Filtration Tests Of Hatea River Water

Northern Advocate, 15 January 1948, Page 4

Filtration Tests Of Hatea River Water

TESTS today indicated that the taste and smell of Hatea water may be eliminated by filtration. This was demonstrated by the engineer and manager of Candy Filters (N.Z.), Ltd (Mr Dennis B. Mansergh), who supervised the installation and testing of the pilot filtration plant at the intake in the Hatea stream. The Mayor of Whangarei (Mr Jones), members of the Borough Council, the medical officer for Northland (Dr J. L. Newman), and the inspector of health for Whangarei district (Mr A. S. Quennell) were present at the tests made today at Whareora.

Samples of the filtered water were tasted by an Advocate reporter who noticed none of the unpleasant smell, and very little of the taste, that has been causing so much controversy. The filter plant is new, and some of the metallic taste remaining in the water is said to be due to this fact. Experiments will be carried out with aeration, and Mr Mansergh is confident that this will reduce the taste to an absolute minimum. Tests were taken with a colorimeter which classifies water in degrees ol colour and compares it with a check sample of distilled water. The colour rating permitted for town water supplies is 10 points or lower. Samples of the raw stream taken yesterday showed a colour rating ot 125, which, after filtration, was reduced to a figure lower than that ot the distilled water check sample. Water taken from the stream today registered 50 points and filtered down to 10. BACTERIA TESTS Dr Newman said that he would like to see the results of the tests for bacteria, which Mr Quennell will make, before he gave on opinion on the water, but he was impressed with the change in colour, taste and smell. When the water was boiled this morning it gave off a slight odour of chlorine which, it is claimed, will be removed when dechlorination is practised in the main plant. There was no trace of the unpleasant odour usually associated with the Hatea water.

The floe tends to sink to the bottom of the tank, but is forced up by the uu-flow of water from the inlet. Thus it finds a level in the tank and forms a blanket across the tank, which catches the greater portion of the finely-divided colour stain and organic impurities. From the top ol! the tank the water is led into the filtration tank which is a concrete pipe containing 3ft Gin. of gravel and sand.. Some of the fioc is carried over to the filter and this forms round the sand grains and completes the work of collecting the impurities. SAMPLES COMPARED After the water leaves the filter it has lost 90 per cent of its bacteria, Mr Mansergh said, and a small portion of chlorine is introduced at this point to complete sterilisation. Samples were taken from the clear water tank into which the water is led and the taste compared favourably with the supplies in other cities ;n New Zealand. Demonstrating the effectiveness of the filter a glass of raw stream water was placed along the sample glass, and ,t was obvious that the colour had Dec:, removed.

The type of filtration plant that > plain ed foi Whangarei, if it is decided to go on with the project, is the s.-ire as that used with satir,rectory results in Hamilton and Auckland on water much dirtier than that from the Hatea River. When the test was completed the filter was washed out and the colour of the water that came away from it showed that the amount of colour stain and, impurities collected in a short time was considerable. Mr Mansergh, who conducted the tests, is a representative of the worldwide firm of Candy Filters Ltd., with headquarters in England. He has made a life study of water filtration and holds the B.A. (Engineering). He recently visited England to take a refresher course in water filtration.

The pilot filter consists of an upflew fank eight feet deep with a twofoot diameter. Into this tank is fed the stream water at the rate of 60 gallons an hour, mixed with 2.4 parts per 100,000 of aluminium sulphate (common alum). This aluminium sulphate combines with the natural carbonates in the stream water to form an insoluble precipitate called luminium hydroxide. This is technically known as floe.