GENERAL MEETING A General Meeting of the Society was held on 26th October, 1970, in the Edward Lewis Lecture Hall, Middlesex Hospital Medical School, London, W1

The President, Mr. T. ldwal Jones, was in the Chair.

SUBJECT: CONSERVATION - EFFLUENT PROBLEMS

Total nutrients (units) Awilable nutrients (units)

N I p2os /--TI N I P20s I K20

C . T. RILEY A N D V. C . N I E L S E N

National Agricultural Advisory Service, Guildford

Value of available nutrients

f s. d. 1 f p

The agricultural waste problem, particularly with cows, is one of magnitude rather than of under- standing complicated biological treatments. Our cow herds probably produce around 45 million tons of fresh excreta per annum and with the nine million animals described as 'other cattle' account for about 80 per cent of the total tonnage of livestock wastes. Much of this is of course spread on land by ranging animals, but nevertheless the amount deposited by animals lying in, particularly during the winter, is very large. It is generally agreed that a dairy cow produces a weight of pollution equivalent to that from 10 people. I f we pick any 10 persons, it is probable that we shall find a gross income amongst them of around fl0,000/year which can be taxed for sewage treatment among other things. However the gross income of a cow is only about f 150/year. Thus the assumption that one can take technology straight from human sewage and apply it directly to an agricultural concept is not a viable one. The equivalent of a human sewage treatment plant would probably have a capital cost in the region of f200 to f300/cow. Nevertheless it may be possible to borrow some of the technology and to apply it in a farm situation where the high costs of civil works can be more conveniently reduced. Fortu- nately dairy farming still relies on the maintenance part of the cow's ration being grown on the farm,

and thus there is land on which to return the manure and urine produced, and there is no doubt that in the foreseeable future the return of the total excreta to the land is the most economic and convenient form of disposal. It is along these lines that most dairy farmers will have to solve their disposal problems.

MANURE I N EFFLUENT The quantities of cow manure and urine, manure

in effluent and of other materials and liquids which find their way into a disposal system, must be looked at and carefully considered before planning an individual farm system.

Cow manure, i.e. faeces plus urine, has a high water content of around 87 per cent (roughly of the same order as milk). The quantity voided will vary with breed, size of animal and feed. A cow on ad lib. silage will eat and excrete more than one on a restricted hay and cake diet. A good approxima- tion is that the cow will void daily 7-8 per cent of her body weight. On average again a good rough guide is that the cow will produce total excreta of around 13 ft3/day, roughly 100 Ib or 10 gal (0.14 m3, 45.4 kg or 45.4 I), with a proportion of manure to urine roughly as 7:3. There is consider- able information on the nitrogen, phosphate and potash values of cow manure and a series of median figures is shown in Table 1 .

1 toncowmanure I I2 I 6 I 12 I 8 I 3 1 9 I 1 1 3 I 0.56

I I I I I I I

Taken from: Composition of organic manures and waste products used in agriculture. NAAS Advisory Paper No. 2. Farm waste disposal. Short term leaflet 67. Ministry of Agriculture, Fisheries and Food.

Journal of the Society of Dairy Technology, Vol. 24, No. I , 1971 9

Thus if a cow is producing 15 t excreta/year this has a cash value at present subsidized prices in the region of €7-8/year. She is in fact producing more than enough nitrogen to grow an acre of wheat and if, as 1 suspect, the cost of disposing manure on most systems is around f5-7/cow, then obviously there is scope here, for making an economy.

A term which is becoming familiar to our community is the biochemical oxygen demand (BOD). Roughly this is a measure of the amount of oxygen used to degrade the organic portion of wastes and there are well established systems for its measurement. It is not particularly accurate when applied to very strong animal manures because it was designed for work with human sewage which is a very much weaker solution from the pollution point of view. Nevertheless it is a measure that we have to try and use, with all its defects in the agricultural context, because it is the normal pollution measure used by river authorities, local authorities and others involved. Again it is the only measurement we know to which it is possible to relate horsepower demands and machinery design in a constructive manner. Efforts are being made to find a better measurement but for the moment we shall have to use it. It is measured normally in Ib dissolved oxygen/cow, and figures run from 1 to 1.3 lb dissolved oxygen/cow day. Alternatively it is quoted in parts per million (ppm) and values from 10,000 to 20,000 have been recorded. Our impression is that the range is from 10,OOO to 12,000 ppm (A. B. Wheatland, private communica- tion). A normal BOD of human sewage will be around 400 ppm and this indicates the vast difference in strength between human sewages and animal wastes. The normal standard for discharge into water courses is a BOD of 20 and a suspended solids of 30 ppm. Thus there is a very considerable (and expensive) reduction necessary to achieve such standards, and we must recognize that the standards are more likely to go down than remain static.

One very important point to remember about cow manures is that unlike many other animal wastes they have already been subjected to a considerable bacterial/microbial breakdown in the rumen of the cow. If parts of the excreta have survived this treatment it is therefore extremely unlikely that they are going to be easily broken down or degraded by another ‘synthetic’ biological treatment. Among such constituents we shall find lignins, celluloses, pieces of silage, etc., which will undoubtedly form a problem. Thus one has considerable reservations with regard to the treatment of cow wastes in an artificial biological situation.

OTHER COMPONENTS OF EFFLUENT Bedding materials. The most common materials used for bedding dairy cows are straw and sawdust.

Other materials used include dried manure, sand and ground limestone or chalk. It has been shown (NAAS, 1970) that in loose housing systems where the yard design follows recommended practice, the minimum straw requirement is adequate and for a bedded area of 40 ftz/cow (3.7 m*/cow), and a winter period of 150 days, IO-lOt cwt litter/cow will be sufficient (500-550 kg/cow).

In a cubicle system, the type of material used does not affect the quantity, nor does it affect the time taken to litter the cubicles. The quantity of material used in a six-month winter period was about 3 cwt/cow (150 kg/cow) (NAAS, 1970).

Wash water. Water can enter the manure system through the washing and cleaning of concrete areas, the cleaning of dairy equipment and as rainwater.

In a report on slurry removal from cowyards and sheds (NAAS, 1962) it was shown that, to clean concrete areas, the most suitable hose was 36 ft (13 m) long and 13 in dia. (40 mm), with a I-in nozzle (26 mm). A working pressure of I 5 Ib/in2 (100 kg/m2) and a flow of 60 gal/min (270 I/min) achieved the best results in terms of area cleaned per minute. Higher pressure caused too much splashing and excessive quantities of water. Even so, this could result in increasing the amount of slurry per cow by as much as 8 1 per cent.

Another survey (NAAS, 1970) showed that the amount of water used to clean various types of milking parlours twice a day was 100-120 gal (450-550 I ) according to the method employed, i.e. buckets or power hoses. It was found that a smaller hose size could be employed to get the maximum cleaning in the shortest time. A hose 36 ft long, 13 in dia. with a 4 in nozzle (135 I/min at 35 kg/mz I + in dia. with a 4 in nozzle was recommended (13 m, 40 mm and 20 mm). A flow rate of 30 gal/min at 5 Ib/in2 will clean 150 ftzlmin ( I 35 l/min at 35 kg/m* will clean 14 m*/min).

There is little difference in the quantity of water used to clean dairy and milking equipment. Hand cleaning by accepted routines usually requires at least a 10 gal (45 I) cold scrub, followed by a 10 gal (45 I) hot scrub with cleaning and sterilizing agents, followed byacoldrinse. This routine involves 25-30 gal water ( 1 10-135 I ) and is usually carried out twice a day. The same quantities apply to circulation cleaning or acidified boiling water systems. It is therefore fair to say that the total daily gallonage will be 40-60 gal (180-270 I) depending on whether the plant is given complete cleaning twice a day. To this can be added a further 20-30 gal (90-140 I ) if a bulk milk tank is used.

Cooling water. Cooling the milk by water from the mains requires 3 gal water to cool 1 gal milk. There is very little difference in water quantities used whether the plant is a surface cooler or inchurn cooler. Thus 100 cows producing 500 gal/day (2,250 I/day) require 1,500 gal/day fresh

10 Jourtial of the Society of’ Dairy Tc.c/taology, Vol. 24, No. I, 1971

water (6,750 I/day). It would be a substantial help if the water could be re-used.

Rainwater. Each inch of rainfall on a square foot constitutes 3 gal water. Except where rainwater can be used for dilution of manures, it is essential to get it out of the effluent disposal system. Rainwater falling on clean concrete or roofs can be diverted into natural watercourses, and disposed of immediately. Rainwater on collection and open feed areas will be directed into the manure handling system. There is a point where the volume of rainfall makes it more economic to cover these areas than deal with the increased volume of waste material. This point occurs when the rainfall exceeds 30 in/year (75 mm/year) (Jones & Riley, 1970).

REMOVAL AND DISPOSAL O F MANURE There is a range of possible systems, from complete solid handling through the slurry systems to liquid organic irrigation. A solid system where straw or other litter is plentiful will mean that all materials are left in the building and removal takes place once a year during the summer. The more common version of solid handling means that the excreta plus bedding is moved to a store daily and from the store at periods to be decided by the farmer. Slurry systems are more often associated with either cubicle or kennel housing. Bedding is minimal and the material collecting in feed areas and passageways consists of dung, urine, some water, a little fodder and some bedding. Removal can be by scraper and tractor or by a purely mechanical scraper. Where tractors and scrapers are used it is essential to have room for manoeuvre when planning these areas. Liquid removal and handling of excreta can be carried out by hose either off th,e mains, from a power pump or by a flushing system using tipple tanks or similar methods. Where this sort of system is practised, attention should be given to the possibility of re-use of re-cycled water.

Various factors affect the disposal of manure. The soil type and water table have a big effect on any waste disposal system and often dictate in particular the length of storage required. Rainfall is also an important factor because this affects the movement of machinery and the run-off into watercourses. In difficult areas a long storage period of up to eighteen months gives more latitude in disposal. The location of the farm and its relation to urban areas in particular again exerts pressures. In urban areas care must be taken to reduce odours wherever possible and to avoid using spraying equipment in situations that can give offence. Farmsteads built by streams and rivers will need to exercise much more care with direct run-off of wastes, silage liquor, etc.

The type of farming and husbandry will also affect disposal. We have said that the cow still

obtains the bulk of her maintenance from the farm and therefore an area of fodder crop is involved. One has the very strong impression that this area is extremely valuable to the dairy farmer in lieu of high capital cost disposal equipment. Cropping programmes do not always correlate with cleaning out periods, especially on all grass farms, and here again the length of storage is very much affected.

Smell is a factor which cannot be ignored. In theory if manure is taken straight on to land before it goes anaerobic, then we have virtually no smell problem. Unfortunately such daily disposal is not possible and therefore one tends to ask why we do not store for a year and have only one smell per annum on spreading. Certainly the most acute smell problems arise where the unit is designed for weekly disposal or spreading of liquid manure, particularly when it is sprayed upwards into the air. Dribble bars or direct deflection down on to grassland should do much to reduce this difficulty.

We have strong indications towards longer storage, for crop husbandry and environmental reasons and, furthermore, much of this storage will be above ground rather than below. A further point is that if any package deal systems do emerge, then the above ground situation is ideal for something to be erected on a prepared site.

As previously mentioned cows mean acres and there is a current belief in Europe and indeed in North America that 1 acre/cow (0.4 ha/cow) means long term waste disposal without trouble, i.e. the total excreta can go on to theland and in general can be disposed of without toxic metals or other problems. On our last check only 2 per cent of herds and 4 per cent of cows exceeded this area/cow figure. If the dairyman decides he must exceed this, perhaps aiming at 0.5 acre/cow (0-2 ha/cow), then he will undoubtedly create waste disposal problems for himself and at the same time inevitably higher costing for the industry as a whole. I t is not our place to dispute the rights and wrongs of such an issue but it is interesting to note that Sweden last year passed a law which related acreage to animals on the basis that no more than 50 tons manure/ha may be spread per annum (approximately 23 t/acre). Canada has a draft law under discussion where one acre and one cow are directly related and there are other points concerning the location of buildings, particularly new buildings, to habitations.

Looking therefore at the small group of people who are undoubtedly going to have a real problem, perhaps 10 per cent of the total, if they must have the equivalent of a milk factory then it is critically important to put the waste disposal costs in the original cow budgeting exercise, because both capital and running costs may well be extremely high.

Looking at the other 90 per cent, it is clear that the manure has to go back to the land, although we hope for better handling equipment and some smell

Journal of the Society of Dairy Technology, Vol. 24, No. I , 1971 11

control. Assuming this is so what then will happen to any surplus liquids involved, and the question of river pollution ? At the moment we see development in all livestock housing and waste disposal following a pattern, and this pattern having two stages. Firstly an 'agricultural' stage, in which the excreta will be pushed or dragged as a solid to a heap or hold for a year's storage. This will probably be above ground, earth banked, sometimes on concrete, and perhaps with sleeper walls. In most cases provision to catch seepage, rainwater and other run-off will be essential. Alternatively the excreta will be washed to a liquid hold above or below ground with provision to catch and control any overflow water. In general this is a fair concept and we have a great deal of information with regard to handling, equipment, design of such holds, etc.

It is interesting to speculate whether if these long storage periods become more general it will pay the farmer to keep his own disposal equipment or whether it will be better to use a contractor for the job. Indeed one can ask whether, if contractors do not exist, it may be more appropriate to form a group amongst farmers.

In the second stage one would attempt to treat the liquids only, i.e. the liquids from the heap of solid or the overflow from the liquid hold, thus applying the expensive treatment equipment to the minimum volume and obtaining the lowest cost factor. Almost certainly this will be an aerobic treatment and will lead to either partially-treated effluents being discharged over land (with no smell), or perhaps to a reduction down to Royal Commission Standards for direct discharge into a river. In many cases the final treatment may be by the accumulation of these treated liquids in a lagoon which will give say 30 to 50 days' retention and provide facilities for irrigation, fire precautions or the re-cycling of water.

TYPES OF AEROBIC TREATMENT I n aerobic treatment, air is introduced to the waste by a variety of means and aerobic microflora digest the organic portion. In general most of the systems mentioned provide 3-4 Ib dissolved oxygen/ kWh (1.5-2 kg/kWh). Further, aerobic systems func- tion without smell and this is one of their major advantages because it enables the wastes to be sprayed on to the land without smell problems arising. Such units will work in the lower tempera- tures common in the U K . Some are designed to rough out crudely the bulk of the pollution, and others function better as polishing machines. Thus it is extremely unlikely that any one unit will handle the whole waste, and more probable that atreatment will consist of a small complex of unils. The following types may be used (Jones & Riley, 1970).

The oxidurion ditch, or Pusveer ditch. These units were developed in Holland for the treatment of human sewage, and have been applied with some

success to agricultural and other wastes. Essentially they are of race track design with a rotor or paddle wheel pushing the liquid around the ditch and at the same time introducing air and consequently dissolved oxygen into the waste. Provision is made for withdrawing clear or settled final liquid from them for distribution to the land or river as the case may be. There are some disadvantages in agriculture in that these ditches are not necessarily suited to taking the whole waste direct from the animals. They can pose problems in civil engineer- ing on hilly land or where high water tables exist. In general they are probably regarded as a polishing instrument, and they are likely to be suitable as a final treatment where discharge to the river is needed. It is interesting to note that i n Holland their agricultural use seems to be declining, and attention is being paid more to the surface aerator.

Surface uerution. This system requires a rotor, either floating on or suspended into the surface of the liquid. The principle is the same in that the waste is pushed around the tank and at the same time air is introduced. From the agricultural point of view such appliances are much nearer the package deal concept and have the advantage that they can be sited above ground in hilly or very wet or high water table areas, so that the civil works can be reduced. These units function rather as a roughing agent in that they will remove coarse pollution. We are attempting to use them for the treatment of liquors from waste storage and to effect polishing by putting the waters from the treatment plant through a settlement tank and into a lagoon before discharge.

The Biologicd filter. This comprises a plastics material stacked into a tower, presenting a very large surface area within the tower. The liquid waste ispumped to the top of the tower and runs down through the plastics media to be aerated. At the same time microbial slime forms on the plastics surface and breaks down or consumes the organic part of the waste. Essentially this plant is again a roughing tool in that it removes gross pollution quite efficiently, and experiments are currently going on with cow, pig and poultry wastes. The liquids discharged will probably need further treatment before they can be put into a river but would be odour free when sprayed on to farm land or used as part of an irrigation system. It will be seen that the construction is relatively simple and again the civil works are not excessive.

Aerobic lugoon. Here we are talking about an area of water not more than 2-3 ft deep which, taking in surface oxygen, is able to maintain an aerobic status. These lagoons have been used successfully in other parts of the world but are dependent upon light and temperature and in areas of high rainfall special provision for overflow has to be made. They are not suitable for treating crude wastes. Very large areas would be needed probably at the rate

12 Jourriul of !he Suciety of Dairy Teclitiology, Vol. 24, No. I , 1971

of say 10 cows/acre water on a permanent basis (25 cowslha). Nevertheless they may be suitable for discharged effluent from one of the plants men- tioned above, and provide a base for fire prevention, irrigation, etc., before final discharge.

The graded ditch. This is a fairly recent idea in the agricultural sense, but can be used for polishing water discharged from other systems where the ground circumstances permit.

The aerobic concept has much to recommend it to agriculture. It is relatively easy to design and to run; there is a low power consumption and the system as a whole is almost always completely smell-free when functioning properly. It appears that most workers are concentrating their efforts upon an aerobic solution, at least in the treatment of liquid wastes. We should however, note one difficulty. In all the systems mentioned above there will be produced what the sewage industry calls a ‘sludge’, i.e. a waste from the activated microbial treatment. This will consist of 3-4 per cent solids, some of which have to be circulated round the system again and some of which will have to be settled before discharge, particularly if discharge to a river is contemplated. We are thus faced with the true facts of the situation, the liquid still exists in volume however clean it may have been made during treatment. Somewhere the solids will have broken down or settled out, and you will appreciate that this is not so easy as it seems. There can be no disappearing act. The first or agricultural stage storage will have to be emptied. There will always be a final sludge to be reckoned with, and in the opinion of myself and many colleagues the treat- ment of the sludge from such aeration plants is

going to be the biggest problem of all. Perhaps we may be able to re-cycle it on to a midden, use the midden as a filter and let the liquid run back into the system. Other forms of filters may have to be devised and time alone will tell us what the ultimate solution may be.

Clearly we have to work with natural processes as far as we can. We have to reduce any concept of civil works to the utmost simplicity and look for methods that are manageable in a farm situa- tion. I am confident that simp!e methods can be evolved that will be within the capabilities of the able staff that one normally finds on a farm. Many farms, of course, will manage without any sophisti- cated system at all but our job is to t ry and find methods which can be used where no other altern- ative exists. By this I mean that we are not searching for time and money consuming processes, but attempting to meet a demand which already exists and we think will be greater in the future because there is no doubt in my own mind that demands, in terms of pollution control, are going to be greater and not less in the years to come.

Much of this paper is based on the thoughts and ideas of the authors’ colleagues in the Advisory Services.

REFERENCES

Jones, K . B. C. & Riley, C. T. (1970) Proceedings of the Syniposium on Farm Wastes. University of Newcastle- upon-Tyne.

NAAS (1962) A Rvport on Slurry Removal from Cowyards and Sheds. National Agricultural Advisory Service.

NAAS (1970) The User’s Giticle to Modern Milking, No. 5. Cleaning and Littering Co wyards and Citbiclcs and Washing Milking Pnr1octr.s. National Agricultural Advisory Service.

B Y M . W . ASKEW, B.SC., F.R.I.C., M.I.BIOL., A.M.1NST.W.P.E.

Technical Director, Environmental Control Consultancy Services Ltd.

It is not the intention of this paper to consider in detail the law relating to the disposal of effluents nor the historical aspects of dairy and creamery effluent disposal, but rather to consider the practi- calities and technology involved against the background of water and wastes management at large.

In this European Conservation Year no-one can fail to be aware that pollution of the environment is an ever-present and growing problem, so that the technological and economic sanctions with which we are concerned in dealing with the wastes of an industrial society become ever more severe. Long gone are the days when liquid effluents could be disposed of cheaply to the drains of the Local

Authority or freely to rivers and streams. Today in almost every situation means of disposal of effluent are either immoral, illegal or expensive. In the future it will become increasingly necessary to consider water management as an integral part of the planning of any production operation, be it the establishment of a new factory or something as simple as a variation of product.

THE ORIGIN OF DAIRY AND CREAMERY EFFLUENTS

Over the years a wide variety of effluents has been described to me as ‘of the dairying type.’ On investigation they have proved to be as diverse as churn washings and the waste liquids from the

Journal of the Society of Dairy Technology, Vol. 24, No. I , 1971 13