For an incompressible, steady flow state on an L-length planar plate with velocity profile u = ay + b

n a) Find the velocity profile by writing the boundary conditions.

n b) Calculate the boundary layer thickness (x).

n c) Calculate the coefficient of friction Cf(x)n

Activated Sludge (Pages 501-502, 510 Davis & Cornwell 5th edition), 3. (40 points) Study the section "Sludge Problems" on textbook, Page 510, and the additional materials from the Manual on the Causes and Control of Activated Sludge Bulking, Foaming, and Other Solids Separation Problems. edited by David Jenkins, Michael G. Richard, Glen T. Daigger. All the reading materials are copied below. Discuss the common causes of sludge bulking and how to control the sludge bulking. Sludge problems. A bulking sludge is one that has poor settling characteristics and poor compactability. There are two principal types of sludge bulking. The first is caused by the growth of filamentous organisms, and the second is caused by water trapped in the bacterial floc, thus reducing the density of the agglomerate and resulting in poor settling. Filamentous bacteria have been blamed for much of the bulking problem in activated sludge. Although filamentous organisms are effective in removing organic matter, they have poor floc-forming and settling characteristics. Bulking may also be caused by a number of other factors, including long, slow-moving collection-system transport; low available ammonia nitrogen when the organic load is high; low pH, which could favor acid-favoring fungi; and the lack of macronutrients, which stimu- lates predomination of the filamentous actinomycetes over the normal floc-forming bacteria. The lack of nitrogen also favors slime-producing bacteria, which have a low specific gravity, even though they are not filamentous. The multicellular fungi cannot compete with the bacteria normally, but can compete under specific environmental conditions, such as low pH, low nitrogen, low oxygen, and high carbohydrates. As the pH decreases below 6.0, the fungi are less affected than the bacteria and tend to predominate. As the nitrogen concentrations drop below a BODs: N ratio of 20:1, the fungi, which have a lower protein level than the bacteria, are able to produce normal protoplasm, while the bacteria produce nitrogen-deficient protoplasm. A sludge that floats to the surface after apparently good settling is called a rising sludge. Rising sludge results from denitrification, that is, reduction of nitrates and nitrites to nitrogen gas in the sludge blanket (layer). Much of this gas remains trapped in the sludge blanket, causing globs of sludge to rise to the surface and float over the weirs into the receiving stream. Rising-sludge problems can be overcome by increasing the rate of return sludge flow (Q.), by increasing the speed of the sludge-collecting mechanism, by decreasing the mean cell residence time, and, if possible, by decreasing the flow from the aeration tank to the offending tank. 4 Control of Activated Sludge Bulking and Other Settling Problems The y demands bill penis experientations and the boy Frk 18-24 MA Me activit ben The ligh facts can be manipulados atid proces pece and city the Cred fand e the the identi done for ioloeution is tiv sueel al' s lawlilpe of flor qyeai: uditin al valever danced lemine the L INTRODUCTION side Since the left kineral 1964 much has been mod about f et action de ling chance and how the long beunden the case can be di lg stichity is conted by the phyical chemical vide and mar de te id peaing Te past toe donabs fare as iifa anuptia Froatpi understanding of the specific fact that com vated sale stiebliny and the measures that pl designers and open can achieve b of sale stability. 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