Biofiltration of volatile organic compounds

Assessing the impact of packaging materials on anoxic biotrickling filtration of siloxanes in biogas: Effectiveness of activated carbon in removal performance

Siloxanes (VMS) represent a class of organosilicon compounds known for their adverse effects on both the environment and human health. Their presence in biogas significantly hinders its economic valorisation, highlighting the need for effective treatment methods. This study investigates the performance of three different packing materials in the anoxic biofiltration of VMS (L2, L3, D4 and D5). The materials evaluated included plastic rings (BTF-1), polyurethane foam (BTF-2) and plastic rings combined with activated carbon (80:20) (BTF-3). Among them, BTF-3 exhibited superior performance, achieving maximum VMS removal efficiencies (REs) of 90%, including the complete elimination of L3 and D4, and ∼80% removal of D5, attributed to the presence of activated carbon. However, the abatement of L2 was inferior to that of other VMS (<80%), which was attributed to the activated carbon's affinity for larger molecular weights and critical diameters. In contrast, BTF-1 and BTF-2 supported maximum VMS removals of 40%. Notably, neither increasing the trickling liquid velocity from 2 to 4.5 m h⁻1 nor adding Fe-carbon nanoparticles to the solution had any impact on the BTFs' performance. Following the successful results observed in BTF-3, gas residence time was reduced from 60 to 42 min, consequently leading to an increase in the EC from 366 to 509 mg m-3 h-1 (corresponding to an RE = 87%). Despite the different performance of the BTFs, comparable bacterial communities were identified, dominated by the genera Thermomonas, Corynebacterium, Aquimonas, Thauera and Parvibaculum. The results obtained in this study highlighted the potential of activated carbon as packing material for enhancing abatement performance during biotrickling filtration and identified new bacterial genera with potential for VMS degradation.

Exploring the potential of biofiltration for mitigating harmful gaseous emissions from small or old landfills: a review

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.

Simultaneous biofiltration of H2S, NH3, and toluene using compost made of chicken manure and sugarcane bagasse as packing material

Offensive odors from wastewater treatment plants (WWTP) are caused by volatile inorganic compounds such as hydrogen sulfide and ammonia and volatile organic compounds (VOCs), such as toluene. To treat these pollutants, biofiltration is an effective and economical technology used worldwide due to its low investment and environmental impact. In this work, a laboratory-scale prototype biofilter unit for the simultaneous biofiltration of hydrogen sulfide, ammonia, and toluene was evaluated by simulating the emission concentrations of the El Salitre WWTP Bogotá, Colombia, using a compost of chicken manure and sugarcane bagasse as packing material for the biofilter. The prototype biofilter unit was set to an operation flow rate of 0.089 m3/h, an empty bed residence time (EBRT) of 60 s, and a volume of 0.007 m3 (6.6 L). The maximum removal efficiency were 96.9 ± 1.2% for H2S, at a loading rate of 4.7 g/m3 h and a concentration of 79.1 mg/m3, 68 ± 2% for NH3, at a loading rate of 1.2 g/m3 h and a concentration of 2.0 mg/m3, and 71.5 ± 4.0% for toluene, at a loading rate of 1.32 g/m3 h and a concentration of 2.3 mg/m3. The removal efficiency of the three compounds decreased when the toluene concentration was increased above 40 mg/m3. However, a recovery of the system was observed after reducing the toluene concentration and after 7 days of inactivity, indicating an inhibitory effect of toluene. These results demonstrate the potential use of the prototype biofilter unit for odor treatment in a WWTP.

Deodorizing bacterial consortium: community analysis of biofilms and leachate water collected from an air biofiltration system in a piggery

Intensive livestock production is a source of water, soil, and air contamination. The first aspect that negatively affects the quality of life of residents in the vicinity of piggeries is malodorous aerosols, which are not only responsible for discomfort but can be an etiological factor in the development of various diseases during prolonged exposure. One of the proven and efficient ways to counteract odor emissions is the usage of air biofiltration. The purpose of this study was to qualitatively analyze the bacterial community colonizing the biofilm of a biofilter operating at an industrial piggery in Switzerland. The study material consisted of biofilm and leachate water samples. The microbiological analysis consisted of DNA isolation, amplification of the bacterial 16S rRNA gene fragment (V3-V4), preparation of a library for high-throughput sequencing, high-throughput NGS sequencing, filtering of the obtained sequencing reads, and evaluation of the species composition in the studied samples. The investigation revealed the presence of the following bacterial genera: Pseudochelatococcus, Methyloversatilis, Flexilinea, Deviosia, Chryseobacterium, Kribbia, Leadbetterella, Corynebacterium, Flavobacterium, Xantobacter, Tessaracoccus, Staphylococcus, Thiobacillus, Enhydrobacter, Proteiniclasticum, and Giesbergeria. Analysis of the microbial composition of biofilters provides the opportunity to improve the biofiltration process.

A review of the recent progress in biotrickling filters: packing materials, gases, micro-organisms, and CFD

Organic pollutants in the air have serious consequences on both human health and the environment. Among the various methods for removing organic pollution gas, biotrickling filters (BTFs) are becoming more and more popular due to their cost-effective advantages. BTF can effectively degrade organic pollutants without producing secondary pollutants. In the current research on the removal of organic pollutants by BTF, improving the performance of BTF has always been a research hotspot. Researchers have conducted studies from different aspects to improve the removal performance of BTF for organic pollutants. Including research on the performance of BTF using different packing materials, research on the removal of various mixed pollutant gases by BTF, research on microbial communities in BTF, and other studies that can improve the performance of BTF. Moreover, computational fluid dynamics (CFD) was introduced to study the microscopic process of BTF removal of organic pollutants. CFD is a simulation tool widely used in aerospace, automotive, and industrial production. In the study of BTF removal of organic pollutants, CFD can simulate the fluid movement, mass transfer process, and biodegradation process in BTF in a visual way. This review will summarize the development of BTFs from four aspects: packing materials, mixed gases, micro-organisms, and CFD, in order to provide a reference and direction for the future optimization of BTFs.

Effects of Water Content and Irrigation of Packing Materials on the Performance of Biofilters and Biotrickling Filters: A Review

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.

A review on biofiltration techniques: Recent advancements in the removal of volatile organic compounds and heavy metals in the treatment of polluted water

Good quality of water determines the healthy life of living beings on this earth. The cleanliness of water was interrupted by the pollutants emerging out of several human activities. Industrialization, urbanization, heavy population, and improper disposal of wastes are found to be the major reasons for the contamination of water. Globally, the inclusion of volatile organic compounds (VOCs) and heavy metals released by manufacturing industries, pharmaceuticals, and petrochemical processes have created environmental issues. The toxic nature of these pollutants has led researchers, scientists, and industries to exhibit concern towards the complete eradication of them. In this scenario, the development of wastewater treatment methodologies at low cost and in an eco-friendly way had gained importance at the international level. Recently, bio-based technologies were considered for environmental remedies. Biofiltration based works have shown a significant result for the removal of volatile organic compounds and heavy metals in the treatment of wastewater. This was done with several biological sources such as bacteria, fungi, algae, plants, yeasts, etc. The biofiltration technique is cost-effective, simple, biocompatible, sustainable, and eco-friendly compared to conventional techniques. This review article provides deep insight into biofiltration technologies engaged in the removal of volatile organic compounds and heavy metals in the wastewater treatment process.

Biological biogas purification: Recent developments, challenges and future prospects

Raw biogas generated in the anaerobic digestion (AD) process contains several undesired constituents such as H₂S, CO₂, NH₃, siloxanes and VOCs. These gases affect the direct application of biogas, and are a prime concern in biogas utilization processes. Conventional physico-chemical biogas purification methods are energy-intensive and expensive. To promote sustainable development and environmental friendly technologies, biological biogas purification technologies can be applied. This review describes biological technologies for both upstream and downstream processing in terms of pollutant removal mechanisms and efficiency, bioreactor configurations and different operating conditions. Limitations of the biological approaches and their future scope are also highlighted. A conceptual framework Driver-Pressure-Stress-Impact-Response (DPSIR) and Strengths-Weaknesses-Opportunities-Threats (SWOT) analysis have been applied to analyse the present situation and future scope of biological biogas clean-up technologies.

Treatment of gaseous emissions from tire manufacturing industry using lab-scale biofiltration pilot units

Continuously seeking the improvement of environmental protection, the limitation of exhaust emissions is of significance for the tire manufacturing industry. The aim of this study is to assess the potential of biofiltration for the treatment of such gaseous emissions. This work highlights that biofiltration is able to remove both hydrophilic and hydrophobic compounds within a single pilot unit of biofiltration. Due to Ethanol/Alkanes ratios (95/5 and 80/20), high performance levels were observed for low EBRT (16 and 12 s). After twenty days of stable running, the dynamic of stratification patterns could be explained as a result of species coexistence mechanisms. While its impact on performance has not been observed under stable operating conditions, the use of an adsorbent support such as granular activated carbon (GAC) could be relevant to promote system stability in the face of further perturbations, such as transient regimes, that are problematic in full-scale industrial applications.

Bioelimination of low methane concentrations emitted from wastewater treatment plants: a review

Sewage from residents and industries is collected and transported to wastewater treatment plants (WWTPs) with sewer networks. The operation of WWTPs results in emissions of greenhouse gases, such as methane (CH₄), mostly due to sludge anaerobic digestion. Amounts of emissions depend on the source of influent, i.e. municipal and industrial wastewater as well as sewer systems (gravity and rising). Wastewater is the fifth-largest source of anthropogenic CH₄ emissions in the world and represents 7-9% of total global CH₄ emissions into the atmosphere. Global wastewater CH₄ emission grew by approximately 20% from 2005 to 2020 and is expected to grow by 8% between 2020 and 2030, which makes wastewater an important CH₄ emitter worldwide. This review initially considers the emission of CH₄ from WWTPs and sewer networks. In the second part, biotechniques available for biodegradation of low CH₄ concentrations (<5% v/v) encountered in WWTPs have been studied. The paper reviews major bioreactor configurations for the treatment of polluted air, i.e. biotrickling filters, bioscrubbers, two-liquid phase bioreactors, biofilters, and hybrid reactor configurations, after which it focuses on CH₄ biofiltration systems. Biofiltration represents a simple and efficient approach to bio-oxidize CH₄ in waste gases from WWTPs. Major factors influencing a biofilter's performance along with knowledge gaps in relation to its application for treating gaseous emissions from WWTPs are discussed.

Proposed mechanisms of toluene removal by vermicompost and earthworms Eisenia fetida

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.

Simultaneous biodegradation of methane and styrene in biofilters packed with inorganic supports: Experimental and macrokinetic study

Four upflow 0.018 m³ biofilters (3 beds), B-ME, B-200, B-500 and B-700, all packed with inorganic materials, were operated at a constant air flow rate of 0.18 m³ h^-1 to eliminate methane (CH₄), a harmful greenhouse gas (GHG), and styrene (C₈H₈), a carcinogenic volatile organic compound (VOC). The biofilters were irrigated with 0.001 m³ of recycled nutrient solution (NS) every day (flow rate of 60 × 10^-3 m³ h^-1). Styrene inlet load (IL) was kept constant in each biofilter. Different CH₄-ILs varying in the range of 7-60 gCH₄ m^-3 h^-1 were examined in B-ME (IL of 0 gC₈H₈ m^-3 h^-1), B-200 (IL of 9 gC₈H₈ m^-3 h^-1), B-500 (IL of 22 gC₈H₈ m^-3 h^-1) and B-700 (IL of 32 gC₈H₈ m^-3 h^-1). Finally, the effect of C₈H₈ on the macrokinetic parameters of CH₄ biofiltration was studied based on the Michaelis-Menten model. Average C₈H₈ removal efficiencies (RE) varying between 64 and 100% were obtained at CH₄-ILs increasing from 7 to 60 gCH₄ m^-3 h^-1 and for C₈H₈-ILs range of 0-32 gC₈H₈ m^-3 h^-1. More than 90% of C₈H₈ was removed in the bottom and middle beds of the biofilters. By increasing C₈H₈-IL from 0 to 32 gC₈H₈ m^-3 h^-1, maximal EC in Michaelis-Menten model and macrokinetic saturation constant declined from 311 to 39 g m^-3 h^-1 and from 19 to 2.3 g m^-3, respectively, which confirmed that an uncompetitive inhibition occurred during CH₄ biofiltration in the presence of C₈H₈.

Characterization of eubacterial communities by Denaturing Gradient Gel Electrophoresis (DGGE) and Next Generation Sequencing (NGS) in a desulfurization biotrickling filter using progressive changes of nitrate and nitrite as final electron acceptors

Anoxic biotrickling filters (BTFs) represent a technology with high H₂S elimination capacity and removal efficiencies widely studied for biogas desulfurization. Three changes in the final electron acceptors were made using nitrate and nitrite during an operating period of 520 days. The stability and performance of the anoxic BTF were maintained when a significant perturbation was applied to the system that involved the progressive change of nitrate to nitrite and vice versa. Here the impact of electron acceptor changes on the microbial community was characterized by denaturing gel gradient electrophoresis (DGGE) and next generation sequencing (NGS). Both platforms revealed that the community underwent changes during the perturbations but was resilient because the removal capacity did not significantly change. Proteobacteria and Bacteroidetes were the main Phyla and Sulfurimonas and Thiobacillus the main nitrate-reducing sulfide-oxidizing bacteria (NR-SOB) genera involved in the biodesulfurization process.

Aspects Determining the Dominance of Fomitopsis pinicola in the Colonization of Deadwood and the Role of the Pathogenicity Factor Oxalate

Carbon and mineral cycling in sustainable forest systems depends on a microbiome of basidiomycetes, ascomycetes, litter-degrading saprobes, ectomycorrhizal, and mycoparasitic fungi that constitute a deadwood degrading consortium. The brown rot basidiomycete Fomitopsis pinicola (Swartz: Fr.) P. Karsten (Fp), as an oxalate-producing facultative pathogen, is an early colonizer of wounded trees and fresh deadwood. It replaces basidiomycetous white rot fungi and non-basidiomycetous fungal phyla in the presence of its volatilome, but poorly in its absence. With the goal of determining its dominance over the most competitive basidiomycetes and its role in fungal successions within the forest microbiome in general, Fp was exposed to the white rot fungus Kuehneromyces mutabilis (Schaeff.: Fr.) Singer & Smith (Km) in aseptic dual culture established on fertilized 100 mm-long wood dust columns in glass tubes with the inclusion of their volatilomes. For the mycelia approaching from the opposite ends of the wood dust columns, the energy-generating systems of laccase and manganese peroxidase (MnP), the virulence factor oxalate, and the exhalation of terpenes were determined by spectrophotometry, High Pressure Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS). Km mycelia perceived the approaching Fp over 20 mm of non-colonized wood dust, reduced the laccase activity to 25%, and raised MnP to 275%–500% by gaining energy and presumably by controlling oxalate, H2O2, and the dropping substrate pH caused by Fp. On mycelial contact, Km stopped Fp, secured its substrate sector with 4 mm of an impermeable barrier region during an eruption of antimicrobial bisabolenes, and dropped from the invasion mode of substrate colonization into the steady state mode of low metabolic and defensive activity. The approaching Fp raised the oxalate production throughout to >20 g kg−1 to inactivate laccase and caused, with pH 1.4–1.7, lethal conditions in its substrate sector whose physiological effects on Km could be reproduced with acidity conditions incited by HCl. After a mean lag phase of 11 days, Fp persisting in a state of high metabolic activity overgrew and digested the debilitated Km thallus and terminated the production of oxalate. It is concluded that the factors contributing to the competitive advantage of F. pinicola in the colonization of wounded trees and pre-infected deadwood are the drastic long-term acidification of the timber substrate, its own insensitivity to extremely low pH conditions, its efficient control of the volatile mono- and sesquiterpenes of timber and microbial origin, and the action of a undefined blend of terpenes and allelopathic substances.

Influence of phosphorus and trace metals in biofilters treating gaseous VOCs using a novel irrigation system

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.

Optimisation of bioscrubber systems to simultaneously remove methane and purify wastewater from intensive pig farms

The use of bioscrubber is attracting increasing attention for exhaust gas treatment in intensive pig farming. However, the challenge is to improve the methane (CH₄) removal efficiency as well as the possibility of pig house wastewater treatment. Three laboratory-scale bioscrubbers, each equipped with different recirculation water types, livestock wastewater (10-times-diluted pig house wastewater supernatant), a methanotroph growth medium (10-times-diluted), and tap water, were established to evaluate the performance of CH₄ removal and wastewater treatment. The results showed that enhanced CH₄ removal efficiency (25%) can be rapidly achieved with improved methanotrophic activity due to extra nutrient support from the wastewater. The majority of the CH₄ was removed in the middle to end part of the bioscrubbers, which indicated that CH₄ removal could be potentially optimised by extending the length of the reactor. Moreover, 52-86% of the ammonium (NH₄⁺-N), total organic carbon (TOC), and phosphate (PO₄^3--P) removal were simultaneously achieved with CH₄ removal in the present study. Based on these results, this study introduces a low-cost and simple-to-operate method to improve CH₄ removal and simultaneously treat pig farm wastewater in bioscrubbers.

An innovative nutritional slow-release packing material with functional microorganisms for biofiltration: Characterization and performance evaluation

The type of packing material for biofiltration has a great impact on microbial growth and pollutant removal. This study evaluated the feasibility of a nutritional slow-release packing material with functional microorganisms (NSRP-FM) in a biofilter for the removal of gaseous n-butyl acetate. Through the emulsification-cross linked process and microbial immobilization, an innovative packing material was obtained, with a specific surface area of 2.45 m² g^-1 and a bulk density of 40.75 kg m^-3. The cumulative release rates of total phosphorus and total nitrogen were 90.6% and 75.6%, respectively, as measured while continuously spraying deionized water. To evaluate the performance of biofiltration, NSRP-FM was compared with the commercial polyurethane foam (PU-foam), in two identical biotrickling filters (BTFs). The BTF packed with the prepared NSRP-FM maintained a consistent removal efficiency (over 95%) without nutrients addition and pH adjustment. The other BTF had poor removal performance, and the removal efficiency declined to 65% when there was no pH adjustment. Energy dispersive X-ray spectroscopy (EDS) analysis of NSRP-FM showed that inorganic elements were released during the operation of BTF. The abundance of functional microorganisms suggested that the prepared NSRP-FM provided a better environment for microbial growth, despite changes in the operating conditions.

Use of mature compost as filter media and the effect of packing depth on hydrogen sulfide removal from composting exhaust gases by biofiltration

A study was conducted to investigate the utilization of mature compost as a biofilter medium for the removal of hydrogen sulfide (H₂S) from the exhaust gases of the composting process. Source-selected kitchen waste from municipal solid waste was composted in a reactor, and the exhaust gas was passed through a biofilter packed with a 1:4 (wet weight) mixture of mature compost and sand. Two treatments were applied under sterilized and unsterilized conditions to quantify the contribution of microbial activity. The effect of packing depth on H₂S removal efficiency was also studied. A global H₂S removal efficiency of 51% was obtained in the biofilter for loading rates in the range of 0-429 mg H₂S m^-3 h^-1. The adsorption capacity was the main factor affecting H₂S removal efficiency, contributing 64.2% to the total removal efficiency, with microbial activity contributing 35.8%. The relationship between the cumulative amount of H₂S removed and the packing height was well-described by a linear equation. The equation indicated that 99% H₂S removal efficiency could be achieved using a packing height of 96 cm for unsterilized packing material or 158 cm for sterilized packing material.

Biofilter with mixture of pine bark and expanded clay as packing material for methane treatment in lab-scale experiment and field-scale implementation

Low methane (CH₄) emission reduction efficiency (< 25%) has been prevalent due to inefficient biological exhaust gas treatment facilities in mechanic biological waste treatment plants (MBTs) in Germany. This study aimed to quantify the improved capacity of biofilters composed of a mixture of organic (pine bark) and inorganic (expanded clay) packing materials in reducing CH₄ emissions in both a lab-scale experiment and field-scale implementation. CH₄ removal performance was evaluated using lab-scale biofilter columns under varied inflow CH₄ concentrations (70, 130, and 200 g m^-3) and corresponding loading rates of 8.2, 4.76, and 3.81 g m^-3 h^-1, respectively. The laboratory CH₄ removal rates (1.2-2.2 g m^-3 h^-1) showed positive correlation with the inflow CH₄ loading rates (4-8.2 g m^-3 h^-1), indicating high potential for field-scale implementation. Three field-scale biofilter systems with the proposed mixture packing materials were constructed in an MBT in Neumünster, northern Germany. A relatively stable CH₄ removal efficiency of 38-50% was observed under varied inflow CH₄ concentrations of 28-39 g m^-3 (loading rates of 1120-2340 g m^-3 h^-1) over a 24-h period. The CH₄ removal rate was approximately 500-700 g m^-3 h^-1, which was significantly higher than relevant previously reported field-scale biofilter systems (16-50 g m^-3 h^-1). The present study provides a promising configuration of biofilter systems composed of a mixture of organic (pine bark) and inorganic (expanded clay) packing materials to achieve high CH₄ emission reduction. Graphic abstract ᅟ.

Anaerobic degradation of glycol ether-ethanol mixtures using EGSB and hybrid reactors: Performance comparison and ether cleavage pathway

The anaerobic biodegradation of ethanol-glycol ether mixtures as 1-ethoxy-2-propanol (E2P) and 1-methoxy-2-propanol (M2P), widely used in printing facilities, was investigated by means of two laboratory-scale anaerobic bioreactors at 25^oC: an expanded granular sludge bed (EGSB) reactor and an anaerobic hybrid reactor (AHR), which incorporated a packed bed to improve biomass retention. Despite AHR showed almost half of solid leakages compared to EGSB, both reactors obtained practically the same performance for the operating conditions studied with global removal efficiencies (REs) higher than 92% for organic loading rates (OLRs) as high as 54 kg of chemical oxygen demand (COD) m^-3 d^-1 (REs of 70% and 100% for OLRs of 10.6 and 8.3 kg COD m^-3 d^-1 for E2P and M2P, respectively). Identified byproducts allowed clarifying the anaerobic degradation pathways of these glycol ethers. Thus, this study shows that anaerobic scrubber can be a feasible treatment for printing emissions.

Effects of concentration and gas flow rate on the removal of gas-phase toluene and xylene mixture in a compost biofilter

The aim of this work was to study the performance of a compost/ceramic bead biofilter (6:4 v/v) for the removal of gas-phase toluene and xylene at different inlet loading rates (ILR). The inlet toluene (or) xylene concentrations were varied from 0.1 to 1.5gm^-3, at gas flow rates of 0.024, 0.048 and 0.072m³h^-1, respectively, corresponding to total ILR varying between 7 and 213gm^-3h^-1. Although there was mutual inhibition, xylene removal was severely inhibited by the presence of toluene than toluene removal by the presence of xylene. The biofilter was also exposed to transient variations such as prolonged periods of shutdown (30days) and shock loads to envisage the response and recuperating ability of the biofilter. The maximum elimination capacity (EC) for toluene and xylene were 29.2 and 16.4gm^-3h^-1, respectively, at inlet loads of 53.8 and 43.7gm^-3h^-1.

Efficacy of wood charcoal and its modified form as packing media for biofiltration of isoprene

The efficacy of wood charcoal (WC) and nutrient-enriched wood charcoal (NWC) as biofilter packing media were assessed for isoprene biodegradation in a bioreactor comprising bioscrubber and a biofilter connected in series and inoculated with Pseudomonas sp. The bioreactors using WC and NWC exhibited >90% removal efficiency and around 369 g m^-3 h^-1 elimination capacity at around 404 g m^-3 h^-1 inlet loading rate. In both the bioreactors, the biofilter component showed better degradation capacity compared to the bioscrubber unit. The kinetic parameters, maximum elimination capacity, EC_max; substrate constant, K_s and EC_max/K_s for Michaelis-Menten model were evaluated. The lower K_s for the WC packed bioreactor indicated that EC_max achieved, was faster compared to others, while higher EC_max and EC_max/K_s for the NWC packed bioreactor suggests its superiority in isoprene abatement in the continuous mode. A comparison of the available published information on biofiltration of isoprene reflected polyurethane foam as the superior packing media.

A biochar-based medium in the biofiltration system: Removal efficiency, microorganism propagation, and the medium penetration modeling

Biofiltration is a method of biological treatment belonging to cleaner technologies because it does not produce secondary air pollutants, but helps to integrate natural processes in microorganisms for decomposing volatile air pollutants and solving odor problems. The birch wood biochar has been chosen as a principal material for biofilter bed medium. The experiments were conducted at the temperatures of 24, 28, and 32 °C, while the concentration of acetone, xylene, and ammonium reached 300 mg/m(3) and the flow rate was 100 m(3)/hr. Before passing through the stage of the experimental research into the packing material inside biofilters, microorganisms were introduced. Four strains of microorganisms (including micromycetes Aspergillus versicolor BF-4 and Cladosporium herbarum 7KA, as well as yeast Exophiala sp. BF1 and bacterium Bacillus subtilis B20) were selected. At the inlet loading rate of 120 g/m(3)/hr, the highest elimination capacity of xylene in the biochar-based biofilter with the inoculated medium was 103 g/m(3)/hr, whereas that of ammonia was 102 g/m(3)/hr and that of acetone was 97 g/m(3)/hr, respectively. The maximum removal efficiency reached 86%, 85%, and 81%, respectively. The temperature condition (though characterized by some rapid changes) can hardly have a considerable influence on the biological effect (i.e., microbiological activity) of biofiltration; however, it can cause the changes in physical properties (e.g., solubility) of the investigated compounds.

IMPLICATIONS

The birch biochar can be successfully used in the biofiltration system for propagation of inoculated microorganisms, biodegrading acetone, xylene, and ammonia. At the inlet loading rate of 120 g/m(3)/hr, the highest elimination capacity of xylene was 103 g/m(3)/hr, that of ammonia was 102 g/m(3)/hr, and that of acetone was 97 g/m(3)/hr, respectively. The morphological structure of biochar can be affected by the aggressive air contaminants, causing the change in the medium specific surface area, which is one of the factors controlling the biofilter performance. Although biological effects in biofiltration are typically considered to be more important than physical effects, the former may be more important for compounds with high Henry's Law coefficient values, and the biofilter design should thus provide conditions for better compound absorption.

Research into acetone removal from air by biofiltration using a biofilter with straight structure plates

The biological air treatment method is based on the biological destruction of organic compounds using certain cultures of microorganisms. This method is simple and may be applied in many branches of industry. The main element of biological air treatment devices is a filter charge. Tests were carried out using a new-generation laboratory air purifier with a plate structure. This purifier is called biofilter. The biofilter has a special system for packing material humidification which does not require additional energy inputs. In order to extend the packing material's durability, it was composed of thermally treated birch fibre. Pollutant (acetone) biodegradation occurred on thermally treated wood fibre in this research. According to the performed tests and the received results, the process of biodestruction was highly efficient. When acetone was passed through biofilter's packing material at 0.08 m s-1 rate, the efficiency of the biofiltration process was from 70% up to 90%. The species of bacteria capable of removing acetone vapour from the air, i.e. Bacillus (B. cereus, B. subtilis), Pseudomonas (P. aeruginosa, P. putida), Stapylococcus (S. aureus) and Rhodococcus sp., was identified in this study during the process of biofiltration. Their amount in the biological packing material changed from 1.6 × 107 to 3.7 × 1011 CFU g-1.

Investigating bacterial populations in styrene-degrading biofilters by 16S rDNA tag pyrosequencing

Microbial biofilms are essential components in the elimination of pollutants within biofilters, yet still little is known regarding the complex relationships between microbial community structure and biodegradation function within these engineered ecosystems. To further explore this relationship, 16S rDNA tag pyrosequencing was applied to samples taken at four time points from a styrene-degrading biofilter undergoing variable operating conditions. Changes in microbial structure were observed between different stages of biofilter operation, and the level of styrene concentration was revealed to be a critical factor affecting these changes. Bacterial genera Azoarcus and Pseudomonas were among the dominant classified genera in the biofilter. Canonical correspondence analysis (CCA) and correlation analysis revealed that the genera Brevundimonas, Hydrogenophaga, and Achromobacter may play important roles in styrene degradation under increasing styrene concentrations. No significant correlations (P > 0.05) could be detected between biofilter operational/functional parameters and biodiversity measurements, although biological heterogeneity within biofilms and/or technical variability within pyrosequencing may have considerably affected these results. Percentages of selected bacterial taxonomic groups detected by fluorescence in situ hybridization (FISH) were compared to results from pyrosequencing in order to assess the effectiveness and limitations of each method for identifying each microbial taxon. Comparison of results revealed discrepancies between the two methods in the detected percentages of numerous taxonomic groups. Biases and technical limitations of both FISH and pyrosequencing, such as the binding of FISH probes to non-target microbial groups and lack of classification of sequences for defined taxonomic groups from pyrosequencing, may partially explain some differences between the two methods.

Potentialities of coupling biological processes (biotrickler/biofilter) for the degradation of a mixture of sulphur compounds

This study deals with the potential of biological processes combining a biotrickler and a biofilter to treat a mixture of sulphur-reduced compounds including dimethyl sulphide (DMS), dimethyl disulphide (DMDS) and hydrogen sulphide (H2S). As a reference, duplicated biofilters were implemented, and operating conditions were similar for all bioprocesses. The first step of this work was to determine the efficiency removal level achieved for each compound of the mixture and in a second step, to assess the longitudinal distribution of biodegradation activities and evaluate the total bacteria, Hyphomicrobium sp. and Thiobacillus thioparus densities along the bed height. A complete removal of hydrogen sulphide is reached at the start of the experiment within the first stage (biotrickler) of the coupling. This study highlighted that the coupling of a biotrickling filter and a biofilter is an interesting way to improve both removal efficiency levels (15-20% more) and kinetics of recalcitrant sulphur compounds such as DMS and DMDS. The total cell densities remained similar (around 1 × 10(10) 16S recombinant DNA (rDNA) copies g dry packing material) for duplicated biofilters and the biofilter below the biotrickling filter. The relative abundances of Hyphomicrobium sp. and T. thioparus have been estimated to an average of 10 ± 7.0 and 0.23 ± 0.07%, respectively, for all biofilters. Further investigation should allow achieving complete removal of DMS by starting the organic sulphur compound degradation within the first stage and surveying microbial community structure colonizing this complex system.

Indoor-biofilter growth and exposure to airborne chemicals drive similar changes in plant root bacterial communities

Due to the long durations spent inside by many humans, indoor air quality has become a growing concern. Biofiltration has emerged as a potential mechanism to clean indoor air of harmful volatile organic compounds (VOCs), which are typically found at concentrations higher indoors than outdoors. Root-associated microbes are thought to drive the functioning of plant-based biofilters, or biowalls, converting VOCs into biomass, energy, and carbon dioxide, but little is known about the root microbial communities of such artificially grown plants, how or whether they differ from those of plants grown in soil, and whether any changes in composition are driven by VOCs. In this study, we investigated how bacterial communities on biofilter plant roots change over time and in response to VOC exposure. Through 16S rRNA amplicon sequencing, we compared root bacterial communities from soil-grown plants with those from two biowalls, while also comparing communities from roots exposed to clean versus VOC-laden air in a laboratory biofiltration system. The results showed differences in bacterial communities between soil-grown and biowall-grown plants and between bacterial communities from plant roots exposed to clean air and those from VOC-exposed plant roots. Both biowall-grown and VOC-exposed roots harbored enriched levels of bacteria from the genus Hyphomicrobium. Given their known capacities to break down aromatic and halogenated compounds, we hypothesize that these bacteria are important VOC degraders. While different strains of Hyphomicrobium proliferated in the two studied biowalls and our lab experiment, strains were shared across plant species, suggesting that a wide range of ornamental houseplants harbor similar microbes of potential use in living biofilters.

Neural network models for biological waste-gas treatment systems

This paper outlines the procedure for developing artificial neural network (ANN) based models for three bioreactor configurations used for waste-gas treatment. The three bioreactor configurations chosen for this modelling work were: biofilter (BF), continuous stirred tank bioreactor (CSTB) and monolith bioreactor (MB). Using styrene as the model pollutant, this paper also serves as a general database of information pertaining to the bioreactor operation and important factors affecting gas-phase styrene removal in these biological systems. Biological waste-gas treatment systems are considered to be both advantageous and economically effective in treating a stream of polluted air containing low to moderate concentrations of the target contaminant, over a rather wide range of gas-flow rates. The bioreactors were inoculated with the fungus Sporothrix variecibatus, and their performances were evaluated at different empty bed residence times (EBRT), and at different inlet styrene concentrations (C(i)). The experimental data from these bioreactors were modelled to predict the bioreactors performance in terms of their removal efficiency (RE, %), by adequate training and testing of a three-layered back propagation neural network (input layer-hidden layer-output layer). Two models (BIOF1 and BIOF2) were developed for the BF with different combinations of easily measurable BF parameters as the inputs, that is concentration (gm(-3)), unit flow (h(-1)) and pressure drop (cm of H(2)O). The model developed for the CSTB used two inputs (concentration and unit flow), while the model for the MB had three inputs (concentration, G/L (gas/liquid) ratio, and pressure drop). Sensitivity analysis in the form of absolute average sensitivity (AAS) was performed for all the developed ANN models to ascertain the importance of the different input parameters, and to assess their direct effect on the bioreactors performance. The performance of the models was estimated by the regression coefficient values (R(2)) for the test data set. The results obtained from this modelling work can be useful for obtaining important relationships between different bioreactor parameters and for estimating their safe operating regimes.

A comparative study of biodegradation of vinyl acetate by environmental strains

Four Gram-negative strains, E3_2001, EC1_2004, EC3_3502 and EC2_3502, previously isolated from soil samples, were subjected to comparative studies in order to select the best vinyl acetate degrader for waste gas treatment. Comparison of biochemical and physiological tests as well as the results of fatty acids analyses were comparable with the results of 16S rRNA gene sequence analyses. The isolated strains were identified as Pseudomonas putida EC3_2001, Pseudomonas putida EC1_2004, Achromobacter xylosoxidans EC3_3502 and Agrobacterium sp. EC2_3502 strains. Two additional strains, Pseudomonas fluorescens PCM 2123 and Stenotrophomonas malthophilia KB2, were used as controls. All described strains were able to use vinyl acetate as the only source of carbon and energy under aerobic as well as oxygen deficiency conditions. Esterase, alcohol dehydrogenase and aldehyde dehydrogenase were involved in vinyl acetate decomposition under aerobic conditions. Shorter degradation times of vinyl acetate were associated with accumulation of acetic acid, acetaldehyde and ethanol as intermediates in the culture fluids of EC3_2001 and KB2 strains. Complete aerobic degradation of vinyl acetate combined with a low increase in biomass was observed for EC3_2001 and EC1_2004 strains. In conclusion, P. putida EC1_2004 is proposed as the best vinyl acetate degrader for future waste gas treatment in trickle-bed bioreactors.

Biofiltration of ethylbenzene vapours: influence of the packing material

In order to investigate suitable packing materials, a soil amendment composed of granular high mineralized peat (35% organic content) locally available has been evaluated as carrier material for biofiltration of volatile organic compounds in air by comparison with a fibrous peat (95% organic content). Both supports were tested to eliminate ethylbenzene from air streams in laboratory-scale reactors inoculated with a two-month conditioned culture. In pseudo-steady state operation, experiments at various ethylbenzene inlet loads (ILs) were carried out. Maximum elimination capacity of about 120 g m(-3) h(-1) for an IL of 135 g m(-3) h(-1) was obtained for the fibrous peat. The soil amendment reactor achieved a maximum elimination capacity of about 45 g m(-3) h(-1) for an inlet load of 55 g m(-3) h(-1). Ottengraf-van den Oever model was applied to the prediction of the performance of both biofilters. The influence of gas flow rate was also studied: the fibrous peat reactor kept near complete removal efficiency for empty bed residence times greater than 1 min. For the soil amendment reactor, an empty bed residence time greater than 2 min was needed to achieve adequate removal efficiency. Concentration profiles along the biofilter were also compared: elimination occurred in the whole fibrous peat biofilter, while in the soil amendment reactor the biodegradation only occurred in the first 65% part of the biofilter. Results indicated that soil amendment material, previously selected to increase the organic content, would have potential application as biofilter carrier to treat moderate VOC inlet loads.

Elimination of volatile organic compounds by biofiltration: a review

Volatile organic compounds (VOCs) are pollutants that are responsible for the formation of the tropospheric ozone, one of the precursors of smog. VOCs are emitted by various industries including chemical plants, pulp and paper mills, pharmaceuticals, cosmetics, electronics and agri-food industries. Some VOCs cause odor pollution while many of them are harmful to environment and human or animal health. For the removal of VOCs, biofiltration, a biological process, has proved to be reliable when properly operated. This process has therefore been widely applied in Europe and North America. The main advantages associated with the use of biofiltration are related to its set-up, maintenance, and operating costs which are usually lower than those related to other VOCs control technologies and because it is less harmful for the environment than conventional processes like incineration. In the present paper, the main parameters (type, moisture, pH, and temperature of filter bed, microbial population, nutrients concentrations, and VOCs' inlet load) to be controlled during the biofiltration are identified and described in detail. The main phenomena involved in biofiltration are also discussed. For improving the efficiency of VOC control biotechnology, new techniques are now proposed that include the use of membranes, biphasic reactors, UV photolysis, and many others.

Microbial degradation of styrene: biochemistry, molecular genetics, and perspectives for biotechnological applications

Large quantities of the potentially toxic compound styrene are produced and used annually by the petrochemical and polymer-processing industries. It is as a direct consequence of this that significant volumes of styrene are released into the environment in both the liquid and the gaseous forms. Styrene and its metabolites are known to have serious negative effects on human health and therefore, strategies to prevent its release, remove it from the environment, and understand its route of degradation were the subject of much research. There are a large number of microbial genera capable of metabolizing styrene as a sole source of carbon and energy and therefore, the possibility of applying these organisms to bioremediation strategies was extensively investigated. From the multitude of biodegradation studies, the application of styrene-degrading organisms or single enzymes for the synthesis of value-added products such as epoxides has emerged.