MODERN DRAINAGE.

Hastings Standard, Volume XI, Issue 5567, 27 July 1907, Page 2

MODERN DRAINAGE.

(By E.F.H.) i | Specially written for the Hastings | Standard. ! (Continued from yesterday.) THE BACTERIOLOGICAL TREATMENT OF SEWAGE.

Those who have followed the cours e of municipal politics in the Old Country during the past few years will have noticed the prominent place occupied by the sewage disposal problem. The appalling outbreak of typhoid at Maidstone some 13 years ago, following close upon the heels of an equally disastrous visitation of the same malady at Worthing some five or six years before, brought home at last to the minds of the various authorities the urgent need for reform in connection with household drainage Up till then sanitary matters throughout the length and breadth of England were in a very primitive state. The system of sewage disposal could be classed under the three following headings:—■ (1) The cesspit or middle system, which was almost universal throughout the country districts. (2) The pan system, which obtained in most of the smaller and in a few of the larger towns. (3) Drainage by means of the ordinary sewer, the effluent consisting of sewage in a crude state, no effort being made to purify it prior to its reaching its final destination.

It is small wonder therefore that as time went on, outbreaks of typhoid gradually became more and more frequent, culminating eventually in the terrible epidemics we have mentioned. Eventually, in 1898, a Royal Commission which had been set up to inquire into the matter came to an important decision, which served in no small degree to revolutionise the system of sewage disposal that was then in vogue. They reported as follows : " After carefully considering the whole of the evidence, together with the results of our own work, we are satisfied that it is practicable to produce by artificial processes alone, either from sewage or from certain mixtures of sewage and trade refuse, such for example as are met with at Leeds and Manchester, effluents which will not putrify, which would be classed as good according to ordinary chemical standards, and which might be discharged into a stream without fear of creating a nuisance." The Commission referred of course to the Bacteriological treatment of sewage or what is more commonly known now-a-days as the septic tank system.

Some 17 years previous to the sitting of the Commission, that is in 1881, a Frenchman invented a closed tank in which sewage and kitchen refuse was transformed into a fluid of a more or less turbid nature. Ten years later Mr Scott - Moncrieff brought forward a somewhat similiar scheme, having previously discovered that the process of liquefaction was due to the agency of bacteria. .Five years later in 1806—Just II years ago it will be noticed—a Mr Cameron, of Exeter, still further improved upon the discoveries of ScottMonrrieff and showed how it was possible to successfully deal with sewage by first liquifying it in a septic tank and afterwards oxidising or nitrifying it on bacteria beds. This system, or a modification of it, is the system that is generally in vogie throughout the world at the present day—the septic tank system. Now for a word or two about it.— What is it? Briefly, it is applying for our own use, the aids which Nature has expressly given us in the shape of bacteria. —These microbes, invisible to the naked eye, carry out all the necessary work —work which i.ian himself for thousands of years had previously been unable to accomplish. How is it done ? The whole of the working is simplicity itself. In a nutshell it is this —At the extremity of the main sewer is a closed concrete tank or chamber, absolutely watertight of course. This is the septic tank proper, in which are bred the anaerobic microbes (those that live without air) w'hich act upon the sewerage and cause it to liquefy. Into this tank the sewerage enters in a crude state, passing onward after being liquified, to what is known as " contact beds " open to the air and in which the " aerobic microbes (those that live with air) congregate and carry on the good work of their cousins, the anaerobic microbes. These contact beds or filters consist of masses of either coal, cinders, coke, breeze, pumice or like substances, over which the effluent from the septic tank is distributed and afterwards filtered through. By the action of sunlight, air, and bacteria, the effluent, after passing through this bed or filter, contains practically no suspended matter, and cannot be told from ordinary river water, ir fact it is clearer than that of most rivers, especially those running through thickly-populated districts. In many cases the resultant liquid is still further purified before it enters its final destination —usually the sea or a river—by being carried in an open j irrigation channel for some distance. By this means a still higher standard of purification is reached, thanks to the aid of additional air and sunlight. By processes such as 1 have named an effluent of a very high order can be obtained. In one town 1 know of in the colony where the septic tank system has been in use for the past four years, the effluent when, analysed, was found to have a far higher standard of purity than any of the standard effluents quoted in text books, this satisfactory result being attributable to the successful design of the tanks and the length of irrigation channel along which the effluent flowed before it entered the river. It might, perhaps be as well to quote the analysis of the effluent from the town we have referred to and to compare it with analysis of crude sewage and model effluents as set out in works dealing with the sewage problem.

The analysis of this effluent was as follows : Parts per 100,000 Chloride in chlorides ... i"24 Nitrogen as nitrate.-, '035 Free ammonia ... ... "168 Albuminoid ammonia ... 'O2l Oxygen absorbed in 4hrs at Bodeg. Fahr 'llß Total solids 7 - o That is tlie New Zealand effluent. Now for a suggested standard effluent. it is as follows : Paris per i 00,000 Chlorine 120 Nitrogen in nitrates 1-5 Free ammonia ... ... I"5 Albuminoid ammonia ... 005 Oxygen absorbed in at Bodeg. Fahr ooi Total solids ~ ioo'OO

The following is an analysis of crude sewage:— Parts per 100.000 Chlorine 12*? Nitrogen as nitrates ... Nil Free ammonia ... ... s"° Albuminoid ammonia ... I 0 Oxygen absorbed in 4hrs at Bodeg. Fahr. ... ... 2'5 Total solids I4»;0 Solids in suspension ... ... 4'° It will be noticed that in both the N.Z. effluent and the standard one the solids in suspension have been removed, and the total of solids reduced from 140 parts, per ioo.ooo to 7 '" t' ie case of the N.Z. sample a splendid advertisement for the engineer who designed and supervised the work of constructing the tank. * I have referred to this particular tank at some length in order to show that septic tanks, when properly constructed, constitute the most effective means yet discovered of dealing with the problem of sewage disposal. There have to my knowledge been instances when the efficacy of the the septic tank system has been questioned, but in each case on inves-. tigation by experts it was conclusively proved that it was either the design, or construction of the tank or both that was at fault, and not the system itself.

That drainage of the very best description should be one of the first cares of a municipality no one will venture to deny. Statistics go 10 show that there are no less than 400 per cent more cases of typhoid in houses not connected with a drainage system than in houses that are. It is to be hoped that the day is not far distant when every municipality in the Colony will see that it possesses a drainage system that is at once up-to-date and effective.