Abstract: Through field investigations on distribution of high As underground water and degrees of As pollution of the underground water in Shanyin of Shanxi,a study was carried out on As forms in the high As water environment and laws of their enrichment and transformation.On such a basis,a set of water treatment technology was developed,consisting of aerated oxidation,drugs addition(adding a mixture of FeCl₂ and FeCl₃ as coagulant) and filtration.Results show that in the highly arsenic polluted areas in Shanyin County,the redox potential of groundwater was between-50-142 mV and pH between 8.28-8.73.Such an environment provided formation of high-arsenic groundwater with favorable conditions.When the concentration of hydrogen sulfide in the groundwater was less than 140 μg·L^-1,continuous aeration for 1.5 h,using a 5 W double nozzled oxygen pump(Songbao SB-648) could basically remove all the hydrogen sulfide(H₂S) from the groundwater.Take groundwater from depth of 25 m for example.Its As content was 275 μg·L^-1.After hydrogen sulfide in the water was removed,the mixture of n(FeCl₂)∶n(FeCl₃)=1∶1 was added into the water,which was then aerated continuously for 5 h.As a result,over 60% of trivalent As was changed into pentavalent As in the water.Then the treated water was filtered in a timely manner to reduce As content in the water to 5-8 μg·L^-1,which satisfies the National Hygienic Standard for Drinking Water(GB 5749—2006),and Fe content in the water to 0.03 mg·L^-1,far less than the criteria in GradeⅠof the National Groundwater Standard(GB/T 14848—93).The technology can quickly and effectively turn trivalent As into pentavalent As,which is adsorbed by coagulant and settled down together,thus making the As-removing effect high.Filtration may prevent flocs of hydroxide colloids and arsenates from entering into the water environment again,and reduce the concentration of ferric ions in the water.Results show that this water treatment system is simple in operation and low in cost,and can be widely extended for use in households in regions with high As groundwater.

Key words: arsenic, aerated oxidation, coagulant, filtration, drinking water, Shanyin County