Orientador: Jorge de Lucas Junior / Coorientador: Ana Carolina Amorim Orrico / Banca: Adhemar Pitelli Milani / Banca: Mara Cristina Pessoa da Cruz / Banca: Mônica Sarolli Silva de Mendonça Costa / Banca: Maria Fernanda Ferreira Menegucci Praes / Resumo: Objetivou-se com a execução deste trabalho o estudo a respeito dos níveis recomendados de inclusão de óleo de descarte aos dejetos de suínos bem como a influencia da inclusão de níveis de lipase ou Biol®, com o intuito de avaliar o efeito do acréscimo de produção de biogás, metano e redução dos teores de sólidos. Foram realizadas duas etapas, sendo a primeira a respeito dos níveis recomendados de adição de óleo e a segunda utilizando os níveis de óleo que apresentaram efeito negativo adicionados à lipase ou Biol®. Para desenvolvimento do ensaio de co-digestão da primeira etapa foram preparados substratos contendo 4% de sólidos totais (ST), compostos por dejetos de suínos, óleo de descarte (nas proporções de 0, 2, 4, 6, 8, 10 e 12%) além de água para diluição destes resíduos e inóculo, para abastecimento de biodigestores batelada. Para desenvolvimento da segunda etapa foi realizado abastecimento de biodigestores batelada com substratos contendo 4% de ST, compostos por dejetos de suínos, óleo de descarte (nas proporções de 8, 10 e 12%), lipase (nas proporções de 0,05; 0,10; 0,15; 0,20 e 0,25%) ou Biol® (10 g/m3 ou 15 g/m3) além de água para diluição destes resíduos e inoculo. Com relação a influencia da adição de níveis de óleo verificou-se que as máximas reduções de ST e SV foram de 36,8 e 41,1% e ocorreram nos níveis de 5,2 e 5,8% de óleo aos substratos, as inclusões de 5,4 e 6,1% de óleo permitiram o alcance de potenciais de 222,9 e 263,6 litros de biogás por kg de ST e SV adicionados. Referindo-se a influencia da adição de níveis de óleo e lipase verificou-se que as reduções máximas de ST e SV foram de 56,13 e 64,49% e ocorreram nos níveis de inclusão 0,15 e 0,13% de lipase e 12% de óleo adicionado aos substratos e ainda que os maiores potenciais de produção de metano por g de ST e sólidos voláteis (SV) adicionados (0,23 e 0,29 litros) foram alcançados pela ... / Abstract: The objective of the implementation of this work the study on the recommended levels of disposal of oil addition to swine manure as well as the influence of the inclusion of lipase levels or Biol®, in order to evaluate the effect of increased production of biogas, methane and reduction of solids. Two steps were conducted, the first with respect to recommended levels of oil addition and using the second oil levels that were negative effect on lipase or Biol® added. For assay development co-digestion of the first stage substrates were prepared containing 4% total solids (TS), composed of swine manure disposal of oil (in the ratios of 0, 2, 4, 6, 8, 10 and 12 %) addition of water for dilution of this waste and inoculum to supply batch digesters. For development of the second stage was performed supply of batch digesters with substrates containing 4% TS, composed of swine manure disposal of oil (in the ratios of 8, 10 and 12%), lipase (in the proportions of 0.05; 0.10, 0.15, 0.20 and 0.25%) or Biol® (10 g/m3 to 15 g/m3) than water for dilution of these residues and inoculum. Regarding the influence of the oil addition levels found that the maximum TS and VS reductions were 36.8 and 41.1% and occurred at levels of 5.2% oil and 5.8 to substrates, the additions of 5.4 and 6.1% enabled the oil potential range of 222.9 and 263.6 liters of biogas per kg TS and VS added. Referring to influence of adding oil and lipase was found that reductions of TS and VS were 56.13 and 64.49% and were in inclusion levels of 0.15 and 0.13% lipase and 12% of oil added to the substrates and that the greatest potential of methane production per g of TS and volatile solids (VS) added (0.23 and 0.29 liters) were achieved by greater inclusion of oil (12%) was added when the levels of 0.12 and 0.11% lipase. Regarding the inclusion of Biol®, it was found that the higher potential production of methane per g TS and VS added (0.22 and 0.27 liters, respectively) were ... / Doutor

<p>This thesis is made by Carl Persson and Alejandro Saavedra for Gryaab. Gryaab is Gothenburg’s water processing plant and produces about 60 GWh biogas annually with a flow around 1150 Nm3/h. Gryaab wants to research their possibilities to become independent with electrical energy and the possibilities to enrich, upgrade biogas. The use of methane rich gases like biogas and natural gas is today low in Sweden compared to major parts of the world. Natural gas is one of the most established energy sources in the world, it contributes to about a quarter of the world energy supply. In Sweden natural gas only contributes about 2 % of the energy supply. The natural gas in Sweden is being imported from Denmark and the gas net goes from Malmo to Gothenburg. Usage of gas in that region is about 20 % of total energy usage. There are a total of 26 municipalities along the south- and west coast. Biogas is climate neutral and all infrastructures being used today with natural gas can potentially be used with biogas. The purpose of this thesis is to examine old and new technology intended to harvest energy in biogas and compare these technologies in a decision matrix. We have chosen two areas, combined heat and power (CHP) and upgrading biogas. In this report there are short reviews of heat engines, gas turbines, fuel cells, PSA, scrubbers, cryogenics, internal methane enrichment, ecologic lung, sulphide- and water removal. Interesting and appropriate technologies for Gryaab might be high temperature fuel cells, like molten carbonate fuel cells, or big gas engines in MW range, like Jenbacher J624 GS, in combined heat and power. These CHP systems are flexible in fuel quality, the biogas only need simpler purification, and they have a high electrical efficiency. To upgrade biogas to vehicle gas quality are water scrubbers, PSA and cryogenics all good choices. Cryogenically treated biogas gives liquid or combusted methane and liquid carbon dioxide as a byproduct.</p><p>Det här examensarbetet är gjort av Alejandro Saavedra och Carl Persson åt Gryaab. Gryaab är reningsverket i Göteborg vilka producerar cirka 60 GWh biogas årligen med ett flöde runt 1150 Nm3/h. Gryaab vill undersöka deras möjligheter att bli självförsörjande av elenergi och möjligheter att förädla, uppgradera biogasen. Användning av metanhaltiga gaser som biogas och naturgas är idag i Sverige låg jämfört stora delar av världen. Naturgas är en av världens mest etablerade energikällor, den står för cirka en fjärdedel av världens energiförsörjning. I Sverige står naturgasanvändningen för bara 2 %. Naturgasen i Sverige importeras från Danmark och stamnätet sträcker sig från Malmö till Göteborg. Användningen i den regionen uppgår till cirka 20 % av total energiförbrukning. Det är totalt 26 kommuner längst syd- och västkusten. Biogas är CO2-neutral och all infrastruktur som idag används för naturgas är potentiellt användbar för biogas. Syftet med examensarbetet är att undersöka ny och gammal teknik för att nyttja biogas på samt att utvärdera och jämföra teknikerna i en utvärderingsmatris. Vi har riktat in oss på två områden, el- och värmegenerering samt förädling av biogas. I det här arbetet står det kortfattade summeringar om värmemotorer, gasturbiner, bränsleceller, PSA, scrubbers, kryoteknik, processintern metananrikning, ekologisk lunga, svavelväte- och vattenavskiljning. Intressanta och lämpliga tekniker för Gryaab kan vara högtempererade bränsleceller, som smältkarbonat-bränsleceller, eller stora gasmotorer i MW- skala, som Jenbacher J624 GS i el- och värmegenerering. Dessa kraftvärmesystem är mycket flexibla när det gäller bränslekvalité, biogasen kräver endast enklare rening och dessutom har de hög elverkningsgrad. För att förädla biogasen till fordonsgaskvalité är vattenscrubber, PSA och kryoteknik alla bra val. Kryoteknisk uppgradering av biogas kan ge flytande eller gasformig metan samt flytande koldioxid som biprodukt.</p>

El objetivo de la presente investigación fue producir biogas a partir de estiércol porcino y residuos orgánicos, por fermentación semicontinua. La experimentación se llevó a cabo en el INPREX; Facultad de Ciencias Agropecuarias, Universidad Nacional Jorge Basadre Grohmann de Tacna. Se utilizó un biodigestor tipo chino modificado de fibra de vidrio de 250 cm3 de capacidad para realizar en ella la fermentación. Se prefermentó el substrato fermentativo formado por excremento de cerdo, resto de vegetales del mercado, hojas de pecana y agua para obtener un compost que constituyó el material fermentativo que se cargo al biodigestor para la producción de biogas. La fermentación se realizo a temperatura de ambiente durante 4 meses (Octubre 2009-Enero 2010). Se obtuvo una producción promedio diario de biogas de 14,864 cm3 a partir de los 18 días de iniciada la fermentación y una producción acumulada, hasta los 58 días en que terminó la fermentación; Se obtuvo un volumen total de biogas de 644,668 cm3 durante la etapa del experimento.

This thesis is made by Carl Persson and Alejandro Saavedra for Gryaab. Gryaab is Gothenburg’s water processing plant and produces about 60 GWh biogas annually with a flow around 1150 Nm3/h. Gryaab wants to research their possibilities to become independent with electrical energy and the possibilities to enrich, upgrade biogas. The use of methane rich gases like biogas and natural gas is today low in Sweden compared to major parts of the world. Natural gas is one of the most established energy sources in the world, it contributes to about a quarter of the world energy supply. In Sweden natural gas only contributes about 2 % of the energy supply. The natural gas in Sweden is being imported from Denmark and the gas net goes from Malmo to Gothenburg. Usage of gas in that region is about 20 % of total energy usage. There are a total of 26 municipalities along the south- and west coast. Biogas is climate neutral and all infrastructures being used today with natural gas can potentially be used with biogas. The purpose of this thesis is to examine old and new technology intended to harvest energy in biogas and compare these technologies in a decision matrix. We have chosen two areas, combined heat and power (CHP) and upgrading biogas. In this report there are short reviews of heat engines, gas turbines, fuel cells, PSA, scrubbers, cryogenics, internal methane enrichment, ecologic lung, sulphide- and water removal. Interesting and appropriate technologies for Gryaab might be high temperature fuel cells, like molten carbonate fuel cells, or big gas engines in MW range, like Jenbacher J624 GS, in combined heat and power. These CHP systems are flexible in fuel quality, the biogas only need simpler purification, and they have a high electrical efficiency. To upgrade biogas to vehicle gas quality are water scrubbers, PSA and cryogenics all good choices. Cryogenically treated biogas gives liquid or combusted methane and liquid carbon dioxide as a byproduct. Det här examensarbetet är gjort av Alejandro Saavedra och Carl Persson åt Gryaab. Gryaab är reningsverket i Göteborg vilka producerar cirka 60 GWh biogas årligen med ett flöde runt 1150 Nm3/h. Gryaab vill undersöka deras möjligheter att bli självförsörjande av elenergi och möjligheter att förädla, uppgradera biogasen. Användning av metanhaltiga gaser som biogas och naturgas är idag i Sverige låg jämfört stora delar av världen. Naturgas är en av världens mest etablerade energikällor, den står för cirka en fjärdedel av världens energiförsörjning. I Sverige står naturgasanvändningen för bara 2 %. Naturgasen i Sverige importeras från Danmark och stamnätet sträcker sig från Malmö till Göteborg. Användningen i den regionen uppgår till cirka 20 % av total energiförbrukning. Det är totalt 26 kommuner längst syd- och västkusten. Biogas är CO2-neutral och all infrastruktur som idag används för naturgas är potentiellt användbar för biogas. Syftet med examensarbetet är att undersöka ny och gammal teknik för att nyttja biogas på samt att utvärdera och jämföra teknikerna i en utvärderingsmatris. Vi har riktat in oss på två områden, el- och värmegenerering samt förädling av biogas. I det här arbetet står det kortfattade summeringar om värmemotorer, gasturbiner, bränsleceller, PSA, scrubbers, kryoteknik, processintern metananrikning, ekologisk lunga, svavelväte- och vattenavskiljning. Intressanta och lämpliga tekniker för Gryaab kan vara högtempererade bränsleceller, som smältkarbonat-bränsleceller, eller stora gasmotorer i MW- skala, som Jenbacher J624 GS i el- och värmegenerering. Dessa kraftvärmesystem är mycket flexibla när det gäller bränslekvalité, biogasen kräver endast enklare rening och dessutom har de hög elverkningsgrad. För att förädla biogasen till fordonsgaskvalité är vattenscrubber, PSA och kryoteknik alla bra val. Kryoteknisk uppgradering av biogas kan ge flytande eller gasformig metan samt flytande koldioxid som biprodukt.

The demand for biogas as vehicle fuel has risen sharply and there is a great need for increased production. A possible addition of vehicle gas can be produced by upgrading landfill gas which is formed by degradation of organic waste. This thesis investigates the potential of producing vehicle fuel from landfill gas in the region of Biogas Öst. In 2008, an amount of 32 million Nm3 landfill gas was extracted in the region. This level can be maintained for another ten years if the efficiency of gas extraction is improved. The annual production will decrease with time since landfills aren’t allowed to receive more organic waste. Landfill gas is hence a large but not lasting source of vehicle fuel. The amount of available landfill gas that is possible to upgrade to vehicle gas is limited by technical and financial issues. With certain limitations taken into account, an estimation of the regions potential gives an annual production of 8.2 million Nm3 vehicle gas. This means that more than 7 000 private cars or 250 buses could be operated with vehicle fuel from landfills in the region.

I såväl Brasilien som runt om i världen finns stora mängder organiskt avfall som skulle kunna utnyttjas på ett bättre sätt. Många potentiella substrat för biogasproduktion deponeras, eldas upp eller komposteras utan att den energi som skulle kunna utvinnas vid denna process tas tillvara. Detta examensarbete inriktade sig på att i laboratorium undersöka potentialen för biogasproduktion från några av dessa avfallsprodukter. Från biodieselproduktion, vilket är en snabbt växande industri i Brasilien, fås exempelvis 1 kg av restprodukten råglycerol per 9 kg producerad biodiesel. Detta är en restprodukt som man i dagsläget letar efter fler tillämpningar för och biogasproduktion har visat sig vara en möjlighet. Biogas har som förnybart bränsle dessutom ökat i attraktivitet under de senaste åren som ett alternativ till fossila bränslen. Syftet med undersökningen var att se om en liten mängd tillsatt råglycerol, eller glycerin som det också kallas, till en redan pågående rötningsprocess kunde öka den totala mängden producerad biogas från huvudsubstratet i fråga. Under arbetets gång utfördes två separata laboratorietester på olika typer av substrat. Det ena var slakteriavfall från ett kycklingslakteri och det andra var ett rötslam från en avfallshanteringsanläggning där industriellt avfall behandlas i bassänger med anaerobisk rötning. Dessa två substrat representerade två mycket olika mikrobiologiska processer där den ena var en ganska ostabil, nystartad process medan den andra var mycket stabil och etablerad. Resultaten från testerna visar att den ostabila processen inte alls klarade påfrestningen som det tillsatta glycerinet innebar, samtidigt som den stabila klarade sig mycket bra. Därför är en av slutsatserna som dras av arbetet att stor försiktighet måste tas när glycerin ska fasas in i en pågående rötningsprocess. Testerna visar dock att en satsvis tillsats av glycerin till rötslammet från avfallshanteringsanläggningen Ecocitrus skulle kunna öka biogasproduktionen från denna anläggning markant, vilket är ett intressant resultat då de står nära en investering i en riktig biogasanläggning. En tillsats av 6,0 eller 9,0 vol.% glycerin till en sådan anläggning har potential att fördubbla biogasproduktionen, samtidigt som metanhalten hålls på en godtagbar nivå. / In both Brazil and around the world, there are large amounts of organic waste that could be exploited in a better way. Many potential substrates for biogas production is deposited in land fillings, burned or composted, without taking advantage of the energy that could be extracted in this process. This thesis focuses on the potential for biogas production from some of these waste products. From biodiesel production for example, which is a rapidly growing industry in Brazil, 1 kg of the waste product crude glycerol is obtained per every 9 kg of produced biodiesel. This is a waste product that is beginning to be in a need for more applications, and biogas production has proven to be a possible application. Biogas as a renewable fuel has furthermore increased in attractiveness in the latest years, as an alternative to fossil fuels. The purpose of this study was to see if a small amount of added crude glycerol, also known as glycerine, to an ongoing digestion process could increase the total amount of biogas produced from the main substrate in question. During the test period, two separate laboratory tests were carried out on various types of substrates. One was the waste from a chicken slaughterhouse and the other was sludge from a waste treatment plant where industrial waste is being treated in pools with anaerobic digestion. These two substrates represented two very different microbiological processes of which one was a quite unstable, recently started process, while the second one was very stable and established. The results of the tests show that the unstable process could not manage the stress that the glycerine meant for the microorganisms, while the stable managed to handle it very well. One of the conclusions drawn from the work is that great care must be taken when glycerine is added to an ongoing anaerobic digestion process. The tests show that a batch addition of glycerin to the substrate from the waste treatment plant Ecocitrus could increase the biogas production from this plant considerably. This is an interesting result since this company is close to an investment in a real biogas plant. An addition of 6.0 or 9.0 vol.% glycerine to such a plant has the potential to double the biogas production, while methane concentration is still kept on an acceptable level.

Considering that the price and demand for energy gradually has risen over the past decade and a wider discussion about the human impact on the environment has become increasingly more important and given a clearer role in modern society. This has contributed to increased incentives to reduce the use of fossil fuels and increase the use of renewable energy.The agriculture currently accounts for 20 % of Sweden's total greenhouse gas emissions. A way for an agricultural company like Wapnö AB to reduce their emissions could be to utilize existing renewable energy sources within their own premises.The report's aim is to create an energy audit of Wapnö’s existing energy system and how it changes with a future biogas plant in operation. The energy audit is used to illustrate how the company’s climate footprint could change. The report also investigates the economics of different heating options for the biogas process and the completion of the current refrigeration compressors with a heat-driven chiller, all to increase the usage of the waste heat from the cogeneration, and minimize the need of purchased energy.The results show that Wapnö can reduce their carbon emissions with 5600 tons of carbon dioxide per year with a future biogas plant in operation. The results also show that the waste heat, combined with a heat pump, is the most cost efficient way to heat the biogas process. Furthermore, the report also shows that the investment in an absorption chiller will be refunded within approximately 6 years, and that in a comparison of the reduced climate impact of either cogeneration or production of vehicle gas, at Wapnö, cogeneration provides a slightly larger reduction of greenhouse gas emissions. / Under det senaste decenniet har priset och efterfrågan på energi i världen successivt stigit. Diskussionen kring människans klimatpåverkan har blivit allt större och fått en tydligare roll i dagens samhälle. Detta har bidragit till ökade incitament att minska användningen av fossila bränslen och öka användningen av förnybara energikällor.Jordbruket står idag för 20 % av Sveriges totala utsläpp av växthusgaser. En möjlighet för ett lantbruksföretag som Wapnö AB att minska sina utsläpp kan vara att utnyttja existerande förnyelsebara energikällor inom den egna verksamheten.Rapporten syftar till att kartlägga mjölkgården Wapnös befintliga energisystem och hur det förändras med en framtida biogasanläggning i bruk. Energikartläggningen ska användas som underlag för att belysa hur Wapnös klimatpåverkan kan komma att förändras. Rapporten avser även att utreda de ekonomiska förutsättningarna för olika uppvärmningsalternativ till biogasprocessen samt kompletteringen av dagens eldrivna kylmaskiner med en värmedriven kylmaskin. Allt för att kunna öka användningen av värmen från kraftvärmeproduktionen och minska gårdens behov av köpt energi.Resultaten visar på att Wapnö kan minska sin klimatpåverkan med 5600 ton koldioxid per år med en framtida biogasanläggning. Arbetsgruppens beräkningar visar också att spillvärme, kompletterad med en värmepump, är det mest kostnadseffektiva sättet att värma biogasprocessen. Vidare i rapporten framkommer även att investeringen i en absorptionskylmaskin blir återbetald efter drygt sex års tid samt att vid en jämförelse mellan kraftvärme- och fordonsgasproduktion på Wapnö ger kraftvärmeproduktion något större reducering av växthusgasutsläpp.

Biogas, composed principally of methane, has limited use in energy generation due to the presence of hydrogen sulphide (H2S). Biogas cannot be burned directly in an engine as H2S present causes corrosion in the reaction chamber. There currently exist various technologies for the removal of H2S from a gas stream, but most are chemically based, expensive, and are limited in use. The purpose of this study was to determine a biogas purification technique suitable for a small scale farm application; including using a technology inexpensive, efficient, robust and easy to operate. As such, biofiltration was investigated for H2S removal from biogas. Factors considered in the design of the biofiltration system included the source and conditioning of inoculum, type of packing material, and general operating conditions including inlet gas flow rate and H2S loading rate to the biofilter. Activated sludge conditioned in A. ferrooxidans media was an effective inoculum source. This was tested for growth support compatibility with gravel packing material, to be used in the biofilter. The inoculated packing material was loaded into the biofilter initially during start-up and acclimatization. In this study, synthetic biogas (49.9%volCH4, 49.9%volCO2, 2000ppmv H2S) mixed with air (totalling 4%vol O2) was added at 5-10L/hr to a biofilter of 0.4L gravel packing inoculated with conditioned activated sludge. Baseline H2S removal studies in a non-inoculated biofilter were performed with anticipated operating conditions, including an inlet gas stream at 7.5L/h (25oC, 1atm), resulting in 31-56% H2S removal. A factorial test performed found that air content in the inlet gas stream was the significant factor affecting the removal of H2S in the non-inoculated biofilter. Operation of the biofilter with biogas was done for 61 days, including 41 days for start-up and acclimatization and 20 days of H2S loading tests. Start-up and acclimatization with biogas resulted in complete H2S removal after 2 days, with an average overall H2S removal of 98.1%±2.9 std deviation over 34 days. Loading tests performed on the system ranged 5-12.4L/h (25oC, 1atm), with a loading rate of 27.8 to 69.5gH2S/m3h of filter bed. Throughout this test the average H2S removal rate was 98.9%±2.1 std deviation over 20 days. Although complete H2S breakthrough studies were not performed, these results indicate that biofiltration is a promising technology for H2S removal from biogas in a small scale application.

During the 19-century a global warming has been observed, which includes increases in global air and ocean temperatures, widespread melting of ice and snow, and rising global sea level. There is a clear connection between emissions of greenhouse gases caused by the human and the increase in temperature. Climatic changes caused by global warming can be stopped trough decreased emission of fossil fuels, for example by an increased use of biogas. Biogas is a renewable energy source which is produced through anaerobic (oxygen free) digestion of organic material. The gas is a mixture of methane (CH4) and carbon dioxide (CO2) and can be among others used as fuel in vehicles. Greengas is biogas produced from grains. The aim with this master’s thesis was to investigate a two-stage process for digestion of a rest by product from ethanol production, called drankvatten. Laboratory experiments were carried out with two process sets, each with two continues stirred tank reactors (CSTR). The process consisted of a thermophilic (55ºC) reactor as the first step in which the substrate was added. Afterwards there was a mesophilic (38ºC) second reactor in which the material from the first reactor was further degraded to produce more gas. The results were intended to be used for an assessment of whether a two-stage process is more efficient then a single-stage process in a full-scale production facility. One of the reasons to have a thermophilic first reactor is that the material has an average temperature around 80 ºC when it arrives to the facility today. It was proved that a two-stage process with this type of substrate generated a higher gas production but the improvements weren’t big enough to motivate a reconstruction of the facility into a two-stage process. The thermophilic process was stable with a retention time of 15 days and a loading rate of 6 g VS/(l•dygn). This retention time was the shortest which was achieved during that loading rate. During earlier mesophilic experiments a higher loading rate was achieved however the used retention time was longer. On the basis of this work no conclusions could be drawn whether a thermophilic process could withstand a higher loading rate then a mesophilic one. Longer adaptation times is probably needed to reach higher loading rates. In this work it also has been studied if it’s necessary to have continues mixing in the biogas reactors. The conclusion of this experiment is that continues mixing isn’t necessary, which results in less mixing and in that way less energy costs.

In this study, a set of full-scale two-stage-in-series scrubbing tower was constructed to test its performance for desulfurization of biogas from three anaerobic UASB (upflow anaerobic sludge blanket) reactors of a wastewater plant for treating corn-syrup processing wastewater. Each stage of the absorbing towers was constructed from a 0.6m ¡Ñ 6 m (I.D. ¡Ñ H) plastic column packed with plastic packings (4¡¨ K6 Heilex-Type or 2.5¡¨ Crown-Biopacks with packing heights of 5 m and 3.65 m, respectively). Effluent from the activated sludge sedimentation tank of the wastewater plant was used as a scrubbing liquid and the tower effluent liquid was discharged into the activated sludge tank for oxidation of the absorbed hydrogen sulfide. Results of a continuous operation period of 20 weeks indicate that H2S of 380-19,000 ppm in the biogas could be reduced to 1-2,100 ppm by the scrubbing towers with superficial liquid and gas velocities of GL = 13.2-28.1 and GV = 306-642 m/h, respectively. On an average, the effluent gas contained a H2S concentration of less than 300 ppm and the removal efficacy was more than 96%. Results also indicate that as pH of the scrubbing liquid increased from 7.7 to 8.8, the overall H2S removal efficacy raised from 86 to 98%. About 1/3 of the absorbed H2S-S was detected as H2S-S and SO4-2-S in the tower effluent. The rest was supposed to be as elemental sulfur in a slimy form which sticked to the packing surface. This might be the reason for the increasing pressure drop with the operation time. A set of performance and gas-liquid equilibrium equations were proposed to estimated the influence of liquid pH, gas and liquid flow rates, and packing height on the H2S removal efficacy. Calculation results indicate, at 30oC, the minimum liquid/gas ratios (L/G)min for the absorption are 0.043 and 0.014 m3/m3, respectively, for fresh absorbing liquids with pH = 8.0 and 8.5. Based on the proposed equations and the experimental data, the volumetric mass-transfer coefficient Kya for H2S absorption in the towers could be expressed approximately as Kya =1.15¡Ñ1017GV1.0GL-3.0 with GV =304-644 and GL = 15.1-28.1 m3/m2.h, and liquid pH 7.7-8.6. It was supposed that too much liquid loading leads to a decrease in the specific area a for mass transfer which results in the Kya decrease.