Fluidized Bed Bioreactor Research Articles

Seasonal dynamics of bacterial composition and functions in biological treatment of coking wastewater

Seasonal dynamics of bacterial composition and functions were demonstrated for the biological fluidized-bed bioreactors combined in the anoxic/aerobic1/aerobic2 (AOO) coking wastewater (CWW) treatment sequences. The bacterial composition and functions in the CWW activated sludge samples were revealed by 16S rRNA genes amplicon sequencing. Thiobacillus, Cloacibacterium, Alkaliphilus and Pseudomonas were determined as core genera with seasonal changes. Mutable microbial community composition fluctuated in different seasons in same bioreactor. Distributions of predicted KEGG pathways along four seasons consistently demonstrated enrichment in biodegradation of carbon- and nitrogen-containing compounds. The major contaminants were removed from CWW by biochemical pathway of xenobiotics biodegradation and metabolism. This Level 2 pathway mainly owned the Level 3 pathways of benzoate degradation, drug metabolism-other enzymes, drug metabolism-cytochrome P450, metabolism of xenobiotics by cytochrome P450, and aminobenzoate degradation. The RDA results showed that dissolved oxygen with seasonal fluctuation was the main parameter shaping the microbial community. The observed dynamics within the microbial community composition, coupled with the maintained stability of CWW treatment efficiencies and a consistent profile of microbial functional pathways, underscore the presence of functional redundancy in the AOO bioreactors. The study underscored stable and effective operational performances of bioreactors in the AOO sequences, contributing the knowledge of microbiological basics to the advancement of CWW biological treatment.Key points• Seasonal fluctuations of bacterial composition described for the AOO system.• Seasonal distributions of metabolic functions focused on carbon and nitrogen removal.• Functional redundancy was revealed in the AOO microbial community.

Pharmaceuticals removal from hospital wastewater by fluidized aerobic bioreactor in combination with tubesettler

Micropollutants, especially pharmaceutical compounds, are of significant concern owing to their ngL− 1 to µgL− 1 concentration, making them difficult for conventional treatment plants to remove from wastewater. Despite municipal wastewater treatment plant being a primary source of these compounds to be released into the wastewater, on comparison little attention has been given to hospital wastewater. The major focus of studies addressing pharmaceutical compounds is based on synthetic wastewater. This study addresses this research gap by treating wastewater to remove micropollutants (Fluvastatin, ketoprofen, paracetamol, ciprofloxacin, carbamazepine, sulfamethoxazole, and lorazepam) by employing a fluidized aerobic bioreactor. Tubesettler was attached to a fluidized-bed bioreactor to see if it could be used as a polishing unit rather than a secondary clarifier. The environmental risk from the effluent discharge into the environment was assessed regarding the hazard quotient. The paracetamol and ketoprofen were removed at an efficiency of 51% and 60%, respectively, followed by carbamazepine at 50%, ciprofloxacin at 40%, fluvastatin at 47%, sulfamethoxazole at 31%, and lorazepam at 20%. The influent posed moderate environmental risk with (Hazard Quotient) HQ > 0.5, while in effluent the risk was reduced with HQ value 0.4. For effluent from fluidized bed bioreactors (HQ 0.13) and tube setters (HQ 0.15). The associated tube settler was found suitable for polishing units with additional removal efficiencies of 15–43% for all the targeted pharmaceutical compounds. Further studies are required to explore disinfectants’ effect on the reactor’s biodegradation efficiency. Also, further modification and a hybrid version of the fluidized bed bioreactor can be used.

Innovative high-performance and energy-positive Co-treatment of organic kitchen waste and domestic wastewater using a fluidized bed ceramic membrane bioreactor

The aim of the study was to efficiently treat organic kitchen waste (FW) and domestic wastewater (DWW) together in an anaerobic fluidized bed bioreactor equipped with a ceramic membrane (AnFCMBR) through a sustainable approach considering energy recovery. The system operated continuously for 519 days at room temperature, and different filtration fluxes (1.7 and 5 L/m2/h), hydraulic retention times (HRTs) (22 h and 7 h), and organic loading rate (OLRs) (0.46, 1.52, 3.42, 6.08 kg/m3.d) were tested. The amount of organic matter in DWW may be insufficient for feasible gas production, but this challenge can be resolved through the addition of food waste. Influent chemical oxygen demand (COD) of 500 ± 143 mg/L gradually increased to 2000 ± 196 mg/L by increasing the portion of FW. The COD removal ranged from 92 to 98% throughout the study, with the membrane and the cake layer contributing 5–8% to the performance. Average supernatant SMP and EPS concentrations increased from 5 ± 1 to 45 ± 5 mg COD/L and from 54 ± 7 to 254 ± 26 mg COD/g VSS, respectively, when the highest amount of FW was added to the synthetic wastewater. This significant increase in SMP and EPS concentrations due to the addition of FW negatively impacted the filtration performance. SRF and CST values also increased with rising OLR, especially with the supplementation of synthetic wastewater with FW.After FW started to be mixed with DWW, the methane production increased approximately 5.5 times. With the use of AnFCMBR for the co-treatment of FW and DWW, it is possible to achieve energy-positive treatment with high-quality effluent that can be reused for various applications, such as irrigation. The methane produced provided 12 times more energy than was needed to operate the bioreactor.This is the first study evaluating the co-treatment of FW and DWW in AnFCMBR under varying operational parameters.

A hybrid BOA-SVR approach for predicting aerobic organic and nitrogen removal in a gas-liquid-solid circulating fluidized bed bioreactor

This study introduces the hybrid of the Bayesian optimization algorithm and support vector regression (BOA-SVR) models to predict the removal of aerobic organic (total chemical oxygen demand, COD) and nitrogen compounds such as total Kjeldahl Nitrogen (TKN), ammonium nitrogen (NH4-N), and nitrate nitrogen (NO3-N) from municipal wastewater in a gas-liquid-solid circulating fluidized bed (GLSCFB) bioreactor. GLSCFB bioreactors treat wastewater by removing nutrients biologically. The downer of a GLSCFB bioreactor provided experimental data on TKN, NH4-N, NO3-N, and TCOD removal. The hybrid optimal intelligence algorithm (BOA-SVR) has improved model accuracy across multiple domains by combining BOA and SVR. The coefficient of determination (R2), residual, mean absolute error (MAE), root mean square error (RMSE), and fractional bias (FB) were used to analyze BOA-SVR model performance. The models match experimental data from four operational stages well, with R2 or adj R2 values above 0.99 for all responses. The model's accuracy was confirmed by relative deviations and residual plots showing dispersion around the zero-reference line. The BOA-SVR model consistently predicted dependent variables with low RMSE and MAE values (≤ 2.24 and 2.21, respectively) and near-zero FB. Computing efficiency was shown by optimizing TCOD, TKN, NH4-N, and NO3-N models in 70.61, 72.89, 74.37, and 54.07 s. A rigorous test on unseen data with different noise levels confirmed the model's stability. Furthermore, BOA-SVR performs better than traditional multiple linear regression (MLR). Overall, the BOA-SVR model predicts biological nutrient removal in municipal wastewater utilizing a GLSCFB bioreactor quickly, correctly, and efficiently, reducing experimental stress and resource use.

Achieving decarbonization considering green hydrogen production: Case study of Oman

Life Cycle Assessment (LCA) method is employed to study and mitigate negative environmental impacts using various approaches via OpenLCA software. This paper investigates the LCA of green hydrogen gas production from produced water in Oman, using the Activated Sludge Method (ASM) and Fluidized-Bed Bioreactor (FBB), as treatment technologies. Different scenarios were considered, utilizing the ReCiPe midpoint impact method over 100 years, to evaluate global warming potential (GWP100), fossil depletion potential (FDP), and water depletion (WDP). The objective is to compare and evaluate the sustainability of Dark Fermentation (DF) and Electrolysis methods for hydrogen gas production from both treatment technologies to achieve Oman's Vision 2040. The DF method involves utilizing sludge from both primary and secondary treatment stages, while the Electrolysis method uses the tertiary treatment stage. Results show that using 50 % (15,000 m³/day) of the flow for hydrogen production, the DF yields 60,000 kg of H2/day, while the electrolysis method produces 833,333 kg of H2/day. This difference arises because the DF method depends on sludge production, impacting hydrogen gas production, whereas, the electrolysis method relies entirely on treated water. Both processes significantly impact GWP100. Incorporating solar power for ASM and FBB, as a green energy source, reduces CO2 emissions by 7560.28 kg CO2-eq for DF and 8245.18 kg CO2-eq for electrolysis. This study provides a novelty application, which contributes to advancing sustainability practices through evaluating the environmental impacts of using produced water for green hydrogen production in waste-to-energy and advocates for energy policy making regarding recent climate change commitments.

Modeling and analysis of particle behavior in fluidized bed bioreactors during non-Newtonian sewage treatment

The stability of biofilms attached to support particles plays a crucial role in fluidized bed bioreactors (FBBRs) when treating non-Newtonian sewage. Biofilm instability is governed by particle-particle (P-P) and particle-wall (P-W) collisions. This paper presents a numerical study of particle behavior in a FBBR using a combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) tailored for non-Newtonian flow systems. Following validation, the CFD-DEM model is utilized to quantify the FBBR performance regarding bed expansion, void fraction distribution, and P-P/W interactions. The impacts of three variables are examined, including sewage superficial velocity and two rheological properties, i.e., sewage temperature and solid concentration. The results reveal that increasing sewage superficial velocity and sewage solid concentration or decreasing sewage temperature, leads to a transition in particle flow from symmetrical to asymmetrical in the radial direction, along with a circulating flow at the lower part of the bed. The relationships between the variables and the bed expansion, uniformity, and P-P/W interactions are also established, identifying optimum conditions to enhance bed uniformity and reduce P-P/W interactions. Overall, the findings demonstrate the value of the CFD-DEM model for understanding, designing, and optimizing FBBRs.

Steady state characteristics of a three-phase fluidized bed bioreactor with partial biomass recirculation

Steady state characteristics of a three-phase fluidized bed bioreactor with partial biomass recirculation

Modelling selenite and chemical oxygen demand removal in an inverse fluidized bed bioreactor using genetic algorithm optimized artificial neural network

AbstractBACKGROUNDA genetic algorithm (GA) optimized artificial neural network (ANN) model was developed to simulate selenite removal efficiency (SRe) and chemical oxygen demand (COD) removal efficiency (CRe) in a single‐stage inverse fluidized bed reactor (IFBR) operated under different hydraulic retention time (HRT) (12–48 h), and inlet selenite concentration (12.7–635 mg L−1). Multi‐objective optimization for SRe and CRe with the ANN model was adopted to estimate the pareto optimal solutions in the bioreactor system.RESULTSGA optimized ANN topology suggested five neurons in the hidden layer, and the optimal data partitioning between training, test, and validation subsets (in 70:15:15 ratio) using cross‐validation. The average fitness for SRe and CRe of the resulting ANN model over training (R2 = 0.885), test (R2 = 0.967) and validation (R2 = 0.972) subsets were reasonably good. Sensitivity analysis suggested an increase in SRe and CRe with HRT, while an increase in inlet selenite concentration had a negative effect on SRe. Local interpretable model‐agnostic explanations and SHapley Additive exPlanations for the developed model suggested a positive coefficient of the predictors on CRe. Pareto optimal solution for SRe (92.87%–95.26%), and CRe (91.33%–99.35%) were suggested for HRT and inlet selenite concentration varying between 35.67 h and 36 h, and 0.1 g L−1 and 0.884 g L−1, respectively.CONCLUSIONSThe GA optimized ANN model could be exploited for the prediction of contaminant removal efficiencies in the bioreactor system with a fair degree of complexity (i.e., IFBR). Multiple objective pareto optimal solutions can identify the best operating conditions relevant for wastewater treatment. © 2023 Society of Chemical Industry (SCI).

Exergetic analysis and optimization of process variables in xylitol production: Maximizing efficiency and sustainability in biotechnological processes

This study presents an exergetic analysis of xylitol fermentative production from hemicellulose hydrolysate, aiming to optimize operational conditions in a fluidized bed bioreactor. The aerobic fermentation conditions evaluated in this study (gas flow rate - x1, hydrolysate concentration factor - x2, and recirculation flow rate - x3) were optimized using various exergetic parameters and xylitol yield as objective functions. Four objective functions were defined for the mono-objective optimization process: rational exergetic efficiency, normalized destroyed exergy, thermodynamic sustainability index, and xylitol yield factor. The results reveal that the optimization problem involves conflicting objectives when considering both yield-based and exergy-based approaches. Thus, the bioreactor's performance was formulated as a multi-objective problem, where the yield factor and thermodynamic sustainability index were simultaneously maximized. For the multi-objective optimization, the ideal operational variable ranges were found to be: 594 ≤x1≤ 619 mL/min, x2= 7 e 37 ≤x3≤ 57 L/h.

Treatment of phenolic wastewater by anaerobic fluidized bed microbial fuel cell using carbon brush as anode: microbial community analysis and m-cresol degradation mechanism.

Anaerobic fluidized bed microbial fuel cell (AFB-MFC) is a technology that combines fluidized bed reactor and microbial fuel cell to treat organic wastewater and generate electricity. The performance and the mechanism of treating m-cresol wastewater in AFB-MFC using carbon brush as biofilm anode were studied. After 48h of operation, the m-cresol removal efficiency of AFB-MFC, MAR-AFB (fluidized bed bioreactor with acclimated anaerobic sludge), MAR-FB (ordinary fluidized bed reactor with only macroporous adsorptive resin) and AST (traditional anaerobic sludge treatment) were 95.29 ± 0.67%, 85.78 ± 1.81%, 71.24 ± 1.86% and 70.41 ± 0.32% respectively. The maximum output voltage and the maximum power density of AFB-MFC using carbon brush as biofilm anode were 679.7mV and 166.6 mW/m2 respectively. The results of high-throughput sequencing analysis indicated the relative abundance of dominant electroactive bacteria, such as Trichococcus, Geobacter, and Pseudomonas, on the anode carbon brushes was higher than that of AST, and also identified such superior m-cresol-degrading bacteria as Bdellovibrio, Thermomonas, Hydrogenophaga, etc. Based on the determination of m-cresol metabolites detected by Gas Chromatography-Mass Spectrometry (GC-MS), the possible biodegradation pathway of m-cresol under anaerobic and aerobic conditions in AFB-MFC was speculated. The results showed that m-cresol was decomposed into formic acid-acetic anhydride and 3-methylpropionic acid under the action of electrochemistry, which is a simple degradation pathway without peripheral metabolism in AFB-MFC.

Development of a magnetically stabilized fluidized bed bioreactor for enzymatic synthesis of 2-ethylhexyl oleate.

This study aimed to develop and investigate the synthesis of 2-ethylhexyl oleate catalyzed by Candida antarctica lipase immobilized on magnetic poly(styrene-co-divinylbenzene) (STY-DVB-M) particles in a magnetically stabilized fluidized bed reactor (MSFBR) operated in continuous mode. The physical properties of the copolymer were characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The glass transition temperature was 85.68°C, and the onset of thermal degradation occurred at 406.66°C. Syntheses were performed at 50°C using a space time of 12h and a bed porosity of 0.892. Assays were conducted to assess the influence of magnetic field intensity (5 to 15 mT) on reaction yield, ester concentration, and productivity. The highest productivity was 0.850 ± 0.023mmolg-1h-1, obtained with a magnetic field intensity of 15 mT. An operational stability test was performed under these conditions, revealing a biocatalyst half-life of 2148h (179 operation cycles) and a thermal deactivation constant of 3.23 × 10-4h-1 (R2 = 0.9446). Computational simulations and mathematical modeling were performed using Scilab based on ping-pong bi-bi kinetics and molar balances of reaction species. The model provided consistent results of interstitial velocity and good prediction of reaction yields, with R2 = 0.926. These findings demonstrate that the studied technique can provide improvements in biocatalytic processes, representing a promising strategy for the enzymatic synthesis of 2-ethylhexyl oleate.

A synergistic approach combining Adsorption and Biodegradation for effective treatment of Acid Blue 113 dye by Klebsiella grimontii entrapped Graphene Oxide-Calcium Alginate Hydrogel Beads

This study investigated the degradation of Acid Blue 113 (AB 113) dye using Klebsiella grimontii entrapped Graphene Oxide-Calcium Alginate Hydrogel beads (KG-GO-CA) in a Fluidized Bed Bioreactor (FBBR) under varying inlet loading rates. The minimum fluidization velocity of the KG-GO-CA hydrogel beads in FBBR was found to be 0.15 mm/s. The KG-GO-CA beads showed a maximum removal efficiency of 94.6% at an inlet flow rate of 20 mL/h over 15 days. Reusability studies indicated a removal efficiency of 70.6 ± 2.5% for AB 113 after the 12th cycle. Langmuir adsorption isotherm showed the best fit (R2 = 0.98724) with model parameters of Qm (203.83 mg/g) and Ki (0.0101 L/g). The study also confirmed that treated wastewater was more environmentally safe for domestic and commercial uses than untreated wastewater. The research highlights the potential use of KG-GO-CA hydrogel beads for removing dyes from wastewater.

Prediction of the bed expansion of a liquid fluidized bed bioreactor applied to wastewater treatment and biogas production

The high potential of water treatment and biogas production systems using liquid fluidization is still underexplored. The design of this equipment is usually done using the simple Richardson-Zaki equation for bed expansion predictions, which is powerful but overlooks the interactions between fluid and particles. In this work, an alternative method based on a force balance on the bed and drag correlations to estimate the bed porosity was proposed. The accuracy of the methods was assessed by comparing bed porosity estimations with experiments carried out in a wide range of regimes (Reynolds numbers between 498 and 18664), using 7 different particles with various diameters (2.66 to 6.37 mm) and densities (1022 to 3585 kg/m3). On average, the fitting between the Richardson-Zaki equation and the experimental results was improved by 60% when the wall effects were considered. The alternative approach using the drag correlations showed promising results, presenting a coefficient of determination higher than 80% for all particles, and better precision in 4 out of the 7 particles compared to Richardson-Zaki. The results show that, in general, both the Richardson-Zaki equation and the drag correlation approach can be used to predict the liquid fluidized bed expansion. However, the proposed approach using drag correlations showed more reliable results, especially when the Rong drag model was applied, with an average coefficient of determination of 0.92. Comparisons with other results in the literature confirm the extent and the scalability of the method. The use of the proposed method to estimate the liquid fluidized bed expansion allows for easier and safer applicability of the technology in areas such as wastewater treatment and biogas production.

Promoting β-cells function by the recapitulation of in vivo microenvironmental differentiation signals.

The study aims to transdifferentiate rat bone marrow-derived mesenchymal stem cells (BM-MSCs) more efficiently into islet-like cells and encapsulate and transplant them with vital properties like stability, proliferation, and metabolic activity enhanced for the treatment of T1DM. Trans-differentiation of BM-MCs into islet-like cells induced by high glucose concentration combined with Nicotinamide, ꞵ-Mercaptoethanol, ꞵ-Cellulin, and IGF-1. Glucose challenge assays and gene expression profiles were used to determine functionality. Microencapsulation was performed using the vibrating nozzle encapsulator droplet method with a 1% alginate concentration. Encapsulated ꞵ-cells were cultured in a fluidized-bed bioreactor with 1850 μL/min fluid flow rates and a superficial velocity of 1.15cm/min. The procedure was followed by transplanting transdifferentiated cells into the omentum of streptozotocin (STZ)-induced diabetic Wistar rats. Changes in weight, glucose, insulin, and C-peptide levels were monitored for 2months after transplantation. PDX1, INS, GCG, NKx2.2, NKx6.1, and GLUT2 expression levels revealed the specificity of generated β-cells with higher viability (about 20%) and glucose sensitivity about twofold more. The encapsulated β-cells decreased the glucose levels in STZ-induced rats significantly (P < 0.05) 1week after transplantation. Also, the weight and levels of insulin and C-peptide reached the control group. In contrast to the treated, the sham group displayed a consistent decline in weight and died when loss reached > 20% at day ~ 55. The coated cells secrete significantly higher amounts of insulin in response to glucose concentration changes. Enhanced viability and functionality of β-cells can be achieved through differentiation and culturing, a promising approach toward insulin therapy alternatives.

Extended Biosynthesis of Rhamnolipid by Immobilized Pseudomonas aeruginosa USM-AR2 Cells in a Fluidized Bed Bioreactor.

This study aims to evaluate rhamnolipid production by immobilized Pseudomonas aeruginosa USM-AR2 cells using waste cooking oil (WCO) as the carbon source. P. aeruginosa USM-AR2 cells were entrapped in polyvinyl alcohol (PVA)-alginate hydrogel beads. The performance of entrapped cells was compared with free cells in shake flasks before cultivation in a custom-designed fluidized bed reactor (FBR). A mass of 1 g wet cells entrapped in PVA-alginate hydrogel beads were successfully recycled 3 times in shake flasks at 200 rpm, producing between 0.66-1.34 g L-1 rhamnolipid after 120 h. Meanwhile, cultivation of entrapped cells in FBR with broth recirculation showed that the suitable hydrogel beads to medium ratio was 1:20 ratio at an aeration rate of 0.5 vvm, producing between 0.77 to 1.58 g L-1 rhamnolipid, degrading 8.67 to 20.93 g L-1 of waste cooking oil in 15 cycles of repeated batch cultivation. Entrapped P. aeruginosa USM-AR2 cells achieved a higher rhamnolipid production, by 1.03-fold during cycle 3 in shake flasks and 1.19-fold during cycle 11 in an FBR, compared to free cells. These results show that entrapment enables reusability of viable cells and maintains stability of rhamnolipid production throughout the extended cultivation, increasing cell tolerance to perturbations in fermentation conditions.

Investigation of process stability of a whole-cell biocatalyst with Baeyer–Villiger monooxygenase activity in continuous bioreactors

The stability of a whole-cell biocatalyst based on genetically modified Escherichia coli cells harboring cyclohexanone monooxygenase was investigated in a free and immobilized form in continuous bioreactors. The biotransformation of a bicyclic ketone to a racemic mixture of the corresponding lactones by an enzymatic cascade was performed in a membrane bioreactor (MBR) for free cells and in a fluidized-bed bioreactor (FBBR) for immobilized cells. Both reactors were operated at the residence time of 6.25 h with the biocatalyst concentration of 1 % w/w. Different oxygen mass transfer rates were set via the impeller speed in MBR or air flow rate in FBBR, respectively. The potential of continuous bioreactors to achieve a steady state was utilized for the analysis of different factors affecting the biocatalyst stability. An apparent steady state could be maintained in these bioreactors up to 40 h. The operation at high conversions or high oxygenation rates allowed to exclude poisoning by substrate or oxygen as causes of biocatalyst activity loss. Further experiments showed that the cells did not lose viability or plasmid. The problem in biocatalyst stability was not in the stability of cyclohexanone monooxygenase but in insufficient regeneration of cofactors. The only partially effective measure was the addition of catalase with the feed concentration of 0.025 g/L that decomposed hydrogen peroxide formed in the enzymatic cascade. However, both free and immobilized biocatalysts lost their activity completely in about a week.

Bioleaching of zinc from e-waste by A. aquatilis in fluidised bed bioreactor

ABSTRACT Technological advancements with the use of new-generation electronic devices and accumulated electronic wastes (e-wastes) raise environmental concerns. E-waste, especially mobile phone Printed Circuit Boards (PCBs) is a rich source of metals. Bioleaching, a microbe-mediated metal dissolution process is employed for the recovery of metals. The operational parameters like particle size, inoculum percentage (v/v) and e-waste load (w/v) were optimised for Zn bioleaching by Alcaligenes aquatilis in shake flasks and fluidised bed bioreactor (FBR). The e-waste feed particle size of 0.175 mm and 5% inoculum was found to be the optimum for Zn bioleaching in both the shake flask and FBR. The optimum e-waste load was 5% in the shake flask and 2% in FBR. The maximum recovery of Zn was 0.6 mg/g (13.73%) in the shake flask and 0.57 mg/g (13%) in FBR, implying that FBR exhibits similar efficiency of Zn bioleaching as in the shake flask. Further three sequential batch runs increased the recovery to a maximum of 1.66 mg/g from 4.37 mg/g Zn present in the PCBs ie., 38% Zn recovery. This shows that efficient bioleaching of Zn on a larger scale can be achieved with sequential batches and applied for the simultaneous recovery of metals from PCBs.

Simultaneous removal of selenite and heavy metals from wastewater and their recovery as nanoparticles using an inverse fluidized bed bioreactor

Occurrence of selenium oxyanions and different heavy metals as co-pollutants in various waste streams is common from industries such as mining, coal burning, thermal power plants, petrochemical refinery, etc. Among the available technologies to treat such wastewater, biological removal using anaerobic microbes is one of the most advantageous. This study examined simultaneous removal and recovery of selenite and heavy metals using an inverse fluidized bed bioreactor (IFBR). The effect of commonly occurring heavy metals namely Zn, Cu and Cd on selenite removal was evaluated at 24 h hydraulic retention time (HRT). The maximum selenite removal of 93.9% was obtained in the absence of any heavy metals. The presence of heavy metals negatively impacted the selenite removal (45.8–85.3%), and the inhibitory effect due to Cu was the most significant among the three metals at 50 mg/L of influent concentration (47% lower). The heavy metal removal efficiency values were more than 70%, except in the case of Cd at 50 mg/L. The recovery values of selenium and heavy metals using the continuous bioreactor were in the range 45.1–73.9% and 59.2–69.8%, respectively, under different experimental conditions. Elemental selenium nanoparticles were formed inside the bioreactor due to selenite bioreduction and the nanoparticle size ranged from 50 to 300 nm. Furthermore, formation of small sized (<10 nm) metal selenide nanoparticles of the respective metals were detected during the bioreactor operation. Overall, this study clearly demonstrated the potential of the IFBR system for the removal of selenite and heavy metals from wastewater as well as their recovery as elemental selenium and metal selenide nanoparticles, respectively.

Bio-Treatment Technologies of Produced Water: A Review

Petroleum is a vital source of energy for most human activities. The growth of the oil and gas sector is associated with releasing a significant amount of produced water (PW) from onshore and offshore fields. Thus, undesirable toxic pollutants in produced water have become a major concern for those concerned with environmental issues. Therefore, interest in recycling and beneficial reuse of pollutants has increased due to large amounts of PW. In general, various physical and chemical technologies and bio-treatments for PW or combined between them are applied. Bio-treatment is preferred due to its efficiency and eco-friendly compared with other PW treatments. To clarify the prospective role of PW bio-treatments, this review highlights the main bio-treatment technologies in aerobic and anaerobic conditions to reduce salinity, organic components, and toxicity from PW. Also, challenges of environmental factors for PW and future research directions are included. Activated sludge is an essential part of aerobic bio-treatments of polluted water as inoculum rich in microbial cells that can degrade pollutants. Membrane bioreactors (MBR), fluidized bed bioreactors (FBBs), aerated biological filter (BAF), and aeration lagoons are also reviewed. Moreover, bio-treatments are extended to include anaerobic conditions. Furthermore, bio-treatment techniques can treat organic compounds of wastewater, especially with low oil concentrations and poor solubility that cannot be treated with conventional treatments.

Comparison of hydrodynamic characteristics of Tulsion and Siran immobilised beads in a fluidised bed bioreactor

The fluidised bed reactors are successfully utilised in various bioprocesses to produce high value products using immobilised cells and enzymes. The present work aims at evaluating hydrodynamic characteristics of a three phase fluidised bed bioreactor using Tulsion® A-1X MP, Tulsion® ADS-400 and Tulsion® ADS-800, polystyrene and polyacrylic based three types of free and immobilised cells solid carriers viz. and comparing their performance with Siran® SIKUG41 glass beads. The hydrodynamic parameters such as particle density (cells and beads), drag coefficient, minimum and maximum fluidisation velocity, particle settling velocity were estimated and compared in water and biological media (E2 and MSM) having varying rheological properties. The relationships between drag coefficient (CD)–Reynolds numbers (NRe), superficial liquid velocity (Uf)–void fraction(ε), expansion index(n)–NRe were obtained.The scanning electron microscopy studies revealed that the pore sizes of Tulsion beads (20–300 nm) were significantly smaller compared to Siran carriers (7–120 μm) leading to cells growth only on the surface of the beads. The biomass grown was estimated to be 0.75–1.2 mgCDW/g for Tulsion beads and 1.27–1.3 mgCDW/g for Siran beads with immobilised cells of P. putida and R. erythropolis, respectively. As per the results obtained, the reactor could be operated as a fluidised bed reactor with Tulsion and Siran beads at ε>0.4 and ε>0.6. The cell immobilised Tulsion and Siran beads have shown higher drag co-efficient in E2 and MSM media compared to water. The empirical correlations describing beads properties in falling (NRe) and fluidisation conditions in the form of Archimedes Number (NAr) were developed for ε in the range of 0.3–0.8 at 0.3<NRe<100 and 10<NAr<1000. The experimental data was statistically analysed using percentage mean relative error ± standard deviation and values were found to be at 95% confidence level.The evaluation of hydrodynamic characteristics of Tulsion and Siran carriers could be used to set up an operating window for three phase fluidised bed reactor for a bioprocess.