Comparative assessment of the performance of one- and two-liquid phase biotrickling filters for the simultaneous abatement of gaseous mixture of methanol, α-pinene, and hydrogen sulfide.

A gaseous mixture of methanol (M), α-pinene (P), and hydrogen sulfide (H) was treated in one/two-liquid phase biotrickling filters (OLP/TLP-BTFs) at varying inlet concentrations and at an empty bed residence time (EBRT) of 57 s. The performance of TLP-BTF [BTF (A)] improved significantly in terms of M and P removal due to the presence of silicone oil at 5% v/v. The maximum elimination capacities (ECs) of M, P, and H in BTF (A) were obtained as 309, 73, and 56 g m-3 h-1, respectively. While, the maximum ECs achieved in the BTF operated without silicone oil [BTF (B)] were 172, 28, and 21 g m-3 h-1 for M, P, and H removal, respectively. Increasing the inlet concentration of H from 32 to 337 ppm inhibited P removal in both the BTFs. The presence of silicone oil enhanced gas-liquid mass transfer, prevented the BTF from experiencing substrate inhibition effects and allowed reaching high ECs for M and P. The experiments showed promising results for the long-term operation of removal of M, P, and H mixture in a one-stage TLP-BTF with the decreasing negative effects of M and H on P degradation.

Neural network-based performance assessment of one- and two-liquid phase biotrickling filters for the removal of a waste-gas mixture containing methanol, α-pinene, and hydrogen sulfide.

The performance of one- and two-liquid phase biotrickling filters (OLP/TLP-BTFs) treating a mixture of gas-phase methanol (M), α-pinene (P), and hydrogen sulfide (H) was assessed using artificial neural network (ANN) modeling. The best ANN models with the topologies 3-9-3 and 3-10-3 demonstrated an exceptional capacity for predicting the performance of O/TLP-BTFs, with R2 > 99%. The analysis of causal index (CI) values for the model of OLP-BTF revealed a negative impact of M on P removal (CI = -2.367), a positive influence of P and H on M removal (CI = +7.536 and CI = +3.931) and a negative effect of H on P removal (CI = -1.640). The addition of silicone oil in TLP-BTF reduced the negative impact of M and H on P degradation (CI = -1.261 and CI = -1.310, respectively) compared to the OLP-BTF. These findings suggested that silicone oil had the potential to improve P availability to the biofilm by increasing the concentration gradient of P between the air/gas and aqueous phases. Multi-objective particle swarm optimization (MOPSO) suggested an optimum operational condition, i.e. inlet M, P, and H concentrations of 1.0, 1.1, and 0.3 g m-3, respectively, with elimination capacities (ECs) of 172.1, 26.5, and 0.025 g m-3 h-1 for OLP-BTF. Likewise, one of the optimum operational conditions for TLP-BTF is achievable at inlet concentrations of 4.9, 1.7, and 0.8 g m-3, leading to the optimum ECs of 299.7, 52.9, and 0.072 g m-3 h-1 for M, P, and H, respectively. These results provide important insights into the treatment of complex waste gas mixtures, addressing the interactions between the pollutant removal characteristics in OLP/TLP-BTFs and providing novel approaches in the field of biological waste gas treatment.

Antifouling potential of enzymes applied to reverse osmosis membranes.

Many companies in the food industry apply reverse osmosis (RO) membranes to ensure high-quality reuse of water. Biofouling is however, a common, recalcitrant and recurring problem that blocks transport over membranes and decreases the water recovery. Microorganisms adhering to membranes may form biofilm and produce an extracellular matrix, which protects against external stress and ensures continuous attachment. Thus, various agents are tested for their ability to degrade and disperse biofilms. Here, we identified industrially relevant bacterial model communities that form biofilms on RO membranes used for treating process water before reuse. There was a marked difference in the biofilm forming capabilities of bacteria isolated from contaminated RO membranes. One species, Raoultella ornithinolytica, was particularly capable of forming biofilm and was included in most communities. The potential of different enzymes (Trypsin-EDTA, Proteinase K, α-Amylase, ß-Mannosidase and Alginate lyase) as biofouling dispersing agents was evaluated at different concentrations (0.05 U/ml and 1.28 U/ml). Among the tested enzymes, ß-Mannosidase was the only enzyme able to reduce biofilm formation significantly within 4 h of exposure at 25 °C (0.284 log reduction), and only at the high concentration. Longer exposure duration, however, resulted in significant biofilm reduction by all enzymes tested (0.459-0.717 log reduction) at both low and high concentrations. Using confocal laser scanning microscopy, we quantified the biovolume on RO membranes after treatment with two different enzyme mixtures. The application of proteinase K and ß-Mannosidase significantly reduced the amount of attached biomass (43% reduction), and the combination of all five enzymes showed even stronger reducing effect (71% reduction). Overall, this study demonstrates a potential treatment strategy, using matrix-degrading enzymes for biofouled RO membranes in food processing water treatment streams. Future studies on optimization of buffer systems, temperature and other factors could facilitate cleaning operations based on enzymatic treatment extending the lifespan of membranes with a continuous flux.

Degradation of phenol in the bio-cathode of a microbial desalination cell with power generation and salt removal.

In this study, the performance of a three-chamber microbial desalination cell (MDC) was assessed to simultaneously remove salt (35 g.L-1) from water and degrade phenol as a hazardous compound. Two parallel MDCs with the same configurations were run using glucose as the chemical oxygen demand (COD) at an initial concentration of 1.5 g.L-1 as the anolyte. MDC#1 operated with 10 mM phosphate buffer solution (PBS), while MDC#2 operated with bio-cathode as the catholyte for the degradation of 100 mg.L-1 of phenol. The use of MDC#1 resulted in a power density, desalination efficiency, and COD removal of 366.2 mW.m-2, 50.3 ± 4.0 %, and 79.3 ± 2.2 %, respectively. All performance parameters were improved in MDC#2 with bio-cathode so that power density, desalination efficiency, and COD removal reached 660.1 mW.m-2, 72.1 ± 3.0 %, and 92.6 ± 2.4 %, respectively. Also, more than 96 % of phenol was degraded using bio-cathode within 7 h of operation. Bio-cathode could enhance the performance of the MDC reactor through catalyzing the final reactions of electron acceptors compared to MDC#1 with a chemical cathode. In general, the results indicated that heterotrophic microorganisms, able to grow alongside autotrophic bacteria, could effectively extend the applications of MDC reactors to degrade hazardous compounds in cathode chambers.

Increasing-Aeration Strategy: a Practical Approach to Enhance the Schizophyllan Production and Improve the Operational Conditions of Schizophyllum commune Cultivation in the Stirred Tank and Bubble Column Bioreactors.

In the present study, the effect of employing the increasing- aeration strategy (IAS) in the oxygen-limited situation and proportionate to increasing oxygen demand of the fungus Schizophyllum commune (S. commune) has been investigated in both stirred tank (STB) and bubble column (BCB) bioreactors. The purpose was to enhance schizophyllan (SPG) production by preventing oxygen starvation, improve mixing conditions of pseudoplastic culture, and intensify shear stress on fungus pellets to release SPG. At first, a constant-aeration rate of 0.08 vvm was implemented in both bioreactors to evaluate the new strategy compared to the previously studied methods. In the second set of experiments with IAS, along with the increasing oxygen demand of culture, the inlet airflow was increased gradually, while the dissolved oxygen (DO) was maintained higher than zero and below 1%. Using IAS in STB significantly raised productivity by about 100% in 96 h from 0.035 to 0.073 g/L.h. Also, employing this strategy in BCB led to a 30% increase in the maximum SPG production from 3.2 to 4.2 g/L. IAS can effectively help handle the operation of S. commune cultivation on a large scale by improving mixing conditions, mass transfer, and shear stress in both bioreactor types. This method had a significant impact on STB cultivation and its productivity so that it can be a practical approach to SPG's industrial production.

Enhancement of schizophyllan production in Schizophyllum commune using microparticles in medium.

Schizophyllum commune is a wood-rotting filamentous fungus that secrets a homopolysaccharide called as schizophyllan. Schizophyllan has several applications such as enhanced oil recovery, pharmaceutical materials and an anti-cancer drug carrier. Biomass growth and schizophyllan production increase the viscosity of the cultivation medium, thus resulting in mass transfer limitation for the substrate. In this study, adding talc and aluminium oxide microparticles into the cultivation medium was studied to improve the fungal growth and morphology. The response surface methodology and one factor at a time were applied to find the effects of microparticles with different sizes and concentrations on the schizophyllan production. The optimum concentration and size of aluminium oxide microparticles were obtained as 20 g L-1 and < 30 µm, respectively. Aluminium oxide microparticles in shake flask culture caused to increase the schizophyllan production from 10 to 15 g L-1 and decrease the cultivation time from 10 to 7 days. The production yield also increased from 0.11 to 0.30 g of schizophyllan/g glucose. Bioreactor cultivation showed a twofold increase in schizophyllan production from 1.5 to 3 g L-1. The results of this study suggested a significant increase in the production of schizophyllan using a low-cost "microparticle-enhanced cultivation" without any further optimization of the culture medium.

Fungal elimination of toluene vapor in one- and two-liquid phase biotrickling filters: Effects of inlet concentration, operating temperature, and peroxidase enzyme activity.

In this study, performance of biotrickling filters (BTFs) inoculated with fungus Phanerochaete chrysosporium at 30 °C and 40 °C in the absence and presence of silicone oil (10% v/v) was investigated. Removal of toluene was carried out at empty bed residence time (EBRT) of 1 min and at inlet concentrations of 0.5-4.4 g m-3 and 0.5-24.7 g m-3 for one-liquid phase (OLP-BTF) and two-liquid phase BTF (TLP-BTF), respectively. In general, at 40 °C, removal efficiencies (REs) > 80% were obtained in OLP-BTF for the inlet toluene concentrations < 2.5 g m-3, and REs > 70% were obtained for concentrations < 18 g m-3 in TLP-BTF. Based on the balanced equation for biodegradation, fungal respiration produced more CO2 in OLP-BTF (1.38 mol CO2/mole toluene) in comparison to TLP-BTF (0.67 mol CO2/mole toluene). In other words, the presence of oil enhanced microbial growth due to the increase of hydrophobic substrate bioavailability. The activity of extracellular ligninolytic manganese peroxidase (MnP) enzyme produced by the fungal culture was detected in the range of 27.6-71.6 U L-1 (µmol min-1 L-1) at 40 °C in TLP-BTF, while no enzymatic activity was detected in OLP-BTF.

Performance assessment of gas-phase toluene removal in one- and two-liquid phase biotrickling filters using artificial neural networks.

The main aim of this work is to study gas-phase toluene removal in one- and two-liquid phase biotrickling filters (O/TLP-BTF) and model the BTF performance using artificial neural networks (ANNs). The TLP-BTF was operated for 60 d in the presence of silicone oil at empty bed residence times (EBRTs) of 120, 60, and 45 s, respectively, and toluene concentrations in the range of 0.9-3.1 g m-3. A t-test analysis indicated that increasing the silicone oil volume ratio from 5 to 10% v/v, did not significantly improve the TLP-BTF performance (p-value = 0.65 > 0.05). The results from ANN modeling showed that toluene removal was more negatively affected by the inlet concentration (casual index, CI = -5.63) due to the kinetic limitation. The CI values for inlet concentration (+4.01) and liquid trickling rate (-2.45) indicated that the diffusion-limited regime controlled the removal process in the OLP-BTF.

Cometabolic degradation of bisphenol A by pure culture of Ralstonia eutropha and metabolic pathway analysis.

Bisphenol A (BPA) is a toxic compound emitting to the environment mainly by polycarbonate production facilities. In this research, BPA with the initial concentrations in the range of 1-40 mg l-1 was degraded by Ralstonia eutropha. The bacteria were unable to use BPA as the sole carbon source. Therefore, resting and growing cells of phenol-adapted R. eutropha were used for cometabolic biodegradation of BPA with phenol at the concentration of 100 mg l-1. The optimum initial concentrations of BPA were 20 mg l-1 in both approaches of cometabolism. By using resting cells, BPA removal efficiency (RE) reached to 57%, however, RE decreased to 37% by growing cells in the presence of phenol. BPA-degrading activity was inhibited at BPA concentrations >20 mg l-1. Liquid chromatography-mass spectrometry technique was used to identify some metabolic intermediates generated during BPA degradation process as 1,2-bis(4-hydroxyphenyl)-2-propanol, 4-(2-propanol)-phenol, 4-hydroxyacetophenone, 4-isopropenylphenol, and 4-hydroxybenzoic acid. Finally, metabolic pathways for BPA degradation were proposed in this study.

Mathematical modeling of ethanol production in solid-state fermentation based on solid medium' dry weight variation.

In this work, mathematical modeling of ethanol production in solid-state fermentation (SSF) has been done based on the variation in the dry weight of solid medium. This method was previously used for mathematical modeling of enzyme production; however, the model should be modified to predict the production of a volatile compound like ethanol. The experimental results of bioethanol production from the mixture of carob pods and wheat bran by Zymomonas mobilis in SSF were used for the model validation. Exponential and logistic kinetic models were used for modeling the growth of microorganism. In both cases, the model predictions matched well with the experimental results during the exponential growth phase, indicating the good ability of solid medium weight variation method for modeling a volatile product formation in solid-state fermentation. In addition, using logistic model, better predictions were obtained.

Sustainable pollutant removal by periphytic biofilm via microbial composition shifts induced by uneven distribution of CeO2 nanoparticles.

The responses of periphytic biofilm to CeO2 nanoparticle (CNP) exposure were explored by investigating community shifts and pollutant removal. Results showed that CNPs entered the sensitive microbial cells in the periphytic biofilm, leading to cytomembrane damage and intracellular reactive oxygen species (ROS) generation. The periphytic biofilm communities were, however, able to adapt to the prolonged exposure and maintain their pollutant removal (i.e., phosphorus, nitrogen and copper, organic matter) performance. Observations under synchrotron radiation scanning transmission X-ray microscopy revealed that fewer CNPs were distributed in algal cells compared to bacterial cells, wherein the transformation between Ce(IV) and Ce(III) occurred. High-throughput sequencing further showed that the proportion of algae, such as Leptolyngbya and Nostoc, significantly increased in the periphytic biofilm exposed to CNPs while the proportion of bacteria, such as Bacilli and Gemmatimonadetes, decreased. This change in community composition might be the primary reason for the sustained pollutant removal performance of the periphytic biofilm.

Different strategies for transient-state operation of a biotrickling filter treating toluene vapor.

Biotrickling filters (BTFs) are often subjected to transient-state operation due to different variations in the operation of industrial-scale sources of pollution. In this research, performance of a laboratory-scale BTF packed with pall ring and pumice (1:1 v/v) and inoculated with Ralstonia eutropha was evaluated for the treatment of toluene vapor under various transient conditions. The experiments were performed at empty bed residence times (EBRTs) of 45 and 90 s and toluene inlet concentration in the range of 0.5-4 g m-3. The transient-state experiments consisted of a sudden increase in inlet gas concentration, sudden change of trickling liquid rate, intermittent loading for 10 h day-1, aeration without toluene loading during shutdown periods, and long-term starvation. The maximum elimination capacity (ECmax) was 280 g m-3 h-1 under continuous loading. The removal efficiency (RE) reached 90 % in intermittent loading experiments at toluene inlet concentration of 3 g m-3 in less than 1 h after loading initiation. RE dropped to 50 % due to 4.5-fold increase in the inlet loading rate (ILR) during shock load experiment. The system became completely active after 24 h, when the BTF was subjected to a long-term starvation period for 7 days. The results showed that aeration at non-toluene loading periods could improve the BTF performance under intermittent loading condition.

Effect of operating temperature on styrene mass transfer characteristics in a biotrickling filter.

To study the effect of operating temperature on styrene mass transfer from gas to liquid phase in biotrickling filters (BTFs), overall mass transfer coefficient (KL a) was calculated through fitting test data to a general mass balance model under abiotic conditions. Styrene was used as the volatile organic compound and the BTF was packed with a mixture of pall rings and pumice. Operating temperature was set at 30°C and 50°C for mesophilic and thermophilic conditions, respectively. KL a values increased from 54 to 70 h-1 at 30°C and from 60 to 90 h-1 at 50°C, respectively, depending on the countercurrent gas to liquid flow ratio that varied in the range of 7.5-32. Evaluation of styrene mass transfer capacity (MTC) showed that liquid-phase mass transfer resistance decreased as the flow ratio increased at constant temperature. MTC also decreased with an increase in operating temperature. Both gas-liquid partition coefficient and KL a increased with increasing temperature; however the effect on gas-liquid partition coefficient was more significant and served to increase mass transfer limitations. Thermophilic biofiltration on the one hand increases mass transfer limitations, but on the other hand may enhance the biodegradation rate in favor of enhancing BTFs' performance.

Cometabolic degradation of ethyl mercaptan by phenol-utilizing Ralstonia eutropha in suspended growth and gas-recycling trickle-bed reactor.

The degradability of ethyl mercaptan (EM), by phenol-utilizing cells of Ralstonia eutropha, in both suspended and immobilized culture systems, was investigated in the present study. Free-cells experiments conducted at EM concentrations ranging from 1.25 to 14.42 mg/l, showed almost complete removal of EM at concentrations below 10.08 mg/l, which is much higher than the maximum biodegradable EM concentration obtained in experiments that did not utilize phenol as the primary substrate, i.e. 2.5 mg/l. The first-order kinetic rate constant (kSKS) for EM biodegradation by the phenol-utilizing cells (1.7 l/g biomass/h) was about 10 times higher than by cells without phenol utilization. Immobilized-cells experiments performed in a gas recycling trickle-bed reactor packed with kissiris particles at EM concentrations ranging from 1.6 to 36.9 mg/l, showed complete removal at all tested concentrations in a much shorter time, compared with free cells. The first-order kinetic rate constant (rmaxKs) for EM utilization was 0.04 l/h for the immobilized system compared to 0.06 for the suspended-growth culture, due to external mass transfer diffusion. Diffusion limitation was decreased by increasing the recycling-liquid flow rate from 25 to 65 ml/min. The removed EM was almost completely mineralized according to TOC and sulfate measurements. Shut down and starvation experiments revealed that the reactor could effectively handle the starving conditions and was reliable for full-scale application.

Effect of operating temperature on transient behaviour of a biofilter treating waste-air containing n-butanol vapour during intermittent loading.

Transient-state removal of n-butanol vapour was investigated in a biofilter (BF) packed with compost and lava rock at different operating temperatures in the range of 30-45°C under intermittent loading (8 h per day). Adsorption on the inactive bed and biodegradation in the microbial-active bed were studied separately at an empty bed residence time (EBRT) of 1 min and inlet concentrations of 2.6-3.2 g m(-3), respectively. According to the transient experiments, the highest removal efficiency (RE) around 86% was obtained at 40°C due to a high microbial activity. Comparison of CO2 production and pure adsorption of n-butanol showed that adsorption was the major mechanism in the start-up of BF at each operating condition; although the impact of adsorption declined as temperature increased from 30°C to 45°C. The process was reaction limited at all operating conditions. Based on the determination of stoichiometric coefficients of n-butanol biodegradation, the CO2 production level was significantly lower than that of the chemical oxidation process which resulted in a decrease in environmental pollution.