Treatability studies of groundwater containing high ammonium concentrations using chlorine based compounds

The composition of groundwater is of interest for drinking water service providers due to its implications upon the potabilisation treatment flow. The paper is presenting two case studies from Romania, each groundwater sources containing ammonium and organic load reactive to chlorine. Oxidation tests for NH4+ were performed using chlorine and sodium hypochlorite on water samples with the following characteristics: NH4+ ≤ 4.4 mg/L and DOC < 1 mg/L. Oxidation tests with chlorine at the breakpoint showed that a weight ratios of Cl2 : N-NH4+≥ 10 : 1 and reaction time of 40 min are needed in order to assure a remanent concentration of NH4+ below the admissible value of 0.5 mg/L, residual chlorine concentrations being in the range of 12-20 mg/L, and THM concentration after 24 h in the range of 102-277 µg/L. Oxidation tests with NaOCl showed that even at high doses of active chlorine (30 mg/L) and long reaction time of 24h, remanent ammonium concentration is higher than the admissible value of 0.5 mg/L, residual chlorine concentration being of mg/L order. In this case, selection of an alternative raw water source or the replacement of classical oxidation technology using chlorine by biological nitrification is needed.