Disinfectants killing levels

Water treatment plants employ both primary and secondary disinfection (a) Primary disinfection achieves the desired level of microorganism kill or inactivation and (b) secondary disinfection ensures a stable residual concentration of disinfectant in the finished water to prevent microbial growth in the distribution system (4,7,14,17,18). 

It is common for water suppliers to use disinfectants such as chlorine, chloramines and chlorine dioxide to kill microorganisms such as giardia and E coli. Levels of disinfectants used may be higher after rainstorms in summer months. By-products include trihalomethanes, haloacetic acids, bro-mate, and chlorite. Levels of disinfection products and by-products are regulated. 

Unfortunately, standardization of the methodology to be employed in these efficacy tests has proved difficult, if not impossible, to obtain, as has consensus on what level of killing represents a satisfactory and/or acceptable result. It must be stressed however, that unlike tests involving chemotherapeutic agents where the major aim is to establish antimicrobial concentrations that inhibit growth (i.e. MICs), disinfectant tests require determinations of appropriate cidal levels. 

Disinfectants. Disinfection is the process of removing microorganisms, including potentially pathogenic ones, from the surfaces of inanimate objects. The British Standards Institution further defines disinfection as not necessarily killing all microorganisms, but reducing them to a level ac-... 

Intermediate-level disinfection, which inactivates M. tuberculosis, vegetative bacteria, most viruses, and most fungi but does not necessarily kill bacterial spores. 

Low-level disinfection, which can kill most bacteria, some viruses, and some fungi but does not kill resist t microorganisms such as tubercle bacilli or bacterial spores. 

These agents can kill mycobacterium (TB), many, but not all, types of virus s fungi, and vegetative bacteria. These disinfectants can t kill bacterial spores in any practical exposure time. Examples of intermediate-level disinfectants include phenols, alcohols, iodophors, and combinations of isopropanol and QACs. Noncritical instruments and environmental surfaces may require disinfection with intermediate-level disinfectants. The correct application of intermediate-level disinfectants is for such noncritical items as floors and countertops, patient room furniture, instruments that contact only intact skin, and plastic or metal machine housings that do not directly contact patients. 

These substances do not kill bacterial spores, mycobacterium (TB), or all viruses. Low-level disinfectants can kill vegetative bacteria, fungi, and some lipid-coated viruses such as HIV. Use low-level disinfectants such as QACs on floors, countertops, furniture, and plastic or metal housing of machines. QAC disinfectants contain their active ingredients as n-alkyl dimethyl ethylbenzyl... 

Wipe floors, countertops, furniture, and machinery housing with an intermediate- or low-level disinfectant to remove soil. Then rewipe with fresh disinfectant to complete the killing of microbes. Never rinse enviromnental surfaces unless the label directs or a surface might come into contact with eyes. 

The activity of formaldehyde vapour is dependent on RH. Various RH levels for optimum antibacterial activity have been proposed. An optimum RH of 80-90% but with no great increase in disinfection above 58% has been reported [78, 82]. Another study found an increase in the rate of kill... 

Fluoridation and chlorination generally form the final stages of the water- treatment process. A commonly used compound, which is recommended for maintaining healthy teeth, is sodium fluoride. Approximately half of the U.S. population uses water that is fluoridated at an acceptable concentration level. Chlorination is a very common disinfection method that has been used for nearly a century to kill any residual bacteria and some viruses by adding chlorine gas to the finished water. There are some people who do not like the taste or smell of chlorinated water adding activated carbon into the treatment process can make the water more palatable. One of the benefits of chlorination is that residual amounts of chlorine can remain in the treated water as it travels many miles in the system. The disinfected water travels with the flow until it reaches aU the customers. 

Disinfectants are generally defined as chemical agents that under defined eonditions are eapable of destroying or removing microorganisms, but not usually bacterial spores. They does not neeessarily kill all mieroorganisms, but reduce them to the levels which are acceptable for the defined purpose. 

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