| Περίληψη: | Urbanization, population growth and production needs of food and every day goods, but above all the excessive use of fertilizers in crops and the increasing production of new chemical compounds, result in a significant reduction in available potable water reserves and in their quali-tative degradation. One of the most important problems of surface and groundwater is the pres-ence of nitrates and other nitrogen compounds. The presence of these compounds in potable wa-ter causes undesirable effects on natural systems (such as eutrophication) and in humans (such as methemoglobinemia, blue-baby syndrome, and various forms of cancer) making it essential to develop technologies to effectively remove them.
Various treatment methods have been studied until this day, however in recent years research-ers have focused on the electrochemical treatment of potable water and in biological denitrifica-tion systems as they achieve high yields with small operating costs and are environmentally friend-ly.
Electrochemical denitrification is a treatment method based on the movement and separation of ions in the solution under the influence of an external electric field. Its arrangement consists of cathode and anode electrodes where anion and cation exchange occur. The process takes place on a small surface of electrodes and there is no use of chemicals before and after the water treat-ment. Depending on the material selected for the anode and cathode electrodes, the process that is performed is either electrochemical reduction or electrocoagulation.
Biological denitrification is a treatment method carried out by appropriate cultures of microor-ganisms using NO3- ions as the ultimate electron donor under anaerobic conditions. Hydrogen-otrophic denitrification is a promising method of nitrate removal. H2 is an excellent choice of elec-tron donor due to its pure nature, ease of production by electrolysis in the laboratory, low bio-mass production, as well as the removal of it or its agents is not required from the treated water.
In the present study, the electrochemical denitrification of drinking water was studied in a la-boratory scale (electrolytic cell of 0.150 L volume) to remove nitrates. Experiments were conduct-ed under various operating conditions, aiming at maximum nitrate removal performance, and avoiding operational problems. Specifically, the effect of the initial concentration of nitrates (10-100NO3--Nmg/L), current intensity (10-40mA/cm2), electrolyte concentration (0-1gNaCl/L), and the electrodes’ construction material (Al, Cu, S-S, Fe, Brass, Sn, Ti/IrO2, Ti/IrO2-Pt, Ti/RuO2-Pt) were studied.
Also, autotrophic hydrogenotrophic denitrification using mixed hydrogenotrophic cultivation was studied in laboratory scale reactors of suspended (1L) and attached (0.25L) biomass growth in batch as well as in continuous operation mode. Various operational parameters such as initial nitrate concentration (10-100NO3--Nmg/L), nutrient addition (Na2PO4, KH2PO4), residence time, and appropriate filling material (zeolite) for the fixed bed reactors have been studied.
Also, to reduce the operating costs of the processes, renewable sources of energy from α pho-tovoltaic and a wind turbine were used for the power supply needed.
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