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of working since April 15th was 10 hours per diem. The total quantity pumped has been
1,182 Effluent Water discharged.-Owing to floods at the outlets of the pipes, the quantities of effluent water discharged could not always be gauged. On the 313 days during which the observations could be taken,
39,449,178 gallons=176,112 tons were discharged, being
115,012 gallons=5131 tons per day. Assuming this to be the average quantity for the whole period, the total quantity intercepted from the lower subsoil and discharged through the pipes would be
45,889,788 gallons=204,805 tous, or 47.3 per cent. of the sewage pumped.
Rainfall.-The rainfall at Breton's during the total period of 399 days has been 22:64 inches, or on 1213 acres about 624 million gallons, equal to 277,900 tons, or 2287 tons per acre.
Temperatures.-It will be seen that the temperatures of sewage and effluent water have been very uniform as compared with that of the air, being lower during extreme heat and higher during extreme cold. This was very noticeable during the severe frost of last winter. In one week, when the mean noon-day temperature of the air was 289.5, that of the sewage received, sewage pumped, and effluent water was 43°. The ranges of variation over the total period have been :Atmosphere
28.5 to 76
24 Emuent water
41 64 23 A remarkable feature in the record of temperatures is the extremely slow rate at which the temperature of the effluent water fell
, and the length of time which elapsed before it recovered again. The first week that the average temperature at noon fell below the freezing-point was the one ending 31st December, when the average temperature of the air was 280.5 F., and that of the effluent water was 43°; and after this, although the former rose, the latter fell, so that in the week ending February 4th the average temperature of the air was 36°, and that of the eflluent water 41°. The next week the temperature of the air was 44”, the second weck 47°, and the third week 47°, yet it was not until the third week that the temperature of the efluent water recovered to 43o.
Section III.—(a) Observations on the Sewage-Farın at Tunbriilge Wells.
Before describing the results of the investigation by the Committee, it is desirable to state that, in the selection of the land to be irrigated at Tunbridge Wells, it has been a sine qua non condition that it should be at such a level that the sewage should reach it by gravitation; and to this end two farms
have been laid out, one to the north and the other to the south of the town, and an outfall sewer made to each.
Underdrainage has not been uniformly adopted on both farms; but where it previously existed, a peculiar arrangement has been made for the reapplication of the drainage-water.
The distribution of the sewage is chiefly effected by what is known as the catchwater system, which is necessarily, under ordinary conditions, accompanied by an overflow, in preference to its application in smaller quantities, sufficient to satisfy the demands of vegetation and to wet the land thoroughly without any overflow; while the absence of storage-reservoirs necessitates the continuous application of the sewage to some parts of the land by night as well as by day.
The population of Tanbridge Wells is 19,410.
The total quantity of sewage discharged is 1,000,000 gallons per 24 hours, of which about 400,000 gallons are supplied to the northern farm, and about 600,000 gallons to the southern one.
The northern sewage is applied to 123 acres of land, which have cost £21,000, and the southern to 167 acres, which have cost £27,000.
To deliver the sewage from the two main outlets of the town to the land, culverts or conduits, with precipitating-tanks for the separation of the larger portions of the solid matter from the liquid, have been constructed in a very substantial manner. The delivering-conduits on the north, extending for a length of two miles with the precipitating-tanks, have cost £258713s. 1d., while those on the south (of which the length is three miles) have cost £5809 178. 8d. The tanks on the north farm have cost £833 38. 9d., those on the south £1188 5s. 1d.
Thus the total cost of external delivering works amounts to £10,418 19s. 70., which, added to the cost of the land, will be £58,418 19s.7d., or £201 8s. 11d. per acre.
The solid matter collected in the tanks is removed from time to time, and used on the farms as additional manure. The tanks are not covered ; and there is consequently a strong smell in their proximity, which is not discoverable in any other part of the farms.
The sewage having been delivered on to the land, is conveyed from one part to another by open main carriers and iron pipes, the former following contourlines, and the latter partaking of the nature of inverted siphons in order to cross existing valleys or hollows. The cost of these internal works per acre has beenFor Carriers.
£18 13 0 Drain ..
3 12 0 Iron pipes
4 6 0 Grubbing and trenching 3 16 0 Roads...
6 7 6 Wire fence..
Or in all
£38 0 O per acre. Or a total of.
. £239 8 11 per acre. The soil of nearly the whole of the northern farm is of a stiff clayey character, manifestly requiring underdrainage. It had for the most part been drained by the late owners before the Commissioners of Tunbridge Wells purchased it; but owing to the work being done as ordinary farm-drainage
independently of surface preparation, it was soon found that the sewage descended to the drains so rapidly as to prevent its profitable distribution on the surface. It was stated to the Committee that when this effect was discovered it was determined that the drains should be stopped by digging down to them and plugging them, the result of which then was to keep the soil in a state of saturation, and to allow the unpurified sewage to pass over the surface into the stream. The engineer employed by the Commissioners has since superseded this state of things by adopting the special mode of treatment referred to, which consists of intercepting the existing drains at the depths at which they were originally laid, and bringing the underdrainage water to the surface by outlet drains discharging into lower carriers for redistribution.
At the time of the inspection by the Committee the lowest carriers were receiving effluent liquid of an impure character from the surface, at the same time that the underdrainage water was being discharged into them in the way described.
T'he land of the southern farm is not generally of so heavy a description as that of the northern, though portions of it contain clay. Other parts are peaty, and are naturally very poor. Wherever the engineer has considered it necessary to drain the subsoil, this has been effected in a manner similar to that adopted on the northern farm.
The striking features in the case of Tunbridge Wells are :
1. Instead of concentrating the sewage at one farm under one management, it has been divided, in accordance with the watersheds, into two parts, involving two separate systems of works and management.
2. The main conduits and carriers are more than ordinarily substantial, and are therefore expensively constructed; and, following contour-lines on the surface, have a tortuous course, and so must interfere with approved cultivation.
3. The character of the underdrainage, being designed for the redelivery of the sewage on to a lower surface by drains gradually getting nearer and nearer to it, must necessarily prevent alike a frequent and deep working of the surface-soil.
4. The sewage being run over the surface of the land on the catchwater system (by night as well as day), with the intention of reapplying the overflow, its distribution is necessarily unequal both in quantity and quality, the first land sewaged receiving more than it requires, while the last must suffer from a deficiency unless there is a positive waste of sewage, as the analyses really show that there is.
These several features illustrate the advantage of combining with the services of the civil engineer and the chemist those of the practical agriculturist when laying out a sewage-farm. If they were not pointed out by the Committee thus early in the progress of sewage-irrigation, they might be a source of disappointment and surprise to those who contemplate the utilization of the sewage of their own towns by this the most profitable mode of treatment at present known, when properly conducted. While saying this, it is desirable to point out the superior character of the works carried out at Tunbridge Wells, and at the same time to express approval of the enterprising manner in which they have been undertaken by the Local Authority.
Remarks on the Analyses of the Sewage and Effluent Water from the
Irrigation Farms at Tunbridge Wells. North Farm.-In 100,000 parts. Samples taken in the proportion of doo
part of the flow per minute, by a measure graduated to joo of a gallon.
Sewage from main
sewer, collected July 4th & 5th, 1871
(average temp. 580.5 F). Emuent water taken from 7 drains of Italian Rye-grass, and mixed 4th and 5th July (average temp. 57° F).... Water from stream above the effluent drains on 6th July. (No sewage water had en. tered the stream for two days above the point where the samples were taken; average temp. 62° F).....
(Total nitrogen in efiluent water 1.99.) The sewage from the main, while containing a comparatively small amount of total solid matter in solution, contains a very large proportion of si actual”•ammonia, and also of “ albuminoid” ammonia, when both the suspended and dissolved matters are taken into account; it is a rich sewage whether the proportion of nitrogenous matters to the total solids or to the bulk of the sewage itself be considered. The chlorine is in fair average amount.
The analysis of the average efluent water shows that while the total solids are diminished in amount, the diminution is due to the retention by the soil and vegetation of the more volatile constituents, as the weight of ash left after ignition of the solid matters was greater in the case of the effluent water than in that of the sewage. This may be due to (1) concentration by the evaporation which takes place from the sewage of the soil and from the plants, or (2) to solution of salts already in the soil : that the latter cause is more probably the true one, we see from the diminished amount of chlorine, which, although it may not necessarily indicate dilution with ordinary subsoil water to a great extent, still would certainly not lead us to conclude that any concentration had taken place. That dilution with underdrainage water actually does take place has been already pointed out.
The amount of ammonia in the effluent water is too high, amounting to more than one seventh of that in the same volume of sewage, while albuminoid ammonia still remains to the extent of one fifth of the original amount; and the almost total absence of nitrates and nitrites in the effluent water shows the want of conditions favourable to oxidation; so that the purification of the sewage here, although considerable, is not so satisfactory as could be wished, or as might be effected by making filtration through the soil an essential feature in the process.
South Farm.-In 100,000 parts. Samples taken in the proportion of doo
part of the flow per minute, by a measure graduated to fio of a gallon.
The results attained on the southern farm are, as shown by the above analyses, very unsatisfactory, and at the same time very reliable, as the slight diminution of the chlorine in the effluent water would lead us to believe that the loss of water due to evaporation had been about balanced by the influx of underdrainage water, so that no great amount, at any rate, of concentration had taken place.
We notice at once the large amount of “ actual” and of “ albuminoid" ammonia which escapes unoxidized in the effluent water. No less than four ninths of the “ actual ” ammonia and more than one third of the “albuminoid” ammonia, in the same volume of sewage, escapes in the effluent water, while the amount of nitrates and nitrites is very small; the effluent water is very impure indeed.
The analyses show distinctly that at these two farms, as at present man