Inert filter media for the biofiltration of waste gases – characteristics and biomass control

Soil biofilters and related systems based onthe use of natural filter beds have been usedfor several years for solving specific airpollution problems. Over the past decade,significant improvements have been brought tothese original bioprocesses, among which thedevelopment and use of new inert packingmaterials. The present paper overviews the mostcommon inert packings used in biofiltration ofwaste gases and their major characteristics. Apotential problem recently encountered whenusing inert filter beds is the heterogenousdistribution of biomass on the packingmaterial, and the excessive growth andaccumulation of biomass when treating highorganic loads, eventually leading to cloggingof the biofilter and reduced efficiency.Several strategies that have been proposed forsolving such problems are described in thispaper. Technologies for controlling excessbiomass accumulation can be grouped into fourcategories based on the use of mechanicalforces, the use of specific chemicals, thereduction of microbial growth, and predation.     

Biofilter performance and characterization of a biocatalyst degrading alkylbenzene gases

A biofilter treating alkylbenzene vapors was characterized for its optimal running conditions and kinetic parame-ters. Kinetics of the continuous biofilter were compared to batch kinetic data obtained with biofilm samples as well as with defined microbial consortia and with pure culture isolates from the biofilter. Both bacteria and fungi were present in the bioreactor. Five strains were isolated. Two bacteria, Bacillus and Pseudomonas, were shown to be dominant, as well as a Trichosporon strain which could, however, hardly grow on alkylbenzenes in pure culture. The remaining two strains were most often overgrown by the other three organisms in liquid phase batch cultures μ _max, K_S, K_I values and biodegradation rates were calculated and compared for the difterent mixed and pure cultures. Since filter bed acidification was observed during biofiltration studies reaching a pH of about 4, experiments were also undertaken to study the influence of pH on performance of the different cultures. Biodegradation and growth were possible in all cases, over the pH range 3.5–7.0 at appreciable rates, both with mixed cultures and with pure bacterial cultures. Under certain conditions, microbial activity was even observed in the presence of alkylbenzenes down to pH 2.5 with mixed cultures, which is quite unusual and explains the ability of the present biocatalyst to remove alkylbenzenes with high efficiency in biofilters under acidic conditions.     

Fungal biofiltration of alpha-pinene: effects of temperature, relative humidity, and transient loads

Over the past decade much effort has been made to develop new carrier materials, more performant biocatalysts, and new types of bioreactors for waste gas treatment. In biofilters fungal biocatalysts are more resistant to acid and dry conditions and take up hydrophobic compounds from the gas phase more easily than wet bacterial biofilms. In the present study, a biofilter packed with a mixture of perlite and Pall rings and fed alpha-pinene-polluted air was inoculated with a new fungal isolate identified as Ophiostoma species. alpha-Pinene is a volatile pollutant typically found in waste gases from wood-related industries. The temperature of waste gas streams from pulp and paper industries containing alpha-pinene is usually higher than ambient temperature. Studies were undertaken here on the effect on performance of temperature changes in the range of 15-40 degrees C. The effect of temperature on biodegradation kinetics in continuous reactors was elucidated through equations derived from the Arrhenius formula. Moreover, the effects of the relative humidity (RH) of the inlet gas phase, transient loads (shock or starvation), and the nature of the nitrogen source on alpha-pinene removal were also studied in this research. The results suggest that the fungal biofilter appears to be an effective treatment process for the removal of alpha-pinene. The optimal conditions are: temperature around 30 degrees C, RH of the inlet waste gas stream around 85%, and nitrate as nitrogen source. The fungal biofilter also showed a good potential to withstand shock loads and recovered rapidly its full performance after a 3-7 days starvation period.     

Elimination of methane generated from landfills by biofiltration: a review

The production of biogas in landfills, its composition and the problems resulting from its generation are all reviewed. Biofiltration is a promising option for the control of emissions to atmosphere of the methane contained in biogas issued from the smaller and/or older landfills. A detailed review of the methane biofiltration literature is presented. The microorganisms, mainly the methanotrophs, involved in the methane biodegradation process, and their needs in terms of oxygen and carbon dioxide utilization, are described. Moreover, the influence of nutrients such as copper, nitrogen and phosphorus, and the process operating conditions such as temperature, pH and moisture content of the biofilter bed, are also presented. Finally, the performance of various filter beds, in terms of their elimination capacities, is presented for laboratory scale biofilters and landfill covers.     

Bioremediation of leachate from a green waste composting facility using waste-derived filter media

The evaluation of two waste-derived materials used to treat compost leachate by biofiltration is described in this paper. Nine biofilters were constructed using 240 l, high density polyethylene containers. Three containers were filled without compaction with 200l of each of three types of filter media. Waste-derived filter media (compost and oversize) were compared to a mineral control (granite chips). The filters were fed with compost leachate from a typical green waste composting facility at hydraulic loading rates ranging from 0.05 m3/m3/day to 0.5 m3/m3/day over a period of twelve months. The oversize medium emerged as the most effective demonstrating characteristics of consistency of effluent quality and resilience to stress. The oversize medium produced an effluent of <10mg/l ammoniacal nitrogen on >95% of sampling occasions. The organic component of compost leachate was dominated by compounds that proved to be recalcitrant to biodegradation. The solids content of the treated effluent remained too high to be acceptable for direct discharge to a watercourse without further treatment and if discharge to a watercourse is to be considered, a polishing stage (e.g., reed bed) able to remove solids and dampen occasional peaks of ammoniacal nitrogen should be employed.     

Biomass accumulation and control strategies in gas biofiltration

Uneven distribution and excess accumulation of biomass within gas phase biofilters often result in operational problems such as clogging, channeling, and excessive head loss within biofilter beds, and consequently, the deterioration of performance. In this paper, the characteristics, mechanisms, and patterns of biomass accumulation in gas biofiltration were reviewed, and models for biomass accumulation were also summarized. Strategies for excess biomass control in gas biofiltration, categorized into either physical, chemical, or biological methods were also discussed, with improvements in design and operation of biofilters. Combinations of these approaches are usually necessary in order to maintain a reasonably even distribution and to minimize the accumulation of biomass in gas biofilters.     

The effect of inoculation and the type of carrier material used on the biofiltration of methyl sulphides

 Low elimination capacities (less than 10 g m^-3 day^-1) were observed for the odorant dimethyl sulphide (Me₂S) when either wood bark or compost was used as the carrier material in a laboratory-scale biofilter. Enrichment experiments were set up by incubation of garden soil samples during 4 weeks with 100 ppm (v/v) headspace concentrations of both Me₂S and dimethyl disulphide (Me₂S₂). After transfer to a mineral medium, Me₂S- and Me₂S₂-degrading enrichment cultures were obtained for all five soil samples tested, both compounds being converted stoichiometrically to sulphuric acid. Upon inoculation of the laboratory-scale biofilter with one of these enrichment cultures (±120 g cell dry weight m^-3 reactor), the elimination capacity for Me₂S increased in a 3-week period to 35 g m^-3 day^-1 and 680 g m^-3 day^-1 when wood bark and compost were used as the respective carrier materials. Both inoculated biofilters were able to degrade Me₂S₂, however the elimination capacities obtained for Me₂S₂ were lower (e.g. 24 g m^-3 day^-1 for the wood bark filter) compared to those for Me₂S. For both inoculated biofilters, a gradual decrease of the elimination capacity for the methyl sulphides was observed as a result of acidification of the carrier material, suggesting that pH regulation is necessary if long-term biofiltration experiments are to be performed. Received: 6 June 1995/Received revision: 10 August 1995/Accepted: 22 August 1995     

Biofiltration of composting gases using different municipal solid waste-pruning residue composts: monitoring by using an electronic nose

The concentration of volatile organic compounds (VOCs) during the composting of kitchen waste and pruning residues, and the abatement of VOCs by different compost biofilters was studied. VOCs removal efficiencies greater than 90% were obtained using composts of municipal solid waste (MSW) or MSW-pruning residue as biofilter material. An electronic nose identified qualitative differences among the biofilter output gases at very low concentrations of VOCs. These differences were related to compost constituents, compost particle size (2-7 or 7-20 mm), and a combination of both factors. The total concentration of VOCs determined by a photoionization analyser and inferred from electronic nose data sets were correlated over an ample range of concentrations of VOCs, showing that these techniques could be specially adapted for the monitoring of these processes.     

废气处理生物滤器微生物生态学研究进展

废气生物处理是一项新兴的气体污染控制技术,已成为当前环境领域的研究热点.本文概述了生物滤器系统(包括生物过滤器系统和生物滴滤器系统)结构及其去除气体污染物的原理,重点阐述了生物滤器微生物的分离、鉴定及其降解特性,微生物丰度、活性与微生物群落结构多样性之间的相关性,运行条件对微生物群落的影响,微生物群落结构时空变化规律,生物膜形成机理和模型等方面的研究进展,并对今后废气处理生物滤器微生物生态学研究方向进行了展望.     

Biofiltration of air: a review

In this paper we present a review of the existing air pollution control technologies (APCT), when used essentially for the elimination of volatile organic compounds (VOC). The biotechnologies referred to, bioscrubbers, biotrickling filters and biofilters, are also described. A more detailed review of biofiltration is proposed, presenting the most recent and latest developments achieved in the field of bioprocessing. In particular, the influence of the filter bed, the polluted air flowrates, the pollutants, the pressure drop, bed moisture content, temperature, nutrients, pH and the microorganisms are reviewed. Models of biofiltration are also presented.     

Biofiltration of Air: A Review

Abstract

In this paper we present a review of the existing air pollution control technologies (APCT), when used essentially for the elimination of volatile organic compounds (VOC). The biotechnologies referred to, bioscrubbers, biotrickling filters and biofilters, are also described. A more detailed review of biofiltration is proposed, presenting the most recent and latest developments achieved in the field of bioprocessing. In particular, the influence of the filter bed, the polluted air flowrates, the pollutants, the pressure drop, bed moisture content, temperature, nutrients, pH and the microorganisms are reviewed. Models of biofiltration are also presented.     

Biofiltration of waste gases containing both ethyl acetate and toluene using different combinations of bacterial cultures

To investigate the microbial degradation of ethyl acetate and toluene mixtures in biofiltration, three strains were selected, identified and studied in a shake-flask culture, and finally inoculated into biofilters. These strains, namely AC6, TO3 and B5, can degrade different substrates at a different rate. The results showed that competitive inhibition from substrate and microbial community would affect the toluene degradation efficiency. Owing to substrate competition, the toluene degradation efficiency of strain B5 would decrease in the presence of high concentration of ethyl acetate. However, the addition of strain AC6 would alleviate such inhibition because it could remove ethyl acetate rapidly. Microbial community competition from strain AC6 or B5 would impede the toluene degradation efficiency of strain TO3 unless a large amount of strain TO3 was inoculated. In biofiltration, strain B5 would be a better choice for inoculation into biofilters than strains AC6 and TO3, as it would grow rapidly under a low concentration of ethyl acetate.     

Thermophilic biofiltration of benzene and toluene

In the current studies, we characterized the degradation of a hot mixture of benzene and toluene (BT) gases by a thermophilic biofilter using polyurethane as packing material and high-temperature compost as a microbial source. We also examined the effect of supplementing the biofilter with yeast extract (YE). We found that YE substantially enhanced microbial activity in the thermophilic biofilter. The degrading activity of the biofilter supplied with YE was stable during long-term operation (approximately 100 d) without accumulating excess biomass. The maximum elimination capacity (1,650 g x m(-3) h(-1)) in the biofilter supplemented with YE was 3.5 times higher than that in the biofilter without YE (470 g g x m(-3) h(-1)). At similar retention times, the capacity to eliminate BT for the YE-supplemented biofilter was higher than for previously reported mesophilic biofilters. Thus, thermophilic biofiltration can be used to degrade hydrophobic compounds such as a BT mixture. Finally, 16S rDNA polymerase chain reaction-DGGE (PCR-DGGE) fingerprinting revealed that the thermophilic bacteria in the biofilter included Rubrobacter sp. and Mycobacterium sp.     

Compost liquor bioremediation using waste materials as biofiltration media

Compost liquor results from the percolation of precipitation through composting waste; the release of liquids from high moisture content feedstocks; and as a result of runoff from hard surfaces and machinery. This research aimed to establish the potential for waste materials to act as media for low-cost compost liquor biofilters. Six types of potential biofilter media were packed into experimental biofilters (1 m long x 0.11 m diameter) and irrigated with compost liquor (organic loading rate of 0.6 kg/m3/d) for three months. The pH, BOD5, NH3/NH4+, and phytotoxicity of the effluent was monitored regularly. Natural, organic materials (oversize, compost and wood mulch) performed best, when compared to synthetic materials such as polystyrene packaging or inert materials such as broken brick. On average, the best media achieved 78% removal of both BOD5 and ammoniacal nitrogen during the study period. Although significant improvements in liquor quality were achieved, the effluent remained heavily polluted.     

Biofiltration of waste gases with the fungi Exophiala oligosperma and Paecilomyces variotii

Two biofilters fed toluene-polluted air were inoculated with new fungal isolates of either Exophiala oligosperma or Paecilomyces variotii, while a third bioreactor was inoculated with a defined consortium composed of both fungi and a co-culture of a Pseudomonas strain and a Bacillus strain. Elimination capacities of 77 g m^–3 h^–1 and 55 g m^–3 h^–1 were reached in the fungal biofilters (with removal efficiencies exceeding 99%) in the case of, respectively, E. oligosperma and Paecilomyces variotii when feeding air with a relative humidity (RH) of 85%. The inoculated fungal strains remained the single dominant populations throughout the experiment. Conversely, in the biofilter inoculated with the bacterial–fungal consortium, the bacteria were gradually overgrown by the fungi, reaching a maximum elimination capacity around 77 g m^–3 h^–1. Determination of carbon dioxide concentrations both in batch assays and in biofiltration studies suggested the near complete mineralization of toluene. The non-linear toluene removal along the height of the biofilters resulted in local elimination capacities of up to 170 g m^–3 h^–1 and 94 g m^–3 h^–1 in the reactors inoculated, respectively, with E. oligosperma and P. variotii. Further studies with the most efficient strain, E. oligosperma, showed that the performance was highly dependent on the RH of the air and the pH of the nutrient solution. At a constant 85% RH, the maximum elimination capacity either dropped to 48.7 g m^–3 h^–1 or increased to 95.6 g m^–3 h^–1, respectively, when modifying the pH of the nutrient solution from 5.9 to either 4.5 or 7.5. The optimal conditions were 100% RH and pH 7.5, which allowed a maximum elimination capacity of 164.4 g m^–3 h^–1 under steady-state conditions, with near-complete toluene degradation.     

Compost product optimization for surface water nitrate treatment in biofiltration applications

Compost based material has been proposed for use as media for biofiltration for environmental restoration in many areas to remediate contaminated water and soil. The objective of this project was to develop techniques to produce compost products for nitrate removal in storm water biofiltration applications, from typical solid waste materials. Compost products were manufactured from different feedstocks and evaluated for their nitrate removal efficiencies. Three different compost products manufactured from varying feedstock amounts of wood chips and grass clippings, along with some dry compost material from the City of Brownsville Municipal Landfill Facility (BMLF), were evaluated using column studies. Indicators of the compost product’s quality included moisture % content, pH, and conductivity measurements. The columns were loaded with water containing at least 13.5 mg/L nitrate–nitrogen and effluent water from the columns was tested to determine the nitrate reduction for the different products. All of the manufactured compost products and the BMLF material removed some nitrate. The project demonstrated that compost product materials can be effectively used for some nitrate removal for surface water quality improvement and that compost product feedstocks and blends can influence the materials capability for nitrate removal.     

Active compost biofiltration of toluene

Composting of leaves and alfalfa (i.e. active compost) was used for thebiofiltration of toluene-contaminated air in a 6-L biofilter (initial bedheight: 180 mm). During the thermophilic phase (45 to 55 °C), toluenebiodegradation rates reached 110 gtoluene.m^-3.h^-1 at an inlet concentration ofabout 5 g.m^-3.h^-1 and a gas residence time of 90 seconds. Thehighest rates were obtained late in the thermophilic phase suggesting amicrobial adaptation was occurring. Biodegradation rates decreased rapidly(50% in 48h) in the cooling stage. Under mesophilic conditions, themaximum biodegradation rates that could be obtained by increasing the inlettoluene concentration were near 89 gtoluene.m^-3.h^-1 which issimilar to that reported in the literature for mature compost biofilters. Novolatile by-product was detected by gas chromatography. Mineralization of¹⁴C-toluene and benzene showed that they were completelydegraded into CO₂ and H₂O under boththermophilic and mesophilic conditions. Bacteria isolated from latemesophilic stage had the capacity to degrade all BTEX compounds but were notable to transform chlorinated compounds. No organisms were isolated whichcould use toluene as their sole source of carbon and energy at 50 °C.Active compost biofiltration should be an excellent process for thetreatment of gaseous BTEX by biofiltration. This is the first report ofthermophilic biofiltration of toluene.     

Determination of local elimination capacities and moisturecontents in different biofilters treating toluene and xylene

The removal of toluene and xylene from an artificial waste gaswas investigated in two laboratory scale biofilters filled withmixtures of peat, bark and wood. The packed beds differed in themixture of materials used, so that peat and then bark was thedominant constituent. The biofilters were operated in an upflowmode. Both biofilters showed relatively high removal efficienciesfor both pollutants (74–98%). The evaluation of the localelimination capacities in the peat-loaded biofilter revealed thatthe major part of pollutants was degraded in the middle layer.In this biofilter, larger differences in theremoval rates along the bed height were also observed. In thebiofilter with bark as dominant material, the major part ofpollutants was degraded at the inlet of the bed and also at arelative height of 0.7. Moisture contents of 71–80% and 65–78%were found for the biofilter with peat and bark respectively. Whenthe regular pouring of nutrient solution through the bed wasinterrupted for 1 month, a decrease in efficiency was observed inthe biofilter with bark, whilst the efficiency in the biofilter withpeat remained the same.     

Biofiltration of volatile organic compounds

The removal of volatile organic compounds (VOCs) from contaminated airstreams has become a major air pollution concern. Improvement of the biofiltration process commonly used for the removal of odorous compounds has led to a better control of key parameters, enabling the application of biofiltration to be extended also to the removal of VOCs. Moreover, biofiltration, which is based on the ability of micro-organisms to degrade a large variety of compounds, proves to be economical and environmentally viable. In a biofilter, the waste gas is forced to rise through a layer of packed porous material. Thus, pollutants contained in the gaseous effluent are oxidised or converted into biomass by the action of microorganisms previously fixed on the packing material. The biofiltration process is then based on two principal phenomena: (1) transfer of contaminants from the air to the water phase or support medium, (2) bioconversion of pollutants to biomass, metabolic end-products, or carbon dioxide and water. The diversity of biofiltration mechanisms and their interaction with the microflora mean that the biofilter is defined as a complex and structured ecosystem. As a result, in addition to operating conditions, research into the microbial ecology of biofilters is required in order better to optimise the management of such biological treatment systems.