Biofiltration of H 2 S in air—Experimental comparisons of original packing materials and modeling

Simulation of the Biofiltration of Sulfur Compounds: Effect of the Partition Coefficients

The effect of the partition coefficient on the simulation of the operation of a biotrickling filter treating a mixture of sulfur compounds was analyzed to evaluate the pertinence of using Henry’s law in determining its removal capacity. The analysis consisted of the simulation of a biotrickling filter that bio-oxides hydrogen sulfide (H2S), dimethyl sulfide (DMS), methyl mercaptan (MM) and dimethyl disulfide (DMDS) using different types of models for determining the partition coefficient: Henry’s law for pure water, Henry’s law adjusted from experimental data, a mixed model (Extended UNIQUAC) and a semi-empirical model of two-parameters. The simulations were compared with experimental data. It was observed that Henry’s law for pure water could produce significant deviations from empirical data due to the liquid phase not being pure water. The two-parameter model better fits with similar results compared to the extended UNIQUAC model, with a lower calculation cost and necessary parameter amount. It shows that semi-empirical models can considerably improve simulation accuracy where complex phase interactions are present.

A Two-Stage Biogas Desulfurization Process Using Cellular Concrete Filtration and an Anoxic Biotrickling Filter

A two-stage desulfurization process including an abiotic filtration using cellular concrete waste (first stage) and an anoxic biotrickling filter filling with an inoculated expanded schist material (second stage) was investigated to remove H2S in mimic biogas with limited O2 amount (ranged from 0.5 to 0.8%). The two-stage process was able to satisfactorily remove H2S for all experimental conditions (RE > 97%; H2S concentration = 1500 mg m−3; total Empty Bed Residence Time (EBRT) = 200 s; removal capacity (RC) = 26 g m−3 h−1). Moreover, at a total EBRT = 360 s (i.e., 180 s for each stage), the H2S loading rate (LR) was almost treated by the bed of cellular concrete alone, indicating that abiotic filtration could be applied to satisfactorily remove H2S contained in the gas. According to the H2S concentration entering the biotrickling filter, the majority end-product was either elemental sulfur (S0) or sulfate (SO42−). Thus, the ability of the abiotic filter to remove a significant part of H2S would avoid the clogging of the biotrickling filter due to the deposit of S0. Consequently, this two-stage desulfurization process is a promising technology for efficient and economical biogas cleaning adapted to biogas containing limited O2 amounts, such as landfill biogas.

Biological elimination of a high concentration of hydrogen sulfide from landfill biogas

Hydrogen sulfide (H₂S) is one of the main contaminants found in biogas, which is one of the end products of the anaerobic biodegradation of proteins and other sulfur-containing compounds in solid waste. The presence of H₂S is one of the factors limiting the valorization of biogas. To valorize biogas, H₂S must be removed. This study evaluated the performance of a pilot-scale biotrickling filter system on H₂S removal from landfill biogas. The biotrickling filter system, which was packed with stainless-steel pall rings and inoculated with an H₂S-oxidizing consortium, was designed to process 1 SCFM of biogas, which corresponds to an empty bed residence time (EBRT) of 3.9 min and was used to determine the removal efficiency of a high concentration of hydrogen sulfide from landfill biogas. The biofiltration system consisted of two biotrickling filters connected in series. Results indicate that the biofiltration system reduced H₂S concentration by 94 to 98% without reducing the methane concentration in the outlet biogas. The inlet concentration of hydrogen sulfide, supplied to the two-phase bioreactor, was in the range of 900 to 1500 ppmv, and the air flow rate was 0.1 CFM. The EBRTs of the two biotrickling filters were 3.9 and 0.9 min, respectively. Approximately 50 ± 15.7 ppmv of H₂S gas was detected in the outlet gas. The maximum elimination capacity of the biotrickling filter system was found to be 24 g H₂S·m^-3·h^-1, and the removal efficiency was 94 ± 4.4%. During the biological process, the performance of the biotrickling filter was not affected when the pH of the recirculated liquid decreased to 2-3. The overall performance of the biotrickling filter system was described using a modified Michaelis-Menten equation, and the K_s and V_m values for the biosystem were 34.7 ppmv and 20 g H₂S·m^-3·h^-1, respectively.

Performance evaluation of a biotrickling filter for the removal of gas-phase 1,2-dichlorobenzene: Influence of rhamnolipid and ferric ions

The aim of this study was to evaluate the influence of rhamnolipid (RL) and ferric ions on the performance of a biotrickling filter (BTF) for the removal of gas-phase 1,2-dichlorobenzene (o-DCB). A comprehensive investigation of microbial growth, pollutant solubility, extracellular polymeric substances (EPS) and enzymatic activity in o-DCB degradation by an isolated strain Bacillus cereus DL-1 with/without RL and Fe³⁺ were carried out using batch microcosm experiments. In addition, o-DCB removal performance, biofilm morphology, and microbial community structures in two identical lab-scale biotrickling filters (named BTF1 and BTF2) inoculated with strain DL-1 were studied. The batch microcosm experiments demonstrated that 120 mg L^-1 RL and 4 mg L^-1 Fe³⁺ could enhance the biodegradation of o-DCB, which may be due to promotion on bacterial growth, o-DCB solubilization, C₁₂O enzyme activity, and polysaccharide (PS) and protein (PN) in EPS. Fourier transform infrared (FTIR) spectra indicated that the addition of RL with Fe³⁺ had notable effects on the functional groups of PS and PN in EPS. The experimental results in BTFs indicate that the removal efficiency of o-DCB decreased from 100% to 56.4% for BTF1, which was not fed with RL and Fe³⁺, and from 100% to 80.3% for BTF2, which was fed with RL and Fe³⁺, when the inlet loading rate increased from 4.88 to 102 g m^-3 h^-1 at an empty bed residence time of 60 s. In addition, the microbial adhesive strength and the microbial community structure were different among both BTFs, highlighting the positive effects of RL and Fe³⁺.

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).

Evaluation of a hybrid physicochemical/biological technology to remove toxic H2S from air with elemental sulfur recovery

The removal of toxic hydrogen sulfide (H₂S) from the air at pilot-scale with elemental sulfur recovery was evaluated using Fe-EDTA chelate as a single treatment at a pH of about 8.5. This was later combined with a compost biofiltration process for polishing the pre-treated air. Experiments were performed in a unique container system that allowed deploying either Fe-EDTA chelate or Fe-EDTA chelate/biofiltration treatment (hybrid system). The results showed the feasibility of H₂S removal at concentrations between 200 and 5300 ppmv (H₂S loading rates of 7-190 g m^-3 h^-1) present in fouled air. The Fe-EDTA chelate as a single treatment was able to remove nearly 99.99% of the H₂S at inlet concentrations ≤ 2400 ppmv (107 g m^-3 h^-1), while the hybrid system archived undetectable outlet H₂S concentrations (<1 ppmv) at inlet levels of 4000 and 5300 ppmv. At 5300 ppmv, the Fe-EDTA chelate process H₂S removal efficiency decreased to 99.20% due to the limitation of oxygen mass transfer in the Fe(III) regeneration reaction. Under the previous conditions, the pH was required to be controlled by the addition of NaOH, due to the likely occurrence of undesirable parallel reactions. The elemental sulfur yield attained in the physicochemical module was 75-93% with around 80% recovered efficiently as a solid.

Investigating the nexus among environmental pollution, economic growth, energy use, and foreign direct investment in 6 selected sub-Saharan African countries

This research seeks to enhance the current literature by exploring the nexus among environmental contamination, economic growth, energy use, and foreign direct investment in 6 selected sub-Saharan African nations for a time of 34 years (1980-2014). By applying panel unit root (CADF and CIPS, cross-sectional independence test), panel cointegration (Pedroni and Kao cointegration test, panel PP, panel ADF), Hausman poolability test, and an auto-regressive distributed lag procedure in view of the pooled mean group estimation (ARDL/PMG), experimental findings disclose that alluding to the related probability values, the null hypothesis of cross-sectional independence for all variables is rejected because they are not stationary at levels but rather stationary at their first difference. The variables are altogether integrated at the same order I(1). Findings revealed that there is a confirmation of a bidirectional causality between energy use and CO2 in the short-run and one-way causality running from energy use to CO2 in the long run. There is additionally a significant positive outcome and unidirectional causality from CO2 to foreign direct investment in the long run yet no causal relationship in the short run. An increase in energy use by 1% causes an increase in CO2 by 49%. An increase in economic growth by 1% causes an increment in CO2 by 16% and an increase in economic growth squared by 1% diminishes CO2 by 46%. The positive and negative impacts of economic growth and its square approve the EKC theory. To guarantee sustainable economic development goal, more strict laws like sequestration ought to be worked out, use of sustainable power source ought to be stressed, and GDP ought to be multiplied to diminish CO2 by the utilization of eco-technology for instance carbon capturing, to save lives and also to maintain a green environment.

H2S biotreatment with sulfide-oxidizing heterotrophic bacteria

Many industrial activities produce H₂S, which is toxic at high levels and odorous at even very low levels. Chemolithotrophic sulfur-oxidizing bacteria are often used in its remediation. Recently, we have reported that many heterotrophic bacteria can use sulfide:quinone oxidoreductase and persulfide dioxygenase to oxidize H₂S to thiosulfate and sulfite. These bacteria may also potentially be used in H₂S biotreatment. Here we report how various heterotrophic bacteria with these enzymes were cultured with organic compounds and the cells were able to rapidly oxidize H₂S to zero-valence sulfur and thiosulfate, causing no apparent acidification. Some also converted the produced thiosulfate to tetrathionate. The rates of sulfide oxidation by some of the tested bacteria in suspension, ranging from 8 to 50 µmol min⁻¹ g⁻¹ of cell dry weight at pH 7.4, sufficient for H₂S biotreatment. The immobilized bacteria removed H₂S as efficiently as the bacteria in suspension, and the inclusion of Fe₃O₄ nanoparticles during immobilization resulted in increased efficiency for sulfide removal, in part due to chemical oxidation H₂S by Fe₃O₄. Thus, heterotrophic bacteria may be used for H₂S biotreatment under aerobic conditions.