Nitritation performance and biofilm development of co- and counter-diffusion biofilm reactors: Modeling and experimental comparison
ABSTRACT A comparative study was conducted on the start-up performance and biofilm development in two different biofilm reactors with aim of obtaining partial nitritation. The reactors were both operated under oxygen limited conditions, but differed in geometry. While substrates (O2, NH3) co-diffused in one geometry, they counter-diffused in the other. Mathematical simulations of these two geometries were implemented in two 1-D multispecies biofilm models using the AQUASIM software. Sensitivity analysis results showed that the oxygen mass transfer coefficient (Ki) and maximum specific growth rate of ammonia-oxidizing (AOB) and nitrite-oxidizing bacteria (NOB) were the determinant parameters in nitrogen conversion simulations. The modeling simulations demonstrated that Ki had stronger effects on nitrogen conversion at lower (0-10 m d(-1)) than at the higher values (>10 m d(-1)). The experimental results showed that the counter-diffusion biofilms developed faster and attained a larger maximum biofilm thickness than the co-diffusion biofilms. Under oxygen limited condition (DO<0.1 mg L(-1)) and high pH (8.0-8.3), nitrite accumulation was triggered more significantly in co-diffusion than counter-diffusion biofilms by increasing the applied ammonia loading from 0.21 to 0.78 g NH4+-NL(-1) d(-1). The co- and counter-diffusion biofilms displayed very different spatial structures and population distributions after 120 days of operation. AOB were dominant throughout the biofilm depth in co-diffusion biofilms, while the counter-diffusion biofilms presented a stratified structure with an abundance of AOB and NOB at the base and putative heterotrophs at the surface of the biofilm, respectively.
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- "Biofilms in HfMBR are immobilized on the exterior (convex) surface of hollow polydimethylsiloxane (PDMS) membranes. For aerobic HfMBR, oxygen diffuses across the semi-permeable PDMS fiber wall to the biofilm from the attachment site, and also from the bulk liquid phase into the biofilm (known as counter-diffusion) (Wang et al., 2009). HfMBR have demonstrated improved gas transfer, high areal conversion rates (see Rector et al., 2006 for description of areal conversion rates), low energy demand, low maintenance, and reduced volatile stripping (Casey et al., 1999, 2000; Cote et al., 1989) relative to traditional co-diffusion biofilm reactors. "
ABSTRACT: A suite of techniques was utilized to evaluate the correlation between biofilm physiology, fluid-induced shear stress, and detachment in hollow fiber membrane aerated bioreactors. Two monoculture species biofilms were grown on silicone fibers in a hollow fiber membrane aerated bioreactors (HfMBR) to assess detachment under laminar fluid flow conditions. Both physiology (biofilm thickness and roughness) and nutrient mass transport data indicated the presence of a steady state mature biofilm after 3 weeks of development. Surface shear stress proved to be an important parameter for predicting passive detachment for the two biofilms. The average shear stress at the surface of Nitrosomonas europaea biofilms (54.5 ± 3.2 mPa) was approximately 20% higher than for Pseudomonas aeruginosa biofilms (45.8 ± 7.7 mPa), resulting in higher biomass detachment. No significant difference in shear stress was measured between immature and mature biofilms of the same species. There was a significant difference in detached biomass for immature vs. mature biofilms in both species. However, there was no difference in detachment rate between the two species. Biotechnol. Bioeng. © 2012 Wiley Periodicals, Inc.Biotechnology and Bioengineering 02/2013; 110(2). DOI:10.1002/bit.24631 · 4.16 Impact Factor
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- "They remain free of clogging or wetting problems and their diffusive resistance can be overcome by higher intramembrane pressures . The relatively high permeability of silicone has made it a popular dense membrane choice (Casey et al., 1999; McLamore et al., 2007; Wang et al., 2009), but silicone is only available in outer diameters on the order of millimeters, which limits the specific surface area. Membranes have been specifically designed for gas transfer applications, such as the degassing of water or the oxygenation of blood, but until of late, little research had been carried out on membranes tailored specifically to MBfR applications. "
ABSTRACT: The membrane biofilm reactor (MBfR), an emerging technology for water and wastewater treatment, is based on pressurized membranes that supply a gaseous substrate to a biofilm formed on the membrane's exterior. MBfR biofilms behave differently from conventional biofilms due to the counter-diffusion of substrates. MBfRs are uniquely suited for numerous treatment applications, including the removal of carbon and nitrogen when oxygen is supplied, and reduction of oxidized contaminants when hydrogen is supplied. Major benefits include high gas utilization efficiency, low energy consumption, and small reactor footprints. The first commercial MBfR was recently released, and its success may lead to the scale-up of other applications. MBfR development still faces challenges, including biofilm management, the design of scalable reactor configurations, and the identification of cost-effective membranes. If future research and development continue to address these issues, the MBfR may play a key role in the next generation of sustainable treatment systems.Bioresource Technology 03/2012; 122:83-94. DOI:10.1016/j.biortech.2012.02.110 · 5.04 Impact Factor
Mass Transfer in Multiphase Systems and its Applications, 02/2011; , ISBN: 978-953-307-215-9
- "In this reactor the biofilm is naturally immobilized on an substrate permeable membrane and counter-or (regarding the conventional biofilms where both the dissolved oxygen and substrates diffuse in the same direction) co-diffusion of oxygen and nutrients (organic component, ammonia, etc.) can take place. Several investigators have reported performance advantages of membraneaerated biofilm reactors for wastewater treatment (Aryal et al., 2009; Monthlagh et al., 2006) oxidation of organic components (Casey et al., 2000; Gross et al., 2007), nitrification (Rittman & Manem, 1992; Wang et al., 2009) etc. The structure of the biofilm can be homogeneous or heterogeneous depending on the substrate concentration (Piciorenau et al., 2001) because the growth rate of microorganisms depends strongly on the substrate concentration. "