matter; and, granted these, there is practically no limit to the activity of their processes, nor to the amount of noxious organic matter they can dispose of, converting it into harmless innocuous compounds. These useful little organisms exert a powerful influence in nature, the magnitude of which is seldom realised. They have a wonderful power of adaptability, and can modify their constitution to suit the circumstances, becoming, like most living things, educated to their environments. This will be exemplified later.

Sewage, the other factor in the chemico-biological process I am about to describe, delivered at an outfall after flowing a considerable distance in a closed channel, consists of nitrogenous compounds, chiefly in solution, the solids, for the most part, being suspended in finely-divided particles; but sewage contains also within itself, potentially, the power of its own destruction. Countless myriads of the bacteria of decomposition carry on their disintegrating processes, and all that is required to complete the chemico-biological change initiated by the vital process is a plenteous supply of the ever-obliging oxygen of the air, readily accessible.

We have, then, on the one hand soil—a medium containing in its interstices oxygen as air, and myriads of bacteria, whose favourite diet is dead animal or nitrogenous matter; and on the other hand the water of an abundant water-carriage system—a medium containing this very dead nitrogenous material, with an equal number of greedy bacteria. The oxygen and bacteria in the soil and the nitrogen and bacteria in the sewage are the factors which, when brought together under suitable circumstances, bring about a transformation of the most impure liquids into a pure and sparkling water that the most fastidious could drink of and commend, soluble mineral constituents, known generally as nitrates and nitrites, only being present—the chemical indication that the change known as oxidation or nitrification has been complete.

To illustrate, corroborate, and amplify this, let me describe an experiment conducted in the laboratory: A long glass cylinder is filled with pure sand. There are few or no bacteria and little or no organic matter, but because of the looseness of the sand-particles there is abundance of oxygen as air—about 50 per cent. A small pipe leads a supply of very impure water on to the surface of the sand in this artificial filter, while a tap at the bottom of the cylinder allows the filtrate to be caught and examined.

The first of the fluid filtering through is found to be almost entirely as impure as that distributed on the surface of the sand, only some of the coarser particles being retained. The bacteria are as numerous, the amount of putrescible nitrogenous compounds and ammonia is the same, and there is an

absence of nitrates and nitrites, this absence, as I have already said, being the chemical indication that no oxidation or nitrification has taken place in the passage of the fluid through the sand. But let the process of filtration continue for twenty-four hours and another sample be examined, a marked improvement in the filtered fluid is at once noticed, and chemical and biological examination show that the putrescible nitrogen and ammonia are diminished, and the bacteria are fewer in number, while the nitrates and nitrites are largely increased. This improvement keeps going on till the fluid passing through the sand is as absolutely pure and sparkling as the finest spring water. Chemically tested it reveals absolute freedom from all organic matter and ammonia, with the presence of a considerable amount of the innocent mineral compounds nitrates and nitrites. Tested biologically there is a complete absence of bacteria; in. short, this water is purer than most drinking-water, and no one would hesitate to drink of and appreciate it. This mysterious and marvellous conversion of the foulest liquid into the purest water will continue for many days, but gradually the affluent will lose its purity, and in time will become as noxious as the original fluid, and get extremely foul. But if now the flow of the impure liquid on the surface of the sand be stopped for twenty-four hours, and then resumed, the affluent will again become pure as before, If, further, this cessation of the flow is permitted upon alternate days, or upon one day out of three, by other cylinders being placed beside the original one, the purification of the foul liquid experimented with may go on indefinitely without any renewal of the sand or impairment of its efficiency. This process of purification is known as “intermittent downward filtration.”

If the experiment I have just described be extended by planting in the surface of the sand various garden-plants they will, of course, grow luxuriantly, provided other conditions of warmth and light be attended to, and the nitrates and nitrites hitherto present in the filtrates will diminish and almost entirely disappear, the water issuing from the tap being pure and sparkling as before, differing only in being free from its mineral compounds. This process of purification extended to agricultural land is known as “broad irrigation,” or “sewage farming.”

If the chemical and vital processes which have taken place in the sand be examined more closely they will be found to depend upon the presence and labours of the minute bacteria before referred to. The particles of sand get coated with a slimy material secreted by the bacteria themselves, and in this they live in countless myriads, taking from the organic nitrogenous matter in solution as it slowly trickles past them

the elements they require for the support of their tiny bodies. The other elements of the organic compounds are thus let loose, and are seized by the oxygen of the air between the particles of sand, forming the mineral compounds already referred to as nitrates and nitrites.

The presence of oxygen in the air-spaces of the sand is thus essential to the chemical change; but the constant saturation in the first experiment described prevents the renewal of the air-supply, and the success of the purification process is thus frustrated. Hence the necessity for intermittency in the application of the liquid to be purified. When the flow is stopped the contained fluid drains off, and air, bearing its bounteous supply of oxygen, again fills the spaces. The new compounds formed by this chemical process (oxidation or nitrification, as it is called) are the nitrates and nitrites, which, being soluble, are carried on with the water, providing there are no plants to feed upon them. But nitrates constitute the best and most easily-assimilated food for plants; and as the chemico-biological process I have described takes place most largely near the surface, where the bacteria are most numerous, it is apparent that the most favourable conditions for the growth of plants are here to be found. The assimilation of the nitrates and nitrites by the plants in the above experiment, illustrative of broad irrigation, explains their absence from the effluent water.

These principles applied to the disposal of sewage by application to the soil constitute the scientific basis of sewage farming. But a sewage farm, to be successful, must effectually dispose of sewage as sewage by converting the solids into plants, and the liquids into pure water, without nuisance or injury to health. Now, can this be done? The experience of years rings out a chorus of emphatic affirmation. If the laws arising out of chemico-biological experiments be conformed to in the management of a sewage farm the solids can be converted into the finest plants and the liquids into the purest water without the slightest nuisance or injury to health. Dr. Cornill tells us that he drank freely of the limpid streamlets of the Berlin Sewage Farm. Many sewage farms are favourite Sunday resorts, and strangers are frequently surprised to be told, while they admire the luxuriant vegetation, and breathe the pure air, that they are on one of the walks in the middle of a sewage farm.

But though this brilliant consummation can be attained, and is being attained in some of the most populous towns in different parts of the world, it is not an easy nor an inexpensive matter. Conditions must be favourable to the working of a sewage farm. Land must be available at an elevation sufficient to permit of underdrainage if the soil is retentive of

moisture. Underdrainage by laying porous pipes at a depth of about 6ft. is an important because it is an expensive matter. A loose friable surface-soil, with a subsoil of coarse gravel, can be worked without underdrainage, as in Croydon. But whenever the soil for a considerable depth is favourable to the retention of water underdrainage is necessary, for it must be remembered that sewage must pass through, not over, the soil in order to fulfil sanitary requirements. Many farms have no underdrainage, and in some, with very impervious clayey subsoil, the managers are content to allow the sewage to flow over the land, finding that after about a mile of flow it is comparatively pure, and the amount of water small in quantity. But though underdrainage is necessary to allow of the rapid relief of the land from moisture, and the consequent aëration of the soil, it is found that, except in rainy weather, there is not much flow in the affluent drain-pipes, sometimes the whole quantity of water passing upwards through the vegetation of the farm by evaporation.

Pure sandy soil is an extremely suitable one for sewage farming, and the most luxuriant crops are very soon produced, while the cost of levelling and draining is usually less than for most others. A gentle slope is necessary for the purpose of irrigation, while what is known as the “ridge and furrow” system is adopted for the growth of vegetables, and a system of gentle slopes, with grips, for the growth of grass-crops. Vegetables are planted on the tops of the ridges, and the furrows convey the sewage at a slow pace. The area required where the dry-weather flow varies from 20 to 40 gallons per head is 1 acre for every hundred of the population. If “intermittent downward filtration” alone be adopted for the disposal of sewage, 1 acre for every thousand of the population is sufficient.

It is advisable, whenever much rain-water is admitted to the sewers, to have a small area of well-prepared filter-beds, for downward filtration in wet weather, for the disposal of any excess of sewage, or when it is not required for the purposes of irrigation.

In a properly-laid-out farm tanks receive the sewage at the outfall when it issues from the main sewer, and here the larger solids are retained and collected and dug into the soil with town ashes and refuse, making a very superior and profitable manure. A main open carrier, formed generally of concrete or of split pipes, conveys the sewage from the tanks through the centre of the farm. Grips in the land, or on the tops of ridges, strike out at right-angles from this main carrier, and opposite these grips stoppers are placed by the workmen every now and then, causing an overflow of the sewage, and

its distribution over the land. This is done intermittently, and, as a rule, the irrigation of growing crops is avoided; but as the primary object of a sewage farm is to dispose of the sewage, and not to grow crops, whenever it is necessary for such disposal the sewage is turned on to the crops, in spite of the wholesale destruction often caused by such a procedure. This unfortunate necessity in the name and for the sake of health is the consideration which determines the management of a sewage farm.

It has been shown repeatedly that tenants will not dispose of sewage to the ruin of their crops, and the responsibility of efficient management has therefore devolved entirely upon the Board of Works or local sanitary authority. But small areas can be let to market-gardeners, the local Board agreeing to supply sewage upon demand; or the whole farm may be let if the stipulation be made that the whole of the sewage is to be disposed of without nuisance or injury to health.

The amount of farm produce raised upon sewage farms is sometimes phenomenal. On the Craigentinny Meadows (originally drifting sea-sand), irrigated by the sewage of Edinburgh, from 50 to 70 tons of grass per acre are raised, yielding thus about £36 per acre. Rye-grass is about the most abundant crop grown, as this grass has a wonderful power of absorbing sewage, and five and seven cuttings are taken off each acre annually, yielding in all from 30 to 50 tons per acre. The Sewage of Towns Commission concluded that experience had shown that, with the application of 5,000 tons of sewage per acre per annum to meadow-lands, an average of 1,000 gallons of milk had been produced from the cattle fed upon the produce; and, further, that an average gross return of £30 to £35 per acre per annum in milk, at 8d. per gallon, might be expected. Dr. Corfield quotes evidence to show that land which “formerly let at from £2 to £6 per Scotch acre is now let annually at from £30 to £40, and that poor sandy land on the seashore, which might be worth 2s. 6d. per acre, lets at an annual rent of from £15 to £20.”

These figures might at first sight lead one to suppose that the profits arising from sewage farming must be considerable; but it is not so. The amount of capital absorbed in the acquisition of land, and in its preparation, the number of hands required to do the work, and the constant risk of rainy weather, with its accompanying losses, all tend to make sewage farming a hazardous undertaking from a financial standpoint.

The following table gives some of the information I have been able to collect in reference to the initial outlay, the expenditure, and the incomes of sewage farms:—

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Speaking generally, sewage farming does not pay as an agricultural enterprise, and authorities are unanimous in the opinion that if the farming operations clear expenses, or yield a small profit, this is all any local body is justified in expecting, and this only when the local conditions are favourable. In estimating the profit and loss of sewage farms, rent, in the shape of interest upon the capital outlay, must be left out of account. If this item be taken into the estimate the figures show an enormous loss in the working of most sewage farms.

Dr. Corfield, in his work on the treatment and utilisation of sewage, comes to the following conclusions in reference to broad irrigation: “(1.) That by careful and well-conducted sewage irrigation (especially if combined with a filtration area) the purification of the whole liquid refuse of a town is practically perfect, and has been insured in cases where it was not at all the object of the agriculturist; and that it is the only process known by which that purification can be effected on a large or small scale. (2.) That perfectly worthless land—blowing sea-sand, for instance—can be made in this way to support large and valuable crops. (3.) That the quantity per acre of all crops obtained from even the best land is enormously increased. (4.) That it reduces to a great extent, or renders entirely unnecessary, the usual amount of artificial manures of all kinds by supplying a manure especially adapted, from its complex constitution, for the nourishment of crops; supplying it moreover in a state of solution—that is to say, in the most readily-absorbable condition; and supplying at the same time that most necessary aid to vegetation—water, which often converts what would otherwise have been

a heavy loss into a handsome profit. (5.) That by it the farmer is rendered entirely independent of drought; so that he can be practically certain of his crops, and, moreover, be able to transplant them as much as he pleases. (6.) That when circumstances are favourable it has been found to pay, and when its management is more thoroughly understood it will doubtless in many instances be found to be a source of income to the towns. Where the circumstances are not so favourable it will yet prove to be the most satisfactory way to get rid of the nuisance, although it may not entirely pay its expenses.”

Nothing is more thoroughly established in regard to this subject than the entire absence of anything like nuisance, or injury to the health of those on or in the immediate vicinity of sewage farms. The only semblance of nuisance that ever exists on a well-managed farm is at the outfall, and this is reduced to a minimum by prompt and effective treatment, and, at worst, the odour is no more offensive than that noticeable in the vicinity of any of our present sewer outfalls into the harbour. The bounteous production of ozone by the luxuriant vegetation of the farm corrects any tendency to the rise of miasmata from the soil, and actually purifies the air to a degree beyond that of the towns themselves. Dr. Cresswell says of the Norwood farm at Croydon: “As for effluvia, I will not say there does not exist any, but it is so seldom perceptible that a house built within 200 or 300 yards would command the same rent as if half a mile off.” Dr. Carpenter says that hundreds of persons exercise and recreate in the sewage farms of the Croydon Local Board of Health, and that visitors express surprise at the absence of everything offensive to sight and smell. The travelling correspondent to the Melbourne Age, in describing the sewage farms at Croydon, says, “It is only fair to admit that the health of the people who live upon the farm (seventy-two in number) is very good, and the only place where any unpleasant odour is traceable is at the sieves where the solid matter is arrested, an operation which takes place some distance away, and at the spot where the crude sewage is distributed over the first field.” Mr. Stayton, in his report to the New South Wales Government, says of the Berlin Sewage Farm, “The health of the labourers on the farms is very good, and the death-rate was only 11 per 1,000 during the last year; and it is rather a remarkable fact that, although there was a severe epidemic of typhoid during the first months of 1888 in this city, yet no case of disease occurred on any of the farms.”

Evidence is abundant and emphatic in declaring that the purest and healthiest mode of sewage disposal is by broad irrigation, and this method can be adopted in the immediate

vicinity of populous and favourite suburbs without nuisance or injury or depreciation in the value of property. The germs of disease liable to be carried in sewage are effectively disposed of by the bacteria of the soil; and it is remarkable that many infectious diseases which exist in the towns are conspicuously absent from the farms supplied by the town-sewage.

Generally speaking, the advantages of sewage farming are: (1.) The general wealth is increased by the increased production. (2.) Employment is given to many workmen.(3.) Sewage, as sewage, is absolutely and completely annihilated. (4.) Nature is imitated in the method of disposal, and the utmost use is made of waste products.

In determining whether the sewage disposal of Wellington should be by broad irrigation these general advantages of course apply, and local advantages also exist in the suitability of available land in the vicinity of the already-determined outfall; but the conditions unfavourable to sewage farming are numerous:—

1. The isthmus suggested as the site for a farm is exposed to the severe southerly winds and salt spray.

2. The amount of water to be disposed of is much greater than is found to be convenient on most sewage farms—50 gallons per head of the population is the dry-weather estimate for Wellington. The average applied to sewage farms is about 30 gallons, while in Berlin, where the best results are obtained, the dry-weather flow in twenty-four hours is only 21 gallons per head of the population.

3. The average annual rainfall here, according to a return prepared by Mr. Gore, is about 51in., and, as provision is made for the reception of a large amount of rainfall by the sewers, it is evident that in rainy weather an enormous quantity of sewage will have to be disposed of. The average rainfall of Berlin is 23in.

To justify the establishment of a sewage farm upon the isthmus, the following questions must be decided in the affirmative:—

1. Can a sufficient area of suitable land be bought, levelled, underdrained, and thoroughly prepared for farming at a cost not exceeding that required to extend the outfall to any other suitable place?

2. Would crops and stock be likely to thrive, in spite of the exposure to wind and spray arising from the situation?

3. Would the cost of labour, and the demand for farm and dairy produce, justify the expectation that financial results would compare favourably with those of other typical sewage farms?