Trickling Liquid Research Articles

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.

Removal of cyclohexane vapors from air in biotrickling filters: Effects of gas mixture composition and circular economy approach

This work presents results of investigations on biotrickling filtration of air polluted with cyclohexane co-treated in binary, ternary and quaternary volatile organic compounds (VOCs) mixtures, including vapors of hexane, toluene and ethanol. The removal of cyclohexane from a gas mixture depends on the physicochemical properties of the co-treated VOCs and the lower the hydrophobicity of the VOC, the higher the removal efficiency of cyclohexane. In this work, the performance of biotrickling filters treating VOCs mixtures is discussed based on surface tension of trickling liquid for the first time. A mixed natural – synthetic packing for biotrickling filters was utilized, showing promising performance and limited maintenance requirements. Maximum elimination capacity of about 95 g/(m 3·h) of cyclohexane was reached for the total VOCs inlet loading of about 450 g/(m 3·h). This work presents also a novel approach of combining biological air treatment with management of a spent trickling liquid in the perspective of circular economy assumptions. The waste liquid phase was applied to the plant cultivation, showing a potential for e.g. enhanced production of energetic biomass or polluted soil phytoremediation.

Assessment of the mass transfer strategy and the role of the active bacterial population on the biological degradation of siloxanes

Upgrading of biogas to remove siloxanes is mandatory to meet the standards required for its use as a substitute of fossil fuels. The biological degradation of these pollutants is a low cost and environmental friendly alternative to conventional techniques, albeit certain limitations, such as the low solubility of siloxanes, still hinder its application. In the present work, two parameters were optimized in aerobic and anoxic two-phase biotrickling filters (TP-BTF): the trickling liquid velocity (TLV) and the internal gas recirculation, with the aim of improving siloxanes biological removal. The results obtained showed that the increase in TLV from 2 to 10 m h−1 resulted in higher removal efficiency (RE) under both anoxic and aerobic conditions, reaching maximum values of 55 and 47%, respectively. This effect was more significant for the linear siloxanes. On the contrary, a further increase in the TLV to 20 m h−1 together with the implementation of internal gas recirculation caused an excessive turbulence in the liquid side, detaching the biofilm and having a negative effect for the RE. The cyclic siloxanes were more effectively eliminated along the process (maximum REs of 75% were recorded for decamethylcyclopentasiloxane (D5)), but the studied system modifications exerted a minor effect on their RE. The active bacterial population involved in siloxanes degradation (studied throughout RNA extraction and sequencing) was dominated by the clade Acidithiobacillacea KCM-B-112 and the genus Parvibaculum in aerobic conditions, while the members of the family Phyllobacteriacea and the genera Nocardia and Baekduia dominated in anoxic conditions.

Biological Methanation in an Anaerobic Biofilm Reactor—Trace Element and Mineral Requirements for Stable Operation

Biological methanation of carbon dioxide using hydrogen makes it possible to improve the methane and energy content of biogas produced from sewage sludge and organic residuals and to reach the requirements for injection into the natural gas network. Biofilm reactors, so-called trickling bed reactors, offer a relatively simple, energy-efficient, and reliable technique for upgrading biogas via ex-situ methanation. A mesophilic lab-scale biofilm reactor was operated continuously for nine months to upgrade biogas from anaerobic sewage sludge digestion to a methane content &gt;98%. To supply essential trace elements to the biomass, a stock solution was fed to the trickling liquid. Besides standard parameters and gas quality, concentrations of Na, K, Ca, Mg, Ni, and Fe were measured in the liquid and the biofilm using ICP-OES (inductively coupled plasma optical emission spectrometry) to examine the biofilms load-dependent uptake rate and to calculate quantities required for a stable operation. Additionally, microbial community dynamics were monitored by amplicon sequencing (16S rRNA gene). It was found that all investigated (trace) elements are taken up by the biomass. Some are absorbed depending on the load, others independently of it. For example, a biomass-specific uptake of 0.13 mg·g−1·d−1 for Ni and up to 50 mg·g−1·d−1 for Mg were measured.

Implementation of a Pilot-Scale Biotrickling Filtration Process for Biogas Desulfurization under Anoxic Conditions Using Agricultural Digestate as Trickling Liquid.

A pilot-scale biotrickling filter (BTF) was operated in counter-current flow mode under anoxic conditions, using diluted agricultural digestate as inoculum and as the recirculation medium for the nutrient source. The process was tested on-site at an agricultural fermentation plant, where real biogas was used. The pilot plant was therefore exposed to real process-related fluctuations. The purpose of this research was to attest the validity of the filtration process for use at an industrial-scale by operating the pilot plant under realistic conditions. Neither the use of agricultural digestate as trickling liquid and nor a BTF of this scale have previously been reported in the literature. The pilot plant was operated for 149 days. The highest inlet load was 8.5 gS-H2Sm-3h-1 with a corresponding removal efficiency of 99.2%. The pH remained between 7.5 and 4.6 without any regulation throughout the complete experimental phase. The analysis of the microbial community showed that both anaerobic and anoxic bacteria can adapt to the fluctuating operating conditions and coexist simultaneously, thus contributing to the robustness of the process. The operation of an anoxic BTF with agricultural digestate as the trickling liquid proved to be viable for industrial-scale use.

Ex-situ biological hydrogen methanation in trickle bed reactors: Integration into biogas production facilities

Biological hydrogen methanation (BHM) is a biocatalytic process for biogas upgrading. Integrating ex-situ BHM processes into biogas facilities has the advantage of using inoculum, CO2, and nutrients directly from anaerobic digestion (AD) processes to enhance CH4 productivity. This study investigated the potential of biowaste digestate as an inoculum and digested biowaste reject water as the trickling liquid and nutrient source in thermophilic trickle bed reactors (TBRs). Use of reject water improved H2 conversion efficiency to up to 99 %, thus achieving a H2 loading rate of 10.8 LH2 L Rv-1 d-1 at a gas retention time (GRT) of 1.8 h and CH4 productivity of 2.6 L LRv-1 d-1 implying that reject water contains macronutrients beneficial to enriching hydrogenotrophic methanogens. However, at high H2 loading rates, a trace element supply was necessary to stabilize process performance. Hydrogenotrophic methanogens Methanothermobacter and Methanobacterium were selectively enriched, mainly due to the increased H2 loading rate.

Adding organics to enrich mixotrophic sulfur-oxidizing bacteria under extremely acidic conditions—A novel strategy to enhance hydrogen sulfide removal

Biotreatment of high load hydrogen sulfide (H2S) can lead to rapid acidification of a bioreactor, which greatly challenges the application of bio-desulfurization technology. In this study, the bio-desulfurization performance was improved by enriching acidophilic mixotrophic sulfur-oxidizing bacteria (SOB) by adding organics under extremely acidic conditions (pH < 1.0). A biotrickling filter (BTF) for the removal of H2S was established and operated under pH < 1.0 for 420 days. In the autotrophic period, the maximum H2S elimination capacity (ECmax-H2S) was 135.8 g/m3/h with biofilm mass remaining within 11.1 g/L-BTF. The autotrophic SOB bacterium Acidithiobacillus was dominant (62.1 %). When glucose was added to the BTF system, ECmax-H2S increased by 272 % to 464.3 g/m3/h as biofilm mass increased to 22.3 g/L-BTF. The acidophilic mixotrophic SOB bacteria Mycobacterium (78.4 %) and Alicyclobacillus (20.7 %) were enriched while Acidithiobacillus was gradually eliminated (<0.1 %). Furthermore, the major sulfur metabolism pathways were identified to explore the desulfurization mechanism under extremely acidic conditions. To maintain optimal desulfurization performance and avoid biofilm overgrowth in the BTF system, biofilm mass should be maintained within 20–22 g/L-BTF. This can be achieved by adding 1.0 g/L-BTF glucose every 20 days under a load rate of H2S in 50–90 g/m3/h and a trickling liquid velocity of 1.8 m/h. Extremely acidic conditions eliminated non-aciduric microorganisms so that the addition of organics can increase the abundance of acidophilic mixotrophic SOB (>99 %), thus offering a novel strategy for enhancing H2S removal.

Model-based design and operation of biotrickling filters for foul air H2S removal at wastewater networks

Biotrickling filters (BTFs) are odour control technologies that utilise the action of sulfur oxidising bacteria to treat foul air contaminated with H2S. BTFs are complex systems where an immobilised biofilm is allowed to grow on a supportive solid media, while the foul air flows counter-currently with a stream of trickling liquid. In this work, a mechanistic model is developed, based on first principles where applicable, that describes the interphase mass transfer and biological oxidation kinetics. The model also focuses on the spatial discretisation of a BTF bed and describes the competition between sulfur oxidising bacteria (SOB) and aerobic heterotrophs growing within different niches of the bed. The model successfully produced concentration profiles over time and space of all relevant chemical and biological species within the bed. The model was then used to theoretically investigate the effect of design and operating parameters on the bed performance. It was found that the optimum liquid rate could vary significantly based on other factors such as bed size and inlet H2S concentrations but a typical value lies between 0.3 and 1.3 m/hr, with a larger bed and/or higher H2S loads requiring higher loading rates to achieve the same treatment levels. The model also predicted that bed shape has no significant impact on H2S removal, provided all other conditions are the same. The model successfully allowed for more detailed design of industrial BTF units in terms of both sizing and tuning of operational parameters.

Nitrate-rich wastewater discharged from a bio-trickling filter can be reused as a moisture conditioning agent for organic waste composting

Biotrickling filter (BF) is an effective ammonia-contain odour purification device for organic waste composting. However, proper disposal of nitrogen-rich trickling liquid (TL) discharged from the BF is consider ‘the last-mile problem’ for the application of this coupled system. Although our previous study demonstrated that reusing a TL as moisture conditioning agent for a composting system could promote compost maturity and nitrogen content, the exploration of the intrinsic promotion mechanism was obscured by the complexity (i.e., multiple forms of nitrogen contained) of the TL. Thus, a simulated TL (STL, pH =7.18) containing exclusively nitrate nitrogen was reused to condition the moisture of composting in this study. Effects of STL addition phase [adding STL in mesophilic (days 0–9),​ thermophilic (days 4–13), and cooling period (days 13–22)] on the performance of composting were explored. Results revealed that the organic degradation was partly promoted by adding STL in thermophilic or cooling period, but mightily inhibited in mesophilic period. Furthermore, adding STL in thermophilic period stimulates the denitrification of nitrate-N into dinitrogen at high temperature, whereas most of added nitrate-N was retained in compost product when adding STL in cooling period. Eventually, STL addition effectively increased total nitrogen (TN) by 2%–9%, especially the nitrate nitrogen by 10–11 times. Notably, adding STL rarely affected nitrous oxide and greenhouse gas emission. Therefore, STL can be reused to condition the moisture of compost in a proper composting phase (i.e., thermophilic period) as defined in term of the enhancement of TN and nitrate content of compost product.

Model-Based Analysis of Feedback Control Strategies in Aerobic Biotrickling Filters for Biogas Desulfurization

Biotrickling filters are one of the most widely used biological technologies to perform biogas desulfurization. Their industrial application has been hampered due to the difficulty to achieve a robust and reliable operation of this bioreactor. Specifically, biotrickling filters process performance is affected mostly by fluctuations in the hydrogen sulfide (H2S) loading rate due to changes in the gas inlet concentration or in the volumetric gas flowrate. The process can be controlled by means of the regulation of the air flowrate (AFR) to control the oxygen (O2) gas outlet concentration ([O2]out) and the trickling liquid velocity (TLV) to control the H2S gas outlet concentration ([H2S]out). In this work, efforts were placed towards the understanding and development of control strategies in biological H2S removal in a biotrickling filter under aerobic conditions. Classical proportional and proportional-integral feedback controllers were applied in a model of an aerobic biotrickling filter for biogas desulfurization. Two different control loops were studied: (i) AFR Closed-Loop based on AFR regulation to control the [O2]out, and (ii) TLV Closed-Loop based on TLV regulation to control the [H2S]out. AFR regulation span was limited to values so that corresponds to biogas dilution factors that would give a biogas mixture with a minimum methane content in air, far from those values required to obtain an explosive mixture. A minimum TLV of 5.9 m h−1 was applied to provide the nutrients and moisture to the packed bed and a maximum TLV of 28.3 m h−1 was set to prevent biotrickling filter (BTF) flooding. Control loops were evaluated with a stepwise increase from 2000 ppmv until 6000 ppmv and with changes in the biogas flowrate using stepwise increments from 61.5 L h−1 (EBRT = 118 s) to 184.5 L h−1 (EBRT = 48.4 s). Controller parameters were determined based on time-integral criteria and simple criteria such as stability and oscillatory controller response. Before implementing the control strategies, two different mass transfer correlations were evaluated to study the effect of the manipulable variables. Open-loop behavior was also studied to determine the impact of control strategies on process performance variables such as removal efficiency, sulfate and sulfur selectivity, and oxygen consumption. AFR regulation efficiently controlled [O2]out; however, the impact on process performance parameters was not as great as when TLV was regulated to control [H2S]out. This model-based analysis provided valuable information about the controllability limits of each strategy and the impact that each strategy can have on the process performance.

Application of Response Surface Methodology for H2S Removal from Biogas by a Pilot Anoxic Biotrickling Filter

In this study, a pilot biotrickling filter (BTF) was installed in a wastewater treatment plant to treat real biogas. The biogas flow rate was between 1 and 5 m3·h−1 with an H2S inlet load (IL) between 35.1 and 172.4 gS·m−3·h−1. The effects of the biogas flow rate, trickling liquid velocity (TLV) and nitrate concentration on the outlet H2S concentration and elimination capacity (EC) were studied using a full factorial design (33). Moreover, the results were adjusted using Ottengraf’s model. The most influential factors in the empirical model were the TLV and H2S IL, whereas the nitrate concentration had less influence. The statistical results showed high predictability and good correlation between models and the experimental results. The R-squared was 95.77% and 99.63% for the ‘C model’ and the ‘EC model’, respectively. The models allowed the maximum H2S IL (between 66.72 and 119.75 gS·m−3·h−1) to be determined for biogas use in a combustion engine (inlet H2S concentration between 72 and 359 ppmV). The ‘C model’ was more sensitive to TLV (–0.1579 (gS·m−3)/(m·h−1)) in the same way the ‘EC model’ was also more sensitive to TLV (4.3303 (gS·m−3)/(m·h−1)). The results were successfully fitted to Ottengraf’s model with a first-order kinetic limitation (R-squared above 0.92).

Detailed investigations of dissolved hydrogen and hydrogen mass transfer in a biotrickling filter for upgrading biogas

This study investigated the hydrogen mass transfer limitations in a biotrickling filter inoculated with hydrogenotrophic methanogens for biogas upgrading. A highly sensitive dissolved hydrogen probe allowed measuring concentrations in real-time. Experiments were conducted to test the mass transfer resistance in the gas and liquid films. Results demonstrated that the main resistance resides in the trickling liquid film and that promoting direct gas-biofilm mass transfer could improve upgrading performance by about 20%. Increasing the gas velocity (keeping a constant gas contact time) lowered the upgrading capacity. This was explained by the lowering of the concentration to the average concentration throughout the bed, which resulted a lower reaction rate. At extended gas contact times, the bioreactor shifted from microbial to diffusion limitation, causing lower upgrading capacities. Methane-containing biogas mimics (H2/CH4/CO2) were successfully upgraded to natural gas pipeline standards (>97% methane) with only minor performance reduction compared to upgrading just a H2/CO2 mixture.

Influence of trickling liquid velocity, low molar ratio of nitrogen/sulfur and gas-liquid flow pattern in anoxic biotrickling filters for biogas desulfurization

Hydrogen sulfide has been successfully removed from biogas using anoxic biotrickling filters but an in-depth study of the main operational variables has not yet been carried out. The effect of (i) the empty bed residence time (32–164 s) at a hydrogen sulfide concentration of 2,000 ppmv, (ii) the inlet hydrogen sulfide concentration (2,000–10,000 ppmv), (iii) the trickling liquid velocity (4.8–20.9 m h−1) and (iv) the feed of low nitrogen/sulfur molar ratio (0.334–0.409 mol N-NO3– mol−1 S-H2S) on the hydrogen sulfide removal efficiency have been studied. The BTF (total packed volume of 2.8 L, height/diameter ratio of 9.8) was filled with polypropylene Pall rings (5/8″) and fed continuously with nitrate and a biogas mimic operating in counter-current and co-current flow modes.The maximum elimination capacity was 282.0 gS-H2S m–3 h–1 (RE 97 ± 0.5%) for counter-current flow and 287.5 gS-H2S m–3 h–1 (RE 99 ± 0.4%) for co-current flow mode for an EBRT of 164 s. In addition, in terms of the nitrogen/sulfur molar ratio a higher elemental sulfur production was found in counter-current flow (97.6 ± 2.0%) when compared to co-current flow (87.6±2.8%) since a better depletion of nitrate occurred in co-current flow mode.Finally, three different nitrogen/sulfur molar ratios (0.4, 1.0 and 1.6 mol N-NO3– mol–1 S-H2S) were compared economically. The low and high ratios would involve a nitrate cost of 0.54 and 2.15 € per kg of treated of S-H2S and an elemental sulfur production of 21.5 metric tons and zero production, respectively.

Production of Fungal Phytase in an Innovative Trickle Bed Bioreactor

Excessive temperature rise and drying of substrates are two common problems in solid state fermentation. In order to overcome these problems, an innovative trickle bed bioreactor (TBBR) was designed and tested for the production of fungal phytase by the cultivation of Aspergillus ficuum on wheat straw. In this reactor, a helical perforated bed acts as a support for the substrate. Rotation of this bed in a baffled column produces gentle mixing and separates agglomerated substrates. Intermittent water trickling during fermentation removes product and heat from the fermentation medium partially. For phytase production in the TBBR, the bioreactor was filled with moistened sterilized wheat straw, inoculated with the spores of the fungus. After 3 days, water was trickled on the substrate for 1 min every 24 h. The enzyme in the trickling liquid, and the extracted enzyme from the residual straw after fermentation, were quantified. An equal size traditional packed bed bioreactor (PBBR) was also operated as a control. Phytase production in this TBBR was 54.95% higher than the PBBR. Monitoring the temperature in both bioreactors, moreover, showed lower temperature increase in the TBBR compared to the PBBR.

Anoxic biodesulfurization using biogas digestion slurry in biotrickling filters

In this study, an alternative technology for using chemically produced nitrate/nitrite as an electron acceptor for biogas anoxic desulfurization was developed. The method was validated through the investigation of the impacts of loading rate, trickling liquid velocity, empty bed residence time, liquid height/filler height ratio and restart on H2S removal efficiency in biotrickling filters packed with polyurethane foam (BTF B) and multi-surface hollow spheres (BTF C). The results of this study showed that the best desulfurization efficiency was obtained at a liquid height/filler height ratio of 1/3, rather than at 1/2 or 1/6. In a 122-day experiment, the maximum elimination capacity of 81.29 gH2S m−3h−1 was achieved under a H2S removal efficiency of 94.5%. In addition, the fastest restart process required only 8 days after 25 days of shutdown. High throughput sequencing results indicated that the microbial community structure was more stable below the liquid level than above the liquid level. The genus Sulfurimonas in BTF C was positively correlated with the loading rate (R2 = 0.99, P < 0.01), but the significance of the correlation was lower in BTF B (R2 = 0.76, P < 0.05). In general, the outcomes affirmed that utilizing biogas digestion slurry after nitrification (provided low-cost electron acceptor) could realize a stable and efficient desulfurization efficiency of biogas.

Bioreduction of selenate in an anaerobic biotrickling filter using methanol as electron donor

The anaerobic bioreduction of selenate, fed in step (up to 60 mg.L−1) or continuous (∼7 mg.L−1) trickling mode, in the presence of gas-phase methanol (4.3–50 g m−3.h−1) was evaluated in a biotrickling filter (BTF). During the 48 d of step-feed and 41 d of continuous-feed operations, average selenate removal efficiencies (RE) > 90% and ∼68% was achieved, corresponding to a selenate reduction rate of, respectively, 7.3 and 4.5 mg.L−1.d−1. During the entire period of BTF operation, 65.6% of the total Se fed as SeO42− was recovered. Concerning gas-phase methanol, the maximum elimination capacity (ECmax) was 46.4 g m−3.h−1, with a RE > 80%. Methanol was mainly utilized for acetogenesis and converted to volatile fatty acids (VFA) in the liquid-phase. Up to 5000 mg.L−1 of methanol and 800 mg.L−1 of acetate accumulated in the trickling liquid of the BTF.

Removal of acetone from air emissions by biotrickling filters: providing solutions from laboratory to full-scale

A full-scale biotrickling filter (BTF) treating acetone air emissions of wood-coating activities showed difficulties to achieve outlet concentrations lower than 125 mg C m−3, especially for high inlet concentrations and oscillating emissions. To solve this problem, a laboratory investigation on acetone removal was carried out simulating typical industrial conditions: discontinuous and variable inlet concentrations and intermittent spraying. The results were evaluated in terms of removal efficiency and outlet gas emission pattern. Industrial emissions and operational protocols were simulated: inlet load up to 70 g C m−3 h−1 during 2 cycles of 4 h per day and intermittent trickling of 15 min per hour. The outlet gas stream of the pollutant was affected by intermittent spraying, causing a fugitive emission of pollutant. Complete removal efficiency was obtained during non-spraying. Average removal efficiencies higher than 85% were obtained, showing the feasibility of BTF to treat acetone. The outlet gas stream showed a clear dependence on the pH of the trickling liquid, decreasing the removal at pH < 5.5. Thus, a proper control of alkalinity, with regular NaHCO3 addition, was required for successful operation. The laboratory findings were fruitfully transferred to the industry, and the removal of acetone by full-scale BTF was improved.

Feedforward control application in aerobic and anoxic biotrickling filters for H2S removal from biogas

AbstractBACKGROUNDFeedforward control was implemented at laboratory scale in an aerobic and an anoxic biotrickling filter (BTF) operating under fluctuating H2S loading rate (LR) conditions in order to show the capabilities and added value of this control strategy. Dynamic, long‐term tests with variable H2S LR were performed to simulate disturbances in the inlet gas concentration with and without the implementation of a feedforward control loop based on trickling liquid velocity (TLV) and nitrate feeding rate manipulation for the aerobic and anoxic BTFs, respectively.RESULTSAn average LR of 80 g S‐H2S m–3 h–1 with peaks and valleys of 141 and 28 gS‐H2S m–3 h–1 were tested. At the highest H2S LR, a 68.4% and 62.6% reduction of maximum outlet H2S concentration, and 50.0% and 26.6% reduction of H2S cumulative mass emitted were reached in the aerobic and anoxic BTFs, respectively, thanks to the application of feedforward control strategies. The sulfate selectivity in the aerobic BTF was enhanced up to 100.6 ± 5.0% under controlled conditions. In the anoxic BTF the sulfate selectivity was kept constant at 32.8% ± 0.8%.CONCLUSIONDespite demonstrating that the feedforward controller significantly reduced the impact of disturbances, the utilization of TLV as manipulated variable in the aerobic reactor showed performance problems. However, the feedforward control through nitrate addition was shown to be an adequate, robust strategy for reducing the impact of load perturbation in anoxic BTFs. © 2018 Society of Chemical Industry

Effect of packing material configuration and liquid recirculation rate on the performance of a biotrickling filter treating VOCs

AbstractBACKGROUNDGas–liquid mass transfer still constitutes an important constraint for hydrophobic volatile organic compound (VOC) removal in biotrickling filters (BTFs), packing material and liquid recirculation rate being two key parameters governing this mass transfer. The combined impact of both parameters on the abatement of VOCs has not been yet assessed. This work evaluated the influence of the trickling liquid velocity on process performance under two packed bed configurations (random vs. structured) in a BTF treating toluene and ethylbenzene.RESULTSSimilar removal efficiencies &gt;90% for both toluene and ethylbenzene (corresponding to elimination capacities of ∼50 and 32 g m–3 h–1, respectively) were achieved regardless of the configuration. However, less intensive operating conditions were applied in the structured BTF compared to those implemented in the random packed‐bed BTF (optimal trickling liquid velocities of 10 and 20 m h–1 and liquid renewal rates of 400 and 800 mL d–1, respectively).CONCLUSIONThe superior performance of the structured monolith packing at milder operating conditions was attributed to an improved liquid distribution and the reduction of dead volumes and preferential gas flow channels. Proper selection of the packing material would result in an important reduction in both energy and fresh water consumption. © 2018 Society of Chemical Industry

Different strategies for transient-state operation of a biotrickling filter treating toluene vapor.

Biotrickling filters (BTFs) are often subjected to transient-state operation due to different variations in the operation of industrial-scale sources of pollution. In this research, performance of a laboratory-scale BTF packed with pall ring and pumice (1:1 v/v) and inoculated with Ralstonia eutropha was evaluated for the treatment of toluene vapor under various transient conditions. The experiments were performed at empty bed residence times (EBRTs) of 45 and 90s and toluene inlet concentration in the range of 0.5-4gm-3. The transient-state experiments consisted of a sudden increase in inlet gas concentration, sudden change of trickling liquid rate, intermittent loading for 10hday-1, aeration without toluene loading during shutdown periods, and long-term starvation. The maximum elimination capacity (ECmax) was 280gm-3h-1 under continuous loading. The removal efficiency (RE) reached 90% in intermittent loading experiments at toluene inlet concentration of 3gm-3 in less than 1h after loading initiation. RE dropped to 50% due to 4.5-fold increase in the inlet loading rate (ILR) during shock load experiment. The system became completely active after 24h, when the BTF was subjected to a long-term starvation period for 7days. The results showed that aeration at non-toluene loading periods could improve the BTF performance under intermittent loading condition.