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Calculations for Waste Water

Every day, treatment facilities across the country take the nation's waste water, treat it and release it back into the environment. For a facility to provide the best services to the region it serves, it will often take measurements of its waste water. There are a number of measurements and calculations a treatment facility will take and use, including pH, pounds of influent and effluent, removal efficiency and pounds of chemical per gallon by percentage.

pH
- pH determines how basic or acidic a sample of water is. Samples of water with a high pH are basic, while samples with a low pH are acidic. Samples with a pH of 7 are neutral. For the most part, treatment facilities want the water leaving their plant to have a pH as close to 7 as possible. pH can be measured with a pH probe, or it can be calculated. pH is simply the absolute logarithmic value of the concentration of the H3O+ ions in a solution of water. The concentration must be in molarity. To calculate pH, facilities will use this formula: pH = abs(log[H3O+]), where ̶0;abs̶1; represents the absolute value of the formula in the brackets, and [H3O+] is the concentration of the H3O+ ions in molarity.
Pounds of Target Chemical in Influent and Effluent
- A facility determines the amount of pounds of a target chemical in the influent, the water entering a facility, it receives using the following formula: IP = (F * I) * 8.34. ̶0;IP̶1; stands for the pounds of target chemical in the incoming influent. ̶0;F̶1; represents the treatment unit flow in million gallons per day. "I̶1; represents the concentration of the target chemical in the inflowing water in milligrams per liter. Likewise, a facility determines the pounds of a target chemical in its effluent, the water leaving a treatment facility, using the following formula: EP = (F * E) * 8.34. ̶0;EP̶1; stands for the pounds of the target chemical in the effluent. Once again, ̶0;F̶1; represents the treatment unit flow in million gallons per day. ̶0;E̶1; stands for the concentration of the chemical in the effluent. This should be input into the formula as milligrams per liter.
Removal Efficiency
- Water treatment facilities strive for a high removal efficiency.
  
  Removal efficiency can calculate how efficiently a treatment facility removes a certain chemical from its influent. Facilities will subtract the pounds of the target chemical in the effluent from the pounds of the target chemical in the influent to calculate the pounds of chemical removed. This value is then divided by the pounds of the target chemical in the influent and multiplied by 100 percent to calculate the removal percentage of the chemical by the treatment facility. The formula looks like this: (PR / IP) *100%, where ̶0;PR̶1; represents pounds removed and ̶0;IP̶1; once again stands for the amount of influent in pounds.
Pounds of Chemical per Gallon by Percentage
- Treatment facilities will often want to know the weight of a chemical in a gallon of solution based on the strength of the chemical as a percentage. This can be calculated using the following formula: PC = (SC/100) * (SG * 8.34). ̶0;SC̶1; represents the strength of a chemical as percentage. ̶0;SG̶1; represents specific gravity. It is found by dividing the density in pounds per gallon of the chemical by 8.34. The result of this calculation is the pounds of chemical in a gallon of solution, or ̶0;PC.̶1;

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