Chemical disinfection disadvantages

Chlorine was first used to disinfect water in Britain in 1904, after a typhoid epidemic. (Typhoid is a water-borne, contagious illness that is caused by a species of Salmonella bacteria.) Strict limits are necessary because chlorine is ineffective when its concentration is less than 0.1 mg/L. It gives water an unpleasant taste at concentrations above 1.0 mg/L. Chlorine has a disadvantage, however. It can react with other chemicals in the water to form poisonous compounds, such as chloroform, CHCI3. These chemicals may remain in solution even after the entire treatment process. 

The EPA Surface Water Treatment Ruse (SWTR) requires public water supplies, under the direct influence of surface water, to be disinfected. Some disinfectants produce chemical by-products SWTR requires that their concentration remain within the MCL. Currently, one such by-product is trihalomethanes. Water disinfection is effective when combined with conventional treatment, such as coagulation, flocculation, sedimentation, and filtration. The latter is accomplished by sand or diatomaceous earth. The effectiveness of disinfection is evaluated by determining total coliform bacteria which are not pathogenic, but their presence suggests that certain pathogens may have survived. The various chemicals commonly used as disinfectants are presented below and some of their advantages and disadvantages are listed. 

The disadvantage of a NF treatment is the high energy cost, and the generation of waste streams that need further treatment prior to disposal (Wale and Johnson (1993)). Howev er, the generated waste stream is only a concentration of the natural components of surface water, and not a sludge of added chemicals as in coagulation or PAC. Moreover all water treatment processes inevitably produce a waste (residue stream). Product water stabilisation may also be of concern in NF, and more so, in RO. Kasper (1993) discussed different possibilities of membrane filtrate stabilisation and water disinfection. 

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