Scritpppt.docx

The Dosage Formula is determined from the “Davidson Pie”, which is included in the formula sheet for the certification exams. This formula is represented in the following diagram called the Davidson Pie which was created by Gerald Davidson, Manager, Clear Lake Oaks Water District, Clear Lake Oaks, CA. Davidson Pie Diagram Interpretation and Formulas This diagram can be used to solve for 3 different results: dosage, feed rate, and flow (or volume). As long as you have 2 of those 3 variables, you can solve for the missing variable.

Chlorine Breakpoint

If applied chlorine and residual chlorine are equal, this should go on the 45-degree line. At this this the abscissa is equal to the ordinate (x=y) The x-axis is the chlorine dose, the further along we got on this axis, the more chlorine you have poured. On the y-axis is the chlorine residual. When chlorine is added, the first thing that it does is reacts with metals primarily iron and manganese. It oxidizes these metals and has no effect on the chlorine residual

As you Add more chlorine it builds a little bit of a residual and this is a good thing, because now you are actually starting to burn up that oxygen demand. In this, ammonia and nitrogen or organic matter starts to oxidize, this forms disinfection byproducts otherwise known as chloramines. The more chlorine

you throw at those byproducts the more they progress from monochloramine to dichloramine to trichloramines which eventually go airborne. Chlorine recognizes the chloramines as volatile organic compounds and starts to combat it and therefore the disinfection level goes down. There is a sudden drop in the residual chlorine because after this point organic matter starts getting oxidized. At this point water is highly odorous. After this, all the organic matter are exidized This point is known as the breakpoint, disinfection does not start until this point. From then on you build a free chlorine residual, called as free chlorine or free available chlorine

If we were to expand upon this level, this is called the combined Chlorine. Combined chlorine is basically the used-up oxidant chloramines combined with the free available chlorine. Adding the FAC and CC you get the total available chlorine. The breakpoint indicates how much chlorine has been consumed.

Chloramine

When we add chlorine to water, it forms chloramines