INFLUENCE OF NITRILOTRIACETIC ACID ON HEAVY-METAL TRANSFER IN THE ACTIVATED-SLUDGE PROCESS .1. AT CONSTANT LOADING

Removal of metals in the sewage treatment process is closely related to the chemical forms in which the metals exist. One critical factor controlling the forms of the metals in sewage is the chemical matrix of the sewage; as a consequence of their chelating capacity detergent builders are important in modifying the sewage matrix. Laboratory simulations of the activated sludge process have been studied to estimate the impact of the detergent builder nitrilotriacetic acid on the removal of heavy metals from sewage in this treatment process. The acclimation period for the biodegradation of nitrilotriacetic acid in a hard water synthetic sewage was found to vary from 16 to 31 days. In a soft water synthetic sewage, biodegradation was not observed even after 60 days. Hydrolysis of condensed phosphates in both hard and soft water synthetic sewages occurred within 3 h. Even when substantially biodegraded in hard water synthetic sewage, nitrilotriacetic acid appeared to be adversely affected by the absorption of cadmium, copper and zinc by the biological solids. The greatest absorption of heavy metals to the biological solids occurred when condensed phosphates were present. In soft water synthetic sewage metal absorption was minimal in the presence of nitrilotriacetic acid. In the presence of condensed phosphates absorption was considerably higher but not comparable with that achieved in hard water synthetic sewage. © 1979.