PURE WATER

Gisborne Herald, Volume LXVI, Issue 20068, 14 October 1939, Page 4

PURE WATER

WAIPAOA RIVER TESTS PILOT PLANT WORKING VISIT BY COUNCILLORS TREATMENT EXPLAINED For the purpose of testing the means of . treating the Waipaoa River water in case it is needed to augment the Gisborne Borough water supply, a pilot plant has been installed, and is now in working order. Samples that have gone through the softening, settling, filtration and sterilisation process reveal a crystal clear water, which, it is maintained is superior to the present water running through the borough mains. The plant in operation, which was installed by the Filtration and Water Softening Proprietary, Limited, Melbourne, is believed to be the only one of the type in the Dominion that will accomplish the four processes of softening, settling, filtering and sterilising. Members of the Gisborne Borough Council visited the plant yesterday afternoon on its site beside the railway bridge on tire now disused Patutahi line. The visit followed some heavy showers in the up-country, and the river, though low, was yellow with a fairly large amount of sediment. Method of Treatment Looking first at the discoloured river and then at the clear water coming from the plant, councillors were impressed with the methods of treatment, which were explained in. detail by Mr. W. G. Tobe, the representative of the firm supplying the plant and who is in charge of the operations for a few weeks. It was explained that the plant was only a miniature of what the complete outfit would be to deal with sufficient for the borough’s requirements. The pilot plant was capable of dealing with only 1090 gallons an hour, whereas apparatus to deal with a supply for the borough would need to supply 1,000,000 gallons a day. The main parts of the plant are two double sets of tanks, a filter and a pump. Water from the river is pumped up to a tank set in a larger tank on an elevated platform, and from there the water runs into a similar set of tanks on a slightly lower level before passing through the filters on the ground level. Softening and Filtration. As the discoloured water is pumped into the first tank, lime and soda are added for softening, the water being kept on the move all the time by means of an agitator. Much of the sediment is lost in that process before passing into the larger tank containing the first one, and there mono sodium aluminate is added to assist sedimentation. v Flowing into the second set of tanks, C. 0.2 gas is added to neutralise any of the lime that has come with the water, and then a little more alum is added to assist coagulation. Y Then follows filtration immediately below to remove any remaining sediment. In the filter is sand of varying grades of fineness, together with water-worn quartz, and the manner in which the water flows through the filter and the way in which the sediment is expelled was explained by Mr. Tobe, who also demonstrated how tests on a miniature scale were done' with beakers of water. Finally, water was drawn from the pipe which supplied the plant from the river and in its discoloured state was placed alongside the clear water after treatment, and the difference in the two samples was most marked. Samples For Testing It was stated by the borough engineer, Mr E. R. Thomas, that samples had'been taken of the river water in its raw state and of the treated product for the purpose of analysis, and it was hoped to have the results early next week. It is understood that if the tests over a period when' all conditions of the river will be met are successful, the council will frame proposals for submission to the ratepayers to secure authority to go ahead with an augmentation scheme, using the river water. It is expected that all conditions will be experienced within at least 12 months, possibly earlier. _ Members of the council who made the visit were the Mayor, Mr. D. (W. Coleman, M.F., Crs. J. H. Hall, H. H. De Costa, E. Harris, G. D. Muirhead and A. L. Singer, and with them were the borough engineer, Mr. E. R. Thomas, and the town clerk, Mr. W. M. Jenkins.