On-site removal of H2S from biogas produced by food waste using an aerobic sludge biofilter for steam reforming processing

Implications in the production of defossilized methanol: A study on carbon sources

The transition of the current fossil based chemical industry to a carbon-neutral industry can be done by the substitution of fossil carbon for defossilized carbon in the production of base chemicals. Methanol is one of the seven base chemicals, which could be used to produce other base chemicals (light olefins and aromatics). In this research, we evaluated the synthesis of methanol based on defossilized carbon sources (maize, waste biomass, direct air capture of CO2 (DAC), and CO2 from the cement industry) by considering carbon source availability, energy, water, and land demand. This evaluation was based on a carbon balance for each of the carbon sources. Our results show that maize, waste biomass, and CO2 cement could supply 0.7, 2, 15 times the carbon demand for methanol respectively. Regarding the energy demand maize, waste biomass, DAC, and CO2 from cement demand 25, 21, 48, and 45GJtonMeOH separately. The demand for water is 5300, 220, 8, and 8m3tonMeOH. And lastly, land demand was estimated to 1031, 36, 83, and 77m2tonMeOH per carbon source. The high-demanding-resource production of defossilized methanol is dependent on the availability of resources per location. Therefore, we analyzed the production of defossilized methanol in the Netherlands, Saudi Arabia, China, and the USA. China is the only country where CO2 from the cement industry could provide all the demand of carbon. But as we envision society becoming carbon neutral, CO2 from the cement industry would diminish in time, as a consequence, it would not be sufficient to supply the demand for carbon. DAC would be the only source able to provide the demand for defossilized carbon.

H2S Emission and Microbial Community of Chicken Manure and Vegetable Waste in Anaerobic Digestion: A Comparative Study

In order to solve the problem of H2S corrosion in biogas utilization, it is necessary to understand the characteristics and mechanisms of H2S production in chicken manure anaerobic digestion (CMAD) and vegetable waste anaerobic digestion (VWAD). In this study, lab-scale batch tests of CMAD and VWAD were conducted for 67 days at 35 °C. The results showed that sulfide was found to be the major form of sulfur in CMAD (accounting for 90%) and VWAD (70%). The average concentration of H2S was 198 ± 79 ppm in CMAD and 738 ± 210 ppm in VWAD. Moreover, 81% of total H2S was produced at 20 days of methane production in CMAD, but 80% of total H2S was produced in the first day in VWAD because of the rapid production of biogas and fermentation acidification. The sulfide ion equilibrium model could universally and feasibly predict the H2S production in CMAD and VWAD. The abundance of Firmicutes, Bacteroidetes, Proteobacteria and Euryarchaeota accounted for about 95% of the total microbes in both CMAD and VWAD; the influence of the fermentation stage on the microbial community was greater than that of the difference between CM and VW; the abundance of SRB was 0.01~0.07%, while that concerning organosulfur compounds fermentation was 22.8~30.5%. This study indicated that the H2S concentration of CMAD biogas was more than five times that of VWAD because CM is alkalescent but VW is acidic.

Temporal Variation of Nitrogen and Sulfur Species of Food Waste and Sludge during Anaerobic Co-Digestion

Anaerobic co-digestion (AcoD) has been a widely accepted method to treat food waste (FW) and sewage sludge (SS). However, there is a knowledge gap regarding the key speciation transformation of nitrogen and sulfur in AcoD. Here, we explored the changes of nitrogen (N) and sulfur (S) compounds in liquid digestion and biogas, as well as the composition of microbial community structure and related metabolic functions. The results showed that H2S in the biogas was the main form of S in the early stage, and then, it was converted into SO42− and SO32−, while NH3 and NH4+ were the main forms of N during the AcoD. In addition, bacterial diversity was associated with N and S compounds; Syntrophomonas and Aminobacterium were positively correlated to H2S, NH3, NH4+ and SO32−, and Saccharibacteria_genera_incertae_sedis, Candidatus_Cloacamonas and Thermomonas were positively correlated to SO42− and NO2−. Additionally, the FAPROTAX prediction showed that the functional composition related to N and S metabolism was different from SS and inoculum after the AcoD. This study provides detailed information of conversion of N and S of the AcoD, which could lay a foundation for the subsequent regulation of the mechanism of nitrogen and sulfur compounds in the methanogenic process.

Characteristics and mechanisms of H2S production in anaerobic digestion of food waste

The biogas produced in food waste anaerobic digestion (FWAD) contains H₂S which can lead to corrosion, bad smell and poisoning accident. To control H₂S pollution, the characteristics and mechanisms of H₂S production in FWAD should be known. In this study, a lab-scale FWAD batch test was applied for 20 days under 35 °C. The production potential and average concentration of H₂S were 765 ± 163 g/t (TS) and 1065 ± 267 ppm, respectively. 76% of total H₂S was produced within 6 h on the first day of fermentation, acidification and gas production were key reasons for high H₂S production at this time. Compared to H₂S peak production time, that of methane was long (4 days) and after that of H₂S. Sulfides were found to be the dominant form of sulfur (accounting for 20-70% of total sulfur) in the mixed fermentation liquor in fermentation batch. These sulfides were from protein, which could be decomposed slowly to sulfide by protein-using bacteria and methanogen at the time of methane production peak, and sulfate, which could be converted to sulfide by Sulfate reducing bacteria (SRB) during the first two days of fermentation. Protein would be the main contributor to sulfide/H₂S for the continuous feeding FWAD system in long term operation, due to its presence as the main form of sulfur in food waste.

Full-Scale Study to Treat Hydrogen Sulfide with Biofilter

With the development of urbanization, the odor from municipal wastewater treatment plants has disturbed the neighborhood and the control of odor has become an urgency research subject. The H2S odor was treated by the biofilter. The removal load of the biofilter, end products of H2S degradation, and operation process were studied in this paper. The results of removal H2S odor with the biofilter were as follows: When the gas flow rate was 1000m3/h (resident time 16.2s) and 1250m3/h (resident time 13.0s), and the inlet concentration of H2S ranged from 1.876 to 34.705mg/m3, the removal rate maintained above 99.92%, and the average outlet concentration was 0.001 mg/m3 which was far lower than the national level of discharge standard. The relationship between removal rate and temperature satisfied with the formula , and for H2S, θ=1.016. Furthermore, the end products of H2S degradation were only sulfate without sulfide. With the increase of sulfate, the removal of H2S was not affected. The study of operating parameters with the biofilter provided the necessary technical support for industrial design and operation control.