Kawin Rujisangvittaya* and Sivawan Phoolphundh
Abstract: Presence of hydrogen sulfide (H2S) in biogas is a major problem for biogas utilization due to its corrosive property. H2S contamination can be removed by chemical and physical methods but both of them have high capital costs and demand large energy inputs. The biological process e.g. Biofilter can change biogas into noncorrosive form. Pollutants (e.g. H2S) are utilized by biofilm of microorganisms grown on packing material when contaminated gases stream pass through the filter bed. Many types of microorganisms, either autotrophic or heterotrophic, are capable of utilizing hydrogen sulfide for their growth. Sulfur oxidizing bacteria (SOB) convert hydrogen sulfide (H2S) into elemental sulfur (S0) by partial oxidation, or sulfate (SO42-). Besides H2S, other sulfur compounds like thiosulfate (S2O32-) and tetrathionate (S4O62-) can also be converted to sulfate. In this study, Sulfur oxidizing bacteria isolated from Fang hot-spring in Chaingmai province, from a bio-scrubber tank of cassava starch wastewater treatment plant at Saraburi province and mixed culture of bio-scrubber effluent and hot-spring bacterial biofilm were determined for their hydrogen sulfide removal efficiency in the biofilter (PVC pipe; diameter 0.2 m, height 1.5 m) packed with plastic bio-ball (6.29 m2 surface area). Each biofilter was continuously fed with real biogas (H2S concentration ~ 2,000-3,000 ppm) at the bottom with the flow rate of 0.6 m3/h. Minerals medium was sprayed from a nozzle at the top of biofilter. Hydrogen sulfide concentration from biogas inlet and outlet was monitoring every 4 hours over 3 days and used to calculate the removal efficiency (%). The results showed that biofilter inoculated with hot-spring bacterial biofilm and bio-scrubber effluent biofilm had hydrogen sulfide removal efficiency of more than 75 and 80%, respectively. A hydrogen sulfide removal efficiency of more than 85% was achieved when mixture of two bacterial sources were used.
Keywords: Bacterial biofilm; biofilter; hydrogen sulfide; sulfur oxidizing bacteria; sulfide removal efficiency.
C. Yubolsai, P. Choeisai*, P. Visedkaew, T. Yamaguchi, T. Onodera, and K. Syutsubo
Abstract: In a period of 1 year, the volumetric ratio of wastewater from a cane molasses-based bio-ethanol distillery plant (CMBP) and a cane sugar mill (CSM) was monitored and shown to be 1:2. In order to evaluate the validity of mixing the two wastewaters, their biodegradability and methanogenic activity (MA) were measured under a fixed temperature of 35℃ and fixed FM ratio of 0.5 (i.e., 2 g COD/l for test substrate per 4 g VSS/l for test sludge). The results showed that the mixed wastewater was 4% higher in biodegradability and 1.2 times higher in MA when compared with pure CMBP wastewater. Based on 100% COD input, 46% COD from the mixed wastewater was converted to methane. The MA of the mixed wastewater was 0.0006 g COD-CH4/gVSS.d. Additionally, a lab scale, 2-phase, multi-stage up-flow anaerobic sludge blanket (MS-UASB) reactor was operated at room temperature (22 to 32°C) and fed with CMBP wastewater and with mixed wastewater to investigate anaerobic treatability. Influent COD concentration and hydraulic retention time (HRT) were fixed at 15 g/l and 36 hours, respectively. The treatment process consisted of a conventional UASB reactor with a liquid volume of 24 l for the first phase of sulfate reduction, in addition to acidification by keeping influent pH at 6.0, followed by an MS-UASB reactor with a liquid volume of 12.7 l. Feeding of the wastewater mixture resulted in a sufficient level of COD removal, with an efficiency of 66.8%, higher than CMBP wastewater treatment by 10.6%.
Keywords: Anaerobic treatment, bio-ethanol distillery wastewater, cane molasses based, multi-stage UASB, 2-phase UASB.
Wikanda Thongnueakhaeng and Pawinee Chaiprasert*
Abstract: High concentrations of sulfate and nitrogen have an impact to anaerobic digestionfor biogas production via hydrogen sulphide and ammonia produced by sulfate reducing bacteria and ammonifying bacteria, respectively, have been found to inhibit the methanogenesis. Furthermore, their removal from digested wastewater is required. Biological treatment by sulfate reducing bacteria (SRB), sulfide oxidizing bacteria (SOB), nitrifier and denitrifieris the most widely used microorganisms for this process. The selection of microbial sources for high activities of SRB, SOB, nitrifier and denitrifier was interested in this study. Four sources of microbial seed sludge from anaerobic wastewater treatment system of concentrated latex (CL) in close UASB and open pond (AOP) while the other two sources from open ponds of swine manure (SM) and cassava starch (CS) were used to evaluate the microbial performances. The activities of SRB, SOB, nitrifier and denitrifier were monitored. Between seed sludge from UASB and AOP of CL, AOP had higher activities of SOB, nitrifier and denitrifier except SRB than UASB. Therefore, seed sludge from AOP of CL, SM and CS were chosen to study. These results were found that seed sludge from SM provided the most high activities of SRB, SOB, nitrifier and denitrifier at 0.159 g-SO42--Sconsumed/g-VSS/d, 0.384 g-S2O3-Sconsumed/g-VSS/d, 0.131 g-NH4+-Nconsumed/g-VSS/d and 0.182 g-NO3--Nconsumed/g-VSS/d, respectively. The denitrifier activity of SM had 1.48 and 1.35 times than CL and CS, respectively. Furthermore, the nitrifier activity of SM was higher 3.28 and 1.15 times than CL and CS, respectively. The SOB activity of SM was higher 1.96 times than CS, while lower 1.27 times than CL. In addition, SM provided higher activity of SRB 2.06 times than CS while lower 1.13 times than CL. This study indicated that seed sludge from SM was suitable for simultaneous sulfate and nitrogen removal in wastewater before entering to anaerobic reactor for biogas production.
Keywords: Inoculum seed, microbial activity, sulfate reducing bacteria, sulfide oxidizing bacteria, nitrifier, denitrifier.
Dinh Quoc Viet, Nguyen Van Vinh, Pham Hoang Luong and Van Dinh Son Tho*
Abstract: Vietnam is recognized as an agricultural country and there is a potential of biomass resources originated from residues of agricultural section. Rice husk, rice straw, corn cob and bagasse are main biomass of agricultural residues. In this study, proximate and ultimate analyses of biomass samples were investigated. Thermogravimetric analysis of biomass was carried out to understand its thermal behavior in inert and air environment from ambient temperature to 800°C at the heating rate of 10°Cmin-1. It is observed that all the four biomass samples displayed similar weight loss trend. In nitrogen environment, three reaction zones corresponding to the dehydration, first decomposition that generated volatile and second decomposition of the char. In air environment, three reaction zones are corresponding to the dehydration, devolatilisation and combustion of char.
Keywords: biomass agricultural residues, thermogravimetric analysis.