Cambridge. 



seem to be the best solution of the problem. It 

 mast be borne in mind that, although the sewage 

 was dilute, the volume of sewage treated per acre 

 was exceptionally great." (Part III., page 60.) 



Effluent and 

 Stream Compared. 



Nuisance 

 and Difficulties. 



The effluent does not appear to 

 vary much in character, and its 

 normal ratio to the river water 

 is 1 to 15. A small quantity of sewage fungus was 

 noticeable at times issuing from the main effluent 

 outfall, which has a submerged outlet. The river 

 Cam was in fair condition in January and February, 

 1901. The comparatively large volume of river 

 water minimises any effect that the effluent may 

 exert upon it. 



The dissolved oxygen in the effluents was generally 

 small. In three out of four samples taken from the 

 stream incubation did not by any means exhaust the 

 dissolved oxygen ; in the fourth, which was drawn 

 100 yards below the effluent outfall, the dissolved 

 oxygen was practically exhausted after incubation, 

 but plenty of nitrate remained. (See table on 

 page 26.) 



There is very little smell arising 

 from the se waging operations. 

 The chief difficulty in working the 

 farm is to keep the top soil loosened, as it cannot 

 always be ploughed in the winter. After ploughing 

 subsoiling with a scarifier has been found of great 

 assistance. During summer the land is kept 

 ploughed as frequently as possible. 



" The sewage (mainly domestic) 

 Conclusions, is rather weak, and is treated for 

 the most part on uncropped land. 

 In this respect the farm differs from the others. 

 Even for a filtration farm Cambridge was treating 

 an exceptionally large volume of sewage both per 

 acre of the ' working ' daily irrigable area and 

 per acre of the total irrigable area. It was also 

 treating in the aggregate a large amount of organic 

 matter, but it must be remembered that this organic 

 matter was highly diluted. Nevertheless, the soil 

 and subsoil (sandy loam overlying gravel and sand) 

 are admirably adapted for the purification of a large 

 volume of sewage, and the average filtration depth 

 down to the drains is nearly 5 ft. The sewerage 



system is partially separate, and very little storm 

 water reaches the farm. In conclusion, we consider 

 that 121,600 gallons per acre per twenty-four hours 

 (30,400 gallons per acre of the total irrigable area 

 per twenty-four hours) is rather too large a volume 

 of even a weak sewage to be treated by screening, 

 settling and filtration through even 5 ft. of a soil 

 and subsoil admirably adapted for purification pur- 

 poses. It should be borne in mind here that it is 

 easier to bring a weak sewage down to an absolute 

 standard of purity (such, for example, as the Mersey 

 and Irwell) than a strong sewage (volume for 

 volume), although in the former case the liquid 

 has really undergone less purification." (Part I., 

 page 85.) 



LATER WORK. 



Application has been made for a, loan for further 

 works — namely, a tank to hold about 225,000 

 gallons at the farm and in conjunction with the 

 pumping station further storm-water beds. The 

 following remarks will bear repetition : " In the 

 case of two fields (Nos. 4 and 11) which are used 

 as natural filter-beds, manholes and penstocks are 

 provided by means of which the sewage can be 

 held in contact with the soil for some hours. 

 These plots are sewaged continuously for about six 

 hours a day." This alteration in the method of 

 treatment has been continued, and about one-third 

 of the farm is now being worked in this manner. 

 The description " bacterial areas " has been applied 

 to these plots. On two other fields, together about 

 9^ acres, the land has been divided into three 

 sections, sewage being so applied that it floods the 

 first portion and rises after filtration, floods the 

 second portion and finally percolates through the 

 third portion. This allows of a very large amount 

 of sewage being treated on a small area. It is still 

 necessary to leave much of the land uncropped, and 

 in view of the exceptional quantity of sewage dealt 

 with per acre no other course seems possible. The 

 banks of the carriers have been planted with fruit 

 trees. Some excellent crops of horse-beans have 

 been garnered, and I understand that the holding- 

 up, as far as possible, of the liquid in the soil has a 

 very beneficial effect on root crops. A portion of 

 the sludge, after drying for some time, is now dis- 

 posed of to local farmers. 



27 



