What is the approximate amount of chlorine in pounds per million gallons to achieve 0.5 ppm residual in primary effluents?

To achieve a residual chlorine concentration of 0.5 parts per million (ppm) in primary effluents, it is necessary to understand that 0.5 ppm is equivalent to 0.5 milligrams per liter (mg/L). Since there are approximately 8.34 pounds in one million gallons of water, to calculate the amount of chlorine needed:

1. First, understand that 0.5 mg/L translates to 0.5 pounds of chlorine per million gallons, given the conversion factor (1 mg/L = 8.34 pounds per million gallons).

2. Thus, to reach 0.5 ppm, we multiply 0.5 mg/L by 8.34 (the conversion factor), which results in approximately 4.17 pounds of chlorine per million gallons.

However, when chlorination is applied to treat wastewater, factors such as the concentration of organic matter, the presence of chlorine-demanding substances, and other water quality parameters come into play, necessitating a higher dose to ensure disinfection and achieve the desired residual level.

Therefore, while the theoretical calculation gives a lower requirement, the practical application often requires aiming for a much higher total chlorine addition, thus leading to the recognition of the range of 100