7 Suspended Growth Biological Treatment Processes 7-1 Introduction to the Activated-sludge Process Historical Development The activated-sludge process is now used routinely for biological treatment of municipal and industrial wastewaters. The antecedents of the activated-sludge process date back to the early 1880s to the work of Dr. Angus Smith, who investigated the aeration of wastewater in tanks and the hastening of the oxidation of the organic matter. The aeration of wastewater was studied subsequently by a number of investigators, and in 1910 Black and Phelps reported that a considerable reduction in putrescibility could be secured by forcing air into wastewater in basins. In experiments conducted at the Lawrence Experiment Statio during 1912 and 1913 by Clark and Gage with aerated wastewater, growths of organisms could be cultivated in bottles and in tanks partially filled with roofing slate spaced about 25 mm(I in) apart and would greatly increase the degree of purification obtained( Clark and Adams, 1914). The e res work at the Lawrence Experiment Station were so striking that knowledge of them led Dr. G J. Fowler of the University of Manchester, England to suggest experiments along similar lines be conducted at the Manchester Sewage Works where Ardern and Lockett carried out valuable research on the subject. During the course of their experiments, Ardern and Lockett found that the sludge played an important part in the esults obtained by aeration, as an in their paper of May 3 1914(Ardern and Ratum activated sludge Lockett, 1914). The Ardern and Lockett because it involved the activated mass of microorganisms capable of aerobic stabilization of material in wastewater Retum activated sludge (Metcalf Eddy 930) Fig. 7-I Description of Basic P definition. the basic activated-sludge Te sequence illustrated on Fig 7-la and b. consists of the follow typical activated-sludge processes with different types of reactors: (o) schematic flow diagram of plug flow process and view of plug flow reactor, (b) schematic flow diagram of complete - mix process and view of complete-mix activated-sludge reactor, and component (c) schematic diogram of sequencing batch reactor process and view of sequencing batch reactor. /From H. D Stensel) 1) reactor in which the microorganisms responsible for treatment are kept in suspension and aerated; (2) 7-17-1 7 Suspended Growth Biological Treatment Processes 7-1 Introduction to the Activated-Sludge Process Historical Development The activated-sludge process is now used routinely for biological treatment of municipal and industrial wastewaters. The antecedents of the activated-sludge process date back to the early 1880s to the work of Dr. Angus Smith, who investigated the aeration of wastewater in tanks and the hastening of the oxidation of the organic matter. The aeration of wastewater was studied subsequently by a number of investigators, and in 1910 Black and Phelps reported that a considerable reduction in putrescibility could be secured by forcing air into wastewater in basins. In experiments conducted at the Lawrence Experiment Station during 1912 and 1913 by Clark and Gage with aerated wastewater, growths of organisms could be cultivated in bottles and in tanks partially filled with roofing slate spaced about 25 mm (1 in) apart and would greatly increase the degree of purification obtained (Clark and Adams, 1914). The results of the work at the Lawrence Experiment Station were so striking that knowledge of them led Dr. G. J. Fowler of the University of Manchester, England to suggest experiments along similar lines be conducted at the Manchester Sewage Works where Ardern and Lockett carried out valuable research on the subject. During the course of their experiments, Ardern and Lockett found that the sludge played an important part in the results obtained by aeration, as announced in their paper of May 3, 1914 (Ardern and Lockett, 1914). The process was named activated sludge by Ardern and Lockett because it involved the production of an activated mass of microorganisms capable of aerobic stabilization of organic material in wastewater (Metcalf & Eddy, 1930). Fig. 7-1 Description of Basic Process By definition, the basic activated-sludge treatment process, as illustrated on Fig. 7-la and b, consists of the following three basic component s: (1) a reactor in which the microorganisms responsible for treatment are kept in suspension and aerated; (2)