H2S Concentration In Biogas Research Articles

Enhanced anaerobic digestion of human feces by ferrous hydroxyl complex (FHC): Stress factors alleviation and microbial resistance improvement

Anaerobic digestion (AD) offers a reliable strategy for resource recovery from source-separated human feces (HF), but is limited by a disproportionate carbon/nitrogen (C/N) ratio. Ferrous hydroxyl complex (FHC) was first introduced into the HF-AD system to mediate methanogenesis. Mono-digestion of undiluted HF was inhibited by high levels of volatile fatty acids (VFAs), ammonia, and hydrogen sulfide (H2S). FHC addition at optimum dosage (500–1000 mg/L) increased the cumulative methane (CH4) yield by 22.7%, enhanced the peak value of daily CH4 production by 60.5%, and shortened the lag phase by 24.7%. H2S concentration in biogas was also greatly decreased by FHC via precipitation. FHC mainly facilitated the hydrolysis, acidification, and methanogenesis processes. The production and transformation of VFAs were optimized in the presence of FHC, thus relieving acid stress. FHC elevated the activities of alkaline protease, cellulase, and acetate kinase by 32.3%, 18.2%, and 30.3%, respectively. Microbial analysis revealed that hydrogenotrophic methanogens prevailed in mono-digestion at high HF loading but were weakened after FHC addition. FHC also enriched Methanosarcina, thereby expanding the methanogenesis pathway and improving the resistance to ammonia stress. This work would contribute to improving the methanogenic performance and resource utilization for HF anaerobic digestion.

Improvement of biogas production and quality by addition of struvite precipitates derived from liquid anaerobic digestion effluents of palm oil wastes

When biogas is produced, the liquid anaerobic digestion effluents (LADE) still contain pollutants. Struvite precipitation is a technique for reducing pollutants as well as recovering useful elements such as nitrogen, phosphorus, and magnesium. This study aims to precipitate struvite from LADE and use it as an additive to palm oil mill effluent (POME) feedstocks in subsequent biogas production systems (batch and continuous operational modes). Struvite precipitation was simply performed using NaOH at a pH range of 8–10 without external sources of magnesium and phosphorus. The result showed that the optimum pH for struvite precipitation was 9, giving the highest yield and purity of struvite. The addition of 5% struvite to POME feedstock improved the performance of biogas production in the continuous stirred tank reactor (CSTR) in terms of stability, high COD removal efficiencies, increased methane yields, and decreased H2S concentrations. The greatest methane yield of 509.8 mL/g-VS and the methane concentration of 65.10% were obtained in the CSTR. The significant decrease in H2S concentration in biogas can increase the energy content of biogas, save on the cost of H2S removal, reduce corrosion, and extend the operating time of gas turbines used for electricity production. The results of this study emphasize the role of integrating struvite precipitation with continuous biogas production in improving the process sustainability and economy. Struvite precipitation from LADE diminishes the polluted wastewater, decreases the long-term process problems of fouling and clogging caused by struvite, and improves the performance of the biogas production.

N-Doped Biochar as H2s Adsorbent for the Biogas-Fueled SOFC

Reliability of biogas-fueled SOFC is tied directly to the purity of biogas used as fuel. Even miniscule amount of H2S can poison the anode material and drastically shorten the operation time of biogas-fueled SOFC. In order to prevent the performance degradation caused by H2S poisoning, the aim of this study is to develop an attractive process to obtain a nitrogen (N)-doped carbon derived from biomass feedstock using the digested liquid as a source of N, which can act as an excellent adsorbent material to reduce the H2S concentration in biogas below sub ppm level.Rice husk (RH) was pyrolyzed at 500oC for 2 h under O2-free atmosphere to produce biochar (BC). Rice husk biochar (RH-BC) was then treated with ammonia gas (25% NH3) at 500 or 900°C for 2 h (Intense N-doping) to have N-doped RH-BC (RH-BC(N500-120) and RH-BC(N900-120)). 10% NH3 solution was prepared to simulate the concentrated ammonia solution obtained from the digested liquid discharged from the methane fermentation reactor. The 10% NH3 solution was heated at 30oC through which 100 mL min-1 N2 was passed to obtain the vaporized NH3. RH-BC was treated with the NH3 vapor at 850°C for 90 or 270 min (Mild N-doping) to have N-doped RH-BC (RH-BC(EN850-90) and RH-BC(EN850-270)). Aiming at increasing the total H2S adsorption capacity (ACPH2S ), prior to the mild N-doping, pre-treatment of RH-BC with 15 vol% steam was performed at 850°C for 90 min (RH-BC(S850-90 + EN850-90)).Specific surface area (SSA) of the porous RH-BC was 146 m2 g-1. By the NH3 treatment of the RH-BC, pyridinic-like N can be doped on the surface contributing to the formation of the oxygen radicals to consume H2S, leading to the enhancement of the ACPH2S . RH-BC(N900-120) exhibited the highest breakthrough capacity (APCH2S(0) ) of 8.02 mg H2S g-BC-1 and ACPH2S of 9.58 mg H2S g-BC-1. However, the highest ACPH2S , 25.6 mg H2S g-BC-1, was obtained for RH-BC(S850-90 + EN850-90), while its APCH2S(0) was 3.64 mg H2S g-BC-1.XPS analysis revealed that, during the H2S adsorption, intense N-doping (RH-BC(N900-120)) resulted in the larger amount of sulfate formation on the surface compared to the mild N-doping (RH-BC(S850-90 + EN850-90)). Abundance of oxygen radicals on the surface is preferable for the sulfate formation. This explains the high ACPH2S(0) of the intensely N-doped sample, RH-BC(N900-120). On the other hand, for the mildly N-doped sample, RH-BC(S850-90 + EN850-90), interaction of the surface with H2S was moderately weakened to avoid the blocking of the micropore openings with sulfate, which enables the H2S molecules to adsorb into the micropores, resulting in the higher ACPH2S .

N-Doped Biochar as H2s Adsorbent for the Biogas-Fueled SOFC

The reliability of a biogas-fueled SOFC depends directly on the purity of the biogas. To prevent performance degradation caused by H2S poisoning, this study aimed to develop a nitrogen (N)-doped carbon derived from biomass feedstock using the digested liquid as the N source, which acted as an adsorbent material to reduce the H2S concentration in biogas to below the sub-ppm level. Biochar (BC) derived from rice husk (RH) treated with 25 vol% NH3 gas (balanced with N2) at 900°C for 120 min, RH-BC(N900-120), exhibited the largest H2S breakthrough capacity (APCH2S(0) ) of 8.02 mg H2S g-BC−1 and a total H2S adsorption capacity (ACPH2S ) of 9.58 mg H2S g-BC−1. The largest ACPH2S , 23.0 mg H2S g-BC−1, was obtained for the RH-BC treated with NH3 evaporated from a 10 wt% NH3 solution (simulating a concentrated digested liquid) at 850°C for 270 min, RH-BC(EN850-270), with an APCH2S(0) of 3.96 mg H2S g-BC−1. For a strongly N-doped BC such as RH-BC(N900-120), the formation of surface sulfate after H2S adsorption was more significant compared to a mildly N-doped BC, i.e. RH-BC(EN850-270), in which the interaction of the surface with H2S was moderately weakened, preventing the blockage of micropore openings by the accumulation of sulfate. Consequently, the H2S molecules could be adsorbed into the micropores, resulting in a higher ACPH2S .

Simultaneous phosphorus recovery, sulfide removal, and biogas production improvement in electrochemically assisted anaerobic digestion of dairy manure

Anaerobic digestion (AD) produces renewable biogas from organic-rich waste streams, but the resultant digestate has to be subject to further nutrient recovery processes for better valorization. In this study, an electrochemical treatment unit using stainless steel mesh electrodes was integrated with an up-flow anaerobic sludge blanket (UASB) reactor to treat liquid dairy manure for simultaneous phosphorus (P) recovery, methane production improvement, and hydrogen sulfide (H2S) removal. The 36-d batch AD trial showed that a large portion of total P and reactive P were removed from the liquid dairy manure and were recovered mainly on the cathode deposits in the form of phosphate-bearing minerals. In the continuous USAB trial with an applied voltage of 1.0 V, 65.1% of the total P in the feeding manure was removed, of which 96.7% was achieved by sludge bed accumulation and 3.3% in the cathode deposit. Increases in both biogas production rate (13.0%) and methane yield (10.9%) were observed in the electrochemically assisted UASB system as compared to the one without electrochemical treatment. The electrochemical assistance helped decrease the H2S concentration in biogas by 20.8% at an applied voltage of 0.5 V and by 50.3% at 1.0 V. This electrochemically assisted UASB system can produce more biogas with less H2S content and recover P-enriched sludge in the sludge bed and the cathode deposit.

Key parameters influencing hydrogen sulfide removal in microaerobic sequencing batch reactor

In industry, microaeration is often used for the removal of hydrogen sulfide (H2S) from biogas in full-scale biogas plants. This strategy is very successful when applied in a continuous stirred tank reactor (CSTR), but, due to the fluctuating concentration of H2S in biogas, it is challenging to achieve consistently high H2S removal in an sequencing batch reactor (SBR) or intermittently mixed and/or fed CSTR. To optimize air/oxygen dosing, key parameters influencing the biochemical removal of H2S under microaerobic conditions must be quantified. Here, a lab-scale microaerobic SBR was operated under mesophilic conditions to assess these parameters. In parallel, a mathematical model describing the kinetics of sulfur transformation was developed in AQUASIM software. The experimental data were used to calibrate the model. Subsequent sensitivity analysis identified the liquid-to-gas mass transfer coefficient and biofilm area as the key parameters. We show that the optimization of these parameters is crucial if microaeration is to be successfully utilized for H2S removal from biogas in intermittently mixed reactors.

Enhancing the removal of H2S from biogas through refluxing of outlet gas in biological bubble-column

Biological bubble-column (BBC) is beneficial for elemental sulfur recycle from H2S, but it’s difficult to remove high concentration of H2S in biogas efficiently due to the mass transfer limitation of H2S from gas to liquid. In this study, a novel method with refluxing outlet gas in BBC was investigated. The results showed that gas reflux greatly enhanced the removal of high concentration of H2S (about 5000 ppmv) from biogas. The removal efficiency of H2S was 88.0 ± 4.1% with the reflux ratio at 1.0, which was higher than those without gas reflux (58.4 ± 1.0%), when the inlet H2S loading was 143.1 ± 4.5 g/(m3·h). Moreover, the removal capacity of H2S improved significantly with the increase of the reflux ratios from 1.0 to 4.0 and achieved the maximum at 271.8 ± 2.4 g/(m3·h). This might mainly be attributed to longer residence time and enhanced the mass transfer of O2 and H2S from gas to liquid through gas reflux.

Theoretical framework for the estimation of H2S concentration in biogas produced from complex sulfur-rich substrates.

A theoretical framework was developed and validated for the estimation of H2S concentration in biogas produced from complex sulfur-rich effluents. The modeling approach was based on easy-to-obtain data such as biological biogas potential (BBP), chemical oxygen demand, and total sulfur content. Considering the few data required, the model fitted well the experimental H2S concentrations obtained from BBP tests and continuous bioreactors reported in the literature. The model supported a correlation coefficient (R2) of 0.989 over the experimental data, obtaining average and maximum errors of ~ 25 and ~ 35%, respectively. The theoretical framework yielded good estimations for a wide range of experimental H2S concentrations (0.2 to 4.5% in biogas). This modeling approach is, therefore, a useful tool towards anticipating the H2S concentration in biogas produced from sulfur-rich substrates and deciding whether the installation of a desulfurization technology is required or not.

Performance of ammonium chloride dosage on hydrogen sulfide in-situ prevention during waste activated sludge anaerobic digestion

Based on the phenomenon of the sharp decrease of H2S concentration in biogas during high solid anaerobic digestion (HSAD), the potential inhibitors of H2S production and their impact upon the stability of digesters during waste activated sludge (WAS) anaerobic digestion (AD) were evaluated. The results showed that H2S concentration in biogas decreased over 80% during HSAD compared to conventional AD. The results of biochemical methane potential tests indicated NH4Cl at a dosage ratio of 2.50 g·L−1 was determined as the optimum inhibitor of H2S in-situ prevention (ISP). H2S concentration in conventional AD decreased by over 45% at the same NH4Cl dosage ratio. Subsequent stable biogas yield under a small fluctuation of pH and biogas components in digesters revealed that the stability of digester was not affected. NH4Cl dosage showed an H2S ISP effect during WAS conventional AD under the condition that AD reactors were stable.

Biological Hydrogen Sulfide and Sulfate Removal from Rubber Smoked Sheet Wastewater for Enhanced Biogas Production

The sulfate-rich wastewater from rubber smoked sheet industry could generate hydrogen sulfide (H2S) under anaerobic condition, which created bad smell to the community and might cause toxicity and damage to the environment. The H2S can be removed from the biogas by sulfur-oxidizing bacteria (SOB) with the ability to converted H2S to sulfate. Sulfate-reducing bacteria (SRB) could remove sulfate in wastewater before anaerobic treatment for biogas production. The microbial sludge from wastewater and anaerobic digestion system was collected and test for sulfate and H2S removal efficiency. Anaerobic microbial sludge has a high ability to produced methane from gelatin with a specific methane production rate of 92.4 ml CH4 gVSS-1 day-1. Anaerobic microbial sludge has lower methane production when gelatin and sulfate used as a substrate with a specific methane production rate of 81.4 ml CH4 gVSS-1 day-1. The biomethane potential, hydrogen sulfide removal and sulfate removal in anaerobic digestion system by addition of enriched cultures of SOB and SRB were investigated. The methane yield of SRB consortium was 60.1 ml CH4/gCOD with 20% sulfate reduction from wastewater and no sulfide reduction. The methane yield of SOB consortium was 41.9 ml CH4/gCOD with no sulfate and sulfide reduction from wastewater. The addition of SRB consortium could increase methane production by reducing sulfate concentration in wastewater consequently to a reduced concentration of H2S in biogas.

The use of a silicone-based biomembrane for microaerobic H2S removal from biogas

Abstract A lab-scale bio-membrane unit was developed to improve H2S removal from biogas through microaeration. Biomembrane separated biogas from air and consisted of a silicone tube covered by microaerobic biofilm. This setup allowed efficient H2S removal while minimizing biogas contamination with oxygen and nitrogen. The transport and removal of H2S, N2, O2, CH4 and CO2 through bare membrane, wet membrane and biomembrane was investigated. Membrane allowed the transfer of gases through it as long as there was enough driving force to induce it. H2S concentration in biogas decreased much faster with the biomembrane. The permeation of gases through the membranes decreased in order: H2S > CO2 > CH4 > O2 > N2. H2S removal efficiency of more than 99% was observed during the continuous experiment. Light yellow deposits on the membrane indicated the possible elemental sulfur formation due to biological oxidation of H2S. Thiobacillus thioparus was detected by FISH and PCR-DGGE.

Oxidation reduction potential as a parameter to regulate micro-oxygen injection into anaerobic digester for reducing hydrogen sulphide concentration in biogas

This study aims to evaluate the use of oxidation reduction potential (ORP) to regulate the injection of a small amount of oxygen into an anaerobic digester for reducing H2S concentration in biogas. The results confirm that micro-oxygen injection can be effective for controlling H2S formation during anaerobic digestion without disturbing the performance of the digester. Biogas production, composition, and the removal of volatile solids (VS) and chemical oxygen demand (COD) were monitored to assessment the digester’s performance. Six days after the start of the micro-oxygen injection, the ORP values increased to between −320 and −270mV, from the natural baseline value of −485mV. Over the same period the H2S concentration in the biogas decreased from over 6000ppm to just 30ppm. No discernible changes in the VS and COD removal rates, pH and alkalinity of the digestate or in the biogas production or composition were observed.

Chemical characterization of emissions from a municipal solid waste treatment plant

Gaseous emissions are an important problem in municipal solid waste (MSW) treatment plants. The sources points of emissions considered in the present work are: fresh compost, mature compost, landfill leaks and leachate ponds. Hydrogen sulphide, ammonia and volatile organic compounds (VOCs) were analysed in the emissions from these sources. Hydrogen sulphide and ammonia were important contributors to the total emission volume. Landfill leaks are significant source points of emissions of H2S; the average concentration of H2S in biogas from the landfill leaks is around 1700ppmv. The fresh composting site was also an important contributor of H2S to the total emission volume; its concentration varied between 3.2 and 1.7ppmv and a decrease with time was observed. The mature composting site showed a reduction of H2S concentration (<0.1ppmv). Leachate pond showed a low concentration of H2S (in order of ppbv). Regarding NH3, composting sites and landfill leaks are notable source points of emissions (composting sites varied around 30–600ppmv; biogas from landfill leaks varied from 160 to 640ppmv).Regarding VOCs, the main compounds were: limonene, p-cymene, pinene, cyclohexane, reaching concentrations around 0.2–4.3ppmv.H2S/NH3, limonene/p-cymene, limonene/cyclohexane ratios can be useful for analysing and identifying the emission sources.

Water Scrubbing for Removal of Hydrogen Sulfide (H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;S) Inbiogas from Hog Farms

Biogas from anaerobic digestion of biological wastes is a renewable energy resource. H2S in biogas may cause corrosion or other damage to engines if it is not removed from the gas before utilization. Because the solubility of H2S in water is higher than methane, water can be used as an adsorbent to remove H2S from biogas. A simple water scrubbing column to reduce the H2S content was designed in this study. The biogas purification process took place in the scrubbing column with water where the gas was continuously fed from the bottom of the column through the diffuser which could produce bubbles. The biogas bubbles and the water can accelerate the reaction inside the column. The water in the column was circulated by means of a pump. H2S content in raw biogas was about 6000 ppm. First, the efficiencies of H2S removal for different biogas flow rate and water level were conducted at 30 and 90 sec. Second, the efficiencies of H2S removal with water recycling system were induced. The results showed that the concentration of H2S in biogas decreased significantly with water level and increased with biogas flow rate through the water scrubbing. It was an effective technique for removing H2S in a short operation time, but absorption capability of water declined rapidly with time. To maintain high absorption rate, water scrubbing after adsorption needed to be replaced or regenerated. The water scrubbing system is a simplest and cheapest method. This work is investigated the feasibility of water scrubbing system and its application to a small hog farm.

Stabilization of sewage sludge in the presence of nanoscale zero-valent iron (nZVI): abatement of odor and improvement of biogas production

The potential benefits of nanoscale zero-valent iron (nZVI) on sludge stabilization, either the abatement of odor or the improvement of biogas production, were investigated in this study. Two commercial-grade microscale iron powders were also utilized for comparison. Adding 0.10 wt% of nZVI in sludge during anaerobic incubation significantly reduced the concentration of H2S in biogas by 98.0 % (96.2–98.9 %), probably attributed by reactions between sulfides and the neo-formed hydrous Fe(II)/Fe(III) oxides layer at the surface of ZVI nanoparticles. Meanwhile, the percentage of P in bioavailable fractions decreased from 76.8 to 52.5 %, possibly due to the formation of vivianite [Fe3(PO4)2]. Furthermore, 0.10 wt% of nZVI in anaerobic digestion for 17 days enhanced the concentration of CH4 in biogas by 5.1–13.2 % and improved the production of biogas and methane by 30.4 and 40.4 %, respectively. The amendment of iron nanoparticles during anaerobic digestion can not only effectively reduce H2S in biogas, but also potentially boost methane production significantly.

Elimination of high concentration hydrogen sulfide and biogas purification by chemical–biological process

A chemical–biological process was performed to remove a high concentration of H2S in biogas. The high iron concentration tolerance (20gL−1) of Acidithiobacillus ferrooxidans CP9 provided sufficient ferric iron level for stable and efficient H2S elimination. A laboratory-scale apparatus was setup for a 45 d operation to analyze the optimal conditions. The results reveal that the H2S removal efficiency reached 98% for 1500ppm H2S. The optimal ferric iron concentration was kept between 9 and 11gL−1 with a cell density of 108CFUg−1 granular activated carbon and a loading of 15gSm−3h−1. In pilot-scale studies for biogas purification, the average inlet H2S concentration was 1645ppm with a removal efficiency of up to 97% for a 311d operation and an inlet loading 40.8gSm−3h−1. When 0.1% glucose was added, the cell density increased twofold under the loading of 65.1gSm−3h−1 with an H2S removal efficiency still above 96%. The analysis results of the distribution of microorganisms in the biological reactor by DGGE show that microorganism populations of 96.7% and 62.7% were identical to the original strain at day 200 and day 311, respectively. These results clearly demonstrate that ferric iron reduction by H2S and ferrous iron oxidation by A. ferrooxidans CP9 are feasible processes for the removal of H2S from biogas.

Monitoring and control of biogas desulphurization using oxidation reduction potential under denitrifiying conditions

AbstractBACKGROUND: Hydrogen sulphide (H2S) present in biogas can be oxidized to elemental sulphur (S0) or sulphate (SO42−) using nitrate and nitrite. Both nitrate and nitrite are normally available in most wastewater treatment plants and could be used to oxidize H2S depending on the molar loading ratio of wastewater and biogas. A control approach is required in order to minimize the fluctuations in inlet and outlet H2S concentrations in biogas, and the oxidation potential of the wastewater used.RESULTS: A control scheme has been developed for biogas desulphurization using oxidation reduction potential under industrial conditions. The redox potential was maintained at about + 50 to + 100 mV in the activated sludge plant to monitor the performance of the nitrification process. The redox potential in the bioscrubber was related to sulphide removal from biogas. More than 90% of the hydrogen sulphide was removed from the biogas.CONCLUSION: The oxidation reduction potential can be used as a key parameter for monitoring and controlling biogas cleaning. Fluctuations of the inlet H2S concentration in biogas can be compensated by manipulating the flowrates of wastewater used in order to achieve consistent and desired H2S concentrations in treated biogas. Copyright © 2011 Society of Chemical Industry