SASURU · Development of simple removal units for the treatment of groundwaters contaminated with arsenic or uranium

Final Activity Report Summary - SASURU (Development of simple removal units for the treatment of groundwaters contaminated with arsenic or uranium)

In some areas in Northern Greece people consume drinking water containing arsenic at concentrations higher than the EC parametric value of 10 microg/L. A solution to the problem is thus required and remedial action must be decided. As remedial action strongly depends on arsenic speciation, the presence of other possible contaminants, and on the general water composition, a detailed study with samples from 21 representative locations was undertaken. Our investigation was performed in two regions in Northern Greece, namely Aksios and Kalikratia. Arsenic concentrations were typically 10-70 microg/L and the average arsenic concentration was 30 microg/L in both regions. Uranium, which is also toxic to humans, was detected in the range 0.01-10 microg/L, with the higher concentrations to occur in the oxidising groundwaters of the Kalikratia area. Uranium concentration correlated strongly with As(III)/As(tot) ratios. Boron was found to exceed the EU drinking water standard of 1 mg/L in some wells in the Kalikratia area and its removal should also be considered in the design of a remedial action. In the city of Malgara in the municipality of Aksios, the local groundwater contains arsenic (20 microg/L), phosphate (550 microg/L), manganese (235 microg/L) and ammonium (1.2 mg/L). In January 2005 a treatment unit has been installed by the local water supply company for the removal of these contaminants. We have monitored the operation of this treatment unit in collaboration with the local operator to elucidate processes which lead to the removal of contaminants and understand the reaction mechanisms which take place during treatment. The treatment unit consists of aeration, up-flow filtration for the biological oxidation of ammonium, manganese and arsenic, followed by coagulation with FeClSO4 and final down-flow filtration for the removal of arsenic and the additional iron. In a final stage, the water is disinfected with NaOCl before the distribution to the consumers. During aeration, Fe(II) is oxidised and some phosphate is sorbed on the formed iron oxides but remains in suspension until it is removed during the subsequent biological filtration stage. Mn(II) is oxidised by biological oxidation and the produced insoluble manganese oxides are removed by filtration. NH4+ is biologically oxidised and removed from the water via nitrification and formation of nitrates. As(III) is oxidised but not removed during the biological filtration stage. Arsenic is removed to below 10 microg/L during the subsequent coagulation and filtration treatment stage. Similarly, the final concentrations of Fe(tot), Mn(tot) and NH4+ are below the EC parametric values of 200, 50 and 500 microg/L respectively. These results show the importance of the groundwater composition in the success of a treatment method. In most of the cases, the ratios of the contaminant concentrations rather than the absolute concentrations comprise the key factor for the success or failure of a removal method. This rule applies also for cases such as in Southeast Asia, where arsenic concentrations are in general 10 times higher. In the area of Kalikratia, we have installed a small scale treatment unit, based on the use of Zero valent iron. Laboratory investigations have shown that arsenic(III) is oxidised in the presence of zero valent iron in aerated aquatic solutions. The oxidising agent is the Fenton reagent, which is formed as a result of iron corrosion. The oxidised arsenic is then removed by sorption on the oxides of iron, formed after Fe(II) oxidation and Fe(III) hydrolysis. We are now operating the unit to remove arsenic, uranium and boron from the groundwaters in the area of Kalikratia in Northern Greece. The project is still ongoing in cooperation with the Aristotle University of Thessaloniki and the local operator (DEYA Kalikratia, Northern Greece).

Data: CORDIS, © European Union