F. W. MOHLMAN 359 



Pearse and Mohlman/ and Buswell {loc. cit). Bartow and Russell- demonstrated the 

 bacterial basis of the process; Harris, ^ of Glasgow, states that the presence or ab- 

 sence of protozoa neither increases nor detracts from the efficiency of fully matured 

 activated sludge. Recent experience at the Des Plaines River Activated Sludge 

 Plant of the Sanitary District of Chicago has indicated that larger filamentous bac- 

 teria may be very detrimental. A profuse growth of Sphaerotihis natans has produced 

 a slimy, non-settling sludge which will not stabilize the sewage, will not settle, and 

 will not filter-press. It is probably stimulated by the adventitious presence of ab- 

 normal amounts of carbohydrate in the sewage, with excessive production of carbon 

 dioxide. Attempts to eliminate the growth by lime treatment have been fairly suc- 

 cessful. 



INDUSTRIAL WASTES 



Industrial wastes frequently complicate the treatment of sewage by (i) greatly 

 increasing its biological strength, or (2) by inhibiting bacterial action. The most sat- 

 isfactory evaluation of the first type of waste is based on its biochemical oxygen de- 

 mand. This procedure has been used by the Sanitary District of Chicago.^ Experi- 

 ments on the treatment of a concentrated starch-factory waste at Argo demonstrat- 

 ed that the undiluted starch and gluten wastes would produce neither activated sludge 

 nor a ripened filter. When diluted with at least three volumes of canal water it was 

 possible to treat the mixture biologically, but activated-sludge treatment was still 

 not uniformly successful. Trickling filters were recommended to operate on a very 

 low rate of filtration. 



The inhibitory effect of the second type of waste is injurious to sludge digestion 

 and particularly to activated -sludge treatment. An interesting study has recently 

 been made by Sierp-^ on the effect of various germicidal wastes in Imhoff tanks. He 

 finds that phenol wastes are particularly detrimental to gas production. The con- 

 centration in the sludge used was about 25 parts per million of phenol. Chlorine was 

 quite germicidal, but excessive amounts were used, from 50 to 500 parts per million. 

 Magnesium sulphate, in a concentration of 360 p.p.m. SO,, delayed digestion and 

 produced foul odors of hydrogen sulphide. Sodium chloride in a concentration of 

 5,500 parts per million did not affect digestion, but 30,000 p.p.m. decreased the gas 

 production about 20 per cent. Sierp states that plasmolysis is not appreciable in well- 

 seeded Imhoff sludge. 



The operation of a number of activated-sludge plants has been interfered with 

 by industrial wastes. Gashouse wastes have been detrimental at the Manchester 

 (Davyhulme) and Reading (England) plants. Discharge of mineral oil has seriously 



'Pearse, L., and Mohlman, F. W.: "Doubt Fixation of Atmospheric Nitrogen by Activated 

 Sludge Process," Eng. News-Rec, 90, 843-941. 1923. 



' Russell, R., and Bartow, E.: "Bacteriological Study of Sewage Purification," III. Stale Water 

 Siirv., Bull. I J, pp. 348-58. 1915. 



3 Harris, F. W., Lockburn, T., and Anderson, T.: "The Biological and Physical Properties of 

 Activated Sludge," Surveyor, 70, 30-31. July 9, 1926. 



'' Mohlman, F. W.: "Treatment of Packinghouse, Tannery and Corn Products Wastes," Indust. 

 b' Engin. Cheni., 18, 1076-81. Oct., 1926. 



5 Sierp, F. : "Ueber die Vorgange im Schlammfaubraum," Techn. Gemeindeblatt, 29, 267-312. 

 March, 1927. 



