Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 4 Western Australia, Series 4
Volume 3
Number 12 1962 Article 9
1-1-1962
Water for agriculture. 4. Clearing cloudy or muddy water Water for agriculture. 4. Clearing cloudy or muddy water
R C. Gorman
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Recommended Citation Recommended Citation
Gorman, R C. (1962) "Water for agriculture. 4. Clearing cloudy or muddy water," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 3: No. 12, Article 9.
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WATER FOR AGRICULTURE
4. Clearing Cloudy or Muddy Water
By R. C. GORMAN, B.Sc., Deputy Government Agricultural Chemist
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ATER m a d e cloudy by finely divided clay, silt or organic m a t t e r in suspension may be cleared by simple chemical t r e a t m e n t .T h e r e is n o single m e t h o d of t r e a t i n g cloudy water t h a t is equally applicable to all waters. T h e selection of a satisfactory t r e a t m e n t is often a m a t t e r of practical testing.
There are t h r e e steps in t h e clearing of water.
(1) Selection of a suitable vessel for the w a t e r t r e a t m e n t .
(2) Addition a n d mixing of suitable clearing agent.
(3) Settling of suspended m a t e r i a l a n d removal of t h e clear water.
TREATMENT VESSELS Dams
Clearing w a t e r in d a m s is n o t always satisfactory. T h e clay or silt in suspension a t t h e time of t r e a t m e n t m a y be settled b u t slight disturbances of t h e w a t e r due to wind action will disturb t h e sides a n d bottom of t h e d a m a n d m a k e t h e water cloudy again.
Where a d a m is suitably sited, so t h a t it is protected from wind or when there a r e periods of calm weather, clearing in t h e dam m a y be satisfactory, especially if a floating take-off for clear w a t e r is used.
T a n k s
Tanks are t h e most satisfactory vessels for t r e a t m e n t of water on farms. T h e
size of t h e t a n k s used will depend on w h a t is available on t h e farm, t h e volume of water to be t r e a t e d and t h e frequency w i t h which it is intended to carry out t h e t r e a t m e n t .
T h e most convenient a r r a n g e m e n t is to have two t a n k s . The first t a n k should be used for t r e a t m e n t and settling a n d t h e second either as a holding t a n k for clear water from t h e first, or as a second t r e a t - m e n t t a n k used alternatively with t h e first.
The cleared water from one t a n k is used while w a t e r is being treated in the other.
The t r e a t m e n t t a n k should have two outlets, one in t h e bottom a t the lowest p a r t so t h a t t h e settled material c a n be flushed to waste a n d t h e o t h e r about a foot above t h e bottom for clear water.
Alternatively, a floating take-off m a y be used to remove t h e clear water.
CLEARING AGENTS
Selection of t h e most satisfactory clear- ing agent is generally a m a t t e r of trial a n d error. I t is therefore suggested t h a t t h e methods below be tried, in the order given, on a small quantity of water. The amounts of t h e various clearing agents required to t r e a t 44 gallons of water in a drum are given. Sampling of the surface of the water from time to time will indicate w h e t h e r t h e t r e a t m e n t is effective.
959
1. Lime.—Good quality builders' lime or h y d r a t e d lime a t r a t e s of u p t o 4 oz.
p e r 1,000 gallons.
T h e addition of 4 oz. per 1,000 gallons of lime will theoretically increase t h e h a r d - ness of t h e w a t e r by 3 grains per gallon.
T h e slight increase in h a r d n e s s is normally of little significance, especially as in p r a c - tice some of t h e added lime is absorbed on t h e settled clay. After lime t r e a t m e n t t h e cleared w a t e r should preferably be a e r a t e d by splashing into a second t a n k to remove a n y excess lime.
For t e s t i n g in 44 gallons, a h a n d f u l of lime should be mixed well in a bucket of w a t e r a n d t h e excess lime allowed to settle.
Five p i n t s of t h e clear s a t u r a t e d limewater from above t h e settled lime are placed in t h e d r u m , t h e d r u m is filled w i t h t h e w a t e r requiring t r e a t m e n t , a n d t h e liquid thoroughly mixed,
2. Filter Alum (sulphate of a l u m i n a ) .
—3 to 6 oz. per 1,000 gallons of water.
T h e addition of filter alum increases t h e acidity of t h e w a t e r a n d may m a k e it more corrosive. If t h e r e a r e any signs of i n - creased corrosion, s u c h as increased rust- ing of t a n k s or rusty w a t e r coming out of t h e cleared w a t e r lines, builders' lime or h y d r a t e d lime should be added to the cleared w a t e r a t r a t e s of one t h i r d of a n ounce of lime for every ounce of alum added per 1,000 gallons.
T h e equivalent a m o u n t of alum for t e s t - ing in 44 gallons m a y be obtained by dis- solving 1 oz. of alum in 1 gallon of water.
One p i n t of t h i s solution added to 44 gallons of w a t e r is equivalent to 3 oz. of a l u m per 1,000 gallons a n d 2 p i n t s is equivalent to 6 oz. of alum per 1,000 gallons.
3. Lime a n d Filter Alum.—2 to 4 oz. of builders' or h y d r a t e d lime per 1,000 gallons followed by 3 to 6 oz. of filter alum per 1,000 gallons.
4. Gypsum.—Up to 4 lb. of gypsum or plaster of paris per 1,000 gallons.
If p l a s t e r of paris is used it should be stirred w i t h 10 times its weight of water before addition.
Addition of 4 lb. of gypsum per 1,000 gallons will theoretically increase t h e h a r d n e s s of t h e w a t e r by 16 grains per gallon, which is appreciable. I n practice, t h e increase in h a r d n e s s is rarely greater
t h a n 8 to 10 grains per gallon as m u c h of t h e added gypsum is absorbed on t h e settled clay.
T h r e e ounces of gypsum added to 44 gallons of t h e w a t e r to be t r e a t e d is equivalent to 4 lb. of gypsum p e r 1,000 gallons. As gypsum is only slightly soluble in water, it is necessary to thoroughly stir t h e water after adding t h e 3 oz. of gypsum, to m a k e sure it all dissolves.
5. Salt.—If t h e cloudy w a t e r is low in total soluble salts common salt m a y be used to assist clearing. I t should be noted t h a t t h e addition of 10 lb. of common salt per 1,000 gallons will increase t h e total salts of t h e water by 70 grains p e r gallon.
Seven ounces of common salt per 44 gallons is equivalent to 10 lb. of salt per 1,000 gallons.
Mixing the Clearing Agent
When a satisfactory clearing a g e n t h a s been found it should be mixed w i t h or dis- solved in water a n d added either before or while the t a n k is being filled so t h a t t h e incoming water will cause good mixing.
Tanks should be stirred w i t h long poles or by rapidly raising a n d lowering a bag of clean sand on a rope.
If t h e t r e a t m e n t is applied to a dam t h e n t h e solution or suspension of t h e clearing agent should be broadcast over t h e surface of the d a m a n d t h e d a m stirred by repeatedly pulling a b r a n c h of a t r e e or a similar object t h r o u g h t h e w a t e r with a rope.
NOTE:—1 cubic yard is equivalent to 168 gallons, t h a t is a 1,000 yard d a m when filled contains 168,000 gallons.
SETTLING OF SUSPENDED MATERIAL Settling Time
The time required for t h e treated suspended m a t t e r to settle is n o t predic- table; it may require from two to 48 hours.
Experience with a p a r t i c u l a r w a t e r and t r e a t m e n t is the only way to find t h i s out.
Generally it is convenient to allow t r e a t e d water to settle overnight a n d n o r m a l l y this will be found sufficient with t h e right t r e a t m e n t .
Recovery of Clear W a t e r
The volume occupied by t h e settled material is variable. Some settled clays
are voluminous a n d will settle only to about 30 to 50 p e r cent, of t h e original volume of t h e water, t h a t is from 1,000 gallons of cloudy water only 500-700 gallons of clear water c a n be obtained. Normally t h e settled volume of t h e clay is of the order of 5 to 10 per cent, of t h e original volume, t h a t is 1,000 gallons of water would give 900-950 gallons of clear water.
T h e clear w a t e r is best removed from t h e t r e a t m e n t t a n k or d a m by a floating take-off into a holding t a n k for use as required. A floating take-off m a k e s sure t h a t t h e clearest water is d r a w n off. With a t a n k , the floating take-off can either be a t t a c h e d internally to a t a n k - o u t l e t or by a siphon over t h e side of t h e t a n k . After t h e clear water h a s been removed t h e settled material should be flushed to waste a n d t h e t a n k refilled ready for t h e next t r e a t m e n t .
When a t a n k h a s only one outlet, and this is at t h e bottom, it is possible t o flush
t h e settled material to waste, t h e n use t h e clear water t h r o u g h the same outlet. This is not very satisfactory in practice because of t h e difficulty of flushing under these conditions and because it is wasteful of cleared water to use it for flushing purposes.
IF WATER IS HARD TO CLEAR . . . Where difficulty is experienced in clear- ing cloudy water with t h e above p r o - cedures, i to 1 gallon of water should be forwarded to the Government Chemical Laboratories, Adelaide Terrace, Perth, for further tests.
Accompanying the sample should be a letter, giving details of t r e a t m e n t s tried a n d t h e facilities such as t a n k s and t h e i r sizes, available for t r e a t m e n t of the water.
The fee for this examination is £1 Is.
which is reduced to 7s. for bona-fide farmers.
FAULTY SPARK ARRESTERS DANGER TO WHEAT CROP
FOR the next two months New South Wales farmers will be harvesting what will be a near recoz'd crop.
Apart from climate and disease their greatest source of crop loss is fire caused by sparks from the exhausts of internal combustion engines of tractors, balers, harvesters and other small engines.
There have been frequent cases in the past decade of heavy losses through fire in wheat crops because of faulty spark arresters on tractors.
Losses of £2,000 have not been infrequent.
Pre-season Check
Mr. J. G. Drever, agricultural engineer of the Department of Agriculture, says that it is essential to fit an approved spark arrester in the first place, and equally important to do a pre-season check on the equipment and to check it regularly while it is in use.
Spark arresters, he adds, work under conditions of great heat, take a lot of pounding and are subject to excessive vibration.
Those factors cause the arrester to wear or break down, often with serious results.
He advises all farmers, wheat growers in particular, not to take chances with their spark arresters.
Mr. Drever has available for issue to appplicants copies of reports made by the Australian Tractor Testing Station of tests on spark arresters.
These tests give a brief specification of the arrester, show how it works, how it is constructed, the materials used, an analysis of the effectiveness of the spark arresting, and some comments on factors influencing its prospective life.
These test reports are available on application to Mr. Drever, N.S.W. Department of Agriculture, Box 36, G.P.O., Sydney, or to country offices.
961
WIND EROSION ON SALT LAND
Neglected salt land sometimes gives surprising results when sown. Cereal rye has made excellent growth on this sroded salt land at Bruce Rock. Seasonal conditions limit the usefulness of cereals on salt land h u t salt tol- erant perennials such as bluebush or saltbush give a stable form of land use. However cereal rye is valuable
for assisting establishment
Erosion and salt go hand in hand. Here the tough cereal rye stubble has withstood wind blasting and trapped several Inches of blown soil. Cereal rye is a useful cover crop for protecting salt tolerant perennials when sowing
on sites prone to wind blast
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