02833nas a2200253   450000500170000000800410001703500150005810000200007324500640009326000520015730000220020949000260023150001570025750200580041452017240047265000480219665000180224470000380226270000340230070000480233471000740238281000580245685600650251420260818094318.0271098s1981    th      r     000|  eng d  a.b102163521 aBravo, Helen E.10aDynamics of nitrification in rotating biological contactors  aBangkok :bAsian Institute of Technology,c1981  a69 leaves :bill.1 aThesis ;vno. EV-81-7  aA thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering,  School of Environment, Resources and Development  aThesis (M.Eng.) - Asian Institute of Technology, 1981  aA dynamic model was developed to represent the dynamic responses of  nitrification in a fixed-film rotating biological contactor, the key feature of which is the use of the steady state kinetic model to describe substrate-uptake in the biofilm. Results of the experiment showed that during transient operations, a  pseudo-steady state concentration distribution is established after a short lapse of time, in the diffusion layer and in the biofilm with respect to the bulk-liquid substrate concentration. There was a transient rise in the ammonia flux at the biofilm surface and the shift to steady state flux  level was reached after a few disk rotations. Substrate-uptake rate was observed constant once a certain critical film thickness was exceeded and  was not increased by further accumulation of microorganisms on the slime. It was also observed that the nitrifying bacteria exhibited a very small  lag in growth rate when exposed to sudden changes in concentration. Furthermore, when the concentration of the products accumulated in excessive amounts it was observed that the out-diffusion of products from the internal pores of the biomass to the outer surface of the film affected the rate of substrate utilization resulting to process instability especially with long term transients. Conclusion based on engineering calculations are  presented to illustrate design and operational mode for a more effective control of nitrification in dynamic systems. Simple forcing functions like pulse and step functions were used to verify the dynamic model in the zero-order regime; that is at bulk- ammonia  concentration greater than 3 mg/l. Results of the experiment adequately verified the dynamic models developed. 0aSewagexPurificationxRotating disc process 0aNitrification1 aWatanabe, Yoshimasa,eChairperson1 aLohani, B.N.,eCo-Chairperson0 aChongrak Polprasert,eExamination Committee2 aThe Government of the Federal Republic of Germany,eScholarship Donor2 aAsian Institute of Technology.tThesis ;vno. EV-81-7  3Full-Textuhttp://203.159.5.9/ait-thesis/detail.php?q=B21595