Gas-phase Biofilter Research Articles

Biofilter Media Characterization Using Water Sorption Isotherms

Compost material has been used extensively as a gas-phase biofilter media for contaminant gas treatment in recent years. One of the biggest challenges in the use of this type of material is adequate control of compost moisture content and understanding its effect on the biofiltration process. The present work provides a methodology for characterization of biofilter media under low moisture conditions. Results indicated that low levels of equilibrium moisture content (EMC) were obtained for high levels of equilibrium relative humidity (ERH), i.e., 99% ERH produced EMC of approximately 20% (dry basis) at 25°C. Most bacteria struggle to survive in environments with ERH levels lower than 95%. Compost material from the same source was sieved into four compost particle size (PS) ranges to evaluate its water sorption behavior: 4.76 mm > PS1 > 3.36�mm > PS 2 > 2.38 mm > PS3 > 2.00 mm > PS4 > 1.68 mm. Observed data were tested against isotherm models for their goodness-of-fit. Seven isotherm models were compared: (1) Langmuir; (2) Freundlich; (3) Sips; (4) Brunauer, Emmett, and Teller (BET); (5) BET for n-layers; (6) Guggenheim, Anderson, de Boer (GAB); and (7) Henderson. In comparison with the other models, the Henderson model provided the best fit, as determined by the best combination of regression coefficient standard errors () and coefficients of determination (r 2 ) for all four particle size ranges tested (95% confidence interval, C.I., and prediction interval, P.I.). The Henderson model was then used to test for significant differences in isotherms by particle size ranges. The four tested particle size ranges were not significantly different from each other (p < 0.05), indicating similar water sorption behavior. Data from all four particle size ranges were pooled and regressed, and the minimum required moisture to maintain ERH at or above 95% was 16.41% ±2.68% (dry basis).

Performance evaluation of packing materials in the removal of hydrogen sulphide in gas-phase biofilters: Polyurethane foam, sugarcane bagasse, and coconut fibre

The main objective of this work was to investigate three packing materials (polyurethane foam, sugarcane bagasse, and coconut fibre) for biofiltration of a gaseous mixture containing hydrogen sulphide (H 2S). Mixed cultures were obtained from two sources, aerated submerged biofilters and activated sludge, and were utilised as inoculums. Biofilters reached 100% removal efficiency after two days of operation. The empty bed residence time was 49 s for each of the biofilters. The reactors were operated simultaneously, and the inlet concentrations of H 2S varied between 184 and 644 ppmv during the long-term continuous operation of the biofilters (100 days). Average removal efficiencies remained above 99.3%, taking into consideration the entire period of operation. Average elimination capacities reached by the biofilters packed with polyurethane foam, coconut fibre, and sugarcane bagasse were in the range of 17.8–66.6; 18.9–68.8, and 18.7–72.9 g m −3 h −1, respectively. Finally, we concluded that the packing materials tested in this work are appropriate for the long-term biofiltration of hydrogen sulphide.

Hydrophobic response of the fungus Rhinocladiella similis in the biofiltration with volatile organic compounds with different polarity

Rhinocladiella similis biodegraded volatile organic compounds (VOCs) of different polarity in gas-phase biofilters. Elimination capacities, (EC) of 74 g(hexane) m(-3) h(-1), 230 g(ethanol) m(-3) h(-1), 85 g(toluene) m(-3) h(-1) and 30 g(phenol) m(-3) h(-1) were obtained. EC values correlated with the solubility of the VOCs. R. similis grown with n-hexane or ethanol in biofilters packed with Perlite showed that the surface hydrophobicity was higher with n-hexane than ethanol. The hydrophobin-like proteins extracted from the mycelium produced with n-hexane (15 kDa) were different from those in the ethanol biofilter (8.5 kDa and 7 kDa).

Toluene gas phase biofiltration by Paecilomyces lilacinus and isolation and identification of a hydrophobin protein produced thereof

Paecilomyces lilacinus consumed toluene as the sole carbon source in a gas-phase biofilter packed with perlite obtaining an average elimination capacity of 50 g m(-3) h(-1), a removal efficiency of 53%, and a final biomass of 31.6 mg biomass g dry support(-1). Hydrophobin proteins from the mycelium produced in the biofilter were purified by formic acid extraction and precipitated by electrobubbling, and the molecular weight was found to be 10.6 +/- 0.3 kDa. The peptide mass fingerprinting analysis of the purified hydrophobin by matrix-assisted laser desorption/ionization time-of-flight resulted in the identification of two peptides that presented high homology with sequences of class I hydrophobin proteins from other ascomycetous fungi when compared against the National Center for Biotechnology Information database. The yield of hydrophobin (PLHYD) from P. lilacinus was 1.1 mg PLHYD g biomass(-1). These proteins modified the hydrophobicity of Teflon by lowering the contact angle from 130.1 (+/-2) degrees to 57.0 (+/-5) degrees supporting hot sodium dodecyl sulfate washing. This work is the first report about biodegradation of toluene by the nematophagous fungus P. lilacinus in a gas-phase biofilter and the identification of its hydrophobin protein.

Characterisation and performance of coconut fibre as packing material in the removal of ammonia in gas-phase biofilters

Data from the regular monitoring of a full-scale biofilter, filled with coconut fibre as packing material at a municipal solid waste treatment facility, were analysed to assess potential operational problems and to evaluate reactor performance in terms of ammonia removal, the target compound at the facility. Performance from year-round data was assessed based on ammonia removal efficiency (RE) and elimination capacity (EC). Reduced efficiencies were related to a low water content in the packed bed of the biofilter. Thus, a pilot-scale biofilter filled with coconut fibre as packing material was investigated for the treatment of ammonia. Biological activity of coconut fibre and biofilter performance were assessed during the operation of the pilot-scale biofilter under steady-state and transient conditions at inlet ammonia concentrations in the range of 45–300 ppm v and gas contact times of 36–19 s. A maximum EC of 12 g [NH 3 ] m –3 h –1 at an 80% RE was found for a non-acclimated biofilter under transient conditions. A higher watering of the coconut fibre, as well as an acclimated biomass, allowed an EC of 33.3 g [NH 3 ] m –3 h –1 at a 100% RE. Under transient and steady-state conditions nitrification inhibition was encountered, mostly affecting the conversion of nitrite to nitrate.

A dynamic model for ammonia abatement by gas-phase biofiltration including pH and leachate modelling

A dynamic model of ammonia removal by gas-phase biofiltration is presented. Complex biodegradation kinetics including inhibitions and oxygen limitation were used. Since pH has a strong influence on kinetic parameters and governs the process of ammonia absorption into the biofilm, proton concentration (H+) was included as a state variable in the model. Different approaches to model pH variations in biological systems can be found in literature. Amongst the different approaches tested for modelling pH variations during ammonia biofiltration, an ion balance method based on the electroneutrality condition in the biofilm was chosen in this work. This approach was demonstrated to be reliable and efficient to describe pH profiles in gas-phase ammonia biofiltration. The biofilter model was implemented in a home-made simulation environment developed in MATLAB. Model evaluation was performed by comparison of model predictions with experimental data obtained in a pilot-scale biofilter. The model was able to predict qualitatively and quantitatively the behaviour of the system under dynamic conditions, particularly for pH, nitrite, nitrate and ammonium measured in the leachate of the pilot-scale biofilter.

Relative gene expression quantification in a fungal gas‐phase biofilter

Monitoring of gas-phase biofilter performance generally relies on macroscale measurements that neglect the molecular level phenomena that can control the biodegradation process. The present study was undertaken to determine whether or not quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) could detect changes in relative gene expression resulting from feed variations typically encountered in the field. Specifically, homogentisate-1,2-dioxygenase, ElHDO, expression was quantified as a function of short-term chemical feed variations and shutdown period in a biofilter seeded with a pure culture of the fungus Exophiala lecanii-corni. ElHDO was previously shown to be involved in ethylbenzene degradation in E. lecanii-corni. Overall, relative gene target expression numbers (T(N)) were consistent with gas-phase biofilter performance during each short-term experiment although no direct mathematical correlation was found between T(N) and ethylbenzene removal rate. During the chemical feed experiments, no effect on T(N) was measured in the presence of o-xylene which does not affect ElHDO expression. In the presence of phenylacetate, an inducer of ElHDO, T(N) increased once a threshold substrate concentration was exceeded. When methyl propyl ketone, a repressor of ElHDO, was introduced, T(N) decreased rapidly and acted as a leading indicator of bioreactor failure. In the transient loading experiments, ElHDO expression slowly decreased over a 24-h time period when the ethylbenzene feed was discontinued, but rapidly recovered upon its re-introduction. These results indicate that qRT-PCR reflects microbial activity changes that occur in gas-phase biofilters in response to short-term changes in feed conditions and provides a useful complement to the macroscale measurements typically collected.

Performance optimization of the fungal biodegradation of α-pinene in gas-phase biofilter

A Ophiostoma species using α-pinene as the sole source of carbon and energy converted it into biomass, carbon dioxide and water. The strain was inoculated in a biofilter fed α-pinene polluted air, and it remained the dominant biocatalyst throughout the study. Near complete removal was observed up to a load of 100 g m −3 h −1, while 89% removal efficiency was reached at an elimination capacity of 143 g m −3 h −1. The influence of gas flow rate, pollutant concentration and load was evaluated. For a similar load, the highest removal efficiency and corresponding elimination capacity were reached at the lowest flow rate and at an inlet concentration of 2.47 g m −3. Oxygen had a significant effect on the removal efficiency since the maximum α-pinene degradation rate exceeded 187 g m −3 h −1 at 45% oxygen in the inlet air suggesting that at high loads oxygen transfer becomes limiting. Biokinetic studies led to a good fit between experimental data and mathematical equations, yielding a calculated maximum α-pinene degradation rate of 198.42 g m −3 h −1 with a half-velocity constant, K S, of 0.76 g m −3.

Removal of n-hexane by Fusarium solani with a gas-phase biofilter

A gas-phase biofilter inoculated with the fungus Fusarium solani, isolated from a consortium grown on hexane vapors, was used to degrade this compound. The biofilter, packed with perlite and operated with an empty bed residence time of 60 s, was supplied with hexane concentrations between 0.5 gm(-3) and 11 gm(-3). Biofilter performance was evaluated over 100 days of operation. Several strategies for supplying the nutritive mineral medium were assayed to maintain favorable conditions for the fungal growth and activity. The Fusarium system was able to sustain an average elimination capacity of 90 gm(-3)(reactor) h(-1) with a maximum of 130 gm(-3)(reactor) h(-1) . The mass transfer limitations due to high biomass development in the biofilter were confirmed in batch experiments. Bacterial contamination was observed, but experiments in the biofilter and in batch reactors using selective inhibitors and controlled pH confirmed the predominant role of the fungus. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating hydrophobic compounds.

A detailed model of a biofilter for ammonia removal: Model parameters analysis and model validation

A dynamic model to describe ammonia removal in a gas-phase biofilter was developed. The mathematical model is based on discretized mass balances and detailed nitrification kinetics that include inhibitory effects caused by free ammonia (FA) and free nitrous acid (FNA). The model has been able to predict experimental results for dynamic operation under different loading rates (from 3.2 to 17.2 g NH 3 h −1 m −3 ). In particular the model was capable of predicting the outlet ammonia gas concentrations as well as reproducing satisfactorily the gaseous ammonia concentration profile with time under FA inhibition and under non-inhibitory conditions. A sensitivity analysis showed that pH strongly influences the results of the model. © 2005 Elsevier B.V. All rights reserved.

Fungal biocatalysts in the biofiltration of VOC-polluted air

Gas-phase biofilters used for the treatment of waste gases were originally packed with compost or other natural filter beds containing indigenous microorganisms. Over the past decade much effort has been made to develop new carrier materials, more performant biocatalysts and new types of bioreactors. Elimination capacities reached nowadays are 5 to 10 times higher than those originally reported with conventional compost biofilters. With the recently developed inert filter beds, inoculation is a prerequisite for successful start-up and operation. Either non-defined mixed cultures or pure bacterial cultures have originally been used. The search for efficient fungal biocatalysts started only a few years ago, mainly for the biofiltration of waste gases containing hydrophobic compounds, such as styrene, α-pinene, benzene, or alkylbenzenes. In this review, recently isolated new fungal strains able to degrade alkylbenzenes and other related volatile organic pollutants are described, as well as their major characteristics and their use as biocatalysts in gas-phase biofilters for air pollution control. In biofiltration, the most extensively studied organism belongs to the genus Exophiala, although strains of Scedosporium, Paecilomyces, Cladosporium, Cladophialophora, and white-rot fungi are all potential candidates for use in biofilters. Encouraging results were obtained in most of the cases in which some of those organisms were present in gas-phase biofilters. They allow reaching high elimination capacities and are resistant to low pH values and to reduce moisture content.

Hydrodynamic behaviour and comparison of technologies for the removal of excess biomass in gas-phase biofilters

The hydrodynamic behaviour of a biofilter fed toluene and packed with an inert carrier was evaluated on start-up and after long-term operation, using both methane and styrene as tracers in Residence Time Distribution experiments. Results indicated some deviation from ideal plug flow behaviour after 2-year operation. It was also observed that the retention time of VOCs gradually increased with time and was significantly longer than the average residence time of the bulk gas phase. Non-ideal hydrodynamic behaviour in packed beds may be due to excess biomass accumulation and affects both reactor modeling and performance. Therefore, several methods were studied for the removal of biomass after long-term biofilter operation: filling with water and draining, backwashing, and air sparging. Several flow rates and temperatures (20–60°C) were applied using either water or different chemicals (NaOH, NaOCl, HTAB) in aqueous solution. Usually, higher flow rates and higher temperatures allowed the removal of more biomass, but the efficiency of biomass removal was highly dependant on the pressure drop reached before the treatment. The filling/draining method was the least efficient for biomass removal, although the treatment did basically not generate any biological inhibition. The efficiency of backwashing and air sparging was relatively similar and was more effective when adding chemicals. However, treatments with chemicals resulted in a significant decrease of the biofilter's performance immediately after applying the treatment, needing periods of several days to recover the original performance. The effect of manually mixing the packing material was also evaluated in duplicate experiments. Quite large amounts of biomass were removed but disruption of the filter bed was observed. Batch assays were performed simultaneously in order to support and quantify the observed inhibitory effects of the different chemicals and temperatures used during the treatments.

Polyurethane foam based biofilter media for toluene removal

Polyurethane foam medium was manufactured and analyzed to determine its suitability as a solid support medium for use in gas-phase biofilters. Physical and chemical studies were conducted to determine the medium's characteristics. The medium's ability to support an active biofilm capable of degrading volatile organic compounds was assessed using a laboratory scale biofilter fed a model waste stream containing toluene for more than 250 days with empty bed residence times (EBRTs) ranging from two to four minutes. Results are presented that show how a polyurethane foam medium with high porosity, suitable pore size, low density, and an ability to sorb water was able to remove over 99% of the influent toluene when fed at a concentration of 200 ppm. An operating strategy is described which effectively prevented two problems common to conventionally operated biofilter systems: nutrient limitations and biosolid accumulation.

Polyurethane Foam Medium for Biofiltration. I: Characterization

Although biological treatment has been applied successfully to treat waste gases using conventional organic packing media such as compost, there is currently a need for further research on ways to optimize the medium selected. Use of a superior filter-bed medium could overcome or minimize many of the problems encountered in conventional biofilter operation (e.g., medium clogging, difficulty in control of moisture content, and nutrient limitation). In research described herein, polyurethane foam was manufactured and characterized to determine its suitability as a solid support medium for use in gas-phase biofilters. Part I of this paper describes studies conducted to determine the medium's porosity, pore size, head loss characteristics, density, sorption capacity, and chemical resistance. Results are presented that characterize the polyurethane foam medium's properties and suggest how it can be used effectively in treating gas-phase volatile organic compound contaminants. Part II of this paper describes studies conducted to determine the medium's ability to support an active biofilm and to study feasibility of a novel nutrient addition and biomass wasting strategy.