SEWAGE PURIFICATION 311 



Special methods have to be used in each case, according to 

 the character of the effluent to be treated, and dilution is fre- 

 quently necessary, e.g., in the case of pot ale from distilleries, 

 before purification can be effected. In the case of effluents 

 containing sugar or starch, care has to be taken lest acid 

 fermentation should set in, especially formation of butyric 

 acid, which is liable to create serious nuisance. For this 

 reason it is generally found necessary to avoid anaerobic 

 treatment in the case of these effluents, and a preliminary 

 addition of lime is often advantageous. 



