Biofiltration of methane using hybrid mixtures of biochar, lava rock and compost

Using hybrid packing materials in biofiltration systems takes advantage of both the inorganic and organic properties offered by the medium including structural stability and a source of available nutrients, respectively. In this study, hybrid mixtures of compost with either lava rock or biochar in four different mixture ratios were compared against 100% compost in a methane biofilter with active aeration at two ports along the height of the biofilter. Biochar outperformed lava rock as a packing material by providing the added benefit of participating in sorption reactions with CH₄. This study provides evidence that a 7:1 volumetric mixture of biochar and compost can successfully remove up to 877 g CH₄/m³·d with empty-bed residence times of 82.8 min. Low-affinity methanotrophs were responsible for the CH₄ removal in these systems (K_M(app) ranging from 5.7 to 42.7 µM CH₄). Sequencing of 16S rRNA gene amplicons indicated that Gammaproteobacteria methanotrophs, especially members of the genus Methylobacter, were responsible for most of the CH₄ removal. However, as the compost medium was replaced with more inert medium, there was a decline in CH₄ removal efficiency coinciding with an increased dominance of Alphaproteobacteria methanotrophs like Methylocystis and Methylocella. As a biologically-active material, compost served as the sole source of nutrients and inoculum for the biofilters which greatly simplified the operation of the system. Higher elimination capacities may be possible with higher compost content such as a 1:1 ratio of either biochar or lava rock, while maintaining the empty-bed residence time at 82.8 min.

A comparison of removal performance of volatile organic and sulfurous compounds between odour abatement systems

Three types of odour abatement systems in sewer networks in Australia were studied for 18 months to determine the removals of different compounds. Six volatile sulfurous compounds and seven volatile organic compounds (VOCs) were further investigated. All types of odour abatement systems exhibited good removal of hydrogen sulfide with the biotrickling filters (BTFs) showing the highest consistent removal. Biofilters outperformed BTFs and activated carbon (AC) filters in the removal of dimethyl mono-, di- and tri-sulfide species at the low inlet concentrations typically found. AC filters exhibited little VOC removal with no compound consistently identified as having a removal greater than 0%. Biofilters outperformed BTFs in VOC removal, yet both had high removal variability.

A two-stage combined trickle bed reactor/biofilter for treatment of styrene/acetone vapor mixtures

Performance of a two-stage biofiltration system was investigated for removal of styrene-acetone mixtures. High steady-state acetone loadings (above C(in)(Ac) = 0.5 g.m(-3) corresponding to the loadings > 34.5 g.m(-3).h(-1)) resulted in a significant inhibition of the system's performance in both acetone and styrene removal. This inhibition was shown to result from the acetone accumulation within the upstream trickle-bed bioreactor (TBR) circulating mineral medium, which was observed by direct chromatographic measurements. Placing a biofilter (BF) downstream to this TBR overcomes the inhibition as long as the biofilter has a sufficient bed height. A different kind of inhibition of styrene biodegradation was observed within the biofilter at very high acetone loadings (above C(in)(Ac) = 1.1 g.m(-3) or 76 g.m(-3).h(-1) loading). In addition to steady-state measurements, dynamic tests confirmed that the reactor overloading can be readily overcome, once the accumulated acetone in the TBR fluids is degraded. No sizable metabolite accumulation in the medium was observed for either TBR or BF. Analyses of the biodegradation activities of microbial isolates from the biofilm corroborated the trends observed for the two-stage biofiltration system, particularly the occurrence of an inhibition threshold by excess acetone.

Air purification from TCE and PCE contamination in a hybrid bioreactors and biofilter integrated system

A two-stage waste air treatment system, consisting of hybrid bioreactors (modified bioscrubbers) and a biofilter, was used to treat waste air containing chlorinated ethenes - trichloroethylene (TCE) and tetrachloroethylene (PCE). The bioreactor was operated with loadings in the range 0.46-5.50gm(-3)h(-1) for TCE and 2.16-9.02gm(-3)h(-1) for PCE. The biofilter loadings were in the range 0.1-0.97gm(-3)h(-1) for TCE and 0.2-2.12gm(-3)h(-1) for PCE. Under low pollutant loadings, the efficiency of TCE elimination was 23-25% in the bioreactor and 54-70% in the biofilter. The efficiency of PCE elimination was 44-60% in the bioreactor and 50-75% in the biofilter. The best results for the bioreactor were observed one week after the pollutant loading was increased. However, the process did not stabilize. In the next seven days contaminant removal efficiency, enzymatic activity and biomass content were all diminished.

Hydrogen sulfide and odor removal by field-scale biotrickling filters: influence of seasonal variations of load and temperature

Two biotrickling filters were set up at two wastewater treatment plants (WWTP) in The Netherlands to investigate their effectiveness for treatment of odorous waste gases from different sources. One biotrickling filter was installed at Nieuwe Waterweg WWTP in Hook of Holland to study the hydrogen sulfide removal from headworks waste air. The other reactor was installed at Harnaschpolder WWTP (treating wastewater of the city of The Hague) to remove mercaptans and other organic compounds (odor) coming from the emissions of the anaerobic tanks of the biological nutrient removal (BNR) activated sludge. The performance of both units showed a stable and highly efficient operation under seasonal variations of load and temperature over nearly one year of monitoring. The Nieuwe Waterweg unit achieved removals of up to 99%, corresponding to a maximum daily average elimination capacity (EC) of 55.8 g H(2)S/m(3)/h at an empty bed residence time (EBRT) as short as 8.5 s. Odor reduction at the Harnaschpolder unit was 95% at an EBRT of 18.9 s, with average outlet concentration lower than the objective value which was established as 1000 European Odor Units (OU(E)/m(3)).

Combined biological and physicochemical waste-gas cleaning techniques

This review presents a general overview of physical, chemical and biological waste-gas treatment techniques such as adsorption, absorption, oxidation and biodegradation, focusing more extensively on combined processes. It is widely recognized that biological waste-gas treatment devices such as biofilters and biotrickling filters can show high performance, often reaching removal efficiencies above 90 % for pollutant concentrations below 5 g/m(3). However, for concentrations exceeding this limit and under transient shock-load conditions that are frequently encountered in industrial situations, a physicochemical gas cleaning process can sometimes be advantageously combined with a biological one. Besides improving the overall treatment efficiency, the non-biological, first-stage process could also serve as a load equalization system by reducing the pollutant load during periodic shock-loads, to levels that can easily be handled in the second-stage bioreactor. This article reviews the operational advantages of integrating different non-biological and biological processes, i.e., adsorption pre-treatment+bioreactor, bioreactor+adsorption post-treatment, absorption pre-treatment+bioreactor, UV pre-treatment+bioreactor, and bioreactor/bioreactor combinations, for waste-gas treatment, where different gas-phase pollutants have been tested.

Two-stage gas-phase bioreactor for the combined removal of hydrogen sulphide, methanol and alpha-pinene

Biological treatment systems have emerged as cost-effective and eco-friendly techniques for treating waste gases from process industries at moderately high gas flow rates and low pollutant concentrations. In this study, we have assessed the performance of a two-stage bioreactor, namely a biotrickling filter packed with pall rings (BTF, 1st stage) and a perlite + pall ring mixed biofilter (BF, 2nd stage) operated in series, for handling a complex mixture of hydrogen sulphide (H2S), methanol (CH3OH) and alpha-pinene (C10H16). It has been reported that the presence of H2S can reduce the biofiltration efficiency of volatile organic compounds (VOCs) when both are present in the gas mixture. Hydrogen sulphide and methanol were removed in the first stage BTF, previously inoculated with H2S-adapted populations and a culture containing Candida boidinii, an acid-tolerant yeast, whereas, in the second stage, alpha-pinene was removed predominantly by the fungus Ophiostoma stenoceras. Experiments were conducted in five different phases, corresponding to inlet loading rates varying between 2.1 and 93.5 g m(-3) h(-1) for H2S, 55.3 and 1260.2 g m(-3) h(-1) for methanol, and 2.8 and 161.1 g m(-3) h(-1) for alpha-pinene. Empty bed residence times were varied between 83.4 and 10 s in the first stage and 146.4 and 17.6 s in the second stage. The BTF, working at a pH as low as 2.7 as a result of H2S degradation, removed most of the H2S and methanol but only very little alpha-pinene. On the other hand, the BF, at a pH around 6.0, removed the rest of the H2S, the non-degraded methanol and most of the alpha-pinene vapours. Attempts were originally made to remove the three pollutants in a single acidophilic bioreactor, but the Ophiostoma strain was hardly active at pH <4. The maximum elimination capacities (ECs) reached by the two-stage bioreactor for individual pollutants were 894.4 g m(-3) h(-1) for methanol, 45.1 g m(-3) h(-1) for H2S and 138.1 g m(-3) h(-1) for alpha-pinene. The results from this study showed the potential effectiveness of a two-stage bioreactor for treating H2S together with two hydrophilic and hydrophobic VOCs that are typically emitted from wood industries.

Removal of hydrogen sulfide by immobilized Thiobacillus thioparus in a biotrickling filter packed with polyurethane foam

In the work described here, a biotrickling filter with Thiobacillus thioparus (ATCC 23645) immobilized on polyurethane foam is proposed for the removal of hydrogen sulfide contained in air. The effect of surface velocity of the recirculation medium (5.9-1.2 m/h), sulfate concentration inhibition (3.0-10.7 g/L), pH (6.0-8.2), empty bed residence time (EBRT) (150-11 s) for constant loads of 11.5 and 2.9 g S/m(3)/h, and pressure drop of the system were investigated. The total amount of biomass immobilized on the carrier was 8.2+/-1.3x10(10) cells/g. The optimal values of the operating variables were: pH between 7.0 and 7.5, surface velocity of 5.9 m/h and sulfate concentration below 5 g/L. The critical EC value was 14.9 g S/m(3)/h (removal efficiency of 99.8%) and the EC(max) was 55.0 g S/m(3)/h (removal efficiency of 79.8%) for an EBRT of 150 s. For loads of 2.89+/-0.05 and 11.5+/-0.1 g S/m(3)/h, the removal efficiency was higher than 99% for an EBRT over 90 s.

Numerical simulation of air flow through a biofilter with heterogeneous porous media

Based on the ideal biofilter model, numerical simulation using lattice Boltzmann method is carried out to investigate the effect of Darcy number and porosity on removal efficiency of low headloss biofilter. The generalized Navier-Stokes model (Brinkman-Forchheimer-extended Darcy model) is applied making several assumptions. It is found that the Darcy number has determinant influence on the removal efficiency, and the effect of porosity on removal efficiency is very weak at lower Darcy numbers but very strong at higher Darcy numbers. It was found there was strong evidence of flow heterogeneity in the biofilter (Chitwood, D.E., Devinny, J.S., Reynolds Jr., F.E., 1999. Evaluation of a two-stage biofilter for treatment of POTW waste air. Environ. Prog. 18, 212-221). In this study we have found the biofilter performance can be improved by adjusting local Darcy number of the porous media in the biofilter.

Microbial populations analysis and field application of biofilter for the removal of volatile-sulfur compounds from swine wastewater treatment system

A biofilter packed with granular activated carbon (GAC) was applied to eliminate volatile-sulfur compounds (VSC) emitted from solid-liquid separation tank in swine wastewater treatment system. Hydrogen sulfide, methanethiol, dimethyl disulfide, and dimethyl sulfide were effectively reduced to 96-100% at gas residence times of 13-30s. Elemental sulfur and sulfate are their primary oxidation metabolites. Regarding odor, an average of 86% reduction was achieved at short residence time (13s). In addition, bioaerosol emissions could also be effectively reduced by 90% with the biofilter. Advantages of the system include low moisture demand, low pressure drop, and high biofilm stability. Further characterization of bacterial populations of the activated carbon samples using the fluorescent in situ hybridization (FISH) technique revealed that Pseudomonas sp. remained the predominant community (56-70%) after long-term evaluation of 415 days.

Removal of formaldehyde, methanol, dimethylether and carbon monoxide from waste gases of synthetic resin-producing industries

The removal of mixtures of gas-phase pollutants released from formaldehyde- and formaldehyde resin-producing industries was studied in different bioreactor systems. The waste gases contained formaldehyde, methanol, dimethylether and carbon monoxide. The use of a hybrid two-stage bioreactor, composed of a biotrickling filter and a conventional biofilter connected in series, led to very high elimination capacities and removal efficiencies close to 100% for overall pollutant loads exceeding 600g m(-3)h(-1). The presence of low concentrations of dimethylether in the gaseous mixture did not have a significant effect on the removal of formaldehyde or methanol under our operating conditions, although moderate concentrations of these compounds did negatively affect the biodegradation of dimethylether. When a mixture of all four compounds, at concentrations around 100, 100, 50 and 50mg m(-3) for formaldehyde, methanol, carbon monoxide and dimethylether, respectively, was fed to a conventional biofilter, removal efficiencies higher than 80% were obtained for the first three pollutants at empty bed retention time values above 30s. On the other hand, dimethylether was removed to a lower extent, although its reduced environmental impact allows to conclude that these results were satisfactory.

Performance of two biofilters with neutral and low pH treating off-gases

Two different functional biofilters were carried out and compared for the treatment of off-gas containing multicomponent odors and volatile organic compounds (VOCs) in this study. The effects of pH values and the empty bed retention time (EBRT) on the performance of the bioreactors were studied; and the characteristics of microbial populations in the two biofilters were also determined. The experimental results indicated that the removal efficiencies of hydrophilic compounds such as butyric acid and ammonia were higher in the neutral pH biofilter (NPB) than those in the low pH biofilter (LPB). In contrast, the removal efficiencies of the compounds with poor water solubility such as styrene and ethyl mercaptan were higher in the LPB than those in the NPB. The characteristics of microbial population in the two biofilters revealed that the heterotrophic bacteria, nonacidophilic thiobacteria, ammonia oxidizing bacteria, and nitrite oxidizing bacteria were major microorganisms in the NPB, whereas acidophilic thiobacteria and fungi were dominant in the LPB. Therefore, the performance of the biofilter depended on the characteristics of the compound being treated and the type of microorganisms.

Co-treatment of hydrogen sulfide and methanol in a single-stage biotrickling filter under acidic conditions

Biofiltration of waste gases is cost-effective and environment-friendly compared to the conventional techniques for treating large flow rates of gas streams with low concentrations of pollutants. Pulp and paper industry off-gases usually contain reduced sulfur compounds, such as hydrogen sulfide and a wide range of volatile organic compounds (VOCs), e.g., methanol. It is desirable to eliminate both of these groups of compounds. Since the co-treatment of inorganic sulfur compounds and VOCs in biotrickling filters is a relatively unexplored area, the simultaneous biotreatment of H2S and methanol as the model VOC was investigated. The results showed that, after adaptation, the elimination capacity of methanol could reach around 236 g m(-3) h(-1) with the simultaneous complete removal (100%) of 12 ppm H2S when the empty bed residence time is 24 s. The pH of the system was around 2. Methanol removal was hardly affected by the presence of hydrogen sulfide, despite the low pH. Conversely, the presence of the VOC in the waste gas reduced the efficiency of H2S biodegradation. The maximal methanol removal decreased somewhat when increasing the gas flow rate. This is the first report on the degradation of methanol at such low pH in a biotrickling filter and on the co-treatment of H2S and VOCs under such conditions.

Effect of methanol on pH and stability of inorganic biofilters treating dimethyl sulfide

The biofiltration of dimethyl sulfide (DMS) and other reduced sulfur compounds (RSC) results in acidification of biofilters due to the accumulation of the sulfuric acid in packing material. This may lead to a decrease in biofilter performance due to a drop in pH. Results obtained from continuous experiments using three bench-scale biofilters packed with inorganic material mixed with limestone show that methanol (MeOH) alleviates the pH drop and enhances the stability of biofilter performance and DMS removal. The pH drop in the biofilters treating DMS with MeOH is 4 fold slower than that in the control biofiler treating DMS only. For the biofilters with MeOH addition, the pH of the biofilters drops more gradually (0.044 pH units per day) when compared to the MeOH suspension periods when MeOH is not added (0.23 pH units per day). MeOH addition consumes oxygen and results in a lower conversion ratio of sulfide to sulfuric acid due to the formation of elemental sulfur, reducing acidification in the biofilters. Nitrification was found to be actively taking place in the control biofilter treating DMS without MeOH addition, contributing to the significant pH drop in the reactor. It is proposed that MeOH prevents acid production from nitrification likely by limiting oxygen and nutrients to nitrifying bacteria in the MeOH-fed biofilters.

Application of biological activated carbon as a low pH biofilter medium for gas mixture treatment

Packing material is a crucial component of a bioreactor as it is the microbial population's habitat. This study assessed potential improvements to current biofiltration processes by investigating use of a novel support medium. Biological activated carbon (BAC) with microorganisms growing on granular activated carbon can produce a novel medium in which both adsorption and biodegradation contribute to pollutants removal. Investigation of carbon characteristics demonstrated that BAC was an ideal packing medium for biofiltration. The application of the novel packing medium for gas mixture treatment was evaluated in a low pH biofilter. Results demonstrated that BAC biofilter obtained high removal efficiency for both H(2)S and toluene. The removal mechanisms of BAC were investigated after the biofilter operation and it demonstrated that the performance of the BAC system was mainly controlled by the additive contributions of two removal mechanisms - adsorption and biodegradation. This study also indicated the potential for simultaneous treatment of hydrogen sulfide and toluene at low pH condition.

Biogeochemical analysis of hydrogen sulfide removal by a lava-rock packed biofilter

Although lava-rock-based biofilters have demonstrated their efficiencies for hydrogen sulfide (H2S) removal found in odorous air emissions, the biogeochemical basis for this removal is unclear. In this study, samples of lava rock and rinse water from biofilters at Cedar Rapids Water Pollution Control Facilities (Iowa) were used to study the structure and chemical composition of lava rock and to identify the predominant microorganism(s) present in lava-rock-based biofilters. It was found that iron, in the form of Fe2+ and Fe3+, was present in lava rock. Although literature suggests that Acidithiobacillus thiooxidans are primarily responsible for gaseous H2S removal in biofilters, our study showed that Acidithiobacillus ferrooxidans was the dominant microorganism in the lava-rock-based biofilters. A novel mechanism for H2S removal in a lava-rock-based biofilter is proposed based on the biogeochemical analysis of lava rock.

Effects of pH, CO2, and flow pattern on the autotrophic degradation of hydrogen sulfide in a biotrickling filter

In this study, the effects of pH, CO(2), and flow pattern on the performance of a biotrickling filter (BTF) packed with plastic Pall rings and treating a H(2)S-polluted waste gas were investigated to establish the optimum operating conditions and design criteria. The CO(2) concentration had no effect on the biodegradation at H(2)S concentrations below 50 ppm. In the range of 50-127 ppm H(2)S, CO(2) concentrations between 865 and 1,087 ppm enhanced H(2)S removal, while higher concentrations of 1,309-4,009 ppm CO(2) slightly inhibited H(2)S removal. The co-current flow BTF presented the advantage of a more uniform H(2)S removal and biomass growth in each section than the counter-current flow BTF. Examination of the pH-effect in the range of pH 2.00-7.00 revealed optimal activity for autotrophs at pH 6.00. Under optimal conditions, the elimination capacity reached 31.12 g H(2)S/m(3)/h with a removal efficiency exceeding 97%. In the present research, autotrophic biomass was developed in the BTF, performing both a partial oxidization of H(2)S to elemental sulfur and a complete oxidization to sulfate, which is favorable from an environmental point of view. Results showed that around 60% of the sulfide concentration fed to the reactor was transformed into sulfate. Such autotrophic trickling filters may present other advantages, including the fact that they do not release any CO(2) to the atmosphere. Besides, the limited growth of autotrophs avoids potential clogging problems. Experimental performance data were compared with data from a mathematical model. Comparisons showed that the theoretical model was successful in predicting the performance of the biotrickling filter.

Design and performance characterization strategy using modeling for biofiltration control of odorous hydrogen sulfide

Biofilter, dynamic modeling software characterizing contaminant removal via biofiltration, was used in the preliminary design of a biofilter to treat odorous hydrogen sulfide (H2S). Steady-state model simulations were run to generate performance plots for various influent concentrations, loadings, residence times, media sizes, and temperatures. Although elimination capacity and removal efficiency frequently are used to characterize biofilter performance, effluent concentration can be used to characterize performance when treating to a target effluent concentration. Model simulations illustrate that, at a given temperature, a biofilter cannot reduce H2S emissions below a minimum value, no matter how large the biofilter or how long the residence time. However, a higher biofilter temperature results in lower effluent H2S concentrations. Because dynamic model simulations show that shock loading can significantly increase the effluent concentration above values predicted by the steady-state model simulations, it is recommended that, to consistently meet treatment objectives, dynamic feed conditions should be considered. This study illustrates that modeling can serve as a valuable tool in the design and performance optimization of biofilters.