Effluent treatment and recycling

Effluents from cotton processing are generally the most polluted. A typical composition of the effluent from a cotton dyeing and finishing house is given in Table 5.3. 

The most common form of disposal is through the sewer and then to a central treatment plant. In some rare instances, some plants still discharge directly to streams 

Recycling Recycling rinse waters and other color-free liquors is becoming a frequently used practice. Suitable liquors are recovered, stored in tanks, and then used for scouring, first rinses, or new dyebath liquors. 

In recent decades, a number of techniques and technologies have been developed for effluent neatments and recycling (Christie, 2007 Hauser, 2011 Babu et al., 2(X)7 Vandevivere et al., 1998). A brief description of some of the more common technologies for the treatment of the dyehouse effluents is provided in the following sections. 

Adsorption is a physicochemical efQuent treatment in which effluent is mixed with, or passed through a bed of, activated carbon, a kaolin clay, or a silicon polymer. The different adsorbents have selective adsorption of different dyes. Activated carbon is regarded as the overall best adsorbent for dyeing effluent, but it is expensive (Christie, 2007). Absorption is only feasible in combination with a prior decantation or biological treatment because suspended solids rapidly clog the filter. 

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Hartinger, L., Handbook of Effluent Treatment and Recycling for the Metal Finishing Industry, 2nd ed., Finishing Publications, Warrington, WA, 1994. 

D. Pletcher and F. C. Walsh, Water Purification, Effluent Treatment and Recycling of Industrial Process Streams, Ch.7, Industrial Electrochemistry, Chapman and Hall, London, 1990. 

Membranes have applications in electrochemical separations in the areas of effluent treatment and recycling. Electrodialysis, ED, is a process in which electrolyte solutions are either concentrated or diluted (or deionised). The process has over the years been the dominant technique for the desalination of brackish water. Electrodialysis has many potential applications for the removal or recovery of ionic species and generally the process can be used to perform a number of functions such as ... 

Water purification, effluent treatment and recycling of industrial process streams... 

Finishing chemicals for all kinds of performance aspects of textile goods exist in great variety, and recycling options of these chemicals are largely unexplored. As mentioned previously, chemicals used for finishes such as easy-care, hydrophobic, flame-retardant and soil-release, are usually applied in combination with hand-builders, softeners and other auxiliaries. Their separation and subsequent re-use is problematic and very little has been published in this area. Their impact on the effluent treatment and quality, monitored as BOD and COD is, however, significant. 

Effluent is associated not just with many process industries, as has been illustrated above in the case of the textile finishing industry, but also with most aspects of our urban existence. The need to treat effluent arises for several reasons. Some effluents can be transformed into useful products, such as feedstock for animals or even pharmaceutical products the ability to concentrate effluent, particularly in an energy-efficient manner, can reduce disposal costs and the ability to recycle effluents, once separated from less desirable components, can also be economically beneficial. The link between effluent treatment and PI is strong and growing, as the above influences become the subject of legislation or economic necessity. The range of techniques that can be used to aid clean-up covers both active and passive intensification methods. Included below are several examples including the use of ultrasound already dealt with in a number of process uses in this chapter. 

Additional separation and recycling. Once the possibilities for recycling streams directly, feed purification, and eliminating the use of extraneous materials for separation that cannot be recycled efiiciently have been exhausted, attention is turned to the fourth option, the degree of material recovery from the waste streams that are left. One very important point which should not be forgotten is that once the waste stream is rejected, any valuable material turns into a liability as an effluent material. The level of recovery in such situations needs careful consideration. It may be economical to carry out additional separation of the valuable material with a view to recycling that additional recovered material, particularly when the cost of downstream effluent treatment is taken into consideration. 

If steam is used as stripping agent, either live steam or a reboiler can be used. The use of live steam increases the effluent volume. The volatile organics are taken overhead, condensed, and recycled to the process, if possible. If recycling is not possible, then further treatment or disposal is necessary. 

Industrial Wastes. Closely related to seawater concentration is the simultaneous concentration of industrial effluents and recycle of recovered water (see Wastes, industrial). These appHcations are expected to increase as environmental restrictions increase. Examples are the concentration of blowdown from cooling towers in power plants concentration of reverse osmosis blowdown and the processing of metal treatment wastes (11) (see... 

The scope of the previously addressed CE case study is now altered to allow for stream segregation, mixing, and recycle within the ethyl chloride plant. There are five sinks the reactor (u = 1), the first scrubber (u = 2), the second scrubber (u = 3), the mixing tank (u = 4) and the biotreatment facility for effluent treatment (m = 5). There are six sources of CE-laden aqueous streams (in = 1-6). There is the potential for segregating two liquid sources (lu = 2, 4). The following process constraints should be considered ... 

Medina, B.Y., Torem, M.L., and De Mesquita, L.M.S., Removal of chromium III from liquid effluent streams by precipitate flotation, in Waste Treatment, and Clean Technology, The Global Symposium on Recycling, REWAS 04, Vol. II, Gaballah, I., Mishra, B., Solosabal, R., and Tanaka, M., Eds., Madrid, Spain, September 26-29, 2004. 

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