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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.

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The recombinant polyhistidine-tagged hemoglobin I ((His)6-rHbI) from the bivalve Lucina pectinata is an ideal biocomponent for a hydrogen sulfide (H2S) biosensor due to its high affinity for H2S. In this work, we immobilized (His)6-rHbI over a surface modified with gold nanoparticles functionalized with 3-mercaptopropionic acid complexed with nickel ion. The attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analysis of the modified-gold electrode displays amide I and amide II bands characteristic of a primarily α-helix structure verifying the presence of (His)6-rHbI on the electrode surface. Also, X-ray photoelectron spectroscopy (XPS) results show a new peak after protein interaction corresponding to nitrogen and a calculated overlayer thickness of 5.3 nm. The functionality of the immobilized hemoprotein was established by direct current potential amperometry, using H2S as the analyte, validating its activity after immobilization. The current response to H2S concentrations was monitored over time giving a linear relationship from 30 to 700 nM with a corresponding sensitivity of 3.22 × 10-3 nA/nM. These results confirm that the analyzed gold nanostructured platform provides an efficient and strong link for polyhistidine-tag protein immobilization over gold and glassy carbon surfaces for a future biosensors development.

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We studied the feasibility of the microaerobic process, in comparison with the traditional chemical absorption process (NaOH), on H2S removal in order to improve the biogas quality. The experiment consisted of two systems: R1, biogas from an anaerobic reactor was washed in a NaOH solution, and R2, headspace microaeration with atmospheric air in a former anaerobic reactor. The microaeration used for low sulfate concentration wastewater did not affect the anaerobic digestion, but even increased system stability. Methane production in the R2 was 14 % lower compared to R1, due to biogas dilution by the atmospheric air used. The presence of oxygen in the biogas reveals that not all the oxygen was consumed for sulfide oxidation in the liquid phase indicating mass transfer limitations. The reactor was able to rapidly recover its capacity on H2S removal after an operational failure. Bacterial and archaeal richness shifted due to changes in operational parameters, which match with the system functioning. Finally, the microaerobic system seems to be more advantageous for both technical and economical reasons, in which the payback of microaerobic process for H2S removal was 4.7 months.

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Hydrogen sulfide (H2S) is an extremely toxic colourless gas; it is corrosive and denser than air. It usually happens in oil and natural gas fields, refineries, coal mines, and in some industrial effluent treatment systems. This work presents an alternative method of monitoring and quantifying H2S trapping efficiency by using 1,3,5-tris(2-hydroxyethyl)-1,3,5-triazinane as a sequestering agent, and sodium sulfide as a source of sulfide ion, through (1)H NMR spectroscopy. The results proved that the reaction occurs very quickly at 20 °C at pH 7 and 10. 3,5-di(2-hydroxyethyl)-1,3,5-thiodiazinane and 5-(2-hydroxyethyl)-1,3,5-dithiozinane were observed and quantified; it was evidenced that (1)H NMR spectroscopy can be applied as a fast and effective method to quantify H2S trapping efficiency.

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The performances of three laboratory-scale biofilters (BF1, BF2, BF3) packed with expanded schist for H(2)S removal were studied at different empty bed residence times (EBRT=35, 24 and 16s) in terms of elimination capacity (EC) and removal efficiency (RE). BF1 and BF2 were filled with expanded schist while BF3 was filled with both expanded schist and a nutritional material (UP20; 12% vol). BF1 and BF3 were inoculated with activated sludge, whereas BF2 was not inoculated. A maximum EC of 42 g m(-3) h(-1) was recorded for BF3 at EBRT=35 s demonstrating the ability of schist to treat high H(2)S loading rates, and the ability of UP20 to improve H(2)S removal. Michaelis-Menten and Haldane models were fitted to the experimental elimination capacities while biofilter responses to transient-state conditions in terms of removal efficiency during shock load events were also evaluated for BF1 and BF3.

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Mixtures of volatile reduced sulphur compounds (VRSCs) like hydrogen sulphide (H(2)S), methylmercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS) are found in gaseous emissions of several industrial activities creating nuisance in the surroundings. Hydrogen sulphide (H(2)S) decreases the removal efficiency of volatile reduced sulphur compounds (VRSCs) in biofilters but the kinetics of this effect is still unknown. Kinetic expressions that represent the rate of bio-oxidation of H(2)S, MM, DMS and DMDS are proposed. In order to observe and quantify this effect, equimolar mixtures of MM, DMS and DMDS were fed into a biotrickling filter inoculated with Thiobacillus thioparus at different H(2)S loads. Experimental results shown a good agreement with the simulations generated by the model considering the kinetic equations proposed. The estimated kinetic constants show that H(2)S and MM have a significant inhibitory effect on the bio-oxidation of DMS and DMDS, having the H(2)S the higher effect.

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Four different empirical expressions have been compared for estimating the removal of hydrogen sulphide (H(2)S) from wastewater by chemical oxidation during its treatment in an aerated biofilter. The relative importance of this removal process is considered in a mass balance proposed by an emission model. Two of the four models investigated were able to predict the mean H(2)S removed fraction within a confidence interval of 95% and they demonstrated good agreement with experimental data. Biodegradation and oxidation were the two main removal mechanisms in the biofilter whereas stripping and volatilization made only minor contributions. However they can be of significance when the emission rates are calculated.

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In the present work, the main objective was to evaluate a biofiltration system for removing hydrogen sulfide (H(2)S) and volatile fatty acids (VFAs) contained in a gaseous stream from an anaerobic digestor (AD). The elimination of these compounds allowed the potential use of biogas while maintaining the methane (CH(4)) content throughout the process. The biodegradation of H(2)S was determined in the lava rock biofilter under two different empty bed residence times (EBRT). Inlet loadings lower than 200 g/m(3)h at an EBRT of 81 s yielded a complete removal, attaining an elimination capacity (EC) of 142 g/m(3)h, whereas at an EBRT of 31 s, a critical EC of 200 g/m(3)h was reached and the EC obtained exhibited a maximum value of 232 g/m(3)h. For 1500 ppmv of H(2)S, 99% removal was maintained during 90 days and complete biodegradation of VFAs was observed. A recovery of 60% as sulfate was obtained due to the constant excess of O(2) concentration in the system. Acetic and propionic acids as a sole source of carbon were also evaluated in the bioreactor at different inlet loadings (0-120 g/m(3)h) obtaining a complete removal (99%) for both. Microcosms biodegradation experiments conducted with VFAs demonstrated that acetic acid provided the highest biodegradation rate.

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Hydrogen sulphide (H2S) represents one of the main odorant gases emitted from wastewater treatment plants (WWTP) and a mathematical model can be a fast and low cost tool to estimate its emission. In this work H2S emission rates in a WWTP, composed of an up-flow anaerobic sludge blanket (UASB) reactor and an aerobic biofilter (BF), are estimated using four mathematical models available in the literature (AP-42, GPC, TOXCHEM + and WATER8). The results show that the GPC model leads to the best agreement with the experimental data, except for the biofilter due to its lack of capability to include biodegradation as a H2S removal process. On the other hand, the AP-42 and WATER8 models showed a slightly better ability to predict H2S removal in the biofilter than the TOXCHEM + model, as all models underestimate the H2S concentration decay.

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This paper presents the results of a proposed intervention to deal with the odor problems of a sewage treatment works (STW), which is located near a populated area. The STW consists of a facultative pond. Since this pond functions under close to anaerobic conditions, unpleasant odors are emitted. In this respect, two possible ways to deodorize the pond were evaluated. Firstly, the recirculation of effluent using 1/6 of the flow stream followed by aeration of the pond with a reduced power aerator. In order to study the efficiencies of the deodorization methodologies chemical analyses of the gases NH3 and H2S, olfactometric analyses and evaluation of the environmental perception of the population in relation to the odors originating from the STW, were carried out for each experimental situation. The results showed a significant reduction in odors when aeration with reduced power equipment was utilized in combination with recirculation of effluent in the pond. Reductions in emissions of H2S from 0.1345 mg/m3 to 0.0083 mg/m3 and of NH3 from 0.021 mg/m3 to 0.0073 mg/m3 were obtained. To analyze the behavior of the pond, its planktonic community was investigated, with a difference in species for the situations with and without odor being observed.

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A technique is presented that can be used to estimate the changes in physical structure in a natural biofilter packing medium, such as compost, over time. The technique applies information from tracer studies, grain size distribution, and pressure drop analysis to a model that estimates the number of channels, average channel diameter, number of particles, and specific surface area of the medium. Important operational factors, such as moisture content, pressure drop, and sulfate accumulation also were evaluated both in a conventionally operated biofilter and in one operated with periodic compost mixing. In the conventionally operated laboratory-scale compost biofilter, hydrogen sulfide (H2S) removal efficiency decreased from 100% to approximately 90% over 206 days of operation. In a similar system, operated with compost mixing, the H2S removal efficiency was maintained near 100%. Variations in media moisture conditions and specific surface area can explain the results observed in this study. Under conventional operation, drying near the inlet disintegrated the compost particles, producing a large number of particles and flow channels and increasing the specific surface area. At the top of the column, where moisture was added, particle size increased and specific surface area decreased. In the column with media mixing, moisture content, particle size, and specific surface area remained homogeneous.

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