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Composting of the organic fraction of municipal solid waste (OFMSW) is accompanied by the emission of large volumes of harmful, hazardous and foul-smelling volatile organic compounds (VOCs). To improve the efficiency of terpenes removal, which constitute a significant part of VOCs, pure cultures of microorganisms dominating in its microbiota were isolated from the microbial community of the biofilter, which has been cleaning such emissions for a long time. Seven pure cultures were isolated and then tested for being able to grow on a mineral medium in the presence of terpene vapor as the only source of carbon and energy. Three of the most actively growing cultures were selected, characterized and identified by the 16S rRNA gene as Rhodococcus erythropolis CA1, Rhodococcus pyridinivorans CA3 and Gordonia sp. CA6. Three identical laboratory biofilters (BF) were inoculated with a mix of these cultures to test the possibility of more complete removal of terpenes. Biofilters were adapting to clearing the model mix of terpineols and geraniol vapors for 45 days. During 45 days the purification efficiency of the model mix reached an average of 91.5% with a contact time (CT) of 3.7 ± 0.2 s and the terpene vapors concentration of 14 ± 2 mg m -3 . Then the biofilters number BF2.1 and BF3.1 were connected to real emission from composting OFMSW. The biofilter BF2.1 purified the emission directly, whereas BF3.1 purified similar discharge after the intermediate biofilter of the 1st stage of purification (BF0.0). The BF1.0 was left connected to purification of the model mix as a control. The effectiveness of biofiltration of hard-to-remove terpenes was evaluated by gas chromatography of samples taken at the inlet and outlet of biofilters. The average efficiency of removing terpenes from real emissions by BF2.1 was 93.1 % (CT = 5.5 s). The total efficiency of removing terpenes by (BF0.0 + BF3.1) complex was 93.2 % (total CT = 7.4 s). A study of the microbiota of inoculated biofilters after 60 and 90 days of purification the real emission by cultivation from dilutions, identification by the 16S rRNA gene and fingerprinting showed that in BF2.1 and BF3.1 Rhodococcus erythropolis CA1 and Rhodococcus pyridinivorans CA3 were preserved among living cells at a level of 6.5-12.4 %, and genetically fully corresponded to the original cultures. These results could have a positive impact on improving the results of deodorization of emissions from OFMSW composting by biofiltration, simplifying the design of the biofiltration facility (one stage instead of two) and reducing the total time for effective biofiltration. This, in turn, would contribute to the wider introduction of highly efficient emission purification methods at OFMSW composting facilities in order to create more comfortable and ecologically clean environmental conditions around them., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The removal of volatile organic compounds (VOCs) in air is of utmost importance to safeguard both environmental quality and human well-being. However, the low aqueous solubility of hydrophobic VOCs results in poor removal in waste gas biofilters (BFs). In this study, we evaluated the addition of (bio)surfactants in three BFs (BF1 and BF2 mixture of compost and wood chips (C + WC), and BF3 filled with expanded perlite) to enhance the removal of cyclohexane and hexane from a polluted gas stream. Experiments were carried out to select two (bio)surfactants (i.e., Tween 80 and saponin) out of five (sodium dodecyl sulfate (SDS), Tween 80, surfactin, rhamnolipid and saponin) from a physical-chemical (i.e., decreasing VOC gas-liquid partitioning) and biological (i.e., the ability of the microbial consortium to grow on the (bio)surfactants) point of view. The results show that adding Tween 80 at 1 critical micelle concentration (CMC) had a slight positive effect on the removal of both VOCs, in BF1 (e.g., 7.0 ± 0.6 g cyclohexane m -3 h -1 , 85 ± 2% at 163 s; compared to 6.7 ± 0.4 g cyclohexane m -3 h -1 , 76 ± 2% at 163 s and 0 CMC) and BF2 (e.g., 4.3 ± 0.4 g hexane m -3 h -1 , 27 ± 2% at 82 s; compared to 3.1 ± 0.7 g hexane m -3 h -1 , 16 ± 4% at 82 s and 0 CMC), but a negative effect in BF3 at either 1, 3 and 9 CMC (e.g., 2.4 ± 0.4 g hexane m -3 h -1 , 30 ± 4% at 163 s and 1 CMC; compared to 4.6 ± 1.0 g hexane m -3 h -1 , 43 ± 8% at 163 s and 0 CMC). In contrast, the performance of all BFs improved with the addition of saponin, particularly at 3 CMC. Notably, in BF3, the elimination capacity (EC) and removal efficiency (RE) doubled for both VOCs (i.e., 9.1 ± 0.6 g cyclohexane m -3 h -1 , 49 ± 3%; 4.3 ± 0.3 g hexane m -3 h -1 , 25 ± 3%) compared to no biosurfactant addition (i.e., 4.5 ± 0.4 g cyclohexane m -3 h -1 , 23 ± 3%; hexane 2.2 ± 0.5 g m -3 h -1 , 10 ± 2%) at 82 s. Moreover, the addition of the (bio)surfactants led to a shift in the microbial consortia, with a different response in BF1-BF2 compared to BF3. This study evaluates for the first time the use of saponin in BFs, it demonstrates that cyclohexane and hexane RE can be improved by (bio)surfactant addition, and it provides recommendations for future studies in this field., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Bioactive coatings are envisaged as a promising biotechnology to tackle the emerging problem of indoor air pollution. This solution could cope with the low concentrations, the wide range of compounds and the hydrophobicity of some indoor air VOCs, which are the most important bottlenecks regarding the implementation of conventional biotechnologies for indoor air treatment. A bioactive coating-based bioreactor was tested in this study for the abatement of different VOCs (n-hexane, toluene and α-pinene) at different empty bed residence times (EBRT) and inlet VOC concentrations. The performance of this reactor was compared with a conventional biofilm-based bioreactor operated with the same microbial inoculum. After an acclimation period, the bioactive coating-based bioreactor achieved abatements of over 50% for hexane, 80% for toluene and 70% for pinene at EBRTs of 112-56 s and inlet concentrations of 9-15 mg m -3 . These results were about 25, 10 and 20% lower than the highest removals recorded in the biofilm-based bioreactor. Both bioreactors experienced a decrease in VOC abatement by ∼25% for hexane, 45% for toluene and 40% for pinene, after reducing the EBRT to 28 s. When inlet VOC concentrations were progressively reduced, VOC abatement efficiencies did not improve. This fact suggested that low EBRTs and low inlet VOCs concentration hindered indoor air pollutant abatement as a result of a limited mass transfer and bioavailability. Metagenomic analyses showed that process operation with toluene, hexane and pinene as the only carbon and energy sources favored an enriched bacterial community represented by the genera Devosia, Mesorhizobium, Sphingobacterium and Mycobacterium, regardless of the bioreactor configuration. Bioactive coatings were used in this work as packing material of a conventional bioreactor, achieving satisfactory VOC abatement similar to a conventional bioreactor., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The present study systematically evaluated the potential of Candida subhashii, Fusarium solani and their consortium for the abatement of n-hexane, trichloroethylene (TCE), toluene and α-pinene in biofilters (BFs) and biotrickling filters (BTFs). Three 3.2 L BFs packed with polyurethane foam and operated at a gas residence time of 77 s with an air mixture of hydrophobic volatile organic compounds (VOCs) were inoculated with C. subhashii, F. solani and a combination of thereof. The systems were also operated under a BTF configuration with a liquid recirculating rate of 2.5 L h -1 . Steady state elimination capacities (ECs) of total VOCs of 17.4 ± 0.7 g m -3 h -1 for C. subhashii, 21.2 ± 0.8 g m -3 h -1 for F. solani and 24.4 ± 1.4 g m -3 h -1 for their consortium were recorded in BFs, which increased up to 27.2 ± 1.6 g m -3 h -1 , 29.2 ± 1.9 g m -3 h -1 , 37.7 ± 3.3 g m -3 h -1 in BTFs. BTFs supported a superior biodegradation performance compared to BF, regardless of the VOCs. Moreover, a more effective VOC biodegradation was observed when C. subhashii and F. solani were grown as a consortium. The microbial analysis conducted revealed that the fungi initially introduced in each BF represented the dominant species by the end of the experiment, with C. subhashii gradually overcoming F. solani in the system inoculated with the fungal consortium., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Biofilter (BF) has been regarded as a versatile gas treatment technology for removing volatile organic compounds (VOCs) from contaminated gas streams. In order for BF to be utilized in the industrial setting, it is essential to conduct research aimed at removing VOC mixtures under different inlet loading conditions, i.e. as a function of the gas flow rate and inlet VOC concentrations. The main aim of this study was to apply artificial neural networks (ANN) and determine the relationship between flow rate (FR), pressure drop (PD), inlet concentration (C), and removal efficiency (RE) in the BF treating gas-phase benzene and xylene mixtures. The ANN model was trained and tested to assess the removal efficiency of benzene (RE B ) and xylene (RE X ) under the influence of different FR, PD and C. The model's performance was assessed using a cross-validation method. The RE b varied from 20% to >60%, while the RE x varied from 10% to 70% during the different experimental phases of BF operation. The causal index (CI) technique was used to determine the sensitivity of the input parameters on the output variables. The ANN model with a topology of 4-4-2 performed the best in terms of predicting the RE profiles of both the pollutants. Furthermore, the effect was more pronounced for xylene because an increase in the benzene concentration reduced xylene removal (CI = -25.7170) more severely than benzene removal. An increase in the xylene concentration had a marginally positive effect on the benzene removal (CI = +0.1178)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

This work systematically compared the potential of a conventional fungal biofilter (BF) and a fungal biotrickling filter (BTF) for the abatement of a mixture of hydrophobic volatile organic compounds (VOCs). Candida subhashii was herein used for the first time, to the best of the author's knowledge, to remove n-hexane, trichloroethylene, toluene and α-pinene under aerobic conditions. C. subhashii immobilized on polyurethane foam supported steady state removal efficiencies of n-hexane, trichloroethylene, toluene and α-pinene of 25.4 ± 0.9%, 20.5 ± 1.0%, 19.6 ± 1.5% and 25.6 ± 2.8% in the BF, and 35.7 ± 0.9%, 24.0 ± 1.6%, 44.0 ± 1.7% and 26.2 ± 1.8% in the BTF, respectively, at relatively short gas residence times (30 s). The ability of C. subhashii to biodegrade n-hexane, TCE, toluene and α-pinene was confirmed in a batch test conducted in serum bottles, where a biodegradation pattern (toluene ≈ n-hexane > α-pinene > trichloroethylene) comparable to that recorded in the BF and BTF was recorded., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Biotechnologies have emerged as a promising solution for indoor air purification with the potential to overcome the inherent limitations of indoor air treatment. These limitations include the low concentrations and variability of pollutants and mass-transfer problems caused by pollutant hydrophobicity. A new latex-based biocoating was herein optimized for the abatement of the volatile organic compounds (VOCs) toluene, trichloroethylene, n-hexane, and α-pinene using acclimated activated sludge dominated by members of the phylum Patescibacteria. The influence of the water content, the presence of water absorbing compounds, the latex pretreatment, the biomass concentration, and the pollutant load was tested on VOC removal efficiency (RE) by varying the formulation of the mixtures. Overall, hexane and trichloroethylene removal was low (<30%), while high REs (>90%) were consistently recorded for toluene and pinene. The assays demonstrated the benefits of operating at high water content in the biocoating, either by including mineral medium or water absorbing compounds in the latex-biomass mixtures. The performance of the latex-based biocoating was likely limited by VOC mass-transfer rather than by biomass concentration in the biocoating. The latex-based biocoating supported a superior toluene and pinene removal than biomass in suspension when VOC loading rate was increased by a factor of 4., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The use of biological reactors to remove volatile organic compounds (VOCs) from waste gas streams has proven to be a cost-effective and sustainable technique. However, hydrophobic VOCs exhibit low removal, mainly due to their limited bioavailability for the microorganisms. Different strategies to enhance their removal in bio(trickling)filters have been developed with promising results. In this review, two strategies, i.e. the use of surfactants and hydrophilic compounds, for enhancing the removal of hydrophobic VOCs in bio(trickling)filters are discussed. The complexity of the processes and mechanisms behind both strategies are addressed to fully understand and exploit their potential and rapid implementation at full-scale. Mass transfer and biological aspects are discussed for each strategy, and an in-depth comparison between studies carried out over the last two decades has been performed. This review identifies additional strategies to further improve the application of (bio)surfactants and/or hydrophilic VOCs, and it provides recommendations for future studies in this field., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The current scenario of increased population and industrial advancement leads to the spoliation of freshwater and tapper of the quality of water. These results decrease in freshwater bodies near all of the areas. Besides, organic and inorganic compounds discharged from different sources into the available natural water bodies are the cause of pollution. The occurrence of heavy metals in water and volatile organic compounds (VOCs) in the air is responsible for a vast range of negative impacts on the atmosphere and human health. Nonetheless, high uses of heavy metals for human purposes may alter the biochemical and geochemical equilibrium. The major air contaminants which are released into the surroundings known as VOCs are produced through different kinds of sources, such as petrochemical and pharmaceutical industries. VOCs are known to cause various health hazards. VOCs are a pivotal group of chemicals that evaporate readily at room temperature. To get over this problem, biofiltration technology has been evolved for the treatment of heavy metals using biological entities such as plants, algae, fungi, and bacteria. Biofiltration technology is a beneficial and sustainable method for the elimination of toxic pollutants from the aquatic environment. Various types of biological technologies ranging from biotrickling filters to biofilters have been developed and they are cost-effective, simple to fabricate, and easy to perform. A significant advantage of this process is the pollutant that is transformed into biodegradable trashes which can decompose within an average time period, thus yielding no secondary pollutants. The aim of this article is to scrutinize the role of biofiltration in the removal of heavy metals in wastewater and VOCs and also to analyze the recent bioremediation technologies and methods.

Micro-capillary bioreactors (1 mm ID, 10 cm long) were investigated for the biodegradation of toluene vapors as a model volatile organic compound (VOC). The intended application is the removal of VOCs from indoor air, when such microbioreactor is coupled with a microconcentrator that intermittently delivers high concentrations of VOCs to the bioreactor for effective treatment. The effects of key operating conditions were investigated. Specifically, gas film and liquid film mass transfer coefficients were determined for different gas and liquid velocities. Both mass transfer coefficients increased with gas or liquid velocity, respectively, and the overall gas-liquid mass transfer was dominated by the liquid-side resistance. Experiments with the microbioreactors focused on the effects of gas velocity, liquid velocity and mineral medium renewal rate on the treatment of toluene vapors at different inlet concentrations. The best performance in terms of toluene removal and mineralization to CO 2 was obtained when the gas and liquid velocity ratio was close to one and achieving Taylor or slug flow pattern. Sustained treatment over extended periods of time with toluene elimination capacities ranging from 4000 to over 9000 g m -3 h -1 were obtained, which is orders of magnitude greater than conventional biofilters and biotrickling filters. Biological limitations generally played a more important role than mass transfer limitation. Continuous mineral medium supply at a high rate (10 h liquid retention time) enabled pH control and provided ample nutrient supply and therefore resulted in better toluene elimination and mineralization. Overall, these studies helped select the most suitable conditions for high performance and sustained operation., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Biofiltration is a typical air pollution control process for the treatment of volatile organic compounds (VOCs). Mass transfer of hydrophobic VOCs to the biofilm is limited which leads to low removal efficiency (RE). Aiming to enhance the transport of hydrophobic VOCs, the effect of hydrophobic fumed silica (HFS) addition to a biofilter (BF) for pentane removal was studied in this paper. The effect of HFS on pentane removal was evaluated by daily RE measurements and periodical headspace gas pentane pulse injections using SIFT-MS as analysis apparatus. The BF was operated during more than 100 days at an empty bed residence time (EBRT) of 120 s reaching an elimination capacity (EC) up to 93.8 g pentane m -3  h -1 . At the last stage of the study, when a higher nutrient pulse and HFS to a concentration of 1.5% w/w wet were added, the BF showed better EC (46.3 ± 14.9 g pentane m -3  h -1 ; RE = 96.2%) compared to the previous stages (28.3 ± 4.4 g pentane m -3  h -1 ; RE = 68.3%). This overall performance improvement was in line with the short peak perturbation experiments carried out during the operational time which demonstrated, by net retention time (NRT) determination, to be a fast and reliable tool to gain insights into the behaviour of pollutants inside the BF and its state. Pentane demonstrated to have larger interactions with the packing material when HFS was added. NRT/EBRT ratio variated along the whole operational time, being larger at the last stage., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study aimed to assess the efficiency of removal of volatile organic compounds (VOCs) from process gases from a food industry plant in East Poland, producing high-quality animal (goose, duck, and pig) and vegetable fats, using a two-stage method which is a combination of biological purification and membrane-separation. The research, conducted on the semi-technical scale, compared the effects of traditional and two-stage biofiltration carried out under the same process conditions. The concentrations of VOCs in process gases were measured by means of a multi-gas detector. Additionally the temperature and humidity of gases were determined by a thermoanemometer under filter bed, following the EU and Polish National Standard Methods Two different types of filling materials (the mix of stumpwood chips and bark, and the mix of stumpwood chips, bark, and compost) and two types of membranes (three-layer semi-permeable membrane fabrics were used, with differences in air permeability and water tightness) were analyzed. During all processes basic operational parameters, the biofilters were controlled, including surface load, volumetric load, duration of gas contact with the filling layer, flow rate, and pressure drops (in the biofilter and on the membrane). The analyzed gases were characterized by very high variability of VOC concentrations (ranging from 350 ppb to 11,170 ppb). The effectiveness of VOC removal (RE voc ) was calculated by comparing the analytical results of raw and purified gases. The effectiveness of VOC removal with the application of traditional biofiltration during the experiment varied between 82% to 97% and was related to different parameters of the filling materials (mainly specific surface and moisture), reaching lower value for the mix of stumpwood chips and bark filling. The obtained results showed that the application of membrane improved the efficiency of biofiltration in all the analysed cases from 7% to 9%. The highest effectiveness was obtained using the filter bed in the form of stumpwood chips, bark, and compost in connection with the more permeable membrane. It was maintained between 96% to 99%, reaching an average value of 98%. The selection of the membrane should be determined by its permeability and the values of flow resistance.

The fate of the carbon from degraded pollutants in biofiltration is not well understood. The issue of missing carbon needs to be addressed quantitatively to better understand and model biofilter performance. Elucidating the various carbon end-points in various phases should contribute to the fundamental understanding of the degradation kinetics and metabolic pathways as a function of various environmental parameters. This article reviews the implications of key environmental parameters on the carbon end-points. Various studies are evaluated reporting carbon recovery over a multitude of parameters and operational conditions with respect to the analytical measurements and reported distribution of the carbon end-points., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Volatile organic compounds (VOCs) are significant atmospheric pollutants that cause environmental and health risks. Waste gases polluted with multiple VOCs often need to be purified simultaneously in biofilters, which may lead to antagonistic, neutral, or synergistic effects on removal performance. Antagonism limits the application of biofilters to simultaneous treatment of multiple VOCs, while synergism has not yet been fully exploited. We review the interactions among multiple target pollutants and the changes in the bioavailability and biodegradability of substrates that are responsible for substrate interactions. Potential strategies for enhancing biofilter performance are then discussed. Finally, we propose further efforts to alleviate antagonism by enhancing bioavailability and biodegradability, and discuss possible challenges to take advantage of synergism., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Volatile organic compounds (VOCs) are ubiquitous contaminants that can be found both in outdoor and indoor air, posing risks to human health and the ecosystems. The treatment of air contaminated with VOCs in low concentrations can be effectively performed using biofiltration, especially when VOCs are hydrophilic. However, the performance of biofilters inoculated with bacteria has been found to be low with sparsely water soluble molecules when compared to biofilters where fungi develop. Using conceptual and mathematical models, this review presents an overview of the physical, chemical and biological mechanisms that explain the differences in the performance of fungal and bacterial biofilters. Moreover, future research needs are proposed, with an emphasis on integrated models describing the biological and chemical reactions with the mass transfer using high-resolution descriptions of the packing material., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Industrial emissions of Volatile Organic Compounds are usually discontinuous. To assess the impact of interruptions in pollutant supply on the performance of biological treatment systems, two identical biofilters previously operated under continuous toluene loadings were subjected for 110 days to extended (12, 24, 36, 48, 60, 72, 84 and 96 h) and for a week to daily (8 h on, 16 h off) toluene starvation/shutdown events. One biofilter was operated under complete shutdowns (both air and toluene supply were interrupted), while the other maintained the air supply under toluene starvation. The biofilter operated under complete shutdowns was able to withstand both the extended and daily pollutant interruptions, while starvation periods >24 h severely impacted the performance of the other biofilter, with a removal efficiency decrease from 97.7 ± 0.1% to 45.4 ± 6.7% at the end of the extended starvation periods. This deterioration was likely due to a reduction in liquid lixiviation (from a total volume of 2380 mL to 1800 mL) mediated by the countercurrent airflow during the starvation periods. The presence of air under toluene starvation also favored the accumulation of inactive biomass, thus increasing the pressure drop from 337 to 700 mm H 2 O.m -1 , while decreasing the wash out of acidic by-products with a significantly higher pH of leachates (Student paired t-test <0.05). This study confirmed the need to prevent the accumulation of inhibitory compounds produced during process perturbation in order to increase biofiltration robustness. Process operation with sufficient drainage in the packing material and the absence of countercurrent airflow are highly recommended during toluene deprivation periods., (Copyright © 2017. Published by Elsevier Ltd.)

A composite packing material (CM-5) was prepared in this study, mainly consisting of compost with functional microorganisms, calcium carbonate (CaCO 3 ), perlite, cement and plant fiber. To get stronger compressive strength, mass ratios of these components were optimized based on single factor experiments, and finally adding amounts of perlite, cement, plant fiber, CaCO 3 , compost and binder at 18%, 18%, 7%, 13%, 17% and 27%, respectively. According to the optimum proportion, CM-5 was extruded in cylindrical shape (12 mm in diameter and 20 mm in length) with a bulk density of 470 kg m -3 , a moisture retention capacity of 49% and the microbial counts of × 10 5 CFU g -1 of packing material. The cumulative release rates of total organic carbon (TOC) and total nitrogen (TN) from CM-5 were 3.1% and 6.5%, respectively, after 19 times extraction in distilled water. To evaluate the H 2 S removal capacity, CM-5 was compared with an organic (corncob) and an inorganic (ceramsite) packing material in three biofilters. The results showed that CM-5 had higher H 2 S removal capacity compared with corncob and ceramsite. CM-5 could avoid the large fluctuation of pH value and pressure drop during the operation. The maximum H 2 S removal capacity of CM-5 was 12.9 g m -3  h -1 and the removal efficiency could maintain over 95.4% when the inlet H 2 S loading rate was lower than 11.3 g m -3  h -1 without any addition of nutrients and pH buffer substances. Besides, only 2-3 days were needed for the recovery of biofiltration performance after about two weeks of idle period.

Volatile organic compounds (VOCs) emitted to the environment highly probably result in ecological and health risks. Many biotechnologies for waste gases containing hydrophobic VOCs have been developed in recent years. However, these biological processes usually exhibit poor removal performances for hydrophobic VOCs due to the low bioavailability. This review presents an overview of enhanced removal of hydrophobic VOCs in biofilters. Mechanisms and problems relevant to the biological removal of hydrophobic VOCs are reviewed, and then solutions including the addition of surfactants, application of fungal biocatalysts, biofiltration with pretreatment, innovative bioreactors and utilization of hydrophilic compounds are discussed in detail. Future research needs are also proposed. This review provides new insights into hydrophobic VOC removal by biofiltration., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Changes in the number and species diversity of cultivable microorganisms in a newly developed plate-type biofilter during filtration of various volatile pollutants were studied. The novelty of the investigation is the monitoring of microorganism succession in different parts of biofilter plates with original packing material consisting of birch fibre and needle-punched non-woven fabric. It was shown that the largest number of fungi and yeasts develop on the top and middle, while bacteria develop on the bottom and middle parts of plates. The number of microorganisms depends on the origin of the pollutant, the pH and temperature inside the biofilter and the moisture of the porous plates. The statistically significant correlation between the number of microorganisms and inlet concentration of acetone was estimated, while ammonia showed a negative influence on yeast distribution. Paecilomyces variotii, Rhodotorula mucilaginosa and Bacillus subtilis were the most common organisms found during filtration of all examined volatiles; however, some differences of microbial communities in different parts of the biofilter plates and filtrated volatile compounds were obtained.

Although biofilm-based biotechnologies exhibit a large potential as solutions for off-gas treatment, the high water content of biofilms often causes pollutant mass transfer limitations, which ultimately limit their widespread application. The present study reports on the proof of concept of the applicability of bioactive latex coatings for air pollution control. Toluene vapors served as a model volatile organic compound (VOC). The results showed that Pseudomonas putida F1 cells could be successfully entrapped in nanoporous latex coatings while preserving their toluene degradation activity. Bioactive latex coatings exhibited toluene specific biodegradation rates 10 times higher than agarose-based biofilms, because the thin coatings were less subject to diffusional mass transfer limitations. Drying and pollutant starvation were identified as key factors inducing a gradual deterioration of the biodegradation capacity in these innovative coatings. This study constitutes the first application of bioactive latex coatings for VOC abatement. These coatings could become promising means for air pollution control., (© 2014 Wiley Periodicals, Inc.)

The present study reports on the effect of magnetic field (MF) intensity on the biofiltration of hexane vapors. MF ranging from 0 to 30 mT (millitesla) was used to evaluate the biofiltration of hexane for 191 days under a fixed inlet load of 40 g m−3 h−1. A homogeneous MF generated by Helmholtz coils was used. The performance of the reactors was evaluated in terms of removal efficiency (RE), elimination capacity (EC), biomass content, and exopolysaccharide (EPS) production. Maximal removal efficiencies of 25%, 36%, and 40% were found for the control (H0), 10 mT (H10), and 30 mT (H30) reactors, corresponding to ECs of 14.2, 15, and 18 g m−3 h−1, respectively. In the last period (days 94 to 162), H10 and H30 showed 40% of RE improvement compared with Ho. Also, the removal occurred all along the bioreactor height for biofilters exposed to MF. Reactors achieved a total biomass content of 152, 180, and 147 mg VS (volatile solids) g−1 dry perlite for H0, H10, and H30, correspondingly, associated with EPS production of 30, 30, and 40 mg EPS g−1VS. The main components of EPS affected by the MF were carbohydrates and glucuronic acid; proteins were slightly affected. Experiments with MF pulses of 4 and 2 h confirmed that MF exposure improved the removal efficiency of hexane, and after the pulse, removal enhancement was maintained for 5 days. Thus, the MF application by pulses could be an economically and friendly technology to improve the RE of volatile organic compounds (VOCs). [ABSTRACT FROM AUTHOR]

Landfills are widely employed as the primary means of solid waste disposal. However, this practice generates landfill gas (LFG) which contains methane (CH4), a potent greenhouse gas, as well as various volatile organic compounds and volatile inorganic compounds. These emissions from landfills contribute to approximately 25% of the total atmospheric CH4, indicating the imperative need to valorize or treat LFG prior to its release into the atmosphere. This review first aims to outline landfills, waste disposal and valorization, conventional gas treatment techniques commonly employed for LFG treatment, such as flares and thermal oxidation. Furthermore, it explores biotechnological approaches as more technically and economically feasible alternatives for mitigating LFG emissions, especially in the case of small and aged landfills where CH4 concentrations are often below 3% v/v. Finally, this review highlights biofilters as the most suitable biotechnological solution for LFG treatment and discusses several advantages and challenges associated with their implementation in the landfill environment. [ABSTRACT FROM AUTHOR]

Biofiltration is a method of pollution management that utilizes a bioreactor containing live material to absorb and destroy pollutants biologically. In this paper, we investigate mathematical models of biofiltration for mixing volatile organic compounds (VOCs) for instance hydrophilic (methanol) and hydrophobic (α -pinene). The system of nonlinear diffusion equations describes the Michaelis-Menten kinetics of the enzymic chemical reaction. These models represent the chemical oxidation in the gas phase and mass transmission within the air-biofilm junction. Furthermore, for the numerical study of the saturation of α -pinene and methanol in the biofilm and gas state, we have developed an efficient supervised machine learning algorithm based on the architecture of Elman neural networks (ENN). Moreover, the Levenberg-Marquardt (LM) optimization paradigm is used to find the parameters/ neurons involved in the ENN architecture. The approximation to a solutions found by the ENN-LM technique for methanol saturation and α -pinene under variations in different physical parameters are allegorized with the numerical results computed by state-of-the-art techniques. The graphical and statistical illustration of indications of performance relative to the terms of absolute errors, mean absolute deviations, computational complexity, and mean square error validates that our results perfectly describe the real-life situation and can further be used for problems arising in chemical engineering. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) pose significant risks to human health and environmental quality, prompting stringent regulations on their emissions from various industrial processes. Among VOCs, d-limonene stands out due to its low threshold and contribution to malodorous emissions. While biofiltration presents a promising approach for VOC removal, including d-limonene, a comprehensive understanding of its performance and kinetics is lacking. This study aims to comprehensively assess the performance of a lab-scale biotrickling filter in treating gas-phase d-limonene. The experimental results indicate that the biotrickling filter efficiently removed d-limonene, achieving a critical loading rate of 19.4 g m−3 h−1 and a maximum elimination capacity of 31.8 g m−3 h−1 (correspondingly, up to 85% removal) at the condition of 94.2 s of EBRT. Microbial activity played a significant role in biotrickling filter performance, with a strong linear correlation being observed between CO2 production and substrate consumption. The Michaelis–Menten model was employed to represent enzyme-catalyzed reactions, suggesting no inhibition during biotrickling filter operation. [ABSTRACT FROM AUTHOR]

This study examined the artificial neural network (ANN) modeling of simultaneous biofiltration of methane (CH4) with two volatile organic compounds (VOCs): xylene and ethylbenzene, using an inorganic packed bed biofilter at an empty bed residence time (EBRT) of 4.5 min. Results showed that the removal efficiency (RE) of CH4 was in the range of 50 to 60% for concentrations of 1000 to 10,000 ppmv (0.6 to 6.5 g m−3), while the VOCs-REs were between 70 and 90% for X and EB concentrations in the range of 200 to 500 ppmv (0.9 to 2.2 g m−3). Artificial neural networks were used to predict and simulate the performances of the biofilter, based on a database containing previous biofiltration works. The ANN1 (architecture of 3 (input layer)-18 (hidden layer)-1 (output layer)) accurately predicted CH4 conversion at the pseudo-steadystate condition, while the ANN2 (4 (input layer)-18 (hidden layer)-2 (output layer)) predicted the simultaneous conversion of CH4 and VOCs with slightly lower accuracy than ANN1. The ANN3 (4 (input layer)-30 (hidden layer)-1 (output layer)) successfully predicted the acclimation period and final phase (CH4 concentration of 10,000 ppmv) of the biofilter but could not accurately predict the transient phases and showed differences (up to 20%) from experimental results once the CH4 concentration was changed. This study developed a decision support and prediction tool to anticipate the performance of biofilters in treating residual gases containing CH4 and VOCs, avoiding costs and delays associated with experimentation. [ABSTRACT FROM AUTHOR]

This study describes the operation of two independent parallel laboratory-scale biotrickling filters (BTFs) to degrade different types of binary volatile organic compound (VOC) mixtures. Comparison experiments were conducted to evaluate the effects of two typical VOCs, i.e., ethyl acetate (a hydrophilic VOC) and n-hexane (a hydrophobic VOC) on the removal performance of toluene (a moderately hydrophobic VOC) in BTFs "A" and "B", respectively. Experiments were carried out by stabilizing the toluene concentration at 1.64 g m−3 and varying the concentrations of gas-phase ethyl acetate (0.85–2.8 g m−3) and n-hexane (0.85–2.8 g m−3) at an empty bed residence time (EBRT) of 30 s. In the presence of ethyl acetate (850 ± 55 mg m-3), toluene exhibited the highest removal efficiency (95.4 ± 2.2%) in BTF "A". However, the removal rate of toluene varied from 48.1 ± 6.9% to 70.1 ± 6.8% when 850 ± 123 mg m-3 to 2800 ± 136 mg m-3 of n-hexane was introduced into BTF "B". The high-throughput sequencing data revealed that the genera Pseudomonas and Comamonadaceae_unclassified are the core microorganisms responsible for the degradation of toluene. The intensity of the inhibitory or synergistic effects on toluene removal was influenced by the type and concentration of the introduced VOC, as well as the number and activity of the genera Pseudomonas and Comamonadaceae_unclassified. It provides insights into the interaction between binary VOCs during biofiltration from a microscopic perspective. [ABSTRACT FROM AUTHOR]

Malodors emitted from various industrial activities significantly impact the well-being of nearby residents, becoming a major source of public complaints in recent years. Additionally, odor pollution poses a problem not only for human health but also for the environment. Managing atmospheric pollution is challenging due to its variable and intermittent nature. Therefore, addressing odor abatement is a complex task that requires precise identification of pollution characteristics, including their source and composition. Implementing effective abatement strategies is essential to ensure compliance with relevant emission regulations. This book chapter compiles the fundamentals and recent advances on biological treatments for odor pollution including biofilters, biotrickling filters, bioscrubbers, two-phase partitioning bioreactors, membrane bioreactors, rotating biological contactors, monolith bioreactors, airlift bioreactors and foam emulsion bioreactors. The book chapter presents the mechanisms involved in pollutant biodegradation, the potential and limitations of the different technologies along with typical operation parameters and recent advances on the development of biological systems. A comparative analysis of the typical application range of each biotechnology based on the pollutant load and flow rate treatment capacity will be performed based on case-studies. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model in the biofilm phase and in the gas phase that has been successfully applied to investigate various aspects of the biofiltration process. The mixtures of volatile organic compounds (VOCs) are emitted from a wide range of industries, such as chemical, petrochemical, pharmaceutical, pulp paper mills, printing and paint workshops, etc. The objective of the present study is, presence of high n-propanol loading negatively affected the toluene removal; however, n-propanol removal was not affected by the presence of toluene and was effectively removed in the biofilter despite high toluene loadings. A model for toluene and n-propanol biofiltration could predict the cross-inhibition effect of n-propanol on toluene removal. Further, we studied the effects of many physical and biological parameters on model prediction. The mathematical equations (2.12)-(2.16) which are non-linear partial differential equations are solved by using the homotopy perturbation technique. Also, we derived the semi-analytical results for toluene and n -propanol concentrations for saturated and unsaturated kinetics. It is verified that the proposed solution is validated by comparing it with numerical solutions. • Here mathematical modelling is developed for bio-filtration in the biofilm phase. • The adopted model investigate various aspects of the bio-filtration process. • Analytical results is obtained via Homotopy Perturbation Technique. • The obtained solutions is verified for accuracy with existing literature. [ABSTRACT FROM AUTHOR]

Landfill gas emissions cause serious environmental concerns due to the presence of methane (CH 4), an important greenhouse gas (GHG) and several harmful volatile organic compounds (VOCs) such as xylene (X) and ethylbenzene (EB). A series of 9 up-flow biofilters (3 sections of 0.3 m each) packed with inorganic materials were used to eliminate CH 4 as a single pollutant, a binary mixture of X and EB and a ternary mixture of CH 4 , X and EB. The CH 4 concentration range was 2000–10000 ppmv while the VOCs (X and EB) individual concentrations were 200, 400 and 600 ppmv for empty bed residence times (EBRTs) ranging from 2.25 to 9 min over a period of 242 days. The highest CH 4 removal efficiency (RE) in the ternary mixture was 41 ± 3% at a CH 4 concentration of 2000 ppmv and X and EB individual concentrations of 200 ppmv for an EBRT of 9 min. Meanwhile, the highest X and EB-REs of 58 ± 3 and 57 ± 3% were obtained respectively, at the same concentrations of the components but at a shorter EBRT of 4.5 min. Almost 40% of CH 4 biodegradation took place on the top section of the bioreactor while 50–60% of the VOCs biodegradation occurred in the middle section. [ABSTRACT FROM AUTHOR]

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Biotrickling filtration is a well-established technology for the treatment of air polluted with odorous and volatile organic compounds (VOCs). Besides dozens of successful industrial applications of this technology, there are still gaps in a full understanding and description of the mechanisms of biotrickling filtration. This review focuses on recent research results on biotrickling filtration of air polluted with single and multiple VOCs, as well as process modeling. The modeling offers optimization of a process design and performance, as well as allows deeper understanding of process mechanisms. An overview of the developments of models describing biotrickling filtration and conventional biofiltration, as primarily developed and in many aspects through similar processes, is presented in this paper. [ABSTRACT FROM AUTHOR]

A multi-channel capillary bioreactor devoted to the continuous abatement of hydrophobic volatile organic compounds (VOCs) by a bacterial and bacterial/microalgae consortium was investigated for 200 days. Toluene, α-pinene and hexane removal in the capillary bioreactor was up to 99 %, 98 %, and 55 %, respectively, which is remarkably high considering the low gas contact time of less than 1 second. Addition of silicone oil increased the removal efficiency (RE) of α-pinene within two days from 45 ± 6 % to 98 ± 2 %, probably through alleviation of biokinetic inhibition provided by the oil acting as buffer for the α-pinene and/or its metabolites. The RE of toluene increased after silicone oil addition over a period of about eight weeks from 81 ± 3 % to 99 ± 1 %, most likely via microbial adaptation. On the contrary, the removal of hexane did not increase following silicone oil addition, potentially due to the inhibition of hexane or its metabolites as the bioreactor was deliberately operated without replenishing the recirculation liquid. Interestingly, biomass adhered to the silicone oil phase rather than residing in the water phase. The bacterial diversity was substantially enhanced, and probably contributed to the observed stable performance of the capillary bioreactor. After the introduction of microalgae on day 150, lower CO 2 concentrations at the outlet compared to the inlet were observed immediately. A net CO 2 consumption was recorded, achieving complete carbon sequestration from the removed VOCs, along with additional CO 2 removed from the inlet ambient air. [Display omitted] • A multi-channel capillary bioreactor with up to 10 %(v/v) silicon oil was studied. • Hydrophobic VOCs removal up to 99 % achieved at less than 1 second gas contact time. • The capillary bioreactor displayed stable operation for the 200 days period. • Biomass adhered to the silicone oil phase rather than residing in the water phase. • VOC-CO 2 co-abatement via algal-bacterial synergism gave complete carbon sequestration. [ABSTRACT FROM AUTHOR]

Biofilters (BFs) and biotrickling filters (BTFs) are two types of bioreactors used for treatment of volatile organic compounds (VOCs). Both BFs and BTFs use packing materials in which various microorganisms are immobilised. The water phase in BFs is stationary and used to maintain the humidity of packing materials, while BTFs have a mobile liquid phase. Optimisation of irrigation of packing materials is crucial for effective performance of BFs and BTFs. A literature review is presented on the influence of water content of packing materials on the biofiltration efficiency of various pollutants. Different configurations of BFs and BTFs and their influence on moisture distribution in packing materials were discussed. The review also presents various packing materials and their irrigation control strategies applied in recent biofiltration studies. The sources of this review included recent research articles from scientific journals and several review articles discussing BFs and BTFs. [ABSTRACT FROM AUTHOR]

BACKGROUND Methanol, a common air pollutant, can be converted to CO2 by biofiltration. In turn, biofilter CO2 streams, contributing to the greenhouse effect, could represent a zero‐cost carbon source for microalgal production. To assess the potential of the combination of both bioprocesses, cultivation of Arthrospira maxima, a major source of added‐value natural products, was carried out with three different carbon sources (bicarbonate mineral medium, CO2 from ambient air, and CO2 from a methanol biofilter outlet). RESULTS: Methanol vapors were almost completely treated in the biofilter, achieving an elimination capacity of 148 ± 18 g m−3 h−1 for an inlet load of 157 ± 12 g m−3 h−1, while producing an average of 152 ± 42 g m−3 h−1 of CO2. Compared to cultivation in classic bicarbonate mineral medium, the resulting CO2 concentration in the biofilter outlet (0.5 ± 0.1% (v/v)) allowed for a 20% higher final production of A. maxima (1.3 g dry weight (DW) L−1 of medium). Moreover, the cultivation of A. maxima significantly reduced the carbon footprint of the biofilter, with a fixation rate of 302 mg CO2 L−1 h−1. Additionally, enriched CO2 concentrations coming from the biofilter outlet allowed for a 117% higher A. maxima productivity rate than ambient air (76.5 ± 2.9 vs. 35.3 ± 1.3 mg DW L−1 d−1). CONCLUSION: Substantial reduction of the cost of microalgae production and treatment of gaseous contaminants can be carried out in tandem. Further optimization of hybrid bioprocesses could represent a win–win opportunity from both environmental and economic viewpoints. © 2021 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The physical/chemical abatement of gas pollutants creates many technical problems, is costly and entails significant environmental impacts. Biological purification of off-gases is a cheap and ecologically safe way of neutralization of gas pollutants. Despite the recent advances, the main technological challenge nowadays is the purification of volatile organic compounds (VOCs) of hydrophobic character due to their low solubility in water. Among all known biological methods of air purification, the most cost-effective biodegradation of hydrophobic VOCs is conducted by biotrickling filters. In this context, fungi have gained an increasing interest in this field based on their ability to biodegrade hydrophobic VOCs. In addition, biotrickling filtration using fungi can support a superior hydrophobic VOC abatement when compared to the bacterial biofilters. This paper aims at reviewing the latest research results concerning biocatalytic activity of fungi and evaluating the possibilities of their practical application in biofiltration systems to remove hydrophobic VOCs. [ABSTRACT FROM AUTHOR]

A novel three-stage integrated biofilter (TSIBF) composed of acidophilic bacteria reaction segment (ABRS), fungal reaction segment (FRS) and heterotrophic bacteria reaction segment (HBRS) was constructed for the treatment of odors and volatile organic compounds (VOCs)from municipal solid waste (MSW) comprehensive treatment plants. The performance, counts of predominant microorganisms, and bioaerosol emissions of a full-scale TSIBF system were studied. High and stable removal efficiencies of hydrogen sulfide, ammonia and VOCs could be achieved with the TSIBF system, and the emissions of culturable heterotrophic bacteria, fungi and acidophilic sulfur bacteria were relatively low. The removal efficiencies of different odors and VOCs, emissions of culturable microorganisms, and types of predominant microorganisms were different in the ABRS, FRS and HBRS due to the differences in reaction conditions and mass transfer in each segment. The emissions of bioaerosols from the TSIBF depended on the capture of microorganisms and their volatilization from the packing. The rational segmentation, filling of high-density packings and the accumulation of the predominant functional microorganisms in each segment enhanced the capture effect of the bioaerosols, thus reducing the emissions of microorganisms from the bioreactor. [ABSTRACT FROM AUTHOR]

The disposal of organic waste in processes such as composting is related to the emission of malodorous compounds. Owing to their character and low odour detection threshold, there is often a need for a hundred percent elimination of the contaminants from waste gases. One of alternative methods of treating the waste gases from malodorous contaminants, occurring in low concentrations in post-process air, is the biofiltration method. Most often, the method uses an organic filtration material. However, this method of air purification is still developing; therefore, there is a search for new sorbents among mineral materials, which would be an alternative for organic sorbents. The article presents the research into the application of aluminosilicate sorbents, including halloysite, for deodorization of the gases emitted from the processes of composting municipal waste. The semitechnical scale research was conducted for several weeks in a municipal waste composting plant, passing real gases through two biofilters filled with mineral sorbents. In spite of the fact that some problems occurred and the research cycle was not completed, the experiment proved that halloysite removes odours to a much higher extent than the other examined aluminosilicate sorbent. While the VOCs reduction on a bed with halloysite was 88%, the reduction on a bed with a second aluminosilicate reached 35%. The process conditions were very unstable; therefore, the efficiency of the VOCs removal process varied widely. However, halloysite has always been a better sorbent than the other aluminosilicate. [ABSTRACT FROM AUTHOR]

• Pilot two-stage biofilter (traditional bed and membrane fabrics) was tested. • 4 configurations of biofilter were analyzed (2 beds and 2 membranes). • RE and EC of VOCs, NH 3 and H 2 S from gases in a semi-technical scale was analyzed. • Membrane application allows simultaneous removal of low concentration VOCs, NH 3 and H 2 S with high RE. • Average RE was maintained between 97% (for VOCs) to 99% (for NH 3 and H 2 S). The analysis of biofiltration efficiency was performed with parallel VOC, H 2 S and NH 3 removal using pilot two-stage biofilters including conventional biofiltration and purification on a membrane filter. The scope of the research was to determine the relationship between the technological parameters of the tested device (two beds and two membranes) and gases removal efficiency. Research was carried out in a semi-technical scale in three industrial plants: mechanical-biological municipal waste treatment (MBT), food industry (FI) and wastewater treatment (WWTP) plants. Experimental results indicate the efficiency removal of VOCs from 89% (WWTP) to 98% (FI), NH 3 from 88% (WWTP) to 100% (MBT) and H 2 S from 93% (WWTP) to 100% (MBT). Biofilter with stumpwood chips-bark-compost bed, fortified with the more porous membrane was the most effective, allowing VOC, NH 3 and H 2 S removal with an average efficiency of 99% for NH 3 and H 2 S and 97% for VOCs. The application of membrane fabrics as the second stage of purification allows high efficiency simultaneous removal of VOCs, NH 3 and H 2 S. Unlike two-stage purification, conventional biofiltration is effective at removing individual impurities from process gases. The results of this study indicate a high potential for practical application. [ABSTRACT FROM AUTHOR]

Indoor air pollutant issues have attracted various researchers to investigate alternative solutions to non-biofiltration systems, such as common air purifiers that are generally used in the market. Research has found that active botanical biofilter systems are efficient in filtering indoor air pollutants, as well as providing a refreshing environment to surroundings. The research presented here describes a developed prototype of a botanical indoor air biofilter (BIAB) and evaluates the performance of the BIAB system in reducing common indoor air pollutants. The system was assessed for its single-pass filtration across an aerosol containing particles with the diameter of 2.5 µm (PM2.5), 10 µm (PM10) and volatile organic compounds (VOCs) by burning aromatic cone incense. The system comprises three working sections: a fraction of horizontally grown plants with growth media as the botanical biofiltration section, an evaporative medium (an additional component from a commercial active botanical biofilter) and a mechanical ventilation system that supplies cleaned air to the surroundings. The BIAB system recorded the removal efficiencies of 54.5 ± 6.04% for PM2.5, 65.42 ± 9.27% for PM10 and 46 ± 4.02% for VOCs. [ABSTRACT FROM AUTHOR]

For potential use in air treatment by biofiltration, a new material composed of vermicompost and earthworms (Eisenia fetida) was tested for the removal of a volatile organic compound (VOC), toluene. The removal rate of toluene was measured during batch experiments in presence of vermicompost only, earthworms only and a mixture of both. In the chosen experimental conditions, no mortality of earthworms was recorded and the results showed that the presence of earthworms allowed an increase in toluene removal rate (0.213 mg h−1) compared to vermicompost only (0.084 mg h−1) and earthworms only (0.136 mg h−1). From the experimental data, mechanisms of toluene transfer and adsorption/biodegradation by microorganisms from vermicompost and/or earthworms were proposed. [ABSTRACT FROM AUTHOR]

Designing of air pollution control equipment such as biofilters, also known as gas phase biological reactors, for elimination of toxic volatile organic compounds (VOCs) from air streams require accurate modeling and model solutions. In this work, a novel approach is employed to solve a biofilter model and for performance predictions. The approach is based on expressing the particular solution of the governing equations as an integral containing Green's function. The integral is then tuned to develop a suitable operator in which Krasnoselskii-Mann's fixed point iteration method is applied. In this work, this technique was utilized to model the biological degradation of methanol and alpha-pinene. The results obtained by the proposed technique were compared against the experimental data adopted from literature and the originally published numerical solution. The comparison showed that the approach is highly accurate and converges fast with a uniformly distributed residual error over the entire domain. Furthermore, the method was used to perform a sensitivity analysis on the model equations to evaluate the performance of the biofilter under various conditions. To the authors' knowledge, this is the first time Mann's Green's embedded method (MGEM) is applied in the solution of biofilter models. [ABSTRACT FROM AUTHOR]

Trimethylamine (TMA) is an odorous volatile organic compound emitted by industries. Algal-based biotechnologies have been proven as a feasible alternative for wastewater treatment, although their application to abate polluted air emissions is still scarce. This work comparatively assessed the removal of TMA in a conventional bacterial bubble column bioreactor (BC) and a novel algal-bacterial bubble column photobioreactor (PBC). The PBC exhibited a superior TMA abatement performance compared to the conventional BC. In this sense, the BC reached a removal efficiency (RE) and an elimination capacity (EC) of 78% and 12.1 g TMA m−3 h−1, respectively, while the PBC achieved a RE of 97% and a EC of 16.0 g TMA m−3·h−1 at an empty bed residence time (EBRT) of 2 min and a TMA concentration ~500 mg m−3. The outstanding performance of the PBC allowed to reduce the operating EBRT to 1.5 and 1 min while maintaining high REs of 98 and 94% and ECs of 21.2 and 28.1 g m−3·h−1, respectively. Moreover, the PBC improved the quality of the gas and liquid effluents discharged, showing a net CO2 consumption and decreasing by ~ 30% the total nitrogen concentration in the liquid effluent via biomass assimilation. A high specialization of the bacterial community was observed in the PBC, Mumia and Aquamicrobium sp. being the most abundant genus within the main phyla identified. [ABSTRACT FROM AUTHOR]

Although the appropriate supply of nutrients has been extensively researched, more information is required on the effects of nutrients in treating gaseous volatile organic compounds (VOCs) in biofiltration. In this study, the effects of phosphorous and trace metals on gaseous toluene and methyl ethyl ketone (MEK) removal were investigated. The transfer of nutrients from the irrigation liquid to the packed bed, and the consumption and holding amount of nutrients in the packing material were observed during biofiltration. Under conditions of 20–24 s of empty bed residence time, MEK removal was 95% or more in all conditions of the biofiltration reactors, whereas toluene removal was affected by the operating conditions of the reactors. Consumption ratio of phosphorus to carbon was from 1.7 × 10−4 to 1.1 × 10−3 in the steady state of VOC removal under the conditions of this study. When gaseous VOC treatment was restarted after nine days of shutdown, a significant decline in toluene removal was observed by the reactor in which phosphorus supply was approximately one fifth of the amount in another reactor. Two types of irrigation systems, soaking and spraying, were compared and soaking irrigation achieved a more even distribution of nutrients held inside the packed bed. Soaking irrigation was expected to lead to higher VOC removal capacity by this distribution effect of nutrients, but toluene removal in the reactor with this irrigation was lower than that in the reactor with spraying irrigation. One of the possible reasons for this was the inhibition of nutrients transfer in the bottom part of the reactor. The trend of transfer in all ingredients from the irrigation liquid to the packed bed was synchronized on the whole; however, this transfer relatively tended to be high in nitrate and sodium and low in ammonium and phosphate. Implications: A major concern about using biofiltration systems to treat VOCs is the uncertainty regarding the appropriate nutrient supply to the filter bed to preserve microbial activity. This study showed that all the elements, except nitrogen, were retained sufficiently in the filter bed when a proper composition of nutrient solution was used for irrigation; however, phosphate addition may be needed when restarting a reactor from a prolonged period of shutdown. Distinct differences in the amount of transfer to the filter bed for different ingredients are probable, and may have to be taken into account when operating biofiltration reactors. [ABSTRACT FROM AUTHOR]

Assessment of biofiltration systems under transient conditions is necessary when determining industrial operating conditions of biofiltration beds. The key system variables such as filter bed moisture content, the pollutant type and its concentration, must be evaluated in order to accurately calculate scaling of biofiltration beds. The removal efficiency of two organic volatile compounds (VOCs) was evaluated: acetic acid (hydrophilic) and pentane (hydrophobic). Two independent biofiltration systems were operated (A and B), in each system the bed packing material was the same. The filtration beds were made from compost, with the following mixtures: rice husk-chicken manure (CAS) and pruning waste-chicken manure (POD), each in a ratio of 1:1 (v:v). As part of this study, in system A, the effect of moisture on acetic acid removal efficiency was analyzed, finding that in a moisture range of 50-15% and of 50-25%, efficiencies above 90% are reached for CAS and for POD respectively. On the other hand, in system B, the performance of the biofilters was evaluated against different concentrations of pentane, resulting in removal efficiencies of 25% and 43% for POD and CAS, respectively. In general, these results indicate that there is a significant dependence between the performance of the system and the moisture content of the filter bed and the lower limit in which the bed would operate under industrial conditions is defined. The pollutant water solubility was also considered in order to define the maximum concentrations that the bed would support under transient conditions. [ABSTRACT FROM AUTHOR]