i88 SEWAGE AND ITS PURIFICATION 



tried at Worthing was that it failed to sterilize the interior of 

 solid fajces, and the trials at Nice showed, as I have already 

 mentioned, that an attempt to disinfect hinders or prevents the 

 natural bacteria from breaking down organic debris, therefore 

 the disinfectant should be applied after the breaking down. In 

 the septic tank the suspended substances are reduced to a much 

 finer state of division, and the bacteria are thus more readily 

 attacked. I found, somewhat unexpectedly, that ammonia did 

 not react with oxychloride in the dilutions employed in treat- 

 ment, so that the solution was not destroyed or wasted by the 

 ammonia produced in the tank. Urea also did not interfere 

 with the first action of oxychloride, but tends to remove any 

 trace of the reagent remaining after the process. 



The simple treatment of raw sewage by means of a septic 

 tank and then addition of the solution would be sufficient for a 

 large number of cases where the organic purity was of less 

 importance than the removal of pathogenic organisms, as in 

 localities close to shellfish gathering - grounds or watercress 

 beds. For both of these, and particularly for vegetables, com- 

 plete organic purification might be a disadvantage, as depriving 

 them of food. In places where open septic tanks had been 

 objected to on account of suggested nuisance, closed tanks 

 could be adopted of a rather smaller size than usual, the solution 

 being added in a covered carrier with baffle plates as the effluent 

 passed out, with a certainty of removing all objectionable 

 odours. If existing tanks are divided by a party wall into 

 two unequal chambers ; in the first of say twenty hours' dry- 

 weather capacity, the anaerobic preparation could go on as at 

 present ; while in the second, of say four hours' capacity, the 

 chlorine solution would be added in sufficient quantity to cause 

 the remaining suspended solids to subside in a more or less 

 sterilized condition, and the effluent to be free from smell and 

 objectionable organisms. The cost and space required for 

 primary, secondary, and tertiary beds would in this way be 

 saved. I believe that the method, in the case of seaside towns 

 and those discharging into estuaries, would greatly contribute 

 to local healthy conditions, and would insure the absence of 

 unsightly sewage matter on the shores. 



In the septic tank effluents at Guildford the total organisms 

 were 2,500,000 to 4,500,000, the coH 100,000 to 1,000,000, and 

 the spores of 5. enteritidis sporogenes 10 to 1,000, per c.c. After 

 the addition of available chlorine (regulated by the five minutes' 



