GENERAL CONCLUSIONS. 



Battarlal 

 Oondltlon 

 of 

 EffluenU. 



DIsoharge 

 Effluents 

 No 

 Hulaano*. 



Cffeotlva 



Indefl- 



nltaly. 



Oroppingr 

 Dealrabla. 



Lattlngr 

 Inadvts- 

 abls. 



Manage- 

 ment— 

 Importanoe 

 of Qood. 



The effluents of sewage farms are not bacterially 

 in a proper condition for discharge into drinking- 

 water streams — the bacterial flora is characteristic 

 of sewage and the microbes of the soil are relatively 

 absent. Though the sewage as the result of land 

 treatment does not seemingly become modified in its 

 biological characters to any material extent, yet the 

 numbers of the bacteria are markedly reduced. All 

 the samples of river water taken above the outfalls 

 were contaminated bacteriologically from the point 

 of view of drinking water, and they were not always 

 satisfactory, either chemically or bacterially, in 

 respect of non-drinking water streams. " Generally 

 speaking, the discharge of the effluents into the 

 respective streams did not exercise any marked pre- 

 judicial effect on the water of the stream ; indeed, 

 the reverse was sometimes observed. There seems 

 to be no reason to doubt that the effluents from 

 properly-managed sewage farms would, when dis- 

 charged into non-polluted streams of relatively large 

 volume, neither give rise to any nuisance, nor, so far 

 as may be judged by rate of absorption of oxygen, 

 prove injurious to fish." (Part I., page 105.) 

 "There seems no reason to doubt that, with proper 

 management, land can purify sewage for a prac- 

 tically indefinite period. We are of opinion that 

 sewage, before it is applied to land, should be 

 efficiently screened and settled, unless it is already 

 in a thoroughly disintegrated condition." (Part I., 

 page 106.) 



" Although we are of opinion that sewage farms 

 in general can never be expected to show a profit if 

 interest on capital expenditure is included, the fact 

 that in favourable seasons some of them can more 

 than cover the working expenses is a point in favour 

 of cropping in connection with the land treatment of 

 sewage. Moreover, in our opinion, cropping makes 

 for purification, given good management, a volume 

 of sewage not out of proportion to the average area 

 under sewage at one time, and a suitably large 

 'resting' area. We are not in favour of sewage 

 farms being let; unless the irrigable area is very 

 large a tenant must sometimes be placed in the 

 awkward position of having to choose between 

 damaging a crop on the one hand and purifying 

 sewage imperfectly on the other. It is impossible 

 to lay too much stress on the importance of farms 

 being well managed ; but in this connection we 



desire to state that farm managers have usually a 

 most difficult part to play, and no amount of care 

 and attention will ever enable land of any kind to 

 deal with a volume of sewage out of all proportion 

 to the effective purifying area of the soil. We 

 recommend that farm managers should be taught 

 some simple test, or tests, to enable them to follow 

 for themselves the operations of the land ; that their 

 instructions should be in writing', and should include written 



"' Instruo- 



a definite order to consider the farming results as tions— Purl- 



.. , .. floation 



quite secondary to ' turning out uniformly a satis- Sola Aim. 



factory effluent; that the statistics of the farm 



should be most carefully kept ; and that, wherever 



possible, the flow of sewage and of storm water 



should be gauged throughout the year. In the case Oaugring. 



of all large sewage works permanent provision 



should most certainly be made for recording, by 



some reliable method of gauging, the daily flow of 



sewage." (Part I., page 107.) 



The difflculties which are frequently encountered Jf°™^_ 

 on sewage farms in dealing with the normal dry- 

 weather flow are so great that it is altogether 

 impracticable to consider the treatment of six times 

 this quantity with a view to securing an equal degree 

 of purification. " Assuming, however, the possibility 

 and practicability in all cases of a volume equal to 

 six times the dry -weather flow being brought to the 

 farm, we consider that the difficulty of treatment 

 would be lessened by (1) increasing the capacity of 

 the settling tanks ; (2) having a larger ' resting ' 

 area (not, however, at the expense of the ' working ' 

 area, but by enlarging the total irrigable area) ; and 

 (3) in particular cases by laying out portions of the 

 land in special ways — e.g., lagoons, storm-water 

 filters, &c. — which need not be described here, since 

 these matters would be determined by the local 

 conditions ... In this connection we desire again 

 to emphasise the fact that neither chemically nor 

 bacteriologically is mere dilution synonymous with 

 purification. Granting the impracticability of treat- 

 ing more than a certain proportion of storm water, 

 it should be definitely understood that storm water 

 is diluted, not purified, sewage." (Part I., page 109.) 



" We have already expressed our opinion that the intermit- 

 data available are insufficient to enable us to give 

 any definite statement as to the best rate of inter- 

 mittency either as regards filtration or surface- 

 irrigation farms. By ' rate of intermittency ' is 



71 



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