A critical review on the causative microorganisms, growth kinetics and existing control methods of activated sludge foaming and the introduction of the feast-fast operation (FFO)

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A critical review on the causative microorganisms, growth kinetics and existing control methods of activated sludge foaming and the introduction of the feast-fast operation (FFO)

 

Author: Wong, Che-ho Edwin
Title: A critical review on the causative microorganisms, growth kinetics and existing control methods of activated sludge foaming and the introduction of the feast-fast operation (FFO)
Degree: M.Sc.
Year: 2000
Subject: Sewage -- Purification -- Activated sludge process
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Civil and Structural Engineering
Pages: vi, 72 leaves : ill. ; 31 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1516298
URI: http://theses.lib.polyu.edu.hk/handle/200/1504
Abstract: Foaming is a common operational problem in activated sludge processes that often adversely affects the treated effluent quality. Despite the fact that increasing research and engineering works has been focused on this issue, disagreeing views on characteristics of causative bacteria and control strategies are still commonly found. Firstly, this paper gathers and analyses the new and well-recognized research works in a bid to trend the status and development in filamentous foaming. Secondly, based on the findings of filamentous foaming in Hong Kong, a new control strategy, the Feast-Fast Operation (FF0),. is developed and presented. Overgrowth of the filamentous Nocardia spp. in the microbial ecosystem was previously identified as the cause of foaming in the major sewage treatment works of Hong Kong. The specific growth rate of Nocardia amarae (filamentous bacteria) was found to be much higher than that of Pseudomonas auruginosa (non-filamentous bacteria) under food-to microorganism (F/M) ratios lower than 0.5 mg BOD/mg MLSS-day. This indicates that filamentous overgrowth may occur in normal activated sludge processes that are continualy operated under the usual F/M range of 0.2-0.6 mg BOD/mg MLSS-day. A novel Feast-Fast Operation (FFO) that capitalized on the sensitivity of filamentous bacteria to F/M ratio was designed to prevent and control foaming problems. The F/M ratio in the "feasting" aeration unit was 0.8 mg BOD/mg MLSS-day while that in the "fasting" aeration unit was 0.2 mg BOD/mg MLSS-day. The FFO resulted in an overall process F/M ratio that still remained within the normal range, while avoided prolonged exposure of the activated sludge ecosystem to an F/M ratio below 0.5 mg BOD/mg MLSS-day. The FFO suppressed the overgrowth of filamentous bacteria without adversely affecting the organic treatment efficiency of the modified process.

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