Discharge of Plant Effluent into a River

Let us consider an effluent discharge of 150 1/min and a river flow that varies seasonably from 23,000 to 50,000 1/s. Note that since the regulatory limit has to be met at all times during the year, the lower summer flow rate of 23,000 1/s must be used. The standard used here is that of the U.S. Enviroiunental Protection Agency, which has set the maximum permissible level of benzene in drinking water at 0.05 mg/1 or 5 ppb. The effluent is assumed to be saturated with benzene at the solubility level of 1.8 g/1 (1.8 X 10 ppb) given in Table 6.3. 

With the allowable concentration set at 5 ppb, the required fractional removal R is given by 

In other words, slightly more than 97% of the benzene in the plant effluent will have to be removed to meet the aforementioned standard. It is likely that an adsorption purification process using activated carbon can be used to achieve this goal. Such a process is taken up in Illustration 6.4. 

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Illustration 6.3 Discharge of Plant Effluent into a River We consider here the case of process water saturated with benzene being discharged into a river. The question to be addressed is whether the diluting effect of the river flow is sufficient to reduce the effluent concentrahon to within permissible limits and, if not, how much of the offending substance has to be removed to meet environmental standards. A sketch depicting effluent and river flow is shown in Figure 6.3. 

Illustration 6.5 Discharge of Plant Effluent into a River... 

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