Effluent treatment/removal

The capital cost of most aqueous waste treatment operations is proportional to the total flow of wastewater, and the operating cost increases with decreasing concentration for a given mass of contaminant to be removed. Thus, if two streams require different treatment operations, it makes no sense to mix them and treat both streams in both treatment operations. This will increase both capital and operating costs. Rather, the streams should be segregated and treated separately in a distributed effluent treatment system. Indeed, effective primary treatment might mean that some streams do not need biological treatment at all. 

Toxic or malodorous pollutants can be removed from industrial gas streams by reaction with hydrogen peroxide (174,175). Many Hquid-phase methods have been patented for the removal of NO gases (138,142,174,176—178), sulfur dioxide, reduced sulfur compounds, amines (154,171,172), and phenols (169). Other effluent treatments include the reduction of biological oxygen demand (BOD) and COD, color, odor (142,179,180), and chlorine concentration. 

Groundwater is vulnerable to pollution by chemicals carried by rainwater, leaching from waste sites or from waste water carrying industrial or agricultural effluent. Treatment of drinking water may remove some, but not all, of these contaminants. Some polycarbonate or metal water pipes that are lined with epoxy resin lacquers may release bisphenol A. 

In a recycling system, the aqueous discharge effluent from both centrifiiges is returned to the extractors for additional oil recovery, the water being reused. During this extraction process the viscosity of the emulsions increases because peel polysaccharides, mainly pectins, are transported with the emulsion. Enzymatic breakdown of the internal links of the pectin, catalysed by endopolygalacturonase activity, produces an important decrease in the viscosity of the emulsion [16]. In addition, enzymatic treatment removes pectins from the emulsion and contributes to it destabilization [17]. 

Membrane filtration processes have been successfully applied to the field of environmental engineering for air pollution control,34 potable water purification,22-24 groundwater decontamination,35,36 industrial effluent treatment,37 hazardous leachate treatment,35,36 and site remediation,36 mainly because membrane filtration can remove heavy metals and organics. 

DAF is used to remove suspended solids by decreasing their apparent density they then rise and float on the water surface. DAF is also used to remove soluble iron, VOCs, oils, and surface active agents by oxidation, air stripping, and surface adsorption. The flotation technology is becoming one of the most important technologies for groundwater decontamination, industrial effluent treatment, and water purification.58-6170... 

Figure 26.37a shows a system involving four effluent streams with different inlet concentrations that all need to be treated to remove mass load and bring down the concentration to an acceptable level for environmental discharge Ce. To obtain an overall picture, rather than deal with four separate effluent streams, the streams can be combined together to produce a composite effluent stream16. The construction is analogous to that for the limiting composite curve. The diagram is divided into concentration intervals and the mass load of the streams within each concentration interval combined together, Figure 37b. This provides a picture of the overall effluent treatment problem and what is required to happen to the effluent streams.

Figure 26.39b shows the construction for targeting minimum wastewater treatment flowrate when removal ratio has been specified. If the initial effluent treatment line shown dotted in Figure 26.39b is considered, then there is a point of origin... 

Example 26.4 Consider again Example 26.3. The target for the three streams in Table 26.8 was determined to be 60 t h 1. This corresponded both with a treatment process achieving 10 ppm at its outlet and also one with a removal ratio of 95%. Design an effluent treatment network to achieve the target of 60 t-h-1. 

In order to illustrate the capability of the proposed technique, this multipurpose example has been enhanced by including compulsory washing operations after each of the reactions in each of the 2 reactors. The philosophy is that the reactors need to be cleaned after each reaction in order to remove contaminants that are formed as byproducts, so as to ensure product integrity. Data pertaining to cleaning tasks is shown in Table 6.6. The variation in performance in the 2 reactors could be ascribed to differences in design, which is indeed a common encounter in practice. In addition to this data, it is known that freshwater cost is 2 cost units per kg of water whilst the effluent treatment cost is 3 cost units per kg. 

Since cyclodextrins form complexes with various other substances, including many dyes and surfactants, it is clear that they could be useful in effluent treatment. They are potentially suitable for the reduction or removal of polluting substances either by immobilisation or by solubilisation and extraction and thus can accelerate detoxification [30]. 

It is not surprising, therefore, that chitosan and its basic derivatives will complex with anionic dyes. Giles et al. [68,69] researched the use of chitosan for the removal of dyes from effluent as long ago as 1958. The binding capacity of chitosan for anionic dyes is pH-dependent, but it has been reported [65] that in effluent treatment as much as 10 g dye per kg chitosan can be complexed at pH values above about 6.5. Similarly, chitosan has been used for the aftertreatment of direct dyeings on cotton to improve their fastness. 

To these may be added economy and ease of removal from the substrate, as well as a favourable response to effluent treatment. 

Mechanical and biological methods are very effective on a large scale, and physical and chemical methods are used to overcome particular difficulties such as final sterilization, odor removal, removal of inorganic and organic chemicals and breaking oil or fat emulsions. Normally, no electrochemical processes are used [10]. On the other hand, there are particular water and effluent treatment problems where electrochemical solutions are advantageous. Indeed, electrochemistry can be a very attractive idea. It is uniquely clean because (1) electrolysis (reduction/oxidation) takes place via an inert electrode and (2) it uses a mass-free reagent so no additional chemicals are added, which would create secondary streams, which would as it is often the case with conventional procedures, need further treatment, cf. Scheme 10. 

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