# HW#6 - HOMEWORK NO 6 CE 3400 Introduction of Environmental...

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HOMEWORK NO. 6 CE 3400 – Introduction of Environmental Engineering Material Covered: Chapter 11 (Wastewater Treatment) in Vesilind et al., 2010 Due Date: Friday, 5 November 2010 at 1:10 PM All problems must be prepared on green engineering paper. PLEASE BE SURE YOUR NAME IS ON EACH PAGE OF YOUR HOMEWORK. Note: I have given you the final answers, so that you can check your own work! 1. This is Problem 11.11 in your textbook (reworded slightly for clarification) Mean cell residence time (MCRT or θ c ) is also called ‘sludge age’. Calculate the sludge age if an aeration tank in an activated sludge system has a hydraulic retention time of 2 hours and a suspended solids concentration of 2,000 mg/L. The flow rate of influent wastewater to the aeration basin is 1.5 m 3 /min, the return sludge solids concentration is 12,000 mg/L, and the flow rate of waste activated sludge (WAS) is 0.02 m 3 /min. Assume that Q w = Q r . Hint: You need to calculate values of θ c for sludge wasted from both the aeration basin and the recycle line. Start by calculating the volume of the reactor.

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• Spring '10
• Colberg
• Environmental Engineering, Activated sludge, MLSS, aeration basin, hydraulic retention time, sludge age, cell residence time

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