The effect of water hardness on nitrilotriacetate removal and microbial acclimation in activated sludge

Abstract

The effect of water hardness on microbial acclimation to the removal of nitrilotriacetate (NTA) in the wastewater treatment process was examined in 4 laboratory-scale activated sludge reactors. Consistent high removal (i.e. >90%) was observed in all 4 reactors after acclimation occurred. Removals of greater than 60% of added NTA after 8 days and greater than 90% after 15 days were observed in a continuously fed, hard water (250 mg l −1 as CaCO 3) reactor. In soft water (50 mg l −1 as CaCO 3) comparable removals were observed after 20 and 28 days respectively. In 24 h, semi-continuous activated sludge reactors (24 h, fill-and-draw type) removal was greater in hard water than in soft water initially, but was greater than 95% in both hard and soft water after 4 weeks. The proportion of bacteria in the activated sludge with the ability to utilize NTA increased approx. 100-fold during the acclimation period. This proportion increased faster in hard water than in soft water and faster in semi-continuous activated sludge reactors than continuous activated sludge reactors. Ultimate biodegradation of 14C[U]NTA was greater than 85% in both hard and soft water acclimated units. Accumulation of 14C in the sludge solids was negligible (<1%).