into a large precipitating tank of 130,000 gallons, of which there are three at Acton, side by side. Subsidence of solids during three or four hours' rest takes place, and then the top liquid is run off from the surface, by means of a floating arm, to the filter-bed, formed of gravel at bottom, polarite filtrant next, and sand on top in layers. After passing through this filter-bed the effluent is bright, clear, and inodorous. The only cleansing of the Acton filter-beds found necessary after twenty months' use was the replacement of two inches of surface sand. The sludge is not deprived of the valuable ammonia of the manure, because no lime is used in the process. The polarite in the filter takes the place of the land required for other systems of filtration. A few hours' rest effects complete chemical revival of the polarite. These filter-beds are said to filter sewage effluents effectively, at the rate of a thousand gallons per square yard per twenty-four hours, with better results than can be obtained by land filtration at the rate of one and a half gallon per twenty-four hours, or, in other 112 DOMESTIC SANITARY DRAINAGE AND PLUMBING. words, it is stated that one acre of polarite and sand filter in equal proportions will do better work than 666 acres of land. The importance of this system of sewage purification has been urged upon the writer strongly by an official engineer, who was sent officially to inspect the process, and had no interest whatever in the system above any other with which he was instructed to make comparison.<Callout type="important" title="Efficiency Comparison">One acre of polarite and sand filter can handle more sewage than 666 acres of land.</Callout>
The treatment of sewage by the iron process has the special characteristic of l)eing applicable to the dwelling- house drain, or to any portion of a system of drainage, including cesspools. It is stated that nothing unpleasant attends the clearing out of cesspits where this process is used, and that the bulk of their contents is materially reduced by the action of the iron. Sulphate of iron is the chemical adopted, and it is applied in an instrument called the ferrometer, patented in England. This instrument has a glass dissolving tube, in which the chemical is placed and its action observed. The chemical is caused to dissolve in proportion to the number of persons using the drains, and the solution is allowed to mingle drop by drop with the drainage, which it reduces to a black, inodorous, charcoal- like deposit.<Callout type="tip" title="Sulphate of Iron Usage">Apply sulphate of iron through a ferrometer for effective sewage treatment.</Callout>
The treatment of sewage by intermittent downward filtration has been adopted by numerous towns. Merthyr Tydfil, Kendal, Oakham, Dewsbury, Withington, Hitchin, Croydon, are typical examples of successful sewage disposal by this method. It consists in the alternate transmission of sewage and air through a porous soil. The sewage, when discharged at intervals over the suitable soil, fills the pores with the foul liquid in broken-up, attenuated threads, easily and rapidly attacked by the action of the oxy- genated sand or earth, and the sewage, in passing, draws after it streams of air through the pores of the soil, whose oxygen attacks and purifies all that it comes in contact with. By this process, in numerous experiments, the whole of the suspended matters in the sewage was removed ; and in proportion to the rapidity or slowness of the filtration, and depending also on the porous quality of the soil, a percen- tage varying from eighty-four to ninety per cent, of the putrescible matters in solution w«is removed by the same process at the same time.<Callout type="important" title="Air Filtration">Alternate sewage and air transmission through porous soil effectively purifies sewage.</Callout>
Other instances of the success of intermittent filtration may be found at Kendal, where sixteen acres of land are found amply sufficient for thirteen thousand persons, at a cost of l^d. in the pound on the valuation of the town. At Oakham, in Eutlandshire, with three thousand persons, the sewage is thoroughly purified on three acres of irrigated filtering ground. The crops are made even to yield a profitable return.<Callout type="gear" title="Land Availability">Intermittent filtration requires less land than irrigation but still needs significant space.</Callout>
The purification ef sewage in this process is essentially that of chemical action by oxygen, the organic impurities being changed into carbonic acid, water, and nitric acid. The special practical point to be observed in the management of the work is that a constant supply of air be secured, giving abundant intermittent aeration to the filtering porous soil. So long, and only so long, as nitrates are freely formed by the action of the air on the sewage can effective purifica- tion occur.<Callout type="risk" title="Air Supply">Ensure continuous air supply for optimal filtration.</Callout>
At Birmingham, which has one of the best-arranged irrigation systems in England, the sewage, about sixteen million gallons a day, is first treated with lime, to neutralise the acids, and passed through tanks, where the grosser impurities are deposited ; thence it is conveyed by one main channel, and distributed over the land as required for irrigation. The deposited sludge is pumped into channels, and flows to a certain portion of the farm, where, when it dries, after lying a few days, it is trenched into the land, and crops are grown upon it. About forty acres are devoted to sludge treatment each year.<Callout type="important" title="Irrigation System">Lime treatment followed by irrigation ensures high purity effluent.</Callout>
More than two hundred English towns have adopted these effective systems. The following standard was recommended by the Eivers Pollution Commissioners for adoption, to determine im- purity in waters discharged into streams and rivers: — Any liquid containing in suspension more than three parts by weight of mineral matter or one part by weight of dry organic matter in one hundred thousand parts by weight of the liquid. Any liquid containing in solution more than two parts by weight of organic carbon or 0*3 parts by weight of organic nitrogen in one hundred thousand parts by weight.<Callout type="warning" title="Pollution Standards">Adhere to strict pollution standards for safe effluent discharge.</Callout>
It will be observed that in these deductions no reference is made to the ferrozone and polarite process, as that system had not been well before the public at the date the Congress was held. The midden system, dry earth-closet system, and pail system of disposal, adopted for some towns, give constant daily trouble, create nuisances during removal, and, after all, leave the surface waters of the streets and the slop waters of houses to be dealt with by some system of drainage SEWAGE DISPOSAL. 119 and sewerage, and these waters are found quite as unsuit- able for discharge into rivers as is the drainage of water- closeted towns.<Callout type="warning" title="Alternative Systems">Avoid midden, dry earth-closet, or pail systems due to daily troubles.</Callout>
The Rivers Pollution Commissioners examined and analysed the sewage of a large number of towns arranged on the midden system for excluding solid excreta from the sewers, and also the sewage of a large number of water- closeted towns where all drainage passed into the sewers, with the result as follows in parts per 100,000 : — Average of midden towns Average of water- closeted towns . ToUl SoUdH in Solution. 82-4 72-2 Oi^gan'c carbon. 4-181 4*696 Organic Nitro. gen. Am- monia. 1-976 6-435 2-206 I 6-703 ToUl com- binod Nitro- gen. Ch'o- rine. 6-461 7-728 11-54 10-66 Sus- pended Matti^rs. 39-11 44-69 The Commissioners state that, as a result of their re- searches, it seems hopeless to anticipate any substantial reduction of sewage pollution by dealing with solid ex- crementitious matter only.<Callout type="risk" title="Solid Excreta Treatment">Dealing solely with solid excreta is insufficient for reducing sewage pollution.</Callout>
Since the appearance of the first edition of this work very considerable advance has been made in methods of sewage disposal Scientific accounts of the modern discoveries of developments in the biological processes of treating sewage by the direct action of the bacteria living and growing therein reads more like a fairy tale than a sober statement of facts. It appears that the real business of the sewage microbe on coming into existence on suitable soil is to break up the atoms of sewage, live and thrive upon them, to be in turn consumed by the neighbouring microbes; it may be some consolation to us, who cannot be expected to give our approval to cannibalism, to learn that these microbes, once supposed to be living animals, are now believed to be living plants. It is not easy to convey any idea of 120 DOMESTIC SANITARY DRAINAGE AND PLUMBING. their extreme minuteness, varying as they do in their dimensions from one 5,000 parts of an inch to one 25,000 parts. Pearmain and Moore, in their book on Applied Bacteriology y try to convey some notion of this to our minds by telling us that if a man was magnified as much as is necessary to magnify a microbe in order to render it visible to human sight he would appear to be four miles high — higher than Mont Blanc. We are told that millions of microbes exist in one drop, and their rate of increase is so rapid that under favourable and unrestrained conditions one microbe would become 16,000,000 in one day! One microbe and its offshoots would weigh -^i^js of a grain in one day's growth, one pound in two days, and 7,366 tons in three days if there was no restraint. Fortunately nature has provided many checks to restrain this tremendous inherent vital activity, or the world itself would be quickly devoured.<Callout type="important" title="Microbial Breakdown">Bacteria effectively break down sewage under proper conditions.</Callout>
The bacteriological process of sewage disposal is now under practical trial in many places, and is doing good work with the London sewage at the Outfall Station, Barking Creek, and at Sutton, in Surrey, and from the results obtained promises to solve the difficult problem of sewage disposal and to sweep away all the old methods of costly mechanical and chemical treatment. The principle is applied in various forms which cannot here be compared or dwelt upon at length. Coke breeze, burnt clay, or similar porous material is arranged in a tank or bed, and when sewage is turned on to the sur- face the organic matters adhere to this material, and the bacteria commence to propagate speedily, covering SEWAGE DISPOSAL. 121 the whole surface of the material. The sewage water is drawn off after a sufficient time, air with its large constituent of oxygen is drawn through as tlie water lowers, fresh vigour is given to the growth and multipli- cation of the little vegetable scavengers, and they are ready for a fresh supply of sewage food; and so long as this alternate process goes on the destruction of the dangerous elements is ensured, and the waters are finally rendered sufficiently pure to flow into any stream without fear of pollution.<Callout type="important" title="Bacterial Treatment">Bacteria effectively break down organic matter in sewage.</Callout>
It will be observed that this Septic method is the opposite of every system of Anti-septic or chemical destruction in which the chemicals, such as lime, sulphate of iron, etc., kill the bacteria and living organisms by which the biological method of treatment carries on its work, following nature's simple laws. The Septic Tank System of Sewage Disposal, as now
Key Takeaways
- Filter beds using polarite and sand can effectively purify sewage.
- Iron treatment with sulphate of iron is applicable to household drains and reduces sewage volume.
- Intermittent filtration through porous soil removes suspended and soluble organic matter efficiently.
- Irrigation systems on farms can handle sewage purification while providing manure for crops.
- Bacterial processes offer a natural solution for breaking down sewage.
Practical Tips
- Use filter beds with polarite and sand to purify large volumes of sewage effectively.
- Apply sulphate of iron through ferrometers in household drains to reduce sewage volume.
- Implement intermittent filtration systems on sloping land for efficient sewage treatment.
- Irrigate treated sewage onto farmland to both clean the water and fertilize crops.
- Utilize bacterial processes like septic tanks to naturally break down organic matter in sewage.
Warnings & Risks
- Avoid midden, dry earth-closet, or pail systems as they create daily nuisances and pollution issues.
- Ensure continuous air supply for optimal filtration in intermittent systems.
- Adhere strictly to pollution standards when discharging treated sewage into rivers.
- Do not rely solely on solid excreta treatment methods; address liquid waste too.
Modern Application
While historical techniques like filter beds and bacterial processes remain relevant, modern advancements such as advanced mechanical treatment and centralized wastewater systems have improved efficiency and effectiveness. Understanding these older methods can provide valuable insights for emergency situations or remote locations where conventional infrastructure is unavailable.
Frequently Asked Questions
Q: What are the key differences between the iron process and other sewage treatments mentioned in this chapter?
The iron process involves using sulphate of iron to reduce sewage volume, while other methods like filter beds use physical filtration. Both have their applications depending on space availability and specific needs.
Q: How does intermittent filtration work, and what are its benefits?
Intermittent filtration alternately transmits sewage and air through porous soil, allowing for efficient removal of suspended and soluble organic matter. It requires less land than irrigation systems but still needs significant space.
Q: What is the significance of the polarite filter beds mentioned in this chapter?
Polarite filter beds are highly effective at purifying sewage without using lime, making them a valuable alternative to traditional filtration methods. They can handle large volumes efficiently and require minimal maintenance.