METHOD FOR REMOVING ARSENIC IN RAW WATER

PROBLEM TO BE SOLVED: To provide a method for removing arsenic in raw water by which the raw water can be treated using high speed filtration without using any chemicals such as adsorbing filter mediums, oxidizing agents and flocculant, and sufficient arsenic removal capacity can be obtained even if a ratio of iron content/arsenic in the raw water Fe/As=less than 60.SOLUTION: In a water treatment apparatus including: raw water air mixing nozzles 7 each of which has one end communicated with a raw water supply pipe 6, a raw water blasting port in the other end, and an open air inflow port between both ends; and a filtration tank 5 housing a filter medium layer 2, the upper space of the filter medium layer is filled with raw water to predetermined water level. The raw water blasting ports 7b of the raw water air mixing nozzles are placed in the raw water, the raw water is fed under pressure to the raw water air mixing nozzles, air to is caused to flow from the air inflow ports 15 through an ejector effect and is mixed with raw water, consequently the oxygen concentration dissolved in the raw water is brought into saturation state. The oxygen power of the dissolved oxygen causes iron content dissolved in the raw water to adhere onto the surface of the filter medium as ferric hydroxide, and arsenic is adsorbed on the ferric hydroxide.