated with H3PO4 showed higher efficiency than the heat-treated material (Rajeshvarisivaraj et ah, 2001). 

Micelles are used in many applications. Their largest industrial use is in emulsion polymerization, as detailed in Section 5.9 below. On the other hand, micelles made of ionic surfactants can trap hydrocarbon wastes in polluted water, since these hydrocarbon molecules prefer to be in the hydrocarbon interior of the micelle in an aqueous environment. In addition, ionic wastes dissolved in water adsorb onto the polar heads of these micelles. The resulting waste-filled micelles may be removed by simple ultrafiltration. As an example of another application, micelles can affect the rate of several chemical reactions and are used in micellar catalysis, similar to enzyme catalysis, in biochemistry. The rate of the chemical reaction increases with increasing micelle concentration, eventually leveling off. Nevertheless, micellar catalysts are less specific than enzymes. 

The most frequently applied adsorbent for the removal of organic pollutants in wastewaters is currently activated carbon, which is an expensive material. Mounting apprehension about environmental issues has prompted the textile industry to investigate appropriate and environment-friendly treatment technologies for waste aqueous effluent containing color and heavy metals. Dubey and Rao [24] evaluated a number of alternative and cheaper adsorbents. Results... 

Namasivayam, C. and Ranganathan, K. 1993. Waste Fe(III)/Cr(ni) sludge as adsorbent for the removal of Cr(VI) from aqueous solution and chromium plating industry wastewater. Environ. Pollut. 82 255-261. Namasivayam, C. and Arasi, D. 1997. Removal of Congo red from wastewater by adsorption onto waste red mud. Chemosphere 34 401-417. 

Pollard SJT, Fowler GD, SoUars CJ, Perry R (1992) Low-cost adsorbents for waste and wasteweiter treatment areview. Sci Total Environ 116(l-2) 31-52 Qdais HA, Moussa H (2004) Removal of heavy metals from wastewater by membrane processes a comparative study. Desalination 164(2) 105-110 Rahman MA, Muneer M (2005) Photocatalysed degradation of two selected pesticide derivatives, dichlorvos and phosphamidon, in aqueous suspensions of titanium dioxide. Desalination 181(1-3) 161-172... 

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