Filamentous growth in activated sludge

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Filamentous growth in activated sludge

 

Author: Cheung, Wing-leung Montgomery
Title: Filamentous growth in activated sludge
Degree: M.Sc.
Year: 1995
Subject: Sewage -- Purification -- Activated sludge process
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: viii, 68 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1205018
URI: http://theses.lib.polyu.edu.hk/handle/200/3003
Abstract: The activated sludge process is one of the most widely used biological processes for treating the domestic sewage and industrial effluents. Since its development in 1914, activated sludge process has been reported to encounter operational problem of bulking and foaming. Bulking and foaming in activated sludge process are usually associated with filamentous overgrowth, but the detail mechanisms are not fully understood. Sewage treatment works at Sha Tin and Tai Po in Hong Kong have been frequently experienced with the formation and accumulation of foam which result in difficult operational problems. The branched - filamentous Nocardia amarae was identified as the causative organism. In vitro culture showed that long - chain fatty acids that are commonly present in domestic sewage could be utilized by N. amarae as the sole carbon source. An addition of fatty acids (e.g. C8, C9 and C14) with domestic sewage could also stimulate and promote the growth of N. amarae in activated sludge. In addition, the presence of fatty acids in sewage could directly promote foaming and enhanced foam stability. The reason for this was attributed to the surface - active properties of fatty acids, which increased the stability and resistance against breaking - up of the liquid film of air bubbles. Filamentous N. amarae and non-filamentous Pseudomonas aureginosa were cultivated with fatty acids as sole carbon source. N. amarae could utilize all fatty acids tested (e.g. C2 to C24 ) for growth, while P. aureginosa had difficulty utilizing fatty acids with 12 or more carbons. Maximum growth rate and saturation constant of N. amarae on C24 were 0.048 h-1 and 1.520 gCOD/L respectively, which was much lower that P. aureginosa. In the kinetic selection, N. amarae was a Ks-strategists that grew slowly, but had a relatively strong affinity with long - chain fatty acids and could survive on low concentrations of the fatty acid. On the contrary, P. aureginosa was a 撘峻ax - strategists which grew rapidly, but required high concentration of fatty acids for growth. With readily biodegradable organic (e.g. acetic acid), the maximum specific growth rate and saturation constant of N. amarae at 0.095 h-1 and 0.302 gCOD/L respectively, were still much lower than that of P. aureginosa. Growth yields of N. amarae remained fairly constant, ranging among 0.413 to 0.487 g/gCOD, with all fatty acids tested. Growth yields of P. aureginosa with acetic acid was high, at 0.665 g/gCOD, but values were significantly lower when long-chain fatty acids were used as the sole carbon source. N. amarae was competitive, among other microorganisms, in activated sludge processes that receive sewage containing a high proportion of long - chain fatty acids, oils and fats.

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