Preparation and characterization of a novel packing material for the gas-phase fluidized-bed bioreactor
Introduction
Biological air treatments, mainly with packed beds, have been applied to purify industrial volatile organic compounds (VOCs) such as toluene and chlorobenzene. These treatments have the advantages of high efficiency, low cost, and no resultant secondary pollution (Cheng et al., 2016; Kennes and Veiga, 2004). Packing materials play an important role in biolfiltration by providing support for microbial growth (Haque et al., 2012). Contaminants are adsorbed or captured on the surface of packing materials and degraded by microorganisms.
Various organic, natural, inorganic, or entirely synthetic materials, such as compost, activated carbon, ceramic rings, peat, perlite, glass beads, polyurethane foam (PUF), and polystyrene, have attracted much attention in lab-scale studies and industrial applications (Dorado et al., 2010). Their characteristics, including surface characteristics and density, play an important role in microbial growth and removal performance (Sun et al., 2020). Research on their surface characteristics, hydrophily, moisture retention capacities, and specific surface area have revealed their importance in microbial growth and removal performance (Gaudin et al., 2008; Oh and Choi, 2000).
However, an uneven distribution of biomass causes clogging, channeling, and deterioration of removal performance. This is unavoidable in biofiltration with packed beds (Yang et al., 2010). Difficulties, including increase in pressure drop and performance decline (Xi et al., 2015), have been caused by the uneven nutrient and biomass distribution (Burns and Ramshaw, 1996; Cabrol et al., 2012) and the overgrowth of biomass in the reactor. The high space requirement is yet another problem caused by low efficiency in the utilization of packing materials.
To overcome this limitation, fluidized bed bioreactors have been widely applied in waste water treatment with fluidized packing materials to overcome clogging and obtain a homogenous distribution of nutrients and microorganisms (Qin et al., 2014). High air flow velocity in fluidized bed bioreactors homogenously mixes the packing materials and prevents clogging (Wright and Raper, 1996), resulting in higher mass transfer efficiency. A previous study reported mass transfer coefficients with ethanol treatment ranging from 49 to 81 h−1 in fluidized beds as compared with 13–32 h−1 in packed beds (Clarke et al., 2007).
However, research in air purification has proceeded slowly. Limited research have been reported about successful applications of natural materials such as sawdust, coarse waste wood, fine waste wood, and peat particles in fluidized bed bioreactors, for ethanol and toluene treatments (Clarke et al., 2008, 2007; Clarke et al., 2005; Leslous et al., 2004). Packing materials have strict requirements about the density and surface characteristics. Low density is required for low minimum fluidized velocity, and hydrophilic surfaces are necessary for microbial growth. The lowest velocity reported previously was around 0.4 m∙s−1 to have achieved the fluidized state, which lead to increasing energy consumption and space requirements (Delebarre et al., 2007).
Agar-coated polyurethane foam plastics obtain a considerable biomass but they have a minimum fluidized velocity that is still high for application (Leslous et al., 2004). In addition, several studies have also mentioned the importance of packing materials in gaseous fluidized beds (Clarke et al., 2009; Leslous et al., 2004). As reported earlier, the characteristics of packing materials, including density, particle size, and surface characteristics, influence the performances of fluidized bioreactors (Wirsum et al., 2001). Therefore, suitable packing materials and optimization plans are needed for fluidized bioreactors in VOC purification.
In this study, two kinds of commercial materials, with low density and price, were used as packing materials and their feasibility as packing material was further explored. In order to obtain a hydrophilic surface, potato dextrose medium, fine particle wheat bran, and inorganic glue were selected from agar and other materials for physical coating. Drying temperature, glue concentration, and spray amount were explored to optimize the coating method; the ideal relative humidity was confirmed to obtain a low minimum fluidized velocity.
With these packing materials, a gaseous fluidized bioreactor was set up for the purification of waste air containing volatile organic compounds.
Section snippets
Materials
Six kinds of EPS (expanded polystyrene) and two kinds of EPP (expanded polypropylene) balls were chosen as packing materials in this study (Table S1). The best selection was obtained using measurement of minimum fluidization velocity and pressure drop. Minimum fluidized velocity (vmf) was confirmed by v-P/H (v: gas velocity; P/H: ratio of pressure drop and bed height) curves (Kunii and Levenspiel, 1991). The ratio of pressure drop and bed height increased with the increase of velocity in a
Selection of skeleton
The ratio of pressure drop and bed height (P/H) started to decrease when the air flow rate higher than 0.05 m∙s−1 when the reactor was packed with EPS II. It indicated the minimum fluidized velocity of EPS II was 0.05 m∙s−1. The fluidization characteristics (minimum fluidization velocity and P/H) of eight materials were measured (Fig. 2). EPS II and EPS III obtained the minimum fluidization velocity of 0.05 m∙s−1. The minimum fluidized velocity of EPP (0.23–0.26 m∙s−1) was significantly higher
Conclusion
In this study, a standard procedure was developed to analyze packing materials for fluidized bioreactors. Density increase, agglomeration, microbial growth, and coating stability were chosen for qualitative measurements. Time consumption, weight decline rate, density increase, coverage, and particle agglomeration rate were tested to quantitative parameters to determine the optimal drying temperature, spray amount, and glue addition. Based on these tested standards, an optimizing method for
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
This research was supported by the National Natural Science Foundation of China (Grant No. 52070113). Help from the State Environmental Protection Key Laboratory of Microorganism Application at Tsinghua University is also appreciated. We thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.
References (23)
- et al.
Process intensification: visual study of liquid maldistribution in rotating packed beds
Chem. Eng. Sci.
(1996) - et al.
Treatment of gaseous toluene in three biofilters inoculated with fungi/bacteria: microbial analysis, performance and starvation response
J. Hazard. Mater.
(2016) - et al.
Fluidization of moist sawdust in binary particle systems in a gas-solid fluidized bed
Chem. Eng. Sci.
(2005) - et al.
Improved VOC bioremediation using a fluidized bed peat bioreactor
Process Saf. Environ.
(2008) - et al.
Gas-solid packed and fluidized bed models for bioremediation of volatile organic compounds in air
Biochem. Eng. J.
(2009) - et al.
Packing material formulation for odorous emission biofiltration
Chemosphere
(2008) - et al.
Fungal biocatalysts in the biofiltration of VOC-polluted air
J. Biotechnol.
(2004) - et al.
Particle mixing in bubbling fluidized beds of binary particle systems
Powder Technol.
(2001) - et al.
Biomass accumulation and control strategies in gas biofiltration
Biotechnol. Adv.
(2010) - et al.
Bacterial dynamics in steady-state biofilters: beyond functional stability
FEMS Microbiol. Ecol.
(2012)
Direct comparison of fluidized and packed bed bioreactors for bioremediation of an air pollutant
Int. J. Chem. React. Eng.
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