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SEWAGE PURIFICATION AND DISPOSAL, 



SEWAGE PURIFICATIOX AND DISPOSAL. 



(Edwin H. Wilkinson, Engineer for 

 Drainage, Hobart.) 



(Eead October 13, 1902.) 



The subject of the disposal and the puri- 

 fication of sewage is one that has of late 

 years received the clo?e attention of the 

 greatest scientists. More especiallj- is 

 this the case in the United Kingdom. It 

 will be my endeavour this evening to de- 

 scribe a few of the various methods adopt- 

 ed for purifying the sewage, and the agen- 

 cies whereby this state is brought about, 

 together with various methods of disposal 

 in use in various parts of the worlci. For 

 much of the information contained in this 

 paper (for which I claim no originality) 

 1 am indebted to the work by Mr. Dibdin 

 on the purification of sewage and water. A 

 very great deal of useful matter was also 

 obtained from a recent "'Eeport on the 

 Latest Methods in use in the United King- 

 dom and elsewhere/' by Mr. J, Davis, M. 

 Inst. C.E., who was until lately Engineer- 

 in-Chief for Sewerage Construction in New 

 South Wales. 



In_ the bacterial disposal of sewage, as 

 carried out at many places, we assist na- 

 ture in carrying out her work without 

 offence and without danger to us. AVhen 

 an animal dies and remains unhuned in 

 the fields, Nature^s scavengers, in the form 

 of bacteria, soon make themselves evident, 

 and in a comparatively short time entirely 

 dispose of the carcase. 



In order to more forciblj' impress upon 

 you this bacterial life, which plays such 

 an important part in the purification of 

 •ewage, I ask your permission to be al- 

 lowed to quote from some of the remarks 

 of Mr. W. J. Dibdin, late Chemist to the 

 London County Council. 



Firstly, sewage consists of animal sub- 

 stances, largely composed of fibrine, gela- 

 tine, chondrine, albumen, etc.; and, se- 

 condly, vegetable substances, such as 

 starclf and woody fibre (cellulose), gummy 

 inatters, with tannin, etc. The decom- 

 position takes place by the active organ- 

 isms, "aerobic/^ as they were called by 

 Pasteur in contradistinction to the anae- 

 robic organisms. As their name implies, 

 the first-named live only in the presence 

 of air, whilst the latter live in the absence 

 of air. When air is freely present the 

 aerobic organisms destroy the organic 

 matters in an inoffensive manner. 



According to Dibdin, the nitrogen of 

 the gelatine, etc., is resolved with either 

 the production of ammonia and the oxides 

 of nitrogen, or possibly set free as uncom- 



bined nitrogen. The oxygen and hydro- 

 gen, forming a considerable portion of the 

 matters, are recombined into water, and 

 the carbon into "carbon dioxide,'' or car- 

 bonic acid gas, as it is generally called. 

 Similar transformations take place with 

 these elements in vegetable matters, but a 

 longer time is usually required for the 

 completion of the process than is :he case 

 with animal substances, as they do not 

 form so suitable a medium for the sup' 

 port of the microbic life. Woody fibre, 

 especially paper pulp, is more refractory, 

 find will require a much longer time ifor 

 its disruption, but in the end the same 

 transformation occurs, a'ud carbonic acid, 

 water, etc., are iformed as a result. 



It will be understood that t'he sub- 

 stances mentioned are intended to repre- 

 sent only types of compounds actually 

 present in such a heterogeneous mixture as 

 that which vre are considering. 



In the process known as combustion, or 

 burning, the organic matters combine 

 with oxygen, but the same action is 

 brought about by the life processes of ani- 

 mals. 



In the cpse of the higher animals, when 

 the food is taken into the stomach, it there 

 undergoes the nrocess of digestion, and a 

 portion is absorbed into the system, wnere, 

 by the action of the blood, it is eventually 

 oxidised as it rushes through the lungs, in 

 which it is freely exposed to the air taken, 

 in by the breath. Thus is kept up a slow 

 process of oxidation, marvellous in its 

 character and action. It matters not 

 whether it is meat and bread eaten by 

 human beings; grass, etc., by horses or 

 fowls; or a mixture of these things by 

 microbes or by the direct action of fire; 

 the final result is precisely the same, viz., 

 combustion, fast or slow, as the case may 

 be. But in bringing about this result we 

 must not neglect to ensure an ample sup- 

 ply of oxygen, otnerwise we shall have 

 foul gases formed, such as sulphuretted 

 hydrogen, and so create a nuisance. 



Here we must further consider the ac- 

 tion of the minute organisms already re- 

 ferred to as "bacteria,"" or "microbes.'" 



These are minute living bodies, some of 

 which are ever present m various forma 

 in or on every substance known; and 

 whenever the circumstances are favour- 

 able they bring about the destruction of 

 the organic matters simply by living on 

 them. In reference to their general char- 

 acter that while at first they were thought 

 to belong to the animal kingdom, it is now 

 generally accepted that they are planta. 

 With reference to the size of the bacteria. 



