Anoxic Biotrickling Research Articles

Impact of Different Packing Materials on Hydrogen Sulfide Biooxidation in Biofilters Installed in the Industrial Environment

Three pilot scale anoxic biotrickling filters containing different packing materials were built and tested over an extended period in the municipal wastewater treatment plants (WWTP). Performance of biological beds containing polyethylene elements, ceramic Raschig rings, and keramzite particles was investigated at hydrogen sulfide concentrations in biogas ranging from 369 to 1733 mg/m3. The dependence of the number of colony forming units on hydrogen sulfide concentration and location in the bed was determined. Microbial enumeration was performed for all three columns using cultivation methods. The best results of desulfurization were observed for polyethylene elements. For this material the optimum empty bed retention time was 12 min and the minimum concentration of nitrate ions in a nutrient solution was 50 mg/L. The hydrogen sulfide reduction over 99% was achieved at loading rates (LR) of 1.79–5.08 g/m3/h. The increase in LR to 8.45 g/m3/h reduced the removal efficiency to 96%. The results of kinetic a...

Biogas upgrading from vinasse digesters: a comparison between an anoxic biotrickling filter and an algal‐bacterial photobioreactor

AbstractBACKGROUNDBiological technologies for biogas upgrading such as anoxic biotrickling filters (BTF) and algal–bacterial photobioreactors (PBR) constitute a cost‐effective, environmentally friendly alternative to conventional physical–chemical methods. Nonetheless, there is a lack of studies comparing their performance when treating real biogas.RESULTSA H2S removal efficiency >98% was consistently recorded in both systems, with elimination capacities up to 26 and 12.4 g S‐H2S m−3 h−1 in the BTF and PBR, respectively, at empty bed residence times (EBRTs) of ∼ 30 min. Both bioreactors demonstrated a high robustness towards fluctuations in biogas composition and flowrate, maintaining nearly complete desulfurization despite the variations in sulfur load and EBRT. The BTF also showed an immediate recovery from a 15 days operational shut‐down, and the ability to utilize the nutrients from nitrate‐supplemented digestate during biogas desulfurization. In addition, the PBR supported an average CO2 removal of 23.0 ± 11.8%, increasing to 62% at higher pH of 8.1, with a carbon fixation rate of 285 mg CO2 L−1 d−1.CONCLUSIONSThe BTF was confirmed as a robust technology for the desulfurization of real biogas, even when supplemented with effluent from the digester. High H2S removal was also achieved in the PBR, the CO2 fixation capacity of microalgae enhancing biogas purification. © 2015 Society of Chemical Industry

Operational conditions for start-up and nitrate-feeding in an anoxic biotrickling filtration process at pilot scale

A real biogas effluent was desulfurized using an anoxic biotrickling filter at pilot scale. Guidelines and recommendations have been proposed to achieve the correct inoculation and biofilm development. The hydrogen sulfide inlet concentration (4100–7900ppmV) was not controlled. The operational variables studied were the hydrogen sulfide inlet load (37–149gSm−3h−1), biogas flow rate (1–3.4Nm3h−1) and pH (6.8–7.4). Moreover, three nitrate-feeding modes were studied: manual, continuous and automated. Without the addition of nutrients to the nitrate solution, a removal efficiency greater than 95% was obtained for loads in the range 33–55gSm−3h−1 along with an elemental sulfur percentage of 85±5%. The nitrate solution was mainly composed of NaNO3 (500gL−1), the macronutrients KH2PO4 (10gL−1), NH4Cl (5gL−1) and MgSO4·7H2O (4gL−1), and trace elements. The critical elimination capacity was 94.7gSm−3h−1 (RE>99%) on day 119 and the maximum elimination capacity was 127.3gSm−3h−1 (RE=92.6%) on day 122. The recommended operational conditions for start-up are an inlet load of 100gSm−3h−1, a pH set-point of 6.8 to reduce sulfide accumulation and nitrate-feeding automated by oxide reduction potential.

A review on the state-of-the-art of physical/chemical and biological technologies for biogas upgrading

The lack of tax incentives for biomethane use requires the optimization of both biogas production and upgrading in order to allow the full exploitation of this renewable energy source. The large number of biomethane contaminants present in biogas (CO2, H2S, H2O, N2, O2, methyl siloxanes, halocarbons) has resulted in complex sequences of upgrading processes based on conventional physical/chemical technologies capable of providing CH4 purities of 88–98 % and H2S, halocarbons and methyl siloxane removals >99 %. Unfortunately, the high consumption of energy and chemicals limits nowadays the environmental and economic sustainability of conventional biogas upgrading technologies. In this context, biotechnologies can offer a low cost and environmentally friendly alternative to physical/chemical biogas upgrading. Thus, biotechnologies such as H2-based chemoautrophic CO2 bioconversion to CH4, microalgae-based CO2 fixation, enzymatic CO2 dissolution, fermentative CO2 reduction and digestion with in situ CO2 desorption have consistently shown CO2 removals of 80–100 % and CH4 purities of 88–100 %, while allowing the conversion of CO2 into valuable bio-products and even a simultaneous H2S removal. Likewise, H2S removals >99 % are typically reported in aerobic and anoxic biotrickling filters, algal-bacterial photobioreactors and digesters under microaerophilic conditions. Even, methyl siloxanes and halocarbons are potentially subject to aerobic and anaerobic biodegradation. However, despite these promising results, most biotechnologies still require further optimization and scale-up in order to compete with their physical/chemical counterparts. This review critically presents and discusses the state of the art of biogas upgrading technologies with special emphasis on biotechnologies for CO2, H2S, siloxane and halocarbon removal.

Modeling and control strategies for anoxic biotrickling filtration in biogas purification

AbstractBACKGROUNDAnoxic biotrickling filters have been used to 'sweeten' biogas. Nevertheless, the cost and availability of large amounts of nitrate could limit the use of this technology in comparison with aerobic biotrickling filters. The development of a dynamic mathematical model would be useful for the design of control strategies with regard to nitrate dosage.RESULTSA dynamic model has been developed to describe the performance of an anoxic biotrickling filter for biogas desulfurization. The model considers the most relevant phenomena involved in biotrickling filter operation: advection, absorption, diffusion and biodegradation. Moreover, a fraction of the liquid phase is stagnant – an assumption that increases the importance of diffusion phenomena for low liquid flow rates. Once the model had been validated, six control strategies were analyzed for different scenarios and purposes: i.e. to minimize nitrate consumption and/or to maximize H2S removal efficiency.CONCLUSIONThe mathematical model developed from the description of the phenomena involved in the process is a powerful tool to evaluate all possible strategies when considering and quantifying the savings and improvements in different operating modes. © 2015 Society of Chemical Industry

Treatment of O2-free toluene emissions by anoxic biotrickling filtration

Toluene biotrickling filtration under anoxic denitrifying conditions was evaluated in two identical bioreactors (R1 and R2) operated at liquid recycling rates of 1.3, 2.7 and 5.3mh−1 and liquid renewal rates of 0 and 0.17d−1. R1 and R2 achieved a similar maximum elimination capacity (EC ∼30gm−3h−1) at the same toluene inlet load (∼50gm−3h−1), which was approximately 7 times higher compared with available literature on continuous toluene removal under anoxic conditions. Nevertheless, higher metabolite accumulation was observed in the bioreactor operated without periodical liquid phase renewal (R2), leading to intermittent drops in its toluene removal performance. This is the first work operating an anoxic biotrickling filter at empty bed residence time of 3min, which is comparable with those employed in conventional aerobic systems. A characterization of the metabolites accumulated in the liquid phase revealed a dynamic metabolite production and degradation.

Coupling respirometry and titrimetry for the characterization of the biological activity of a SO-NR consortium

Abstract Determining growth rates and kinetic mechanisms of microbial consortia often needs of combining several tests and techniques. The present work demonstrates that combining titrimetric and respirometric data obtained in a single batch test allows obtaining the stoichiometric coefficients, biomass–substrate yields and biological oxidation rates for sulfide-oxidizing nitrate-reducing consortia obtained from an anoxic biotrickling filter for biogas desulfurization. Thiosulfate oxidation using either nitrate or nitrite was quantified as well as the biological production of proton linked to the process to solve the stoichiometry of the two-step autotrophic denitrification associated to thiosulfate oxidation. To obtain accurate titrimetric data related to the biological activity, carbon dioxide stripping was modeled to improve the sensitivity of titrimetric measurements and also to ensure no carbon source limitation during respirometric tests.

Kinetic and stoichiometric characterization of anoxic sulfide oxidation by SO-NR mixed cultures from anoxic biotrickling filters

Monitoring the biological activity in biotrickling filters is difficult since it implies estimating biomass concentration and its growth yield, which can hardly be measured in immobilized biomass systems. In this study, the characterization of a sulfide-oxidizing nitrate-reducing biomass obtained from an anoxic biotrickling filter was performed through the application of respirometric and titrimetric techniques. Previously, the biomass was maintained in a continuous stirred tank reactor under steady-state conditions resulting in a growth yield of 0.328 ± 0.045g VSS/gS. To properly assess biological activity in respirometric tests, abiotic assays were conducted to characterize the stripping of CO2 and sulfide. The global mass transfer coefficient for both processes was estimated. Subsequently, different respirometric tests were performed: (1) to solve the stoichiometry related to the autotrophic denitrification of sulfide using either nitrate or nitrite as electron acceptors, (2) to evaluate the inhibition caused by nitrite and sulfide on sulfide oxidation, and (3) to propose, calibrate, and validate a kinetic model considering both electron acceptors in the overall anoxic biodesulfurization process. The kinetic model considered a Haldane-type equation to describe sulfide and nitrite inhibitions, a non-competitive inhibition to reflect the effect of sulfide on the elemental sulfur oxidation besides single-step denitrification since no nitrite was produced during the biological assays.

Biogas biodesulfurization in an anoxic biotrickling filter packed with open-pore polyurethane foam

Biogas biodesulfurization by an anoxic biotrickling filter packed with open pore polyurethane foam at the laboratory scale (packed volume 2.4L) has been studied. The biotrickling system was operated for 620 days with biogas supplied continuously and two nitrate feeding regimes were tested (manual and programmed). Biomass immobilization was carried out under the manual nitrate feeding regime and a study was then carried out on the effects on removal efficiency of the following parameters: nitrate source, H2S inlet load, nitrate concentration, sulfate accumulation, temperature, pH and trickling liquid velocity. The effect of increased H2S inlet load was studied under the programmed nitrate feeding regime. The results show that a removal efficiency of 99% can be obtained when working under the following conditions: inlet loads below 130gSm−3h−1, a programmed nitrate feeding system, temperature of 30°C, sulfate concentration below 33gL−1, a pH between 7.3 and 7.5, and a trickling liquid velocity higher than 4.6mh−1.

Hydrogen sulphide removal from biogas by an anoxic biotrickling filter packed with Pall rings

Hydrogen sulphide (H2S) is one of the most problematic contaminants in biogas. In this study, a biotrickling filter with a working volume of 2.4L and packed with polypropylene Pall rings was tested for its ability to remove H2S from biogas under anoxic conditions. The influence of the H2S inlet concentration, nitrate feeding regime (manual and controlled) and liquid flow rate on the elimination capacity of the biotrickling filter was studied. The results indicate that 99% of the H2S was removed for H2S inlet loads lower than 120gSm−3h−1 when using controlled nitrate feeding by ORP.

Simultaneous methylmercaptan and hydrogen sulfide removal in the desulfurization of biogas in aerobic and anoxic biotrickling filters

Hydrogen sulfide (H2S) and methylmercaptan (CH3SH) are the most common sulfur compounds found in biogas. The simultaneous removal of H2S and CH3SH was tested at neutral pH in two biotrickling filters, one operated under aerobic conditions and the other one under anoxic conditions. Both reactors were run for several months treating a H2S concentration of around 2000ppmv. Then, the effect of CH3SH loading rate (LR) on H2S and CH3SH removal was investigated in both reactors maintaining a constant H2S LR of 53–63gS-H2Sm−3h−1, depending on the reactor. Initially, CH3SH concentration was stepwise increased from 0 to 75–90ppmv. Maximum elimination capacities (ECs) of around 1.8gS-CH3SHm−3h−1 were found. After that, the CH3SH LR was increased by testing different empty bed residence times (EBRTs) between 180 and 30s. Significantly lower ECs were found at short EBRTs, indicating that the systems were mostly mass transfer limited. Finally, EBRT was stepwise reduced from 180 to 30s at variable CH3SH and H2S loads. Maximum H2S ECs found for both reactors were between 100 and 140gS-H2Sm−3h−1. A negative influence was found in the ECs of CH3SH by the presence of high H2S LR in both biotrickling filters. However, sulfur mass balances in both reactors and batch tests under aerobic and anoxic conditions showed that CH3SH chemically reacts with elemental sulfur at neutral pH, enhancing the overall reactors performance by reducing the impact of sulfur accumulation. Also, both reactors were able to treat CH3SH without prior inoculation because of the already existing sulfide-oxidizing microorganisms grown in the reactors during H2S treatment. Co-treatment of H2S and CH3SH under aerobic and anoxic conditions was considered as a feasible operation for concentrations commonly found in biogas (2000ppmv of H2S and below 20ppmv of CH3SH).

Removing Hydrogen Sulfide from Digester Gas Using Aerobic and Anoxic Biotrickling Filters

Removing Hydrogen Sulfide from Digester Gas Using Aerobic and Anoxic Biotrickling Filters

Empirical modelling and dual-performance optimisation of a hydrogen sulphide removal process for biogas treatment

This study was conducted in order to investigate the use of a simple, low-cost technology for the removal of hydrogen sulphide (H(2)S) from biogas, consisting of an anoxic biotrickling filter. Modelling and optimisation of the process was achieved by studying two independent variables (H(2)S concentration and biogas flowrate) and two simultaneous performance criteria (H(2)S removal efficiency (%) and H(2)S loading rate (g/(m(3) bed day)), which were inversely related. The experiments were carried out on a bioreactor with a 12 L packing volume. H(2)S concentration and biogas flowrate were varied in the range of 2000-4000 ppm(v) and 10-70 L/h, respectively. A model sensitivity analysis indicated the influence of the process variables on the bioreactor performance. Process optimisation was undertaken on a H(2)S removal efficiency basis, while maintaining a target H(2)S loading rate, depending on the desired quality for the biogas use and the technological requirements.

Study on the Performance of an Anoxic Biotrickling Filter for the Removal of Hydrogen Sulphide from Biogas

Abstract The paper presents aspects related to the performance of an anoxic biotrickling filter designed for hydrogen sulphide (H2S) removal from biogas. In this process, nitrate was supplied through a nutrient solution as an electron acceptor for anoxic growth of H2S-oxydizing microorganisms. The biotrickling filter's packing media consisted of a layer of plastic fibres over volcanic rocks in a ratio 0.78:1 by volume. The total volume of packing media was 0.014 m3. Several H2S loading rates (IL) were tested under continuous dynamic conditions, ranging between 20 and 550 g of H2S feed/(m3bed·day). Maximum process performance (>95%) was observed for IL ranging up to approximately 300 g of H2S feed/(m3bed·day). The degradation of hydrogen sulphide occurred with the formation of both sulphate and elemental sulphur, their formation ratio being dependent on H2S loading rate. Elemental sulphur was found to be the dominant degradation product, particularly at IL > 96.18 g of H2S feed/(m3bed·day). The use of two biotrickling filters in series was also tested, and a significant improvement in process performance was observed. This technology allows simple operation with low maintenance and has the potential for sulphur recovery.

Laboratory pilot scale study for H2S removal from biogas in an anoxic biotrickling filter

The purpose of this laboratory pilot scale study at the Wastewater Technology Centre (WTC), Environment Canada, Burlington, ON was to investigate the anaerobic biological removal of H2S from biogas under real-time operating conditions. Biogas produced in a 538 litre pilot anaerobic digester was continuously fed into a 12 litre biotrickling filter containing plastic fibres as packing bed media. The process was monitored for several months. The biogas flowrate and H2S concentration ranged between 10 to 70 L/h and 1,000 to 4,000 ppmv respectively over the course of the test period. Nitrate-rich wastewater from a pilot scale sequencing batch reactor effluent was used as the nutritive solution for the biotrickling filter. The paper presents the influence of several operational parameters such as biogas flowrate, hydrogen sulphide concentration and composition of nutrient solution on process performance. To date, our results show H2S removal rates up to 100% without adverse effects on the methane concentration of the biogas. No system deterioration was observed over long term operation. This non-conventional technology is very promising and could be considered for full scale applications.