Hydrogen sulfide removal from biogas using a salak fruit seeds packed bed reactor with sulfur oxidizing bacteria as biofilm

A packed bed reactor was evaluated for hydrogen sulfide (H2S) removal by sulfur-oxidizing bacteria attached as a biofilm on salak fruit seeds (SFS). The bacteria were isolated from the sludge of the wastewater of a biogas plant. The promising isolate from the previous work was used in a biofilter, and its capacity to remove H2S was evaluated at effects of time of operation, effects of biogas flow rate, effects of axial distance, and packing material. Obtained results showed that isolate attached to SFS in an 80 cm height and 8 cm inside diameter biofilter column could decrease H2S in biogas from 142.48 ppm to 4.06 ppm (97.15% removal efficiency) for a biogas flow rate of 8550 g m3 h1 corresponding to a residence time of 4 h. Simple kinetic models of sulfide removal and bacterial growth was proposed to describe the operation of the biofilter. The radial H2S concentration gradient in the flowing gas is to be neglected so is the H2S concentration in the biofilm at certain axial distance. Meanwhile, the rate of H2S degradation was approximated by Monod type equation. The obtained simultaneous ordinary differential equations solved by Runge-Kutta method. Comparing the calculated results and the experimental data, it can be concluded that model proposed can sufficiently describe the performance of the H2S removal. The suitable values of the parameters are as follows: max = 0.0000007 (s1), KS = 0.0000039 (g cm3), kG = 0.0086 (cm s1), HS = 0.9 ((g cm3)/(g cm3)), and Yx/s = 10.Directorate General of Higher Educations of Indonesia - scholarship of doctorate program (BPPDN) at Gadjah Mada University ; Hibah Bersaing 2015 and Sandwich-Like program 201

Easy and green route towards nanostructured ZnO as active sensing material with unexpected H2S dosimeter-type behaviour

Nanostructured ZnO particles were prepared through a straightforward, quick and low\u2010temperature synthesis route involving coprecipitation of the metal precursor salts with oxalic acid, followed by hydrothermal treatment at 135 or 160 \ub0C. The synthesised nanostructured powders were thoroughly characterised by a wide array of analytical techniques from the morphological (Scanning Electron Microscopy \u2013SEM\u2010, Transmission Electron Microscopy \u2010TEM\u2010, Energy\u2010dispersive X\u2010ray Spectroscopy \u2010EDXS\u2010), structural (Powder X\u2010Ray Diffraction \u2010PXRD\u2010, Selected Area Electron Diffraction \u2010SAED\u2010), compositional (X\u2010ray Photoelectron Spectroscopy \u2010XPS\u2010) and physical (thermal stability) point of view. As far as functional applications are concerned, the powders were tested as gas sensor materials for H2S detection. Thereby these ZnO particles show unexpected gas dosimeter behaviour at 150 \ub0C. Based on these observations and on a comparison with literature a new model for the interaction of ZnO nanostructures with H2S is proposed

Economic assessment of biogas-to-electricity generation system with H2S removal by activated carbon in small pig farm

This study was conducted to assess the economic feasibility of electricity generation from biogas in small pig farms with and without the H2S removal prior to biogas utilisation. The 2% potassium iodide (KI) impregnated activated carbon selected as H2S adsorbent was introduced to a biogas-to-electricity generation system in a small pig farm in Thailand as a case study. With the average inlet H2S concentration of about 2400 ppm to the adsorption unit, the H2S removal efficiency could reach 100% with the adsorption capacity of 0.062 kg of H2S/kg of adsorbent. Under the reference scenario (i.e., 45% subsidy on digester installation and fixed electricity price at 0.06 Euro/kWh) and based on an assumption that the biogas was fully utilised for electricity generation in the system, the payback period for the system without H2S removal was about 4 years. With H2S removal, the payback period was within the economic life of digester but almost twice that of the case without H2S removal. The impact of electricity price could be clearly seen for the case of treated biogas. At the electricity price fixed at 0.07 Euro/kWh, the payback period for the case of treated biogas was reduced to about 5.5 years, with a trend to decrease at higher electricity prices. For both treated and untreated biogas, the governmental subsidy was the important factor determining the economics of the biogas-to-electricity systems. Without subsidy, the payback period increased to almost 7 years and about 11 years for the case of untreated and treated biogas, respectively, at the reference electricity price. Although the H2S removal added high operation cost to the system, it is still highly recommended not only for preventing engine corrosion but also for the environment benefit in which air pollution by H2S/SO2 emission and impact on human health could be potentially reduced.Biogas H2S Activated carbon Electricity generation

Effect of kaolin addition on ash characteristics of palm empty fruit bunch (EFB) upon combustion

Palm empty fruit bunch (EFB), a by-product of the palm oil industry, is being recognized as one of the most potential kinds of biomass for energy production in Thailand. However, it has been reported that, in combusting EFB in boilers, some compounds evolving from abundant alkali metals in EFB into gas-phase condense and deposit on low-temperature surfaces of heat exchange equipment, causing fouling and corrosion problems. To come up with a solution to impede the deposition, kaolin, which is abundant in kaolinite (Al2Si2O5(OH)4), is employed to capture the alkali metal vapours eluding from the combustion region. The experiments were designed to simulate the combustion situations that may take place when kaolin is utilized in two different approaches: premixing of kaolin with EFB prior to combustion and gas-phase reaction of volatiles from EFB with kaolin. The amounts of kaolin used were 8% and 16% by weight based on dry weight of EFB, which were equivalent to one and two times of the theoretical kaolin requirement to capture all potassium originally present in the EFB. The furnace temperatures used for EFB combustion were 700-900 °C and ashes were analyzed by XRF and XRD. The results revealed that, under the kaolin premixing condition, 8% kaolin addition was sufficient to capture the potassium compounds at low temperature, i.e. 700 and 800 °C. However, when the temperature was increased to 900 °C, 16% kaolin addition was needed to completely capture the potassium compounds. The results from gas-phase experiments showed that kaolin can capture volatile potassium at maximum 25% at 900 °C. The XRD results showed, for both experimental cases, the evidence of formation of the high melting temperature potassium-alumino-silicates, which confirmed the reaction of potassium compounds with kaolin. The study also suggests that the premixing method is better than the other because of its higher overall capture efficiency.Palm empty fruit bunch (EFB) Combustion Biomass Fouling Kaolin Alkali

Biodegradation of Sulphide in Biogas by Biofilm on Salak Fruit Seeds: Accuracy of Quasi-steady-state Approximation

This study tried to explore the quantitative description of removal of hydroden sulphide (H2S) by bio-filtration. H2S is degraded by bacteria immobilized on the packing materials of Salak fruit seeds inside a column. Two kinetics models are proposed. In both models, the biofilm formed on the packing material is assumed to be thin, so intra-film gradient of H2S concentration can be neglected. In model 1, material balances of H2S in the bio-film as well as in the flowing gas are set-up. The growth of the bio-film is modelled by Monod’s equation. A set of three simultaneous partial differential equations are obtained. Model 2 is set-up using the same concepts as in model1, but the gas phase is assumed to be quasi-steady-state. This assumption reduces the partial differential equation in model 1 to be an ordinary differential equation which is easier to be solved. The comparisons of the results of model 1 and model 2 can be applied to justify the applications of quasi-steady-state approximation. It turned out that the differences of calculated H2S concentration results are approximately small, around 6 ppm. Hence, it can be concluded that quasi-steady-state approximation in the gas phase is suggested to be applied