Formation of organic chlorine in activated sludge effluents

Bench scale activated sludge reactors with a solids retention time of 9 days were operated at all combinations of two levels of pH, dissolved oxygen (DO) concentration and feed type (pH 6 and 8; DO 1 and 7 mg 1⁻¹; simple and complex feed). Long-term composite samples were collected and adjusted to neutral pH and equal concentrations of alkalinity and ammonia nitrogen. They were then breakpoint chlorinated with NaO³⁶Cl in order to determine how much chlorine was incorporated into the organic matter. The amounts ranged from 0.019 to 0.067 mg atomic chlorine incorporated per mg soluble organic carbon. Analysis of variance revealed that the DO concentration was the only independent variable to have a significant effect upon the amount of chlorine incorporated, with reactors operated at high DO levels generally producing effluent organics which were less susceptible to adding chlorine.