Abstract
Using an activated sludge pilot plant, the effect of a variation in the load of the potential detergent builder nitrilotriacetic acid on its biodegradation and heavy metal removal has been studied. Variations in the influent nitrilotriacetic acid load have been undertaken at two different base concentrations, 7·5 and 15 mg litre −1. The effectsof sludge age and influent heavy metal concentrations on the biodegradation of nitrilotriacetic acid have also been studied. When the influent nitrilotriacetic acid concentrations was increased to simulate the ‘wash day’ the additional concentrations were not always fully degraded. This effect was most marked at low sludge age and high influent metal concentration. When the biodegradation of nitrilotriacetic acid was incomplete, the removals of lead, nickel and zinc were reduced. Moreover, nickel and zinc previously absorbed were mobilised from the mixed liquor.
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