Conference Papers

The presence of inorganic compounds containing oxidable nitrogen within groundwater sources at various,high concentration levels, especially in the case of NH+4 (NH+4 ≤ 8 mg/l), is asking for the replacement of classical oxidation technology using “break point” chlorination, due to non-conformities generated by high consumptions of chlorogenic agents (tens mg Cl2/l) upon the quality of treated water (acid pH, high ratio of residual bound chlorine, trihalomethans above the maximum admissible concentration). Biochemical oxidation using a bio-filter system in specific operating conditions (media type, temperature, oxygen demand, inorganic carbon and phosphorus sources, biological contact time, etc.) is representing a feasible technological alternative. Taking into account that carbon source used within the biochemical process is inorganic, the dissolved natural organic matters (NOM- humic matters) can react with the chlorine used in the final stage of biological effluent treatment. In the conditions of advanced removal of NH+ 4, oxidation to NO- 3, the chlorine dosages needed for effluent‟s finishing, disinfection are reduced. Experimental tests have as objectives to set up the chlorine dosage (Cl2 = 0,5 † 0,8 mg/l) that assures the disinfection of effluents resulted from biological nitrification step and a minimum ratio of residual bound chlorine, as well as the assessment of trihalomethanes formation potential in case of dissolved organic load, DOC ≤ 1,8 mg C/l (weight rations Cl2 / DOC = 1 † 8).

Chlorine is a common disinfection agent used in the natural water supplies treatment in order to ensure the microbiological safety of drinking water. At the same time, chlorine is used as oxidant agent for removal of oxidable pollutants from groundwater, especially for ammonium ions. The high doses of chlorine imposed by ammonium break point chlorination process (Cl2:NH4+ = 8 ÷15:1) generate also chlorinated by-products such as trihalomethans (THMs) and haloacetic acids (HAAs) with potential carcinogenic effects. The brominated species were suspected to be much stronger carcinogens and mutagens than their chloride – containing analogues. The reaction between chlorine and natural organic matter (NOM), which contain substantial amount of humic substances (HS) and also the THMs concentration level, are affected by several factors as: pH, temperature, dissolved organic carbon (DOC), bromide concentrations, chlorine dose, contact time. The present paper has as main objective the evaluation of halogenation effect on THMs formation and upon evolution of some indicators of NOM quality / reactivity (A254, SUVA) for three groundwater sources with different pollution degrees (DOC = 2 ÷ 4,5 mgC/l, NH4+ = 1,6 ÷ 10mg/l, Br - = 0,1 – 1,1 mg/l).

Mine water treatment can be seen as challenging, but also a long-term task. In addition to better known acidity correction and heavy metals and metalloids removal, the mine water treatment approaches are slowly shifting to advanced methods, targeting the elimination of the salinity. Some methods for the sulfate and calcium removal are advancing to industrial implementation (e.g. ettringite precipitation, membrane separation and combinations of these methods), but the cost is high and the cost to benefit result may be controversial. On other hand, the seeded crystallization of gypsum can lower the sulfate and calcium concentration after conventional treatment by liming. Despite that this technique is limited by the gypsum solubility, it is bringing considerable benefits as a second treatment stage after the conventional liming, by safely lowering the sulfate concentration from 2000...4000 mg/L to about 1500 mg/L, together with the equivalent calcium quantity. Due to the fact that this method is using recycled gypsum produced within the process, it can be seen as a sustainable practice. This is illustrated by a case study for a mine water source with an initial sulfate content of about 5000 mg/L.