456The log of 10 in the base 10 logarithmic system is 1 and the log of 100 is 2, with the log of
1000 being 3, etc. A 1-log reduction is nine out of 10 and would be equivalent to a 90
percent reduction. A 2-log reduction would be 99 out of 100 or 99 percent reduction and
a 3-log reduction would be 999 out of 1000 or 99.9 percent reduction. A 99.99 percent
reduction would be called a 4-log reduction.
- What are the turbidity requirements for Direct and Conventional filtration
plants?
For conventional and direct filtration systems (including those systems utilizing in-line
filtration), the turbidity level of representative samples of a system's filtered water
(measured every four hours) must be less than or equal to 0.3 NTU in at least 95 percent
of the measurements taken each month. The turbidity level of representative samples of
a system's filtered water must not exceed 1 NTU at any time. Conventional filtration is
defined as a series of processes including coagulation, flocculation, sedimentation, and
filtration resulting in substantial particulate removal. Direct filtration is defined as a series
of processes including coagulation and filtration but excluding sedimentation resulting in
substantial particle removal. - What are chloramines, how are they formed, and do they have any beneficial
use?
Chloramines: Ammonia and Chlorine are combined. Cl 2 NH 3 Yes, limited use and this
chemical will create less THMS than chlorine alone. Chloramine is a disinfectant used to
treat drinking water. It is formed by mixing chlorine with ammonia.
Although it is a weaker disinfectant than chlorine, it is more stable and extends disinfectant
benefits throughout a water utility's distribution system (a system of pipes water is
delivered to homes through). Some water systems use chloramine as a secondary
disinfectant to maintain a disinfectant residual throughout the distribution system so that
drinking water remains safe as it travels from the treatment facility to the customer.
Chloramine has been used by water systems for almost 90 years, and its use is closely
regulated. Since chloramine is not as reactive as chlorine, it forms fewer disinfection
byproducts.
Some disinfection byproducts, such as the trihalomethanes (THMs) and haloacetic acids
(HAAs), may have adverse health effects and are closely regulated. Because a chloramine
residual is more stable and longer lasting than free chlorine, it provides better protection
against bacterial regrowth in systems with large storage tanks and dead-end water mains.
Chloramine, like chlorine, is effective in controlling biofilm, which is a coating in the pipe
caused by bacteria. Controlling biofilm also tends to reduce coliform bacteria
concentrations and biofilm-induced corrosion of pipes.