ISSN:
1432-0614
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Abstract An extractive membrane bioreactor has been used to treat a synthetic waste-water containing a toxic volatile organic compound, 1,2-dichloroethane (DCE). Biofilms growing on the surface of the membrane tubes biodegrade DCE while avoiding direct contact between the DCE and the aerating gas. This reduces air stripping by more than an order of magnitude (from 30–35% of the DCE entering the system to less than 1%) relative to conventional aerated bioreactors. Over 99% removal of DCE from a waste-water containing 1600 mg l-1 of DCE was achieved at waste-water residence times of 0.75 h. Biodegradation was verified as the removal mechanism through measurements of CO2 and chloride ion evolution in the bioreactor. No DCE was detected in the biomedium over the operating period. The diffusion-reaction phenomena occurring in the biofilm have been described by a mathematical model, which provides calculated solutions that support the experimental results by predicting that all DCE is biodegraded within the biofilm. Experimentally, however, the rate of DCE degradation in the biofilm was found to be independent of O2 concentration, while the model predictions point to O2 being limiting.Nomenclature A, Membrane area (m2); C, dissolved O2 (DO) concentration in biofilm (kg m-3); CB, DO concentration in bulk biological liquid (kg m-3); Cm, DO concentration at biofilm-membrane interface (kg m-3); DO F, diffusion coefficient of O2 in biofilm (m2 s-1); DS F, diffusion coefficient of DCE in biofilm (m2 s-1); DS R, diffusion coefficient of DCE in membrane (m2 s-1); DS W, diffusion coefficient of DCE in water (m2 s-1); DR E L, relative diffusivity of substrates in biofilm ( - ); F, flow of waste-water inside membrane coil (m3 s-1); k O, overall mass transfer coefficient (m s-1); k W, waste-water film mass transfer coefficient (m s-1); K P, partition coefficient for DCE between membrane and aqueous phases ( - ); K S, Monod rate constant for DCE (kg m-3); K O 2, Monod rate constant for O2 (kg m-3); L, length of membrane tube (m); N, flux of DCE across membrane (kg m-2 h-1); NS h, Sherwood number (−1; NRe, Reynolds number (−1; NSc, Schmidt number; ri, membrane inner radius (m); ro, membrane outer radius (m); S, DCE concentration in biofilm (kg m-3); SB, DCE concentration in bulk fluid (kg m-3); Sm, DCE concentration at membrane-bio- film interface (kg m-3); SW, DCE concentration in waste-water (kg m-3); Si n, DCE concentration in waste-water at entry to membrane module (kg m-3); So u t, DCE concentration in waste-water at outlet of membrane coil (kg m-3); r, distance variable in biofilm (m); Y X / O, yield coefficient for biomass on O2 (kg biomass kg-1 O2); Y X / S, yield coefficient for biomass on DCE (kg biomass kg-1 DCE). Greek symbols: δ, bio- film thickness (m); μ, specific growth rate (s-1); μm a x, maximum specific growth rate (s-1); ρv, biofilm density, e.g. Pv biofilm density (kg (dry cell matter) m-3).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00902752
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