Abstract: Raw water G containing arsenic in an amount exceeding an environmental standard value is poured into a treatment bath filled with particulate carriers. The raw water G in the treatment bath is treated at a flow rate which does not allow production of ferric hydroxide in a suspended form in the raw water while adding an acidic iron solution to the raw water G so that the pH value of the raw water G is adjusted to 6.5-7.5. A ferric hydroxide membrane is produced on the entire surfaces of the carriers by contact oxidation reaction of dissolvable ferrous ions in the raw water G having the adjusted pH value, to cause the arsenic in the raw water G to be adsorbed on the ferric hydroxide.

Abstract: Water treatment apparatus includes raw water special air mixing nozzles (7); filtering tank (5) housing filter layer (4) including two layers of upper layer (2) and lower layer (3), the upper layer including a filter medium with a smaller specific gravity and a larger particle size than a filter medium of the lower layer; a water collection pipe (13) removing filtered water and supplying reverse cleaning water to the filter layer during reverse cleaning; drainage trough (12); and upper layer cleaning apparatus (10), in which the upper layer cleaning apparatus includes upper layer cleaning pipe support member (17), upper layer cleaning water pipe (18), surface-cleaning special air mixing nozzles (19), air suction pipe (20), and horizontal air pipes (31 and 32) and the raw water special air mixing nozzles (7) are attached to raw water inflow tank (70) provided on a part of the drainage trough (12).

Abstract: To reduce the size, scale of construction, and running cost of an apparatus for cleaning a sand filtration layer. A cleaning system which removes clogging sediments from a sand filtration layer 2, used with an apparatus for an infiltration intake of seawater which performs a seawater intake, by means of a water intake pipe 4 buried in the supporting gravel layer 3, after the seawater has been infiltrated through the sand filtration layer 2 and a supporting gravel layer 3 on an ocean floor. This cleaning system is provided with a diffuser pipe 7 having blow holes 6, and which is buried in the supporting gravel layer 3, as well as a compressed air delivery device 8 for feeding an air into the diffuser pipe 7. The system operates by blowing the air from the blow holes 6 to agitate the filtration sand of the sand filtration layer 2, to remove the sediments which have become trapped in or accumulated on the sand filtration layer 2.

Abstract: Water treatment apparatus includes raw water special air mixing nozzles (7); filtering tank (5) housing filter layer (4) including two layers of upper layer (2) and lower layer (3), the upper layer including a filter medium with a smaller specific gravity and a larger particle size than a filter medium of the lower layer; a water collection pipe (13) removing filtered water and supplying reverse cleaning water to the filter layer during reverse cleaning; drainage trough (12); and upper layer cleaning apparatus (10), in which the upper layer cleaning apparatus includes upper layer cleaning pipe support member (17), upper layer cleaning water pipe (18), surface-cleaning special air mixing nozzles (19), air suction pipe (20), and horizontal air pipes (31 and 32) and the raw water special air mixing nozzles (7) are attached to raw water inflow tank (70) provided on a part of the drainage trough (12)