Investigation of arsenic removal in drinking water with low pressure membrane

Nowadays, one of the most important environmental hazards for life and ecological balance are coming from environmental problems. With increasing world population and developing technology, the unconscious consumption of natural sources restricts the needs of individuals being required to maintain vital activity. Drinking water comes at the beginning of these needs. Mostly drinking water sources have been contaminated by many factors such as natural and anthropogenic. One of the important drinking water pollution sources also is arsenic. Arsenic, which is V-a group of the periodic table, is a metalloid. In nature; there are arsenic as +V (arsenate), +III (arsenite), 0 (arsenic) and ?III (arsine). Arsenic, which is one of the most dangerous pollutants in drinking water, is semi-metal element. It can be found everywhere, and there are 20 different forms of its. In our country, as a result of the analysis made in some areas, due to arsenic contamination of drinking water determined to be significant dimension. In our country, conventional treatment plants is commonly used for drinking water treatment and existing units in this facilities not suitable for arsenic removal. Additionally, in drinking water, due to the fact that arsenic concentration level was determined 10 µg/L need to develop better treatment systems. Treatment technologies such as coagulation/flocculation, ion exchange, lime softening, adsorption on activated alumina and iron oxide and reverse osmosis was used for arsenic removal in drinking water. Most of these technologies not effective for As(III) removal. Therefore, As(III) is converted As(V) with pre-oxidation process. Oxidation reagents such as potassium permanganate, chlorine, ozone, hydrogen peroxide and manganese oxide can be used for arsenite oxidation.In this study, chemical and membrane processes, which are easily integrated with the conventional treatment systems, have been investigated. The study can be divided into two separate steps. In the first step consisted of oxidation of arsenite with hypochlorite and ozone and removal by coagulation. The second step consisted of oxidation of arsenite, iron supplementation and removal by ultrafiltration and microfiltration processes. In the study, 100 µg/L As and 1000 µg/L As(III) could be reduced to the concentrations accepted by drinking water regulation after oxidation and coagulation. However, as the requirement of high iron supplementation especially at high As(III) concentration, membrane processes have been studied as an alternative considering high sludge volume and operational expenses. In the membrane studies; arsenite and Fe(II) containing ground water was simulated and chemical oxidation and membrane removal of both chemicals were investigated. Results revealed that the As(III) removal performance depended on the type and concentration of oxidants used, concentration of Fe(II) and the type of membrane. In general, hypochlorite+Fe(II)+membrane process gave much better performance than ozone+Fe(II)+membrane process. Additionally, the required Fe(II) concentration in hypochlorite+Fe(II)+membrane process was much lower than the Fe(II) concentration required in hypochlorite+coagulation process. Therefore, it was concluded that hypochlorite+Fe(II)+membrane process can be successfully used for the removal of as from drinking water. Moreover, results showed that all the membranes used in this study were effective to decrease the As concentration to the target value if high enough oxidant and Fe(II) concentrations were supplemented. Hence, the flux values of the membrane should be considered to decide the membrane to be used in the treatment processes. In this study, low-pressures membranes were studied with the aim of decreasing operational expenses.