Experimental evaluation of a full-scale in-duct UV germicidal irradiation system for bioaerosols inactivation.

Bioaerosols control techniques, especially ultraviolet germicidal irradiation (UVGI) are gaining attention due to increasing needs for controlling of health risk caused by airborne biocontaminants. The effectiveness of a full-scale in-duct UVGI air disinfection system was investigated. One bacterium, a wild type Escherichia coli, and three fungal spores, Penicillium aragonense, Rhodotorula glutinis, and Cladosporium sp., were selected as test organisms and their inactivation under different conditions representative of a real application in HVAC systems were investigated. The results demonstrated that inactivation of airborne E. coli by the UVGI system was extremely effective, with >99.5 % of the input E. coli inactivated at a residence time lower of 0.36 s in the disinfection section. Airborne fungal spores were less susceptible to UV irradiation than E. coli. Under same conditions, viable counts reduction of P. aragonense, R. glutinis, and Cladosporium sp. spores were 53 %, 63 % and 73 %, respectively. The effect of UV light intensity, air flowrate and relative humidity were analyzed separately. A simplified model based on redefinition of the parameters in the classical inactivation kinetic equation was used to simulate the inactivation of airborne contaminants in the in-duct system under different conditions. The results showed that the simplified model was adequate to estimate disinfection efficacy of different bioaerosols by the UVGI system and that such in-duct systems can provide significant control of bioaerosols.

Current advances of chlorinated organics degradation by bioelectrochemical systems: a review.

Chlorinated organic compounds (COCs) are typical refractory organic compounds, having high biological toxicity. These compounds are a type of pervasive pollutants that can be present in polluted soil, air, and various types of waterways, such as groundwater, rivers, and lakes, posing a significant threat to the ecological environment and human health. Bioelectrochemical systems (BESs) are an effective strategy for the degradation of bio-refractory compounds. BESs improve the waste treatment efficiency through the application of weak electrical stimulation. This review discusses the processes of BESs configurations and degradation performances in different environmental media including wastewater, soil, waste gas and groundwater. In addition, the degradation mechanisms and performance-enhancing additives are summarized. The future challenges and perspectives on the development of BES for COCs removal are briefly discussed.

Enhancing biological conversion of NO to N2O by utilizing thermophiles instead of mesophiles.

The production of nitrous oxide (N2O) through the biological denitrification of nitric oxide (NO) from flue gases has recently been achieved. Although the temperature of flue gas after desulphurization is usually 45-70 °C, all previous studies conducted microbial denitrification of NO under mesophilic conditions (22-35 °C). This study investigated the biological conversion of NO to N2O in both mesophilic (35-45 °C) and thermophilic conditions (45-50 °C). The results showed that temperature has a great impact on N2O production, with a maximum conversion efficiency (from NO to N2O) of 82% achieved at 45 °C, which is obviously higher than the reported conversion efficiencies (24-71%) under mesophilic conditions. Additionally, high-throughput sequencing result showed that the genera Enterococcus, Clostridium, Romboutsia, and Streptococcus were closely related to NO denitrification and N2O production. Microbial communities at 40 and 45 °C had greater metabolizing capacities for polymeric carbon sources. This study suggests that thermophilic condition (45 °C) is more suitable for biological production of N2O from NO.

Effect of weak electrical stimulation on m-dichlorobenzene biodegradation in biotrickling filters: Insights from performance and microbial community analysis.

The microbial electrolysis cell coupled with the biotrickling filters (MEC-BTF) was developed for enhancing the biodegradation of gaseous m-dichlorobenzene (m-DCB) through weak electrical stimulation. The maximum removal efficiency and elimination capacity in MEC-BTF were 1.48 and 1.65 times higher than those in open-circuit BTF (OC-BTF), respectively. Weak electrical stimulation had a positive impact on the characteristics of the biofilm. Additionally, microbial community analysis revealed that weak electrical stimulation increased the abundance of key functional genera (e.g., Rhodanobacter and Bacillus) and genes (e.g., catA/E and E1.3.1.32), thereby accelerating reductive dechlorination and ring-opening of m-DCB. Macrogenomic sequencing further revealed that electron transfer pathway in MEC-BTF might be mediated through extracellular electroactive mediators and cytochromes.

Development of a CFD model indicating the quantitative relationship among reactor dimension, bed flow unevenness, and performance for VOCs biofilters.

This study presents a Computational Fluid Dynamics (CFD) based biofiltration model to investigate the airflow distribution and the impact of bed flow unevenness (BFU) on the removal of Volatile Organic Compounds (VOCs) in biofilters. The biofiltration model consists of a gas flow sub-model and a VOCs removal sub-model, which were validated by pilot-scale experiments. The model was used to examine the quantitative relationship among reactor dimensions, including the width to height ratio of the filter bed and empty bed residence time (EBRT), BFU, and performance for VOCs biofilters. Simulation results demonstrate that the flow unevenness index (FUI) of the packing layer changes from 0.06 to 0.48 m2‧s-1 with reactor dimension changes. With an increase in the width to height ratio at a constant EBRT, FUI increases, BFU changes, and flow velocity fluctuation on the cross-section becomes larger, leading to a reduction of about 10% in VOCs removal efficiency. Concentration distribution of VOCs becomes uneven in the horizontal direction. At a constant width to height ratio of the filter bed, an increase in EBRT causes an increase in FUI, leading to a decrease in VOCs removal efficiency. When the width to height ratio is 0.5, velocity fluctuation of filter bed cross-section is small, the concentration of VOCs decreases evenly across the filter bed layer, and FUI is at a low level (0.06-0.11 m2‧s-1).Implication: In this manuscript, a biofiltration model of VOCs biofilter based on CFD has constructed and validated. And the manuscript gave the quantitative relationship among reactor dimension, bed flow unevenness and performance for VOCs biofilters for the first time. This study can lead to enhanced VOCs removal efficiency and improved overall performance of biofilters in practical engineering applications.

Quorum sensing improved the low-temperature performance of biofilters treating gaseous toluene.

Biofilters usually have poor VOC removal performance at temperatures lower than 20 °C. In this study, two quorum sensing (QS) enhancement methods, which are addition of exogenous N-acyl-homoserine lactones (AHLs) and inoculation of AHL-producing bacteria, were applied in biofilters treating gaseous toluene at a low temperature of 12 °C. Their effects on biofilter performance and biofilm characteristics were investigated. The results showed that adding exogenous AHLs and AHL-producing bacteria in biofilters raised the average toluene elimination capacity by 39% and 26% respectively, and raised the average mineralization efficiency by 25% and 47% respectively in first 24 days. In addition, the two QS enhancement methods could increase the attached biomass by 48% and 87% respectively and made the biofilm distribute more uniform by increasing its extracellular polymeric substances content and microbial adhesive strength. The two QS enhancement methods resulted in more mesopores in biofilm, lower O/C and (O+N)/C of organic elements in biofilm, and increased the solubility of toluene in liquid phase, which all benefit VOCs mass transfer in biofilters. These results demonstrate that QS enhancement methods have the potential to optimize the biofilm and thus improve the performance of biofilters treating VOCs at a low temperature. This work provides us a new choice to improve industrial-scale biofilters treating VOCs at high latitude regions or in winter.

Two quorum sensing enhancement methods optimized the biofilm of biofilters treating gaseous chlorobenzene.

In this study, effects of two quorum sensing (QS) enhancement methods on the performance and biofilm of biofilters treating chlorobenzene were investigated. Three biofilters were set up with BF1 as a control, BF2 added exogenous N-acyl-homoserine lactones (AHLs) and BF3 inoculated AHLs-producing bacterium identified as Acinetobacter. The average chlorobenzene elimination capacities were 73 and 77 g/m3/h for BF2 and BF3 respectively, which were significantly higher than 50 g/m3/h for BF1. The wet biomass of BF2 and BF3 with QS enhancement eventually increased to 60 and 39 kg/m3 respectively, and it was 29 kg/m3 for BF1. Analysis on biofilms in three biofilters showed that distribution uniformity, extracellular polymeric substances production, adhesive strengths, viability, and metabolic capacity of biofilms were all prompted by the two QS enhancement methods. Comparisons between the two QS enhancement methods showed that adding exogenous AHLs had more significant enhancing effect on biofilm due to its higher AHLs level in start-up period, while AHLs-producing bacteria had an advantage in enhancing bacterial community diversity. These results demonstrate that QS enhancement methods have the potential to optimize the biofilm and thus improve the performance of biofilters treating recalcitrant VOCs.

Sustaining low pressure drop and homogeneous flow by adopting a fluidized bed biofilter treating gaseous toluene.

A biofilter treating gaseous VOCs is usually a packed bed system which will encounter bed clogging problems with increased pressure drop and uneven gas flow in the filter bed. In this study, a lab-scale fluidized bed reactor (FBR) was set up treating gaseous toluene and compared with a packed bed reactor (PBR) with the same bed height of 150 cm. During 45 days of operation, the average elimination capacity of the FBR was 242 g m-3∙h-1, similar to that in the PBR (228 g m-3∙h-1) under an inlet toluene concentration of 100-300 mg m-3 and an empty bed residence time (EBRT) of 0.60 s. A better mass transfer was also confirmed in the FBR by molecular residence time distribution measurement. The pressure drop of the PBR increased dramatically and exceeded 8000 Pa m-1 while that of the FBR maintained approximately 200 Pa m-1. On the 40th day, the air flow distribution in the FBR was more homogeneous than that in the PBR. The differences in pressure drop and air flow distribution were due to a much lower and more uniform distribution of biomass in the FBR than that in the PBR. The detached biomass collected from the off-gas of the FBR was almost 13 times of that from the PBR. Similar microbial community structures were observed in both systems, with the dominant bacterial genus Stenotrophomonas and the fungal genera Meyerozyma, Aspergillus. The results in this study demonstrated that the FBR could achieve a more stable performance than a PBR in long-term operation.

Development of an H2S emission model for wastewater treatment plants.

Modeling and prediction of H2S emission from wastewater are important since gaseous H2S will induce significant corrosion and odor problems. Most previous studies focused on H2S emission of wastewater in pipeline systems, which may not be fit for H2S emission in wastewater treatment plants (WWTPs). This study provided a two-phase mass transfer model for prediction of H2S emission concentrations. The model is based on the mass transfer rate equation of the mass transfer impetus, expressed by the concentration difference. The main parameters of the model are the mass transfer coefficient, the carrier gas flow rate and the concentration of H2S in liquid phase. The results showed that the model can simulate and predict H2S emission concentrations of various processes in WWTPs. Moreover, the model can analyze and predict the influences of different pH values, mass transfer coefficients and carrier gas flow rates on H2S emission concentrations and loads. Therefore, the model provides theoretical guidance for design of WWTPs regarding H2S emissions.Implications: Modeling and prediction of H2S emission from wastewater are quite important since gaseous H2S will induce significant corrosion and odor problems. Most of previous studies are focused on H2S emission from wastewater in pipeline system, which may not be fit for H2S emission in wastewater treatment plants (WWTPs). Thus in this study, a model for predicting H2S emission from typical units of WWTPs is established and verified. Moreover, the influences of pH values, mass transfer coefficients and carrier gas flow rates on H2S emission are analyzed. The model can be a useful tool to predict the H2S concentration in odor gas collection system of WWTP and understand the behaviors of H2S emission under different WWTPs operating conditions.

Low-dosage ozonation in gas-phase biofilter promotes community diversity and robustness.

BACKGROUND: The ozonation of biofilters is known to alleviate clogging and pressure drop issues while maintaining removal performances in biofiltration systems treating gaseous volatile organic compounds (VOCs). The effects of ozone on the biofilter microbiome in terms of biodiversity, community structure, metabolic abilities, and dominant taxa correlated with performance remain largely unknown. METHODS: This study investigated two biofilters treating high-concentration toluene operating in parallel, with one acting as control and the other exposed to low-dosage (200 mg/m3) ozonation. The microbial community diversity, metabolic rates of different carbon sources, functional predictions, and microbial co-occurrence networks of both communities were examined. RESULTS: Consistently higher biodiversity of over 30% was observed in the microbiome after ozonation, with increased overall metabolic abilities for amino acids and carboxylic acids. The relative abundance of species with reported stress-tolerant and biofilm-forming abilities significantly increased, with a consortium of changes in predicted biological pathways, including shifts in degradation pathways of intermediate compounds, while the correlation of top ASVs and genus with performance indicators showed diversifications in microbiota responsible for toluene degradation. A co-occurrence network of the community showed a decrease in average path distance and average betweenness with ozonation. CONCLUSION: Major degrading species highly correlated with performance shifted after ozonation. Increases in microbial biodiversity, coupled with improvements in metabolizing performances of multiple carbon sources including organic acids could explain the consistent performance commonly seen in the ozonation of biofilters despite the decrease in biomass, while avoiding acid buildup in long-term operation. The increased presence of stress-tolerant microbes in the microbiome coupled with the decentralization of the co-occurrence network suggest that ozonation could not only ameliorate clogging issues but also provide a microbiome more robust to loading shock seen in full-scale biofilters. Video abstract.

Multi-factor analysis of algal blooms in gate-controlled urban water bodies by data mining.

Intense human disturbance has made algal bloom a prominent environmental problem in gate-controlled urban water bodies. Urban water bodies present the characteristics of natural rivers and lakes simultaneously, whose algal blooms may manifest multi-factor interactions. Hence, effective regulation strategies require a multi-factor analysis to understand local blooming mechanisms. This study designed a holistic multi-factor analysis framework by integrating five data mining techniques. First, the Kolmogorov-Smirnov test was conducted to screen out the possible explanatory variables. Then, correlation analyses and principal component analyses were performed to identify variable collinearity and mutual causality, respectively. After collinearity and mutual causality were treated prudently by using orthogonalization and instrumental variables, multilinear regression can be properly conducted to quantify factor contributions to algae growth. Lastly, a decision tree was used innovatively to depict the limiting threshold curves of each driving factor that restricts algae growth under different circumstances. The driving factors, their contributions, and the limiting threshold curves compose the complete blooming mechanisms, thus providing a clear direction for the targeted regulation task. A typical case study was performed in Suzhou, a Chinese city with an intricate gate-controlled river network. Results confirmed that climatic factors (i.e., water temperature and solar radiation), hydrodynamic factors (i.e., flow velocity), nutrients (i.e., phosphorus and nitrogen), and external loadings contributed 49.3%, 21.7%, 21.3%, and 7.7%, respectively, to algae growth. These results indicate that a joint regulation strategy is urgently required. Future studies can focus on coupling the revealed mechanisms with an ecological model to provide a comprehensive toolkit for the optimization of an adaptive joint regulation plan under the background of global warming.

Characteristics and mechanisms of H2S production in anaerobic digestion of food waste.

The biogas produced in food waste anaerobic digestion (FWAD) contains H2S which can lead to corrosion, bad smell and poisoning accident. To control H2S pollution, the characteristics and mechanisms of H2S production in FWAD should be known. In this study, a lab-scale FWAD batch test was applied for 20 days under 35 °C. The production potential and average concentration of H2S were 765 ± 163 g/t (TS) and 1065 ± 267 ppm, respectively. 76% of total H2S was produced within 6 h on the first day of fermentation, acidification and gas production were key reasons for high H2S production at this time. Compared to H2S peak production time, that of methane was long (4 days) and after that of H2S. Sulfides were found to be the dominant form of sulfur (accounting for 20-70% of total sulfur) in the mixed fermentation liquor in fermentation batch. These sulfides were from protein, which could be decomposed slowly to sulfide by protein-using bacteria and methanogen at the time of methane production peak, and sulfate, which could be converted to sulfide by Sulfate reducing bacteria (SRB) during the first two days of fermentation. Protein would be the main contributor to sulfide/H2S for the continuous feeding FWAD system in long term operation, due to its presence as the main form of sulfur in food waste.

Development of a novel fungal fluidized-bed reactor for gaseous ethanol removal.

Fluidized bed bioreactors can overcome the limitations of packed bed bioreactors such as clogging, which has been observed in the industrial application for decades. The key to establish a gaseous fluidized bed bioreactor for treatment of volatile organic compounds is to achieve microbial growth on a light packing material. In this study, Two fungal species and two bacterial species were isolated to build a fungal fluidized-bed reactor (FFBR). A light packing material with wheat bran coated on expended polystyrene was used. The FFBR was operated for 65 days for gaseous ethanol removal and obtained elimination capacities of 500-1800 g∙m-3∙h-1 and removal efficiencies of 20-50%. The pressure drops was well controlled with values around 400 Pa∙m-1. Stress tolerant genera including Aureobasidium, Stenotrophomonas and Brevundimonas were dominant. Meyerozyma, whose species were present in an initial inoculated isolate, was detected among the dominant species with 28.70% relative abundance; they were reported to degrade complicated compounds under similarly stressful environments.

Enhancing biofilm formation in biofilters for benzene, toluene, ethylbenzene, and xylene removal by modifying the packing material surface.

Polyurethane (PU) sponges are popular packing material in biofilters and their smooth and hydrophobic surface often leads to an uneven distribution and detachment of biofilms. In this work, the surface of PU sponge was modified to obtain higher roughness and positive charge. The performances of two biofilters (BF1 with pristine sponge and BF2 with modified sponge) for benzene, toluene, ethylbenzene, and xylene (BTEX) removal were investigated. Total Volatile Organic Compound (TVOC) removal efficiency and CO2 increment were 61% and 804 ppm for BF2 respectively after start-up, compared with 51% and 538 ppm for BF1. Analysis on biofilms showed that the modification of PU sponge significantly improved the microbial growth, viability and adhesive strength in biofilms, reduced extracellular polymeric substance (EPS) and changed the microbial community. These results demonstrate that modified sponge can enhance biofilm formation and BTEX removal in biofilters and may applied in large-scale applications.

Screening and characterization of mixotrophic sulfide oxidizing bacteria for odorous surface water bioremediation.

Eight species of mixotrophic sulfide oxidizing bacteria (SOB) were isolated from activated sludge and identified using 16S rRNA sequence analysis. The effects of organic substances, dissolved oxygen (DO) and nitrate on sulfide oxidation and bacterial growth were studied in this work. The results showed that Paracoccus sp. (N1), Pseudomonas sp. (N2) and Pseudomonas sp. (S4) have strong adaptability to environments with low DO and high concentrations of organic substance. An SOB additive was optimized in artificial, odorous water. The optimized SOB additive is ablendof 80% N1 and 20% N2 bacteria solution with absorbance equal to 0.5 at a wavelength of 600 nm (OD600), and the optimal dose of the additive is 20 ml/L. Oxidation-reduction potential (ORP), ammonia-nitrogen (NH3-N) and released H2S in an odorous river were measured with and without SOB additive, and the results indicated that the optimized SOB additive has excellent performance for odorous river bioremediation.

Remediation of simulated malodorous surface water by columnar air-cathode microbial fuel cells.

Malodorous surface water is an important worldwide environmental concern. Current remediation methods, such as aeration or the addition of chemicals, are not eco-friendly due to their high energy consumption or secondary pollution. This study proposed a modified columnar air-cathode microbial fuel cell as a sustainable and effective remediation module to improve water quality. The excellent and economic sheet air-cathode (activated carbon and carbon black as the catalyst layer) and a carbon brush anode were applied in the columnar air-cathode microbial fuel cell (MFC). The results after 48 h showed that by providing the anode as an electron acceptor and enriching electrochemically-active bacteria, MFCs with different external resistances (5 k Ω, 30 Ω, and 2 Ω) exhibited the much better capacity to improve water quality than the Blank group. The maximum COD and sulfide removal rates in the MFCs were approximately 86.3% and 100%, respectively, which were higher than those of the Blank group by 30% and 35%, respectively. The MFCs also showed maximum sulfate increments from 28 mg L-1 to 98 mg L-1 compared with the sulfate reduction to 10 mg L-1 in the Blank group. The oxidation reduction potential (ORP) of the MFCs dramatically increased from -281.2 mV to -135.7 mV after 24 h, whereas the ORP of the Blank group decreased to -287.7 mV. The enrichment of the aerobic bacteria Acinetobacter on the anodes and chemolithoautotrophic sulfide oxidation bacteria Sulfuricurvum, Thiovirga and Thiobacillus in the MFCs could also contribute to COD and sulfide removal. Cathode reduction, which could produce small amounts of hydroxyl radicals, might assist with the ORP elevation and the complete oxidation of dissolved sulfide to sulfate.

Response of microbial community structure and metabolic profile to shifts of inlet VOCs in a gas-phase biofilter.

The effects of inlet VOCs (Volatile Organic Compounds) shifts on microbial community structure in a biofiltration system were investigated. A lab-scale biofilter was set up to treat eight VOCs sequentially. Short declines in removal efficiency appeared after VOCs shifts and then later recovered. The number of OTUs in the biofilter declined from 690 to 312 over time. At the phylum level, Actinobacteria and Proteobacteria remained dominant throughout the operation for all VOCs, with their combined abundance ranging from 60 to 90%. The abundances of Planctomycetes and Thermi increased significantly to 20% and 5%, respectively, with the intake of non-aromatic hydrocarbons. At the genus level, Rhodococcus was present in the highest abundance (≥ 10%) throughout the experiment, indicating its wide degradability. Some potential degraders were also found; namely, Thauera and Pseudomonas, which increased in abundance to 19% and 12% during treatment with ethyl acetate and toluene, respectively. Moreover, the microbial metabolic activity declined gradually with time, and the metabolic profile of the toluene-treating community differed significantly from those of other communities.

Biotoxicity of Water-Soluble UV Photodegradation Products for 10 Typical Gaseous VOCs.

Ultraviolet (UV) photodegradation is increasingly applied to control volatile organic compounds (VOCs) due to its degradation capabilities for recalcitrant compounds. However, sometimes the UV photodegradation products are also toxic and can affect human health. Here, 10 VOCs at 150~200 ppm in air were treated using a laboratory-scale UV reactor with 185/254 nm irradiation, and the biotoxicity of their off-gas was studied by investigating their off-gas absorption solutions. The CO2 increase and VOC decrease were 39~128 ppm and 0~42 ppm, respectively, indicating that the VOCs and their products were mineralized in off-gas absorption solutions. The total organic carbon (TOC) of the absorption solutions are 4~20 mg∙L-1. Luminescent bacteria and Daphnia magna were used to detect the acute toxicity, and an umu assay was used to determine the genotoxic potential. Trichloroethylene showed a highest toxicity to luminescent bacteria, while chlorobenzene had the lowest toxicity. Water-soluble UV photodegradation products for styrene are very toxic to Daphnia magna. In the umu assay, the genotoxicities of off-gas absorption solutions of trichloroethylene, methylbenzene, ethyl acetate, butyl alcohol, and styrene were 51.26, 77.80, 86.89, 97.20, and 273.62 mg (4-NQO)·L-1 respectively. In addition, the analysis of the genotoxicity/TOC and intermediates products indicated that the off-gas absorption solutions of styrene, trichloroethylene, and butyl alcohol contain many highly toxic substances.

Effect of ozone injection on the long-term performance and microbial community structure of a VOCs biofilter.

For biofilters treating waste gases containing volatile organic compounds (VOCs), biomass accumulation is a common problem which will induce bed clogging and significant decrease in VOCs removal efficiency during long-term operation. In this study, ozone injection was developed as a biomass control strategy, and its effects on the biofilter performance and the microbial community structure were investigated in long-term operation. Two biofilters, identified as BF1 and BF2, were operated continuously for 160 days treating gaseous toluene under the same conditions, except that 200 mg/m3 ozone was continuously injected into BF1 during days 45-160. During the operation period, ozone injection did not change the toluene removal efficiency, while the pressure drop of BF1 with ozone injection was significantly lowered compared with BF2. The wet biomass accumulation rate of BF1 was 11 g/m3/hr, which was only 46% of that in BF2. According to the carbon balance result, ozone injection also increased the toluene mineralization rate from 83% to 91%, which could be an important reason for the low biomass accumulation. The PMA-qPCR result indicated that ozone injection increased the microbial viability of the biofilm. The high-throughput sequencing result also revealed that the dominant phyla and genera were not changed significantly by ozone injection, but some ozone-tolerant genera such as Rhodanobacter, Dokdonella and Rhodococcus were enhanced by ozone exposure. All the results verified that ozone injection is capable of sustaining the long-term performance of biofilters by lowering the biomass accumulation, increasing the microbial viability and changing the microbial community structure.

Simultaneous Removal of Multicomponent VOCs in Biofilters.

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.