title: Modeling hexavalent chromium removal in a Bacillus sp. fixed-film bioreactor.
abstract: A one-dimensional diffusion-reaction model was developed to simulate Cr(VI) reduction in a Bacillus sp. pure culture biofilm reactor with glucose as a sole supplied carbon and energy source. Substrate utilization and Cr(VI) reduction in the biofilm was best represented by a system of (second-order) partial differential equations (PDEs). The PDE system was solved by the (fourth-order) Runge-Kutta method adjusted for mass transport resistance using the (second-order) Crank-Nicholson and Backward Euler finite difference methods. A heuristic procedure (genetic search algorithm) was used to find global optimum values of Cr(VI) reduction and substrate utilization rate kinetic parameters. The fixed-film bioreactor system yielded higher values of the maximum specific Cr(VI) reduction rate coefficient and Cr(VI) reduction capacity (kmc = 0.062 1/h, and Rc = 0.13 mg/mg, respectively) than previously determined in batch reactors (kmc = 0.022 1/h and Rc = 0.012 mg/mg). The model predicted effluent Cr(VI) concentration well with 98.9% confidence (sigmay2 = 2.37 mg2/L2, N = 119) and effluent glucose with 96.4 % confidence (sigmay(w)2 = 5402 mg2/L2, N = 121, w = 100) over a wide range of Cr(VI) loadings (10-498 mg Cr(VI)/L/d).
authors.affiliation: Department of Chemical Engineering, University of Pretoria, 0002, Republic of South Africa. Chirwa@up.ac.za
authors.forename: Evans M
authors.initials: EM
authors.lastname: Nkhalambayausi-Chirwa
authors.forename: Yi-Tin
authors.initials: YT
authors.lastname: Wang
mesh_terms: D000465:Algorithms; D001407:Bacillus / Q000502:physiology*; D018441:Biofilms / Q000254:growth & development*; D019149:Bioreactors / Q000382:microbiology*; D018929:Cell Culture Techniques / Q000379:methods; D049109:Cell Proliferation; D002857:Chromium / Q000493:pharmacokinetics*; D003198:Computer Simulation; D005947:Glucose / Q000378:metabolism*; D008567:Membranes, Artificial; D008954:Models, Biological
chemical_list: D008567:Membranes, Artificial; D002857:Chromium; C074702:chromium hexavalent ion; D005947:Glucose