Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 206

_Hill's process._ Lime and tar are the precipitants. The effluent water is filtered through charcoal. The question now arises as to whether the sewer water after treatment with any of the above substances is in a fit condition to be poured into a stream or river. The Rivers Pollution Commissioners in their first and second reports give a number of a.n.a.lyses, from which it appears that on an average the chemical treatment removes 898 per cent. of the matters suspended in the sewage waters, but only 366 per cent. of the organic nitrogen is dissolved in them.

Of the A. B. C. process, Mr Crookes states that, when properly carried out, it removes all the phosphoric acid; and Professor Voelcker's a.n.a.lysis of the effluent water from sewage treated by the acid phosphate of alumina process gives more ammonia than the original sewer water, less organic nitrogen by one half, and less phosphoric acid. Such a water is said by some authorities to be pure enough to be discharged into streams.

_General Scott's process._ General Scott proposes to treat the sewer water with lime and clay, and instead of employing the precipitate obtained by this means as a manure, would, after burning it, use it as cement. He argues that the deposit contains so much combustible matter as to considerably reduce the quant.i.ty of coal usually expended in the manufacture of cement, and consequently the cement could be sold at a remunerative price.

This, like the 'carbonisation' process, possesses the merit of effectually destroying any noxious principles present in the deposit.

Commenting on the various precipitation processes Dr Parkes writes:--"When the sewer water is cleared by any of these plans is it fit to be discharged into streams? In the opinion of some authorities, if the precipitate is a good one it may be so, and it appears certain that in many cases it is chemically a tolerably pure water, and it will no longer silt up the bed nor cause a nuisance. But it still contains, in all cases, some organic matter, as well as ammonia, potash, and phosphoric acid. It has, therefore, fertilising powers certainly, and possibly it has also injurious powers. No proof of this has been given, but also no disproof at present, and when we consider how small the agencies of the specific diseases probably are, and how likely it is that they remain suspended, we do not seem to be in a position to expect that the water, after subsidence of the deposit, will be safe to drink.

(5) _By irrigation and filtration._ By this process is meant the pa.s.sing of the sewer water over and through soil, with the object not only of effecting its purification to such an extent as to render it fit to be discharged into a river or stream, but also of employing it as a valuable manure. In the present article we shall treat only of the application of the process to the first of these purposes.

There is ample evidence to show that, if carried out with due attention to detail, no process for the treatment of effluent sewage water, so as to render it innocuous, is equal to that which subjects it to irrigation and filtration.

The Rivers Pollution Commissioners thus report on it:--"We are, therefore, justified in recommending irrigation as a safe as well as profitable and efficient method of cleansing town sewage."

The conditions necessary for the successful carrying out of this system are thus stated by Mr T. J. d.y.k.e, in explaining "the process of the downward intermittent filtration of sewage at Troedyrhiw, near Merthyr Tydvil:"--"1. The soil of the land to be used must be porous. 2. A main effluent drain, which must not be less than six feet from the surface, must be provided. 3. The surface of the soil to be so inclined as to permit the sewage stream to flow over the whole land. 4. The filtering area should be divided into four equal parts, each part to be irrigated with the sewage for six hours, and then an interval of eighteen hours to elapse before a second irrigation takes place; each of the four parts would thus be used for six hours out of the twenty-four. An acre of land so prepared would purify 100,000 gallons of sewage per day." At Troedyrhiw the sewage has lime added to it, and the mixture is strained through cinders into tanks. From the tank it flows on to the conduit, by which it is conveyed to the filtering areas.

"These consist of about twenty acres of land, immediately adjoining the road on which the tanks are placed, and have been arranged into filtering areas or beds on a plan devised by Mr J. Bayley Denton. The land is a loamy soil, eighteen inches thick, overlying a bed of gravel. The whole of these twenty acres have been underdrained to a depth of from five to seven feet. The lateral drains are placed at regular distances from each other, and run towards the main or effluent drain. This is everywhere six feet deep. The surface of the land is formed into beds; these have been made to slope towards the main drain by a fall of 1 in 150.

"The surface is ploughed in ridges; on these vegetables are planted or seeds sown. The line of the ridged furrow is in the direction of the under drain. Along the raised margin of each bed, in each area, delivering carriers are placed, one edge being slightly depressed.

"The strained sewage pa.s.ses from the conduits into the delivery carriers, and as it overflows the depressed edges runs gently into and along the farrows down to the lowest and most distant part of the plot. The sewage continues to be so delivered for six hours, then an interval of rest of eighteen hours takes place, and again the land is thoroughly charged with the fertilising stream. The water percolates through the six feet of earth, and reaches the lateral drains, which convey it to the main effluent drain.

"The result of this plan of disposing of sewage by downward intermittent filtration, may be seen in samples of the effluent water taken from the outlet of the main drain. Such water is bright, perfectly pellucid, free from smell, and tastes only of common salt. It may be safely drunk--in fact, is used by the workmen employed on the farm. During the process of irrigation no nuisance is caused, for the soil quickly absorbs all the fluids pa.s.sed on to it; in fact, in two or three hours after the water has ceased to flow on the land, an observer would say that the ground had not been wetted for days. The workmen say that no unpleasant smell is noticed, nor has the health of the persons employed, in any one instance, been affected by any presumed poisonous exhalation.

"The only imperfection of the plan is that, at the end of the furrows nearest the lowest corner of a plot, a slight deposit of sc.u.m is formed.

This sc.u.m is formed by the fine insoluble precipitate caused mainly by the addition of lime to the sewage stream."

The table below, taken from the report of the Rivers Pollution Commissioners, gives the composition of the effluent water after it has pa.s.sed through the soil.

If those results be compared with the condition of the supernatant sewage water, after treatment by any of the chemical precipitants already enumerated, the inferiority of these latter as methods of removal of the organic impurity of the sewage water will be evident.

The best of these precipitants give a removal of only 658 per cent. of organic nitrogen, whilst the A. B. C. process shows a diminution of 589 only. It appears from the first and second reports of the Rivers Pollution Commissioners, that on an average the precipitation processes remove 898 per cent. of the suspended matters, but only 366 per cent. of the organic nitrogen dissolved in the liquid.

The effects of a soil upon sewage water pa.s.sing through it are the following:--

1. The filtering property of the soil mechanically arrests and retains the suspended particles of the sewage.

2 and 3. The porosity and physical attraction of the soil lead to the oxidation of the organic matter contained in the sewage, as instanced in the discovery of nitrates and nitrites in the effluent water, which did not exist previous to filtration.

4. A chemical reaction takes place between the const.i.tuents of the sewage and those of the soil.

If the charges brought against the system of irrigation, viz. that it is detrimental to the health and comfort of those who reside near sewage farms cannot be denied, it seems pretty certain that, in most cases, any ill effects arising from the method may be traced to its defective management. The selection of the soil which is to receive the sewage is a highly important consideration. The best for this purpose seems to be a loose marl, containing oxide of iron and alumina; but sand, as well as chalk, are both said to answer excellently.

+-------------------------------------------+-----------------------+----------+ Percentage of dissolved Percentage Organic Pollution suspended removed. Organic Results of irrigation, in part per 100,000.+----------+------------+Pollution Organic Organic removed Carbon. Nitrogen. +-------------------------------------------+----------+------------+----------+ On fallow land at Chorley (adhesive loam) 623 702 100 At Edinburgh (both sand and clay) 453 811 849 Barking (gravelly soil) 658 862 100 Aldershot (light sand)-- Best result 918 873 997 Worst result 699 829 877 Average result 809 851 937 Carlisle (light loam) 779 598 100 Penrith (light loam) 750 772 100 Rugby (adhesive soil) 723 929 960 Banbury (princ.i.p.ally clay)-- Best result 878 913 960 Worst result 641 801 903 Average result 76 857 932 Warwick (stiff clay) 717 896 100 Worthing (loam) 427 853 100 Bedford (light gravelly soil), average result 716 813 100 Norwood (clay), average result 650 751 100 Croydon (gravelly soil)-- Best result 732 932 100 Worst result 616 904 100 Average result 674 918 100 +-------------------------------------------+----------+------------+----------+

If the soil be of a stiff clayey nature it must be broken up and mixed with sand, lime, or ashes. The upper parts must be comminuted and rendered porous, and it must be efficiently and deeply drained. At Troedyrhiw, as we have seen, the effluent drain is six feet deep.

The sewer water should be poured over the land in as fresh a condition as possible, having been previously deprived of any solid or grosser parts by straining. At Carlisle, decomposition of the sewage during its flow is prevented by adding carbolic acid to it. Lastly, it is of the utmost consequence that the amount of land used as the filtering medium shall be large. Letheby has shown that where this precaution is neglected, not only is the purification of the sewage incomplete, but the plan becomes a public nuisance. The amount of filtering earth should not be less than one cubic yard for eight gallons of sewage in twenty-four hours, in properly prepared soils; in some soils more than a cubic yard is required.

The late Dr Parkes has given a summary of various reports that have from time to time been issued as to the effects of sewage farms upon the public health and comfort. He says:--"That sewage farms, if too near to houses, and if not carefully conducted, may give off disagreeable effluvia is certain; but it is also clear that in some farms this is very trifling, and that when the sewer water gets on the land it soon ceases. It is denied by some persons that more nuisance is excited than by any other mode of using manure. As regards health, it has been alleged that these farms may--1st, give off effluvia which may produce enteric fever or dysentery, or some allied affection; or, 2nd, and in the spread of entozoic diseases; or, 3rd, make ground swampy and marshy, and may also poison wells, and thus affect health."

The evidence of Edinburgh, Croydon, Aldershot, Rugby, Worthing, Romford, the Suss.e.x Lunatic Asylum, is very strong against any influence in the production of typhoid by sewage farms effluvia. On the other hand, Dr Clouston's record of the outbreak of dysentery in the c.u.mberland Asylum is counter evidence of weight, and so is one of the cases noted by Letheby of typhoid fever outbreak in Copley, when a meadow was irrigated with the brook water containing the sewage of Halifax.

The negative evidence is, however, so strong as to justify the view that the effluvia from a well-managed sewage farm do not produce typhoid fever, or dysentery, or any affection of the kind. In a case at Eton in which some cases of enteric fever were attributed to the effluvia, Dr Buchanan discovered that the sewer water had been drunk; this was more likely to have been the cause.

With regard to the second point, the spread of entozoic diseases by the carriage of the sewer water to the land, has been thought probable by Cobbold, though as solid excreta from towns have been for some years largely employed as manure, it is doubtful whether the liquid plans would be more dangerous. The special entozoic diseases which, it is feared, might thus arise, are tapeworms, round worms, trichina, Bilharzia, and distoma hepatic.u.m in sheep. Cobbold's latest observations show that the embryos of Bilharzia die so rapidly, that even were it introduced into England there would be little danger.

The trichina disease is only known at present to be produced in men by the worms in the flesh of pigs which is eaten, and it seems doubtful whether pigs receive them from the land. There remain, then, only tapeworms and round worms for men and distoma hepatic.u.m for sheep to be dreaded. With regard to these, the evidence at present is negative; and though much weight must be attached to any opinion of Cobbold's, this argument against sewage irrigation must be admitted to want evidence from experience.

The third criticism appears to be true.

The land may become swampy and the adjacent wells poisoned, and disease (ague, and perhaps diarrha and dysentery) be thus produced. But this is owing to mismanagement, and when a sewage farm is properly arranged it is not damp, and the wells do not suffer.[153]

[Footnote 153: 'Practical Hygiene.']

The foregoing processes for the removal of excreta from dwellings necessitates the joint employment of sewers and large quant.i.ties of water.

It may, however, sometimes happen that the adoption of either of these appliances may be not only difficult, but altogether impracticable; as for instance, in localities where a sufficient fall cannot be obtained for the sewers; or where the supply of water is not adequate; or when the severity of the climate at certain times is such, that for months in the year the water is frozen. Under these conditions the excreta must either be allowed to acc.u.mulate about houses, or else be removed by methods other than those we have described, at more or less short intervals. Of course their speedy removal is the best and safest; but in cases where they are permitted to acc.u.mulate, it is essential they should be mixed with deodorants, and confined in properly constructed receptacles (as far as possible from dwellings), from which category such pre-eminently unsanitary arrangements as cesspools and dead wells must be excluded.

When excreta are got rid of from houses by other means than those of sewers and water, the processes employed are termed,

2. DRY METHODS. These comprise--

1. Removal of the excreta without admixture.

2. Removal of the excreta after treatment with deodorising and anti-putrescent substances.

1. _Removal without admixture._ In some cases boxes and tanks receive the ordure and urine, and these are changed more or less frequently.

In Glasgow the excreta from a part of the city containing eighty thousand people is thus collected and removed without admixture,[154] daily.

[Footnote 154: Except that from the garbage of the houses.]

In Edinburgh there are also many closets supplied with movable metal pails, which are likewise removed daily. Many large dwelling-houses in this latter city are entirely without water-closet accommodation; hence the custom of placing pails full of excrement, urine, &c., outside the houses to be taken away by the scavenger. In Rochdale the excrement, &c., is collected in tubs, with tight-fitting lids, which are emptied twice or thrice a week. These tubs are manufactured out of disused paraffin casks.

In Leeds, also, the excreta are collected in boxes without being subjected to admixture. In some towns in the north of England the excreta fall into receptacles constructed upon what is termed the 'Goux' principle. In this system the pails or receptacles are lined with some absorbent lining, which abstracts the urine;[155] another contrivance is to have the receptacle fitted with a pipe or drain; the object in each case being to render the faeces drier and to delay their decomposition.

[Footnote 155: The refuse of cloth manufacturers is chiefly used for this purpose.]

The pail or tub system (Fosses Mobiles) which is employed in Belgium, has for its object the collection of the faeces in a state of purity, without admixture with water, in a clean and odourless condition.

The apparatus for carrying it out consists of--

1. _The seat._ This consists simply of a soil-pan of stoneware or _faence_, without woodwork, the soil-pan merely projecting from the top of the descent pipe. Its borders are furnished with a groove filled with water or sand, into which the raised rim of the lid fits.

2. _The connecting pipe._ This pipe is straight without a syphon, and joins the descent pipe at the very acute angle of 22, and is about 4 inches in diameter inside. It is, like the next, made of stoneware, glazed inside.

3. _Descent pipe._ This is from 6 to 8 inches in internal diameter; it is vertical, and is composed of a series of pipes, connected with each other by dry sand joints, without cements, fixed to the wall by iron bands.

It rests at the ground-floor level on a strong flagstone. Its prolongation through and below this stone consists of a sliding pipe of wrought copper capable of being lengthened or shortened, and solidly fixed to the stone by a cast-iron connector. A sort of circular shallow dish (_ecuelle_), which can be hung under this last part of the descent pipe, serves at a given moment to shut its lower orifice.