The Technologies Optimization for the Treatment of Underground Water with Iron and Arsenic Content – A Case Study

Abstract

Generally, in Romania, the water treatment aimed at removing the classic compounds of iron, manganese, ammonium, nitrates / nitrites, etc. by the known classical technologies (chemical coagulation, precipitation, decantation, slow / fast filtration with free / under pressure, disinfection). When in the raw water, besides the classical compounds, heavy metals semi-metals are also found, together with the classical treatment technologies, advanced technologies are required combined, known as hybrid processes (Electro-coagulation / EC, oxidation, adsorption / exchange ions, membrane filtration -UF / NF / RO), which can lead to the desired results. Along with iron, manganese, ammonium, nitrites / nitrates, arsenic is a naturally occurring element in the Earth’s crust. Arsenic in drinking water is a global problem affecting the population worldwide because the arsenic and its components have carcinogenic properties. Regarding the elimination of arsenic (As) found in the water especially collected from the underground, the studies and researches applied were much more restricted and the applications completely isolated, at present the subject being more intensely approached. This situation is also caused by the fact that the Water Framework Directive no.98_83_CEE, transposed into national legislation, lowered the Arsenic (As) chemical indicator limit to 10 μg As / L (from 50 μg As / L). An alternative / complementary technology with low maintenance costs for underground treatment is Electro-oxidation/coagulation (EC), which has been of increasing interest in the last decade. The use of pilot stations / equipment for studying potential treatment technologies is essential for optimizing the treatment schemes and in order to avoid the implementation of costly technologies that cannot work for various reasons. In this case study, it was analysed comparatively from the efficiency point of view combining and optimizing oxidation-coagulation-filtration technologies in a pilot station for water treatment with iron, manganese and arsenic content, coming from the medium depth underground source (western Romania). In the initially provided technological flow (oxidation with ozone, multimedia filtration and disinfection with hypochlorite for the remanence), an electro-coagulation / oxidation (EC) cell was introduced upstream of the multimedia filter. This process aimed at eliminating the use of chemicals (ferric chloride) from the coagulation process that would have caused the rapid alteration of the multimedia filter and consequently increased operating costs. The results showed that compared to conventional technologies, the EC advantage includes high disposal efficiency, a compact treatment plant and the possibility of complete automation.