PROTECTIOX OF RIVER AND HARBOR WATERS 25 



contact and trickling beds are essentially oxidizing mechanisms without 

 filtering action adequate for the removal of micro-organisms. It is true that 

 in the unfavorable environment of the septic tank and trickling filter, many 

 sewage organisms do die out, but their elimination is incomplete and un- 

 certain. If a nearly germ-free effluent is required some special method 

 must be adopted for bacterial removal. This particular problem has come 

 into great importance of late in connection with the protection of shellfish 

 industries, menaced by the sewage of seaboard cities. Fortunately there 

 has been worked out to meet this need a simple and efficient method, a 

 new chemical treatment, not designed as in the old precipitation processes 

 to remove suspended solids but merely to destroy living germs. The appli- 

 cation of ordinary bleaching powder, or chloride of lime, in small amounts 

 of fifteen to thirty parts of bleaching powder to a million parts of sewage 

 will effect a satisfactory reduction of bacteria at a very reasonable cost, 

 as shown first by Mr. S. Rideal in England and by Prof. E. B. Phelps in this 

 country. Baltimore, Maryland, has adopted this procedure as have certain 

 small towns on the Xew Jersey coast; and it promises to be of use in dealing 

 with certain phases of the New York Harbor problems. 



There are many questions still to be solved in the purification of sewage. 

 The removal of suspended matter, for example, urgently demands further 

 careful study; yet the work of the last ten years in England and the United 

 States has blocked out the main outlines of satisfactory sewage disposal 

 practice. The engineer can to-day successfully meet any demand for the 

 purification of domestic sewage; and this purification may be carried to 

 any degree of perfection for which the community in question is prepared 

 to pay. If a clear and sparkling effluent, highly purified bacterially, is 

 desired he can design an intermittent filter for that purpose. If merely 

 a stable effluent which may be discharged into a stream without creating 

 a nuisance is wanted, he can build a trickling filter. If, on the other hand, 

 a disinfected but not organically purified effluent is called for, that end, 

 too, may be attained. 



