Answered: In a biological waste treatment system,…

Solid Waste Engineering

3rd Edition

ISBN:9781305635203

Author:Worrell, William A.

Publisher:Worrell, William A.

Chapter7: Thermal Processes

Section: Chapter Questions

Problem 7.12P

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Transcribed Image Text:1-6. In a biological waste treatment system, solids may enter in the influent, be created or destroyed by biological growth or decay, and may leave in the effluent. Con- sider a waste treatment plant treating 1m'/s of an influent containing 55 mg/L of degradable organic solids. The wastewater also contains 180 mg/L of dis- solved organic carbon (DOC), which may be degraded. For every gram of dissolved organic matter that is degraded, the overall reaction converts a portion of the material into CO, and H20, and another portion into 0.4 g of new biomass. Analytically, this biomass and the degradable solids in the influent are both quantified as volatile suspended solids (VSS); that is, the degradable solids in the influent and the new biomass that grows in the reactor are indistinguishable from one another. (a) In a particular system, the dissolved organic matter (i.e., the substrate, S) is removed from solution at an overall rate (including both the conversion into CO, and into new cells) given by rs = -k,s°X/(S² + K,), where X is the VsS con- centration in the reactor. The values of k1, K, and X in the reactor of interest are 8 mg DOC/mg VSS d, 110 (mg DOC/L)², and 120 mg VSS/L, respec- tively. Write a mass balance and compute the hydraulic detention time, t (i.e., the average amount of time that water resides in the reactor, equal to V/QL) necessary to reduce the concen- tration of substrate to 3 mg DOC/L in a complete mix reactor operating at steady state. (b) Solids decay in the reactor at a rate equal to kax, where ka is the decay rate constant. Write a mass balance on VSS and compute the value of ka.

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