Influence of ammonium ions on the treatment process selection of groundwater supplies intended to human consumption

In Romania, drinking water is produced from surface water (60%) and groundwater (40%). The presence of
inorganic compounds containing oxidizable nitrogen within groundwater sources (NH4+-N, NO2--N) at variable concentration levels in association with other pollutants /micropollutants from natural / anthropogenic origin asks for previous treatability studies before the setting-up of final treatment technology. The ones currently applied for NH4+-N oxidation involve use of chlorine for oxidation of specific pollutants (N-NH4+, S2- a.s.o.) and water disinfection. The high doses of chlorine required by NH4+-N “break point” chlorination process (Cl2:NH4 +-N weight ratio = 7.6÷15:1) are able to generate undesirable chlorinated by-products from which trihalomethanes are the only regulated for drinking water (MACTHM = 100 μg/L). The experimental results of treatability studies using chlorine as oxidant reagent for three groundwater sources located in Bucharest proximity containing among oxidizable pollutants: NH4+-N (≥1 mg/L), natural organic matter (DOC ≤ 3.5mg/L), Mn(II) ions are presented. The noncompliance aspects related to the quality of treated water (THMs concentration, residual chlorine, free and bound chlorine ratio a.s.o.) from groundwater sources containing high concentration NH4+-N impose replacement of classic treatment process based on chlorine chemical oxidation with other process (biological nitrification).