South Norwood. 



samples two had as much as 5 o.o. to 6 o.c. per litre 

 of dissolved oxygen when analysed and one about 

 3 c.c, the amounts in the four others tested being 

 about 1 CO. in each case ; but when the January set 

 of samples was drawn and analysed the temperature 

 was lower. The gases in the January samples were 

 boiled out. Samples tested for dissolved oxygen 

 when drawn (five in number) did not apparently 

 give high results, the maximum figure being 3 c.c; 

 but as these eflluents were all more or less coloured, 

 the comparison with the standard copper chloride 

 tubes was difficult ; hence those dissolved oxygen 

 figures in the November sample must be taken as 

 being almost certainly below the true valne, and no 

 real conclusions can be drawn here. The beck water 

 was fully aerated when analysed and the " mixture " 

 generally so — all kept sweet upon incubation. 



No mention is made of nuisance 

 Nuisanoe ■ ■ f xv 



and DIffloulties. ^"'^''^ ^''"'^ *^^ sewaging opera- 

 tions. The chief difficulty experi- 

 enced in the working of the farm is the selling of 

 the crops. 



" The sewage (purely domestic) 

 Conclusions, is weak. South Norwood may 

 be taken as an example of a 

 surface irrigation farm (with a little filtration). It 

 was treating both per acre of the ' working ' daily 

 irrigfable area, and per aci-e of the total irrigable 

 area, a small volume of sewage, and a very small 

 quantity of organic matter in the aggregate. The 

 soil (a partially modified clay soil resting on London 

 clay) is not very well adapted for purifying even a 

 moderate volume of sewage. The sewerage system 

 is partially separate. All the storm water reaching 

 the sewers is dealt with on the farm. We consider 

 that even 12,000 gallons per acre per twenty-four 

 hours (4,000 gallons per acre of the total irrigable 



area per twenty -four hours) is possibly too largo a 

 volume of even a weak sewage to be treated by 

 screening, settling and surface irrigation (with some 

 little filtration) on surface soil of the above nature. 

 Nevertheless, it should not be forgotten here that 

 the difficulty of treating the storm water at South 

 Norwood must be relatively great. In comparing 

 Leicester and South Norwood — two typical clay 

 farms — it should further be remembered that 

 although the Leicester farm was treating a much 

 larger volume of sewage per acre and a larger 

 amount of organic matter in the aggregate, it had 

 to deal with much less storm water, and in all prob- 

 ability benefited to a greater extent by filtration, 

 which, however, must in any case have been com- 

 paratively small." (Part I., page 91.) 



NoTX. — At the time of visiting the farm bacteria bedg (single oontaot) 

 were being conetructed ; one small one was in active use and treated 

 screened sewage. The efBuent therefrom passed over the land and 

 finally mixed with the general effluent on leaving the farm. 



LATER WORK. 



Since 1900 the population draining to the farm 

 has largely increased, and the sewage is now in 

 some measure partially purified before being applied 

 to the land. In 1901 five single-contact bacteria 

 beds of a total area of f acre were finished. They 

 were filled to a depth of about 3 ft. 6 in. with ballast 

 burnt on the site. In 1905 three storm filters (about 

 1 acre) were made and a detritus tank to the low- 

 level sewer was built. An extension of the five 

 bacteria beds is now in hand, and the area of these 

 when completed will be 1| acres. It is proposed to 

 fill them twice on weekdays and once on Sundays, 

 and to give each bed one week's rest in turn. The 

 bottom of the shallow pits formed by the excavation 

 of the clay to make ballast is so impermeable that 

 it has not been found necessary to lay any concrete 

 as a floor to these beds. 



59 



