Sorption Homework 1. A small, private drinking water plant has noted the product

Question

Sorption Homework 1. A small, private drinking water plant has noted the production of disinfection by-products in its finished water. It is evaluating a new activated carbon to remove them. The treatment plant plans to repack its existing adsorption contact columns with this new activated carbon. A column has a bed depth of 0.9 m, and plan view area 0.09 m. Bulk density of the GAC 490 kg/m'. The plant's water production rate is 0.45 m Three THMs (trihalomethanes) have been selected as representative of the variety of disinfection by- products. Current trihalomethane concentrations are given below as Co 0 ln ug/t) CHCl3 CHBrCIz CHBr2Cl 75 50 25 0.0253 0.1328 0.2578 0.4952 0.5756 0.6019 K and I/n values are based on C in mg/L and q in mg/m For each of the THMs tested above, determine the expected length of time until the carbon is exhausted Remember that in a flow-through column, Cout Cin at exhaustion 2. The finished water contains a mixture of these three THMs. The analysis for THMs is relatively costly, and will not be monitored continuously. On which constituent should the operator base his/her plan to change or regenerate the GAC? About how long can the operator run the contactor? (Assume there is no competition between THMs for sorption sites on the carbon.)

Explanation / Answer

Trihalomethane are formed with other disinfectants by products when chlorine and other disinfectants are used to control microbial contaminants in water. They all are by-products of chlorination. They are carcinogen can cause cancer. THM level increases with temperature, pH, time and level of organic material reacts with chlorine to form THM. So to reduce the level of THM, we have to reduce chlorination, means reaction of chlorine with organic material. We have to reduce the contact of chlorine with water.

By doing some oxidation with pottasium permanganate or peroxide before filatration can reduce the level of THM. Another way to reduce the level of THM is by reducing pH. Also we can use reverse osmosis process to reduce the level of THM.

PAC (powdered activated carbon) can be used instead of GAC. Higher doses of PAC is generally required comparitively to GAC. PAC is cheaper than GAC and also it takes less time than GAC. The time of contact between carbon and water is more so all the microbes attach to the carbon particles easily.

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