Torrefaction of sawdust in a fluidized bed reactor

In the present work, stable fluidization of sawdust was achieved in a bench fluidized bed with an inclined orifice distributor without inert bed materials. A solids circulation pattern was established in the bed without the presence of slugging and channeling. The effects of treatment severity and weight loss on the solid product properties were identified. The decomposition of hemicelluloses was found to be responsible for the significant changes of chemical, physical and mechanical properties of the torrefied sawdust, including energy content, particle size distribution and moisture absorption capacity. The hydrophobicity of the torrefied sawdust was improved over the raw sawdust with a reduction of around 40 wt.% in saturated water uptake rate, and enhanced with increasing the treatment severity due to the decomposition of hemicelluloses which are rich in hydroxyl groups. The results in this study provided the basis for torrefaction in fluidized bed reactors.     

Continuous ethanol production by flocculating yeast in the fluidized bed bioreactor

Abstract: Continuous fermentation by a highly flocculant strain of the yeast Saccharomyces cerevisiae was carried out in a tower fluidized-bed bioreactor. The synthetic and molasses media with a total sugar concentration of 17% (w/v) were used for fermentation. Different dilution rates were tested. Stable cell densities of 50 kg m^-3(dry weight) were maintained for all dilution rates. The ethanol productivity was increasing linearly with dilution rates up to 15—20 kg m^-3 h^-1. Aeration of the culture stabilized flocculating activity and viability of yeast and also permitted long-term operation of the bioreactor.     

Characterization of sulfate-reducing bacteria dominated surface communities during start-up of a down-flow fluidized bed reactor

An anaerobic down-flow fluidized bed reactor was inoculated with granular sludge and started-up with sulfate containing synthetic wastewater to promote the formation of a biofilm enriched in sulfate-reducing bacteria (SRB), to produce biogenic sulfide. The start-up was done in two stages operating the reactor in batch for 45 days followed by 85 days of continuous operation. Low-density polyethylene was used as support. The biofilm formation was followed up by biochemical and electron microscopy analyses and the composition of the community was examined by 16S rDNA sequence analysis. Maximum immobilized volatile solids (1.2 g IVS/L_support) were obtained after 14 days in batch regime. During the 85 days of continuous operation, the reactor removed up to 80% of chemical oxygen demand (COD), up to 28% of the supplied sulfate and acetate was present in the effluent. Sulfate-reducing activity determined in the biofilm with ethanol or lactate as substrate was 11.7 and 15.3 g COD/g IVS per day, respectively. These results suggested the immobilization of sulfate reducers that incompletely oxidize the substrate to acetate; the phylogenetic analysis of the cloned 16S rDNA gene sequences showed high identity to the genus Desulfovibrio that oxidizes the substrates incompletely. In contrast, in the granular sludge used as inoculum a considerable number of clones showed homology to Methanobacterium and just few clones were close to SRB. The starting-up approach allowed the enrichment of SRB within the diverse community developed over the polyethylene support.     

Feasibility study of degradation of phenol in a fluidized bed bioreactor with a cyclodextrin polymer as biofilm carrier

This work is focused on the evaluation of a beta-cyclodextrin polymer as a carrier medium in a fluidized bed bioreactor treating aqueous phenol as a model pollutant. The insoluble polymer support was obtained in the shape of spherical beads by crosslinking beta-cyclodextrin with epichlorohydrin. A batch of swollen polymer particles was loaded into the reactor and inoculated with a mixed bacterial culture. Bacterial growth on the polymer beads was initially stimulated by glucose addition to the medium, and then gradually replaced with phenol. The operational variables studied after the acclimation period included phenol load, hydraulic residence time and recirculation flow rate. Low hydraulic residence times and moderate phenol loads were applied. The elimination capacity was usually about 1.0 kg-phenol/m(3)d, although a maximum of 2.8 kg-phenol/m(3)d was achieved with a retention time of only 0.55 h. The depuration efficiency was not affected by the recirculation flow rate in the range studied. Neither operational nor support stability problems were detected during the operation. A high degree of expansion was achieved in the bioreactor due to the hydrogel nature of the cyclodextrin polymer and, consequently, a low energy requirement was necessary to fluidize the bed.     

Microbial community structure and operational performance of a fluidized bed biofilm reactor treating oil sands process-affected water

This study evaluated the treatment of oil sands process-affected water (OSPW) using a fluidized bed biofilm reactor (FBBR) with granular activated carbon (GAC) as support media. The bioreactor was operated for 120 days at different organic and hydraulic loading rates. The combined GAC adsorption and biodegradation process removed 51% of chemical oxygen demand (COD), 56% of acid-extractable fraction (AEF) and 96% of classical naphthenic acids (NAs) under optimized operational conditions. Bioreactor treatment efficiencies were dependent on the organic loading rate (OLR), and to a lower degree, on the hydraulic loading rate (HLR). Further ultra performance liquid chromatography/high resolution mass spectroscopy (UPLC/HRMS) analysis showed that the removal of classical NAs increased as the carbon number increased. Compared with planktonic bacterial community in OSPW, more diverse microbial structures were found in biofilms colonized on the surface of GAC after 120-day treatment, with various carbon degraders namely Polaromonas jejuensis, Algoriphagus sp., Chelatococcus sp. and Methylobacterium fujisawaense in the GAC-biofilm reactor. The results of this study, therefore, showed that the GAC-biofilm seems to be a promising biological treatment method for OSPW remediation.     

Selection of Type I and Type II methanotrophic proteobacteria in a fluidized bed reactor under non-sterile conditions

Type II methanotrophs produce polyhydroxybutyrate (PHB), while Type I methanotrophs do not. A laboratory-scale fluidized bed reactor was initially inoculated with a Type II Methylocystis-like dominated culture. At elevated levels of dissolved oxygen (DO, 9 mg/L), pH of 6.2–6.5 with nitrate as the N-source, a Methylobacter-like Type I methanotroph became dominant within the biofilms which did not produce PHB. A shift to biofilms capable of PHB production was achieved by re-inoculating with Type II Methylosinus culture, providing dissolved N₂ as the N-source, and maintaining a low influent DO (2.0 mg/L). The resulting biofilms contained both Types I and II methanotrophs. Batch tests indicated that biofilm samples grown with N₂ became dominated by Type II methanotrophs and produced PHB. Enrichments with nitrate or ammonium were dominated by Type I methanotrophs without PHB production capability. The key selection factors favoring Type II were N₂ as N-source and low DO.     

Removal of aqueous phenol using immobilized enzymes in a bench scale and pilot scale three-phase fluidized bed reactor

The main objective of this work was to investigate the removal of aqueous phenol using immobilized enzymes in both bench scale and pilot scale three-phase fluidized bed reactors. The enzyme used in this application was a fungal tyrosinase [E.C. 1.14.18.1] immobilized in a system of chitosan and alginate. The immobilization matrix consisted of a chitosan matrix cross-linked with glutaraldehyde with an aliginate-filled pore space. This support matrix showed superior mechanical properties along with retaining the unique adsorptive characteristics of the chitosan. Adsorption of the o-quinone product by the chitosan reduced tyrosinase inactivation that is normally observed for this enzyme under these conditions. This approach allowed reuse of the enzyme in repeated batch applications. For the bench scale reactor (1.2-l capacity) more than 92% of the phenol could be removed from the feed water using an immobilized enzyme volume of 18.5% and a residence time of the liquid phase of 150 min. Removal rates decreased with subsequent batch runs. For the pilot scale fluidized bed (60 l), 60% phenol removal was observed with an immobilized enzyme volume of 5% and a residence time of the liquid phase of 7 h. Removal decreased to 45% with a repeat batch run with the same immobilized enzyme.     

Preparation and characterization of mixed-mode magnetic adsorbent with p-amino-benzamidine ligand: Operated in a magnetically stabilized fluidized bed reactor for purification of trypsin from bovine pancreas

The magnetic beads were synthesized using glycidylmethacrylate (GMA) and methylmethacrylate (MMA) monomers. A multimodal ligand (i.e., p-amino-benzamidine) was covalently immobilized onto magnetic beads after glutaraldehyde activation, and consequently used for purification of the trypsin from bovine pancreas. The p-amino-benzamidine ligand immobilized magnetic beads were characterized by FTIR, VSM, SEM, and analytical methods. Trypsin adsorption experiments were investigated under different experimental conditions (i.e., medium pH, initial trypsin concentration, temperature, and ionic strength) in a batch system. Maximum trypsin adsorption capacity was found to be 75.9 ± 2.6 mg/g beads. Adsorbed trypsin was eluted by using (0.1 M acetate buffer, pH 3.0) with a 97% recovery. The purification factor of trypsin from crude pancreas extract was 8.7 folds. The purity of the eluted trypsin from p-amino-benzamidine functionalized magnetic beads was determined as 86% by HPLC. The method developed in this report was successfully applied for purification of the trypsin from crude pancreas extract in a magnetically stabilized fluidized bed reactor.     

Treatment of high-strength purified terephthalic acid (PTA) wastewater using a magnetic porous ceramic support in laboratory-scale anaerobic-aerobic fluidized bed reactors

Abstract

Laboratory-scale anaerobic-aerobic fluidized-bed bioreactors (FBR) with porous magnetic ceramics as support were successfully applied to treat purified terephthalic acid (PTA) wastewater. After a short 14-day start-up period, the system was stably operating. During the 40?d stable period, the system organic loading rate (OLR) increased from 6.68 to 23.87?kg chemical oxygen demand (COD)/(m³d), the effluent COD and PTA were below 90 and 30?mg/L, respectively. The FBR presented excellent COD and PTA removal efficiency with a low hydraulic retention time (HRT) value of six hours. The growth kinetic parameters suggested that the biomass in FBR possess high maximum specific growth rate (μ_max?=?2.22?d^?1) and good tolerance to varied OLR (K_s?=?258.67?mg COD/L).     

Isopropanol biodegradation by immobilized Paracoccus denitrificans in a three-phase fluidized bed reactor

A three-phase bed bioreactor including a mix of immobilized microbes was used to degrade isopropanol (IPA). The immobilization method was studied and cells immobilized with calcium alginate, polyvinyl alcohol, activated carbon, and SiO₂ were demonstrated to be the best immobilization method for the degradation of 90% of 2?g/L IPA in just 4 days, 1 day earlier than with free cells. Acetone was monitored as an indicator of microbial IPA utilization as the major intermediate of aerobic IPA biodegradation. The bioreactor was operated at hydraulic retention time (HRT) values of 32, 24, 16, 12, and 10?hr, which correspond to membrane fluxes of 0.03, 0.04, 0.06, 0.08, and 0.10?L/m²/hr, respectively. The chemical oxygen demand (COD) removal efficiencies were maintained at 98.0, 97.8, 89.1, 80.6, and 71.1% at a HRT of 32, 24, 16, 12, and 10?hr, respectively, while the IPA degradations were 98.6, 98.3, 90.3, 81.6, and 73.3%, respectively. With a comprehensive consideration of COD removal and economy, the optimal HRT was 24?hr. The results demonstrate the potential of immobilized mixed bacterial consortium in a three-phase fluidized bed reactor system for the aerobic treatment of wastewater containing IPA.     

Effect of fluidising velocity on the combustion of rice husk in a bench-scale fluidised bed combustor for the production of amorphous rice husk ash

This study was focused on investigating the optimum fluidising velocity during the combustion of rice husk in a bench-scale fluidised bed combustor (ID 210mm) to obtain low carbon ash in the amorphous form. When all other parameters are held constant, the optimum fluidizing velocity aids in almost complete combustion, thereby releasing the entrapped carbon for further conversion. This results in ash with consistently low carbon content (less than 2wt%). The range of fluidising velocities investigated was from as low as 1.5U(mf) to as high as 8U(mf). It was found that the optimum fluidising velocity was approximately 3.3U(mf) as the mixing of rice husk with the bed was good with a high degree of penetration into the sand bed. The resulting ash retained its amorphous form with low residual carbon content (at 2.88wt%) and minimal sand contamination as shown by the X-ray diffraction analysis.     

Detachment of multi species biofilm in circulating fluidized bed bioreactor

In this study, the detachment rates of various microbial species from the aerobic and anoxic biofilms in a circulating fluidized bed bioreactor (CFBB) with two entirely separate aerobic and anoxic beds were investigated. Overall detachment rate coefficients for biomass, determined on the basis of volatile suspended solids (VSS), glucose and protein as well as for specific microbial groups, i.e., for nitrifiers, denitrifiers, and phosphorous accumulating organisms (PAOs), were established. Biomass detachment rates were found to increase with biomass attachment on carrier media in both beds. The detachment rate coefficients based on VSS were significantly affected by shear stress, whereas for protein, glucose and specific microbial groups, no significant effect of shear stress was observed. High detachment rates were observed for the more porous biofilm structure. The presence of nitrifiers in the anoxic biofilm and denitrifiers in the aerobic biofilm was established by the specific activity measurements. Detachment rates of PAOs in aerobic and anoxic biofilms were evaluated.     

Understanding and modeling retention of mammalian cells in fluidized bed centrifuges

Within the last decade, fully disposable centrifuge technologies, fluidized‐bed centrifuges (FBC), have been introduced to the biologics industry. The FBC has found a niche in cell therapy where it is used to collect, concentrate, and then wash mammalian cell product while continuously discarding centrate. The goal of this research was to determine optimum FBC conditions for recovery of live cells, and to develop a mathematical model that can assist with process scaleup. Cell losses can occur during bed formation via flow channels within the bed. Experimental results with the kSep400 centrifuge indicate that, for a given volume processed: the bed height (a bed compactness indicator) is affected by RPM and flowrate, and dead cells are selectively removed during operation. To explain these results, two modeling approaches were used: (i) equating the centrifugal and inertial forces on the cells (i.e., a force balance model or FBM) and (ii) a two‐phase computational fluid dynamics (CFD) model to predict liquid flow patterns and cell retention in the bowl. Both models predicted bed height vs. time reasonably well, though the CFD model proved more accurate. The flow patterns predicted by CFD indicate a Coriolis‐driven flow that enhances uniformity of cells in the bed and may lead to cell losses in the outflow over time. The CFD‐predicted loss of viable cells and selective removal of the dead cells generally agreed with experimental trends, but did over‐predict dead cell loss by up to 3‐fold for some of the conditions. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1520–1530, 2016     

The influence of complex biological feedstock on the fluidization and bed stability in expanded bed adsorption

The stability of expanded bed adsorption systems (EBA) was studied in biomass containing culture broth by residence time distribution (RTD) experiments, using pulse inputs of fluorescent molecules as tracers. Different commercial adsorbents (Streamline DEAE, SP, Phenyl, Chelating, and AC) were tested at various biomass concentrations (2.5–12 %, wet weight) of whole (Saccharomyces cerevisiae) yeast, yeast cell homogenate, and Escherichia coli homogenate. Analyzing the RTD according to the PDE model (PDE: axially dispersed plug‐flow exchanging mass with stagnant zones) allowed the calculation of three parameters: the number of transfer units for mass exchange between mobile and stagnant fraction (N), the Peclet number for overall axial dispersion (P), and the mobile fraction of the liquid in axially dispersed plug flow (φ). When fluidization was performed in particle‐free buffer the normalized response signal (after perfect input pulse) was symmetric (N:0; P: 50–100; φ: 1), thus, demonstrating the formation of a homogeneous fluidized (expanded) bed. Upon application of suspended biomass the RTD was skewed, depending on the adsorbent used and the type and level of biomass present in the sample. This situation leads to three different characteristic pictures: the well‐fluidized system (N: ≥ 7–10; P: ≥ 40; φ: 0.80–0.90), the system exhibiting bottom channeling (N: < 1–2; P: ≥ 40; φ: 0.5–0.7) and, the system where extensive agglomeration develops (N: 4–7; P: 20–40; φ: < 0.5). These results demonstrate that changes in the hydrodynamics of EBA already take place in the presence of moderate concentrations of biomass. Furthermore, those changes can be quantitatively described mainly in terms of the fraction of stagnant zones in the system, which are formed due to the interaction of biomass and adsorbent. The technique described here can be used to evaluate a certain combination of adsorbent and biomass with regard to its suitability for expanded bed adsorption from whole broth. © 1999 John Wiley & Sons, Inc. Biotechol Bioeng 64: 484–496, 1999.     

Impact of long-term partial aeration on the removal of 2,4,6-trichlorophenol in an initially methanogenic fluidized bed bioreactor

A fluidized bed bioreactor (FBBR) was operated for more than 1000 days under two regimes, Methanogenic (M) and Methanogenic-Aerobic (M-A), to remove 2,4,6-trichlorophenol (TCP) and phenol (Phe) from a synthetic wastewater, containing different amounts of TCP and Phe, using different aeration flow-rates (0, 2.13, and 1.06 NL O(2)/L.day). M conditions (80:20 mg/L of TCP:Phe, 0 NL O(2)/L.day) showed similar TCP and Phe removal (>95%). Nevertheless accumulation of 4-chlorophenol (4CP) up to 16 mg/L and Phe up to 4 mg/L was observed, while in M-A conditions (80:20 mg/L of TCP:Phe, 2.13 NL O(2)/L.day) TCP and Phe removal achieved 99.9(+)% and after 70 days no accumulation of intermediates were detected. The increase of TCP and Phe in the influent under M-A conditions from 80:20 to 120:30 mg/L of TCP:Phe did not negatively affect the removal of TCP, intermediates and Phe; in fact, they were similar to those in previous M-A conditions. The decrease in the oxygen flow rate from 2.13 to 1.06 NL O(2)/L.day had no negative effect on pollutant removals, which were as high as in previous two M-A conditions. The specific methanogenic activity of bioparticles of the fluidized bed decreased with long-term partial aeration, starting from 1.097 mmol CH(4)/h.g(TKN) in the M regime (day 60) to <0.02 mmolCH(4)/h.g(TKN) at day 1050, suggesting aerobic regime in the bioreactor rather than an M-A regime. In conclusion, complete removal of TCP and less chlorinated intermediates could be achieved in an initially methanogenic FBBR under conditions of partial aeration, although long-term operation seemed to negatively affect the methanogenic activity of biomass. It is also likely that after extended aeration the microbial community was finally enriched with strains with the ability to attack 2,4,6-TCP under aerobic conditions. This report represents the first evidence of a long exposure to oxygen of an anaerobic microbial consortium that efficiently remove TCP.     

The effect of porosity of seiving particles on the romoval efficiency of organic substances via biofilter in the fixed bed

This paper was investigated to clarify the possibility of a biodegradation of materials adsorbed on different porous granular-activated carbons (GACs) such as coal-& coconut-based GAC. Total organic carbon, humic substance and ammonia were used to compare their removal efficiencies. The objective of this study is to determine the adsorption capacity of bioregenerated GAC. When raw water reacted with chloride, the yield of THMs increased as a function of the input amount of chloride. The formation of trihalomethanes (THMs) was investigated in water treated with chlorine when humic acid was used as THM precursor. As the input amount of chloride in raw water increased by two or five-fold to remove the NH₃, the chloroform of the THMs significantly increased also five or ten-fold. It was found that the chloroform was significantly removed by the treatment of biological activated carbon (BAC) in comparison with the ozone treatment, and the removal efficiency of THMs in coal-typed GAC was 10–30% better than coconut-typed GAC due to the biological degradation on the surface of the activated carbons.     

Effect of coal combustion wastes used as lime substitutes in nutrition of apples in three soils

Summary Fluidized bed combustion represents a feasible technology for energy production utilizing high S fossil fuels. The process generates not only bed waste (FBM) (coal ash plus CaSO₄ and unreacted CaO) but also flyash (FA). The later waste has not been evaluated for its effects on plants and soils. A greenhouse experiment, using apple seedlings, was carried out using FBM, FA and calcitic limestone applied at or up to twice the lime requirement on three soil materials. Seedling growth varied dependent upon the treatment-soil combination. Growth was reduced by 60% on the Manor soil from FA applied at twice the lime requirement and was attributed to the higher initial reactiveness of the FA compared to FBM or limestone. Leaf P, K, N, Cu and Al were not significantly affected by treatments over all soils while Ca, and N decreased and Mg varied depedent upon treatment. Soil pH was increased by all treatments. DTPA (diethylenetriaminepentaacetic acid) extractable Mn and Zn were good estimators of leaf Mn and Zn while DTPA Cu and Fe were not.     

The fluidized bed reactor in the anaerobic treatment of wine wastewater

The aim of the present work is the performance evaluation of a fluidized bed reactor in the anaerobic treatment of a wastewater deriving from the washing operations of the wine industry. The results are in agreement with the ones obtained using a mixture of municipal and food processing wastewaters containing high organic contents. A comparison with other liquid wastes shows that no subtrate inhibition phenomenon occurs with the above substrates. A saturation kinetic model is also presented for describing the dependence of the COD removal rate on the organic loading rate.     

The effect of the particle size of alumina sand on the combustion and emission behavior of cedar pellets in a fluidized bed combustor

A combustion experiment with cedar pellet fuel was carried out in a semi-pilot scale bubbling fluidized bed combustor. The effects of temperature, fluidized velocity, and bed material particle size on the emission of NOx, CO, and CO2 were investigated. The variations in the temperature profile and gas concentration in the vertical and horizontal directions of the combustor were also studied. The results showed that high temperature can improve the combustion efficiency and decrease CO emission. Moreover, increasing the fluidized velocity suppressed CO formation. In addition to temperature and fluidized velocity, the bed material also played an important role during cedar pellet combustion. Coarse bed materials were better than fine materials. In these test runs, the CO emission varied from 20 to 189 ppm, CO2 emission ranged from 5.7% to 19.5%, while NOx emission was quite stable at about 220 ppm.