Gaval, G.

Ochoa, J.

Pellicer i Nàcher, Carles

Smets, Barth F.

Syron, E.

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 19, 2017Assessing the impact of physical and physiological factors on the oxygen masstransfer process in membrane-aerated biofilm reactorsPellicer i Nàcher, Carles; Syron, E.; Gaval, G.; Ochoa, J.; Smets, Barth F.Publication date:2011Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Pellicer i Nàcher, C., Syron, E., Gaval, G., Ochoa, J., & Smets, B. F. (2011). Assessing the impact of physicaland physiological factors on the oxygen mass transfer process in membrane-aerated biofilm reactors. Postersession presented at Specialist Conference on Membrane Technology for Water & Wastewater Treatment,Eurogress Aachen, Germany, .0 2 4 6 8 10 12 14 Permeability  (cm3cm-2s-1cmHg-1) Assessing the impact of physical and physiological factors on the oxygen mass transfer rates in membrane-aerated biofilm reactors  1. Introduction Carles Pellicer-Nàcher1, Boris Roth 1, Gilberte Gaval2, Juan Ochoa2, Barth F. Smets1 1 Department of Environmental Engineering, Technical University of Denmark; 2 Pôle Biotechnologies et Agronomie Veolia Environment  Research and Innovation,  Maisons – Laffitte, France.                                  E-mail: capn@env.dtu.dk  2. Reactors / membranes **This project was economically supported by VEOLIA Environnement Research Institute, France.  Membrane-aerated biofilm reactors (MABRs) are systems where an air/oxygen stream diffuses through a membrane, which is submerged in wastewater and which also serves as the substratum for biofilm growth. The counter-diffusion of nutrients within the biofilm matrix creates unique niches for the co-existence of distinct microbes. A wide range of hydrophobic materials have been used  that can  support biofilm development. Composite membranes are preferred because of their superior mechanical stability and oxygen transfer capabilities. MABRs can be used for simultaneous nitrification-denitrification of wastewaters. After reactor innoculation a layered biofilm develops. Nitrifying bacteria convert the incomming ammonium to nitrite and nitrate in the first 100-200 mm by using the oxygen diffusing from the membrane surface. The produced nitrogen can be denitrified by heterotrophic bacteria in the upper anoxic biofilm region by using the organic carbon present in the wastewater as electron donor. Nitritation-Anammox Nitrification-denitrification Xenobiotic removal P removal Flexibility Trade-off Application example Membranes are arranged in modules in order to satisfy research/application needs. Polyurethane Polyethylene Mitsubishi-Rayon (Japan)  PDMS PAN PET GKSS (Germany)  High specific surface areas Easy inspection and sampling From Robb et al. 1965  PDMS superior (up to 60 cm3cm-2s-1cmHg-1)  3. Oxygen transfer characterization in MABRs We make use of the interfacial mass transfer theory to understand the oxygen transfer in these systems  5. Optimization/Outlook  4. Microelectrode investigations The oxygen transfer capabilities of a certain membrane/reactor system is quantified by standard oxygen transfer tests in clean water. 0 1 2 3 4 5 6 7 8 0 50 100 150 200 250 300 Dissolved oxygen  concentration  (mg/L) t (min) KOL = 0,025 KOL = 0,04 KOL = 0,075 Saturation Deoxygenate Re-aerate BulkLiquidlumenLa SOHSOaKadtdSOdaymOgOTR 22222 122222OTOlumenBulkLiquidlumenOL MWTRPySOSOHSOKOTR Saturated waterOxygen depletionSaturationNa2SO3Re-aeration  tKSOSOtSO Lasatsat  exp)( 222KLa(1/t) Membrane lumenBulk liquidMembraneLiq b. layerJO2,1JO2,2kmkLlumenSO2BulkLiquidSO2iSO2iLumenmO SOHSOkJ 221,2 BulkLiquidiLOSOSOkJ 222,2 Where...  OTR: Oxygen transfer rate (g-O2/m2/day) SO2: Oxygen concentration (g/m3) KLa: Overall film coefficient (1/day) KOL: Overall mass transfer coefficient (m/day) a: Specific surface area (m2/m3)  H: Henry coefficient (unitless) yO2: mass fraction of O2 in air PT: Total pressure in the lumen (atm) R: ideal gas  constant (8.31 atm·m3/K/mol) T: Temperature (K) MWO2: Molecular weight of O2 (g/mol)     Observed OTR s with biofilm >> measured OTR in clean water  -> Why? However...  Considering that no oxygen reacts we can write: Where DSm, DSL, km and kL are the oxygen concentration drops and the individual oxygen mass transfer coefficients through the membrane and the liquid boundary layer. These coefficients are related with KOL as follows:  1,21,222OOBulkLiquidlumenOL JJSOHSOKOTR LmOL kkK111LLmm SkSkOTR DDTherefore...  Can we use of microelectrodes measurements to better estimate the overall mass transfer coefficient that describes the oxygen transfer when a biofilm develops on top of the membrane? How can we make even more efficient oxygen transfers in MABRs? An MABR equipped with 2  silicone hollow-fiber membranes and a specific surface area of 14 1/m  was used. An O2 microelectrode (OX10, Unisense, Denmark) was mounted in a micromanipulator; O2 profiles were measured in 10 mm increments. O2 concentrations in the bulk liquid were measured by a polarographic O2 sensor (CellOx325, WTW, Germany) placed in the recirculation line. Tests were done in clean water. Method  Result  Microprofiles identified the  different gradient areas Assuming that biofilm development  removes BL resistance, yields an increase of the  KOL of about 50%. This increase matches previous experimental observations (Lackner et al. 2010) Liquid boundary layer yields  the highest resistance per unit length in the system Our investigations confirmed that increases in the lumen pressure and the recirculation flow rates in the flow cells enhanced the oxygen transfer rates up to 80 g-O2/m2/day due to increases in the concentration gradient and reductions in the thickness of the liquid boundary layer. Hollow fiber membranes with thinner walls also tend to supply oxygen faster due to their lower mass transfer resistance. Overall: • MABRs are excellent tools for more sustainable and efficient wastewater treatment. • Microelectode inspection allow for an accurate estimation of the individual mass transfer coefficients involved in the transfer of oxygen through MABRs without the use of mis-leading correlations. • The interfacial mass transfer theory properly describes the increase in OTR with respect to the clean water tests once biofilm develops on the membrane. Biochemical reactions are not expected to have a significant effect on OTR. • Our findings allow for more detailed and precise MABR models .  Standard OTR testsKLa,mJO2, atm+m JO2, atmJO2, mkm kLmprofilesResistances

Assessing the impact of physical and physiological factors on the oxygen mass transfer process in membrane-aerated biofilm reactors

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Assessing the impact of physical and physiological factors on the oxygen mass transfer process in membrane-aerated biofilm reactors

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