[Changes of NO3(-)-N and NH4(+)-N concentrations in sewage sludge before and after heavy metals removal by organic acids].

This paper studied the removal effect of citric acid, oxalic acid and acetic acid on cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) in sewage sludge, and the changes of NO3(-)-N and NH4(+)-N concentrations in extracted liquid and sludge before and after treated. The results showed that 0.8 mol x L(-1) of citric acid had better effect, which could remove 76.0% of Pb and 92.5% of Zn in the sludge. After treated with test organic acids for 24 hours, large amounts of NO3(-)-N and NH4(+)-N dissolved in extracted liquid. Compared with the control (distilled water), organic acids greatly increased the NH4(+)-N, but decreased the NO3(-)-N in extracted liquid. Because of the transformation of other forms nitrogen in the process of acid treatment, the NO3(-)-N and NH4(+)-N concentrations in the treated sludge were still high. The extracted liquid after the sludge was treated with 0.5 mol x L(-1) of oxalic acid contained 2.8 mg x L(-1) of NO3(-)-N and 888.1 mg x L(-1) of NH4(+)-N but a few of heavy metals, which was able to be reused as a liquid fertilizer.