CHAPTER XVIII
SAVING THE SEWAGE SLUDGE
In matters pertaining to sanitation and the movement of sewage Great Britain undoubtedly leads the world. There our conquest ends. From that point onwards we can only point to lamentable inefficiency. For instance, the lay-out of the main drainage system of London, undoubtedly the finest illustration of such engineering in the world, has involved a capital expenditure of £12,514,606—$62,573,030. By the provision of enormous conduits and feeders the excrementitious matter from residences, offices, workshops, and factories of the metropolis is borne for miles to central stations. In this manner those natural and trade wastes, construed as being inimical to health, are removed swiftly and hygienically, and we compliment ourselves upon our prowess, which certainly is justifiable so far as it goes.
But when we come to the treatment of this material we fail miserably. At the central station the solid matter, in reality a mud or sludge, is separated from the free liquid. The disposal of the latter offers little or no difficulty. It can be rendered innocuous, and is therefore permitted to resume its part in the scheme of Nature. But the sludge: that is a different proposition. A few figures concerning the situation in regard to London may prove illuminating. Certainly they will serve to demonstrate the magnitude of the volume of this waste. During the year over 100,000,000,000 million gallons of sewage are received from approximately 5,350,000 people occupying 95,000 acres. Each million gallons of sewage yields about 25 tons of sludge. The total quantity of solid matter is approximately 200,000 tons. It costs about 30s.—$7.50—to treat and dispose of each million gallons of raw sewage.
The total yield of sludge exceeds 2,600,000 tons a year. It is an incubus having no ostensible commercial value, so is transferred to vessels to be carried out to sea where it is thrown overboard. Seeing that it costs about £17 13s.—$88—to run each vessel out and back again, and that some 111,000 journeys are made during the year, dumping the sludge costs the ratepayers of London nearly £2,000,000—$10,000,000—a year. The crime incidental to London is repeated throughout the country, and in this way, as Sir William Crookes pointed out, the nation is deliberately discarding 16,000,000 tons of valuable nitrogenous material which, were it subject to proper treatment, might be reclaimed to participate in the nourishment of our broad acres. Estimating the value of this potential fertilizing agent at the modest figure of one ¹⁄₂d.—1 cent—per pound we are, of malice aforethought, throwing away a round £35,000,000—$175,000,000—per annum. But this is not the most disturbing feature. For the most part the sludge, and in the case of seaside towns the crude sewage, is discharged upon potential valuable fishing grounds, to the destruction or infection of the fish, especially shell-fish. Furthermore, one must not imagine because the objectionable and dangerous refuse is abandoned well out to sea its serious dangers are removed. Tides and currents play strange tricks, the result being that much of this filth is thrown back upon the coasts, perhaps at a distant point, to wreak possible havoc.
Civilization breeds a strange fastidiousness. The idea of reclaiming sewage for exploitation is repulsive to the average individual, although he does not turn a hair at the use of the comparative material derived from the animal kingdom for the nourishment of the soil, and the feeding of produce cultivated essentially for the table. The argument often raised against any exploitation of excrement is that it has become associated with many other deleterious substances, which have been thrown or allowed to run down the drain, as the readiest avenue for their disposal. But the very circumstance that such waste has become compounded with other residues, many of which are worth reclamation, should be sufficient to induce us to regard sewage not as an incubus or danger, but as a mine worthy of development to its fullest extent.
Fortunately, the objection to the exploitation of sewage for its commercial contents is in process of being over-ruled by the growth of a more enlightened attitude towards the whole issue, although it is to be feared, in accordance with the precept that what the eye does not see the heart does not grieve, the more progressive policy is being sanctioned unconsciously. It is safe to assert that, but for the war, which retarded the hands of progress very pronouncedly, the new movement in regard to the handling of this material would have made a material advance. Even to-day the outlook is not hopeless, inasmuch as the accentuated need to make every use possible of waste products may result in the sewage exploitation problem being attacked with enhanced energy.
What can be done with sewage is revealed by the action of one or two towns which have taken their courage into their own hands, notably Bradford and Oldham. In these two instances the modern handling of sewage was assumed before the war, so that the experience gathered during the past six years may prove sufficiently convincing to permit the whole subject to be attacked more in consonance with contemporary thought, which views all wastes in one light—potential raw materials for other industries.
Changing conditions and the need to cope with this residue along more comprehensive lines, in accordance with the growth of the population and the quantity of material to be handled, were responsible for the change from the old method to the new in both instances. In the case of Bradford the Corporation found it necessary to establish new works about six miles distant from the centre of the city, and was faced with the necessity to expend £1,250,000—$6,250,000—in connection with the undertaking. In view of such a heavy capital committal perhaps it was only logical to consider the possibility of rendering the sewage more remunerative in the future than it had been in the past. Any revenue to be derived from exploitation in such a field must react to the advantage of the community affected, more especially when such action does not jeopardize the health of the citizens to the slightest degree.
Of course, the situation in so far as it concerns Bradford was somewhat unusual. The city is the hub of the wool-scouring trade of the country, and in treating the sewage much of the wealth allowed to slip down the drains from cleaning the wool is open to reclamation. The one great mistake, if such it may be called, of which Bradford has been guilty, in view of the volume of grease contained in the effluents, is ever to have permitted these wastes to pass into the drains and sewers. They should have been collected and treated as a separate entity. But, as this would have entailed combination of the interests concerned, an admittedly difficult undertaking under voluntary conditions, the city authorities decided to repair the sins of omission upon the part of its industrial citizens and to assume the recovery of the valuable materials which were being allowed to escape.
This manifestation of commendable enterprise and initiative owes its origin mainly to the activity of Mr. Joseph Garfield, A.M.I.C.E., the sewage engineer. Many years ago the idea of turning the sewage of the city to industrial account occurred to him, and he embarked upon a prolonged series of exhaustive experiments. These were sufficiently conclusive and sufficiently promising of profit as to persuade the adoption of the methods he advocated at the critical moment, which arrived when the provision of a new sewage station became imperative.
The plant for dealing with the sludge was moved from the old situation to new buildings specially erected for the purpose at Esholt, and the raw material is fed to the latter station through a special main. The sludge contains only 80 per cent. of water, the free water having been previously removed by settling. It is fed into the main by compressed air. Upon its arrival at the station the sludge is lifted, also by compressed air, into large vats, where it is heated by the waste steam from the engines of the power plant. In this heated condition the sludge passes into close-sealed vessels from which, still at a temperature approaching boiling point, it is forced by compressed air through the filter presses. Each of these presses, of which there are about 100 disposed in rows, contains 47 chambers, each 3 feet square.
As already stated, the sewage of Bradford is heavily charged with grease resulting from wool-washing and other industries, and it is this heavy proportion of grease which renders the process so attractive. Moreover, by keeping the sludge in a heated condition during the pressing process the expression of the fatty content is more readily effected. From 40 to 48 hours are required to fill a press with residuum, that is to say this period of time must elapse before the whole of the available space within the press is occupied by the dry cake from which the grease has been expressed, by which time from four to five tons of sludge have been passed through. Each cake is 3 feet square by 1¹⁄₂ inches thick and weighs about 30 cwt. The grease and water which is driven out of the sludge is carried away from the presses into tanks. Here the water and grease are separated, the water to be re-discharged into the sewage, while the grease is led to the purification tanks. Subsequently the fat is either drawn off into barrels or is pumped into tank wagons for dispatch to the works where it is worked up into articles of commerce, including soap. The oil is found to yield three valuable products—olein, stearine, and pitch. The two last named enter extensively into the dressing of leather, as well as the manufacture of candles and as an insulator for electric cables, respectively.
The installation yields from 12 to 15 tons of grease throughout the twenty-four hours, working, of course, being continuous. This product in the days before the war commanded from £8 to £10—$40 to $50—per ton, but the price is now higher. The sludge-cakes find favour as a fertilizer, mainly from the fact that they are free from lime and carry only from 28 per cent. to 30 per cent. of moisture. This residue fetched from 3s.—75 cents—upwards per ton at the works in pre-war days, when a healthy export was recorded, the product being shipped in appreciable quantities to France and even to the Southern States of America. The output of cake averages from 50 to 60 tons per day. In addition to proving useful as a fertilizer it has been found to furnish, when blended with coal-dust, a serviceable fuel.
The revenue derived from this example of sewage industry is certainly such as to attract widespread attention. In the early days of the process, when only two presses were maintained to establish its possibilities, the grease sales reached £222 10s. 6d.—$1,112.62—per annum. In 1911 the annual revenue had risen to a figure ranging between £20,000 and £30,000—$100,000 and $150,000—from the enlarged battery of presses. When the new works were opened it was anticipated that the Corporation would be deriving £50,000—$250,000—a year from the sale of the products derived from its sewage upon the attainment of the designed maximum output. Up to the year 1911 the total sales amounted to no less than £100,000—$500,000. From the recital of these figures it must be conceded that Bradford has a very profitable commercial enterprise in its sewage works.
Yet even the foregoing figures are undoubtedly capable of improvement owing to the advances made in the whole issue of the recovery of fats from wastes. The pressing system, even when conducted along the most modern lines with up-to-date plant, leaves much to be desired in point of yield. Under the most favourable pressing conditions at least 10 per cent. of the original volume of grease is left in the residue. The presence of this grease reacts against the value of the residue as a fertilizer, grease being the bugbear of the farmer. With the latest process for grease extraction this content can be reduced down to 1 per cent. Not only does this represent an increased yield of 9 per cent. of fat with its attendant enhanced financial return, but it gives a fertilizer which, being exceedingly low in fat, appeals more strongly to the farmer, and accordingly is able to command a higher price. This fact appears to have become appreciated by the Bradford authorities according to recent developments.
Because such a striking success has been recorded at Bradford, it is not to say that the self-same method would be equally profitable at other places, especially those handling what might be termed purely domestic sewage. The conditions existing at the Yorkshire city are peculiar, owing to the wool-washing trade. The process which is more likely to make the widest appeal, being the one adapted to meet the average conditions, is that which has been installed in the borough of Oldham. This is the invention of Mr. J. Grossmann, M.A., Ph.D., F.I.C., the well-known chemical engineer, who has made the exploitation of sewage his life-long study. The plant in question was laid down in 1912, being set in operation in October of that year, since which date it has been working without a break, giving the most satisfactory results. At the time the installation was carried out the population of the borough was 148,840, and both the water-carriage and sanitary-pan system were in vogue, although the latter was giving way to the former method at the rate of about one thousand per year. As the conversion system was carried into effect the quantity of sludge which the sewage works were called upon to handle increased, the quantity pressed in 1911 being nearly 8,000 tons a year as compared with 4,000 tons in 1899. This did not include the several hundred tons which were dealt with in lagoons without pressing. As the quantities of pressed sludge increased so did the difficulty of disposing thereof.
The outlook was somewhat disconcerting. The agricultural land in the vicinity could only absorb a portion of the available volume. The necessity to incur the expense of carrying the residue a considerable distance to dispose of it, which solution would have proved somewhat costly, appeared to be inevitable. Experiments innumerable were carried out, but to no purpose. Agriculture, which is regarded as the obvious outlet for such material, was adverse to the proposal to absorb the accumulation for the land, because it carried approximately 15 per cent. of grease. The only escape from the dilemma appeared to be the installation of further presses with the attendant expense for auxiliaries to yield a dry material, and then to pay for the cartage of this residue to some convenient tipping ground or carriage of the settled sludge to sea to be dumped. As a round 30,000 tons of sludge would have been involved, the sea-dumping expedient would have been extremely costly. Further consideration of the question established the possibility of converting the material into a marketable manure, but this would have required the utilization of a trade process and also would have incurred expense.
At this juncture the attention of the Corporation was attracted to Dr. Grossmann’s process. It was investigated and submitted to searching experiments spread over a period of three years at the sewage works. From the results obtained and the experience gathered, it gave promise of being completely successful when conducted upon a large scale. So it was adopted.
The Grossmann process may be said to represent the most logical exploitation of sewage yet attempted in accordance with the severe hygienic conditions imposed to-day. Curiously enough, when the disposal of sewage by water-carriage was first introduced, the critics of the principle did not hesitate to point out that it represented the most wasteful solution of the problem which had ever been accepted for practice. But against these contentions the advocates of the idea urged that the hygienic advantages to be gained were so overwhelming that the question should not be considered from the commercial view-point at all.
Other days, other manners. In this instance, however, not many years passed before the issue attracted such widespread attention as to demand searching investigation, the difficulty and cost attending the disposal of the sludge being responsible for a pronounced outcry against the method. The sludge problem was thoroughly probed by a Royal Commission, by which the opinion was expressed that the value of this waste, calculated upon the volume of dry substance contained therein, was no more than 10s.—$2.50—per ton at the very outside. But as the sludge is produced in a form showing a high percentage of water it was hopeless to expect farmers to absorb it, owing to the transport charges involved for such a comparatively low manurial return, unless their land happened to be situate close to the centres of production. To overcome the water difficulty attempts were made to dry the sludge, in the effort to reduce its bulk, but it was discovered that drying did not constitute a complete sterilization process, with the result that the material was liable to carry infection. But the greatest objection to drying is that this very process, while it achieves one end—the transport difficulty—provokes another disability. The sewage is worth less after drying than in the saturated form.
The presence of fat in material quantities has always been responsible for agricultural hostility towards this waste as a fertilizer. The fat is due to soap used in the household, and which is thrown down the drains, as well as the grease resulting from other domestic operations. The great objection to grease is that it has the tendency to clog the soil.
In turn efforts were made to dispose of the nuisance as a fuel, the heavy proportion of oil present in the dried cake being the attractive feature prompting this application. This recommendation found scanty favour. Another brilliant mind conceived the idea of consuming the refuse in gas-producers, thus obtaining a low-grade gas for power purposes. This attempt failed to meet approbation. A third expedient was its conversion into an illuminating gas, but this likewise failed to overcome the obstacle. In so far as lighting is concerned, in many places the practice is followed of allowing the gas thrown off by the decomposing fæcal matter during its passage through the sewers, to be led to the burners of adjacent street lamps to mix with the ordinary town gas and thus be consumed. But this is merely a safety precaution; it is not followed from economical motives. Now that electricity is widely displacing gas for street illumination, even this quasi-utilitarian system is meeting with defeat.
Under the Grossmann system, as practised at Oldham, the sludge is subjected to a complete scientific treatment. The process is continuous and automatic throughout. Moreover, the plant is designed and built upon the unit principle, which allows the standardization of parts and ability to meet any desired demand by merely acquiring a sufficient number of units to comply with the sewage resulting from a given population. Each unit is capable of dealing with sludge arising from the purely domestic sewage of 20,000 inhabitants. Thus a town of 100,000 inhabitants would require 5 units, a city of one million souls 50 units, and so on in arithmetical progression. Furthermore, any number of units can be worked together, so that in those centres where the population fluctuates according to season or other conditions, a certain number of units can be shut down during the off period.
The sludge passes to a special tank and is permitted to settle down to approximately 20 per cent. solid matter. It is then scooped up by bucket elevators to be lifted and discharged into another tank at the top of the building. This acts as the storage tank or hopper, whence it is moved automatically by means of screw conveyors and distributed among six hoppers. Each of these hoppers feeds a drying machine. The driers, set out in pairs with their brickwork casings and flues, occupy the upper room. The machines themselves comprise iron cylinders set in the brickwork and coal-fired furnaces. They are fitted with a specially designed gearing and pulley mechanism which gradually moves the crude wet sludge from the inlet towards the opposite end or outlet. Being exposed to heat during this passage the sludge is naturally deprived of the water it contains, this being evaporated to be led to the furnace where any offensive gases and other matter associated therewith in suspension are consumed before passing to the chimney to escape into the outer air. By the time the sludge reaches the outlet it has been completely dried.
The arrangement of the feed from the hopper to the drier is such that only a measured quantity of sludge can be passed through in a given time, which ensures the condition of the sludge at the outlet being uniform. The provision of a similar measuring system at the outlet of the drier ensures only a measured quantity of sludge being discharged at that point. It will be observed that these protective devices guard against forcing the apparatus to the detriment of the delivered sludge which emerges from the drier in the form of a dry powder.
If desired this residue may be burned. Mixed with coke it forms an excellent fuel, and can be employed towards raising the requisite steam to conduct the treatment of further sewage. But, in view of the fact that this powder contains about 15 per cent. of fat, its disposal as a fuel would constitute about the most wasteful conceivable. Accordingly, the next stage is the extraction of the fatty content. As it comes from the drying apparatus the sludge is passed automatically into a distilling retort which is bricked-in and heated. Above this retort is a tank containing acid, a certain quantity of which is passed into the retort to be automatically mixed with the powdered sludge. Simultaneously superheated steam is driven through the mass in such a manner as to permeate the whole. The interior of the retort is fitted with gearing and pulleys similar to those provided to the drier and for a similar purpose—the steady gradual movement of the sludge from one end to the other. By the time it has reached the outlet from the machine the sludge, completely deprived of fat, is automatically discharged as a valuable manure and is ready for distribution upon the land.
The superheated steam charged with the grease is passed into a condenser, where water from a feed tank condenses the water and throws down the grease. The mixture of condensed steam and grease is passed into a recovery tank. The grease settling out on the top is removed for boiling up in a separate vessel, upon the completion of which treatment it is ready for packing and sale. The fatty matter consists largely of stearine and palmitine, which to-day meet with a prompt sale at lucrative prices.
But it is the solid residue in the dry powdered form which attracts the greatest measure of attention. Disposal of the grease from sewage has never occasioned so much difficulty as the utilization of the ultimate residue from reasons already explained. In this particular instance the great problem has been solved. The manure is in the form of a fine powder, containing nitrogen, phosphoric acid, and potash, as well as about 40 per cent. of organic material. It is very fine, brownish in colour, odourless, and what is more to the point, absolutely innocuous, having been completely sterilized. Consequently there is no risk of infection being disseminated by its use.
The circumstance that the process is absolutely automatic from the time the sludge is charged into the hopper to the finished article issuing from the distilling retort, is a distinct recommendation. Not only does it conduce to extremely economical operation, but it reduces the necessity to bring human labour into one of the most offensive of industries, inasmuch as the atmosphere of such an establishment is scarcely fragrant, as may well be imagined, although familiarity breeds strange contempts. The only labour essential is that required for heating up the drying machines and retorts.
There is one overwhelming advantage incidental to this process which cannot fail to arouse attention. Pressing in any form is eliminated. This not only signifies a very pronounced saving in capital expenditure in the first instance, but contributes to lower working charges, while there is an enhanced recovery of grease and an absolutely grease-free residue.
Before the Corporation of Oldham decided to install this system upon a practical scale searching experiments were conducted with the resultant manure, to determine its plant-feeding value. It was the promise of being able to find such a ready market for the ultimate residue which constituted one of the attractions of the process. Experiments were conducted at several farms with various produce, and these proved that the manure gives remarkably good results and is more effective than any other plant-feeder containing the same proportion of nitrogen, potash, and phosphates. Finally it contains an ingredient which is absolutely missing from every chemical fertilizer. The latter is certainly a plant food, but it is imperative that the ground should be treated with a certain quantity of organic matter to assure the physical and mechanical working of the soil. Decaying organic matter fulfils this end admirably, as one would suppose, being a natural process, but during the past five years the bestowal of sufficient quantities of necessary humus has been impossible, owing to the shortage in supplies of farmyard manure.
For this reason every farmer regards a grease-free manure carrying substance of a humus-like nature for the improvement of his soil with a particularly friendly eye, and he is prepared to pay a good price for such an article. The sewage sludge fertilizer prepared under the Grossmann process offers the agriculturist just what he desires in this connection, inasmuch as it carries about 30 per cent. of the humus-like substance. Then, again, the active manurial ingredients are distributed over the mass in such a fine state of division as cannot possibly be attained by resort to mechanical grinding. Finally, it is excellently balanced, and the farmer keenly appreciates a well-balanced fertilizer. Here he gets it because the essential operation has been conducted by Nature, whose process cannot be rivalled. Applied to gardens this manure is found to prevent the growth of yellow leaves, while the green of the foliage is particularly rich and dark. In some quarters there has been a certain degree of hesitation to utilize the fertilizer merely because it is derived from sewage, owing to the prevalence of many fallacious notions. Its origin is regarded with revulsion, and its utilization with a certain degree of dread, but there need be no apprehensions whatever concerning its use. The fact that in the course of the treatment the material is raised to a temperature approaching 600 degrees Fahrenheit—where the superheated steam comes into contact with the waste to expel the fat—effectively disposes of all germ life inimical to the health of both animals and human beings, while it is also clean to handle and odourless, it being impossible, from mere cursory examination of the fertilizer, for the lay mind to determine its origin. Finally, it may be stored for any length of time without creating a nuisance, or deteriorating.
The whole of the output from the Oldham sewage works, which, owing to the process of concentration, is really limited, notwithstanding the volume of crude sewage handled, is readily absorbed by farmers. Disposal was entrusted to a firm to act as the selling agents for the Corporation. Owing to the number of repeat orders received, year after year, this house declares that it could easily place 20,000 tons of the fertilizer, were it forthcoming, without increasing its present staff of travellers.
While the outbreak of hostilities militated against the expansion of the process, although many other Corporations have expressed their readiness to introduce the process into their respective sewage works, the past five years have not been allowed to represent dead time. Improvement upon improvement has been incorporated with the object of securing still higher efficiency. In this direction the inventor has made many distinct progressive strides. The one objection levied against the process was the heavy expense incurred in regard to fuel charges for drying the sludge, and these costs naturally have become accentuated by the 200 to 300 per cent. rise in the price of coal. But in this direction it is now possible to record noticeable reductions.
As a result of experiment the inventor has evolved a new method for settling the sludge. He found that, by adding a very slight amount of sulphuric acid—about 1 part to 1,000—to the sludge coming from the settling tanks, the usual settling process is completely reversed. Instead of the sludge settling to the bottom, the addition of the acid causes it to rise to the surface, and in a much more concentrated form. The water settles to the bottom in a clearer condition and can be drawn off. By further settling and draining this top layer—virtually a thick scum—a sludge can be obtained carrying about 30 per cent. solid matter, and therefore as a less volume of water needs to be evaporated a considerable saving in the consumption of fuel and cost of drying is achieved.
Moreover, it is suggested that in laying down new installations, it will be possible and profitable to install a destructor upon the sewage works. In such cases it would be feasible to draw upon the waste heat from the destructor to conduct the drying and other operations demanding the application of heat. In combining the destructor with the sewage plant the question of transport of the refuse from the collecting ground to the destructor would demand very careful consideration when horse haulage is employed, but with mechanical traction the question of an extra mile or two in distance hauled is not of such moment, especially as it would be off-set by the saving of fuel which would attend the diversion of the waste heat to this useful application. In fact, in cases where new lay-outs are being contemplated it is a matter for serious reflection as to whether it would not be found profitable to centralize destructor, electric generating station and Grossmann sewage treatment plant in one centralized spot, interlocking them together, and taking full advantage of such inter-connection. The destructor would furnish the necessary steam from the combustion of cinders and other refuse which it does not pay at present to exploit, or preferably other low-grade fuel to drive the electric plant, the waste steam being carried to the sewage works for the drying and other machines together with the desired proportion of live steam, while the electric station would furnish the requisite power for operating the automatic mechanical appliances.
The grease recovered from the sewage, which is of a domestic character, is essentially that from soap, cooking and washing operations. It is totally free from all objectionable smell. It can be purified very easily and is of distinct value. In its crude condition the fat contains about 70 per cent. of stearic acid.
During the past few years the dry powdered residue has not only been utilized in a direct form, but has also been exploited in the production of compounded fertilizers. Mixed with phosphates, sulphate of ammonia, and other nitrogenous products it has yielded a manure which has given most excellent results in farming. Considerable improvements with regard to greater efficiency and cheaper production have been made in the manufacture of compounded fertilizers from this residue, and there is every indication that still greater developments are possible in this direction.
Were all the sewage of this country treated along these lines British agriculture would derive distinct benefit, while industry would also be presented with a new source of supply of essential raw material. It would go a long way to enable us to use our greases over and over again, because the drain is the most popular avenue for the escape of this material. Sewage represents the greatest waste incidental to this country. Dr. Grossmann estimates its value at approximately £22,000,000—$110,000,000—per annum, of which but only an infinitesimal fraction is at present recovered. The value of the fat alone thrown down our drains, and reclaimed in a marketable form would realize from £500,000 to £1,000,000—$2,500,000 to $5,000,000—a year. The value of the manurial product, of which at least 1,000,000 tons are recoverable during the twelve months, may be set down at least at £2,000,000—$10,000,000—the contents thereof being equivalent to 50,000 tons of phosphates, 50,000 tons of potash salts, with nitrogen equal to that forthcoming from 100,000 tons of sulphate of ammonia. This manure would suffice for the fertilization of at least 3,000,000 acres of land from which we might safely anticipate gathering, at a modest estimate, additional crops worth £5,000,000—$25,000,000.
There is one other fact which deserves mention. Sewage is eminently adapted to the feeding of sandy soils and other land which, at the moment, is considered too poor for agricultural purposes. If this manure were reserved for such land many thousand additional acres might be brought under cultivation in these islands. At the present moment these acres are being allowed to run to seed, constituting what we erroneously term waste land, but only waste because we are not sufficiently enterprising and energetic to reclaim it.
From the point of view of the towns and cities called upon to handle the sewage, the Grossmann process holds out many inducements. It complies with the demands of sanitation because it precipitates no nuisance. It is the most hygienic process yet evolved for the disposal of sewage sludge. The revenue derived from the sale of the by-products—manure and grease—is such as to render the operation of the plant not only self-supporting but money-making. As a rule the sewage works of the average town represent a sink in more senses than one, more especially when it becomes incumbent to resort to the tipping, dumping or other disposal of the enormous accumulations of the sludge. But signs of awakening are apparent. The Oldham plant has been investigated by Corporations and other authorities, not only of this country but from other parts of the world, who have been satisfied as to its commercial practicability. With the restoration of normal trading conditions it is anticipated that the process will become more extensively adopted, especially as during the past five years ceaseless effort has been devoted to the perfection of details to assure the establishment of the process upon a firm commercial basis.