Generation of biogas using crude glycerin from biodiesel production as a supplement to cattle slurry

The influence of crude glycerin on biogas production and methane content of the produced biogas was studied, when added to cattle slurry. The experimental design consisted of 5% wt (Gli 5), 10% wt (Gli 10), and 15% wt (Gli 15) of crude glycerin added to cattle slurry, and one control digester without addition of crude glycerin. Anaerobic digestion was carried out in 4 laboratory size CSTR-type biogas digesters with a working volume of 3 L, in semi-continuous regime at mesophilic conditions, over a period of 10 weeks. The highest biogas yields (825.3 mL g^?1 and 825.7 mL g^?1, respectively) relative to mass of volatile compounds added, were produced by the treatments Gli 5 and Gli 10. The control treatment produced 268.6 mL g^?1, whereas the treatment Gli 15 produced 387.9 mL g^?1. This low value was due to the breakdown of the process. Compared to the control, methane contents was increased by 9.5%, 14.3%, and 14.6%, respectively, for the treatments Gli 5, Gli 10, and Gli 15.     

Effect of organic loading rate on fermentative hydrogen production from continuous stirred tank and membrane bioreactors

The influence of organic loading rates (OLRs) on the performance of fermentative hydrogen-producing bioreactors operating in continuous stirred tank reactor (CSTR) and membrane bioreactor (MBR) modes was examined. Five OLRs were examined, ranging from 4.0 to 30 g COD L^?1 d^?1, with influent glucose concentrations ranging from 1.3 to 10 g COD L^?1. At OLRs up to 13 g COD L^?1 d^?1, all influent glucose was utilized and the H₂ yield was not significantly influenced by OLR, although the yield in the CSTR mode was significantly higher than that in the MBR mode, 1.25 versus 0.97 mol H₂ (mol Gluc. Conv.)^?1, respectively. At an OLR of 30 g COD L^?1 d^?1, both reactor modes were overloaded with respect to glucose utilization and also had significantly higher H₂ yields of 1.77 and 1.49 mol H₂ (mol Gluc. Conv.)^?1 for the CSTR and MBR modes, respectively, versus the underloaded operation. At the intermediate OLR of 22 g COD L^?1 d^?1, the H₂ yield was maximized at 1.78 mol H₂ (mol Gluc. Conv.)^?1 for both the CSTR and MBR operation. Overall H₂ production was 50% higher in the MBR mode, 0.78 versus 0.51 moles d^?1, because the CSTR mode was overloaded with respect to glucose utilization at this OLR. These results suggest that an optimum OLR that maximizes H₂ yield and H₂ production may be near the OLR that causes overload with respect to substrate utilization. Additionally, while the CSTR mode is easier to operate and provides higher H₂ yields at underloaded and overloaded OLRs, the MBR mode may be preferable when operating near the optimum OLR.     

Bio-methanization of energy crops through mono-digestion for continuous production of renewable biogas

The aim of this laboratory-scale study was to investigate the long-term anaerobic fermentation of an extremely sour substrate, an energy crop, for continuous production of methane (CH₄) as a source of renewable energy. The sugar beet silage was used as the mono-substrate, which had a low pH of around 3.3–3.4, without the addition of manure. The mesophilic biogas digester was operated in a hydraulic retention time (HRT) range between 15 and 9.5 days, and an organic loading rate (OLR) range of between 6.33 and 10 g VS l⁻¹ d⁻¹. The highest specific gas production rate (spec. GPR) and CH₄ content were 0.67 l g VS⁻¹ d⁻¹ and 74%, respectively, obtained at an HRT of 9.5 days and OLR of 6.35 g VS l⁻¹ d⁻¹. The digester worked within the neutral pH range as well. Since this substrate lacked the availability of macro and micro nutrients, and the buffering capacity as well, external supplementation was definitely required to provide a stable and efficient operation, as provided using NH₄Cl and KHCO₃ in this case. The findings of this ongoing long-term fermentation of an extremely acidic biomass substrate without manure addition have reflected crucial information about how to appropriately maintain the operational and particularly the environmental parameters in an agricultural biogas plant.     

Production of methane by co-digestion of cassava pulp with various concentrations of pig manure

Cassava pulp is a major by-product produced in a cassava starch factory, containing 50–60% of starch (dry basis). Therefore, in this study we are considering its potential as a raw material substrate for the production of methane. To ensure sufficient amounts of nutrients for the anaerobic digestion process, the potential of co-digestion of cassava pulp (CP) with pig manure (PM) was further examined. The effect of the co-substrate mixture ratio was carried out in a semi-continuously fed stirred tank reactor (CSTR) operated under mesophilic condition (37 °C) and at a constant OLR of 3.5 kg VS m^?3 d^?1 and a HRT of 15 days. The results showed that co-digestion resulted in higher methane production and reduction of volatile solids (VS) but lower buffering capacity. Compared to the digestion of PM alone, the specific methane yield increased 41% higher when co-digested with CP in concentrations up to 60% of the incoming VS. This was probably due to an increase in available easily degradable carbohydrates as the CP ratio in feedstock increased. The highest methane yield and VS removal of 306 mL g^?1 VS_added and 61%, respectively, were achieved with good process stability (VFA:Alkalinity ratio < 0.1) when CP accounted for 60% of the feedstock VS. A further increase of CP of the feedstock led to a decrease in methane yield and solid reductions. This appeared to be caused by an extremely high C:N ratio of the feedstock resulting in a deficiency of ammonium nitrogen for microbial growth and buffering capacity.     

Low temperature anaerobic digestion of mixtures of llama,cow and sheep manure for improved methane production

Biogas production in anaerobic digestion in farm-scale units is typically performed under mesophilic conditions when used for producing domestic fuel and stabilizing animal waste for the use of digested manure as a fertilizer. Previous studies on the digestion of llama and cow manure have shown the feasibility of producing biogas under altiplano conditions (low pressure and low temperature) and of llama manure as a promising feedstock. The present study concerns the utilization of various mixtures of feedstocks from the Bolivian altiplano under low temperature conditions (18–25 °C). Laboratory scale experiments were performed on the digestion of mixtures of llama, sheep and cow manure in a semi-continuous process using ten 2-L stainless steel digesters to determine the effects of organic loading rate (OLR) and the feed composition. The semi-continuous operation of mixture of llama–cow–sheep manure proved to be a reliable system, which could be operated with good stability. The results suggest that in a system digesting a mixture of llama-cow-sheep manure at low temperature (18–25 °C) the maximum OLR value is between 4 and 6 kg VS m³ d^?1. The methane yields obtained in the mixture experiments were in the range 0.07–0.14 m³ kg^?1 VS added, with a methane concentration in the gas of between 47 and 55%.     

Enhancing biomethane production from flush dairy manure with turkey processing wastewater

The objective of this study was to assess the quantity and quality of biogas produced by co-digesting flushed dairy manure (FDM) and turkey processing wastewater (TPW). An attached growth digester with working volume of 15 L and a 3 L head space was operated at a 5 d hydraulic retention time using five feed mixes containing 100, 67, 50, 33, and 0% FDM by volume. The biogas yield ranged from 0.072 to 0.8 m³ [g VS^?1] and the methane content (quality) of the gas ranging from 56% to 70%. Both the quantity and quality of the biogas increased as the proportion of TPW in the feed increased. An energy balance for the digester based on a dairy farm with 150 animals, showed that augmenting FDM with TPW at 1:1 and 1:2 ratios, feeds C and D, respectively, produced biogas with net positive energy to all year round. The gas produced was enough to run a 50 kW generator to produce electricity for about 5.5 and 9 h for the 1:1 and 1:2 feed mixes. However, the economics were not favorable if the benefits of the digester are based only on the value electricity to be produced. Either, other possible revenues such as carbon credit, renewable energy credits, green tags for electricity, putting a value to the environmental benefits of AD should be considered or subsidies from grants or other incentives programs to make the system economically viable.     

Biomass estimates,characteristics, biochemical methane potential,kinetics and energy flow from Jatropha curcus on dry lands

In this study, we examined the production of Jatropha curcus plants on 1 ha of rain fed dry lands. All of the plant components that would result from plantation tending, fruit harvesting and processing were sampled for their yield and chemical composition, and then subjected to the biochemical methane potential (BMP) assay. The component parts exhibited significant variation in BMP which was reflected in their ultimate methane yield which ranged from 0.08 to 0.97 L g^?1 VS added, and their first order kinetics which ranged from 0.07 to 0.14 d^?1. We examined two integrated utilization schemes: the first which converted plant prunings, fruit hulls and de-oiled seed cake to methane, and the oil to fatty acid methyl-ester (FAME); the second was to convert the seeds, plant prunings and fruit hulls entirely to methane. The basis for the plantation was, a density of 4444 plant ha^?1 (1.5 m × 1.5 m spacing), with a seed yield of 0.911 kg TS plant^?1 (1 kg total weight) with an oil content of 35% providing an annual oil yield of 1.42 t y^?1. The corresponding yields of pruned leaves, fruit hulls and de-oiled cake are 0.97, 1.0, and 2.35 t VS ha y^?1, respectively. An integrated scheme of producing biogas by means of anaerobic digestion of the latter components and oil for biodiesel would produce 90 GJ ha^?1 y^?1 in total with the oil being 54 GJ. The alternative biogas only option which would convert the seed oil into methane instead of biodiesel would produce 97 GJ ha^?1 y^?1.     

Mathematical modeling for the prediction of biogas generation characteristics of an anaerobic digester based on food/vegetable residues

An anaerobic digester of 10 L capacity has been operated in batch mode at an optimum temperature of 40 °C and at a pH of 6.8 using vegetable/food residues as the feed material. The effect of slurry concentration and that of the concentration of carbohydrate, protein and fat in the slurry on the biogas production rate and methane concentration in the biogas have been studied. The slurry concentration has been varied in the range of 72.0–700 kg m⁻³. At a slurry concentration of 67.7 kg m⁻³ the effect of carbohydrate concentration has been studied by varying the ratios of carbohydrate, protein and fat in the range of 6.9:4.3:1–12.1:4.3:1 by using a sole carbohydrate source, namely sucrose. The effect of protein concentration has been studied by varying the ratios of carbohydrate, protein and fat in the range of 5.6:7.0:1–5.6:13.0:1 by using a sole protein source, namely papain and that of fat concentration has been studied by varying the ratios of carbohydrate, protein and fat in the range of 7.2:10:1.6–7.2:10:5 by using a fat source, namely vanaspati. A deterministic mathematical model using differential system equations have been developed and it is capable of predicting the behaviour of the digester satisfactorily.     

Effects of volatile fatty acid concentrations on methane yield and methanogenic bacteria

Volatile fatty acids (VFAs) are important mid-products in the production of methane, and their concentrations affect the efficiency of fermentation. However, their effects on methane yield and methanogenic bacteria growth have been less extensively studied. To address these effects, acetic acid, propionic acid, butyric acid and ethanol were used as substrates and an L₉(3⁴) orthogonal table was adopted to design anaerobic digestion tests. When the highest concentrations of ethanol, acetic acid and butyric acid were 2400, 2400 and 1800 mg L^?1, respectively, there was no significant inhibition of the activity of methanogenic bacteria. However, when the propionic acid concentration was increased to 900 mg L^?1, significant inhibition appeared, the bacteria concentration decreased from 6 × 10⁷ to 0.6–1 × 10⁷ ml^?1 and their activity would not reconvert. These effects resulted in the accumulation of ethanol and VFAs, and the total methane yield consequently became very low (<321 ml). The original propionic acid concentration had a significant inhibitory effect on methanogenic bacteria growth (P < 0.01). An optimization analysis showed that ethanol, acetic acid, propionic acid and butyric acid at concentrations of 1600, 1600, 300 and 1800 mg L^?1, respectively, led to the maximum accumulative methane yield of 1620 ml and the maximum methanogenic bacteria concentration of 7.3 × 10⁸ ml^?1.     

The impact of increasing organic loading in two phase digestion of food waste

This paper examines the impact of increasing organic loading in a two phase anaerobic digestion system treating commercial food waste. The first phase is a series of sequentially fed leach bed reactors (LBRs). The second phase is an upflow anaerobic sludge bed (UASB). Leachate from the leach beds, form the influent to the UASB. Effluent from the UASB is re-circulated over the leach beds. Flow rates corresponded to 1 volume of leachate per effective LBR volume per day. The theoretical organic loading rate (OLR) of the UASB is based on the conversion of volatile solids (VS) in the LBR to chemical oxygen demand (COD). The experiment was set up such that the theoretical OLR would rise from 7.1 to 8.8 to 11.8 kg COD m⁻³ day⁻¹.The system operated effectively at the lowest organic loading rate producing 384 L CH₄ kg VS⁻¹ which corresponded to 72% of the value obtained in a BMP test. COD conversion efficiency was recorded at 75%. The accumulation of COD over the life of the experiment led to a situation whereby the volumetric OLR (product of COD concentration in the leachate by the flow rate) was over twice the theoretical OLR at the end of the experiment (24.3 kg VS m⁻³ day⁻¹ versus 11.8 kg VS m⁻³ day⁻¹). At the highest loading rate total ammonia nitrogen (TAN) reached levels of 4500 mg L⁻¹ with pH levels of 8.15. This resulted in significant reduction of methane production.     

Kinetic study of thermophilic anaerobic digestion of solid wastes from potato processing

Anaerobic treatment of solid wastes from potato processing was studied in completely stirred tank reactors (CSTR) at 55 °C. Special attention was paid to the effect of increased organic loading rate (OLR) on the biogas yield in long-term experiments. Both biogas yield and CH₄ in the biogas decreased with the increase in OLR. For OLR in the range of 0.8 gl⁻¹ d⁻¹–3.4 gl⁻¹ d⁻¹, biogas yield and CH₄ obtained were 0.85 l g⁻¹–0.65 l g⁻¹ and 58%–50%, respectively. Biogas yield y as a function of maximum biogas yield y_m, reaction rate constant k and HRT are described on the basis of a mass balance in a CSTR and a first order kinetic. The value of y_m can be obtained from curve fitting or a simple batch test and k results from plotting y/(y_m−y) against 1/OLR from long-term experiments. In the present study values for y_m and k were obtained as 0.88 l g⁻¹ and 0.089 d⁻¹, respectively. The simple model equations can apply for dimensioning completely stirred tank reactors (CSTR) digesting organic wastes from food processing industries, animal waste slurries or biogas crops.     

Anaerobic digestion of by-products of sugar beet and starch potato processing

Anaerobic digestion (AD) is a promising option for the environmentally friendly recycling of agricultural by-products. However, overloading of the digester with sugar, starch or protein might cause inhibition of the anaerobic processes. The aim of the present project was to investigate the AD of sugar beet, starch potato by-products and effect of pre-treatment by steam on methane yield of potatoes pulp. The investigated by-products have been: sugar beet pulp silage (SBP), sugar beet tail silage (SBT), potato pulp (PP), potato peel pulp (PPP) and potato fruit water (PFW). All by-products were digested in 1 l eudiometer-batch digesters at 37.5 °C during 28–38 days. The specific methane yields of SBP and SBT were 430 and 481 l_N kg^?1 volatile solids (VS), respectively. The specific methane yields of PP, PPP and PFW were 332, 377 and 323 l_N (kg VS)^?1. A steam pre-treatment significantly increased the specific methane yield of PP up to 373 l_N (kg VS)^?1.     

Characterization of Spartina alterniflora as feedstock for anaerobic digestion

Smooth cordgrass (Spartina alterniflora), a saltmarsh plant with high production, was characterized for its potential for use as feedstock for anaerobic digestion processes. The anaerobic digestibility and biogas yield of S. alterniflora were evaluated by anaerobic batch digestion experiments performed at 35 ± 1 °C at initial volatile solids (VS) of 6%. The nutrient content analysis indicated that S. alterniflora contained the required nutrition for anaerobic microorganisms, but its high C/N of 58.8, high K and Na contents of 8.1, 22.7 g kg^?1, respectively, may be disadvantageous to its anaerobic digestion. The cumulative biogas yield was determined to be 358 L kg^?1 VS and the biodegradation efficiency was 45% after 60 days of digestion. The methane content of biogas increased from 53% on day 3 to around 62% after 13 days of digestion. The changes of volatile fatty acids (VFAs) indicated that the acidification of S. alterniflora was propionate-type fermentation with proportion of acetate and propionate ranging from 54.8% to 98.4%, and the hydrolysis of lignocellulose was the rate-limiting step for its anaerobic digestion. The analysis of cations suggested that K⁺ and Mg²⁺, with the maximum concentration of 1.35 and 0.43 g L^?1 in fermentation liquor, respectively, could be inhibitory to the anaerobic digestion of S. alterniflora. It is concluded that S. alterniflora can be transformed into clean energy by anaerobic digestion and the high contents of K, Na, Ca and Mg may be the inhibitory factors when S. alterniflora is digested by continuous or semi-continuous anaerobic process.     

Implementation of an UASB anaerobic digester at bagasse-based pulp and paper industry

Upflow anaerobic sludge blanket (UASB) reactor was installed to replace the conventional anaerobic lagoon treating bagasse wash wastewater from agro-based pulp and paper mill, to generate bio-energy and to reduce greenhouse gas emissions. The plant was designed to treat 12 ML d⁻¹ of wastewater having two 5 ML capacity reactors, 5.75 kg COD m⁻³ d⁻¹ organic loading rate and 20 h hydraulic retention time. In the plant 80–85% COD reduction was achieved with biogas production factor of 520 L kg⁻¹ COD reduced. In 11 months 4.4 million m³ of biogas was generated from bagasse wash wastewater utilizing UASB process. Utilization of the biogas in the Lime Kiln saved 2.14 ML of furnace oil in 9 months. Besides significant economic benefits, furnace oil saving reduced 6.4 Gg CO₂ emission from fossil fuel and conversion of the anaerobic lagoon into anaerobic reactor reduced 2.1 Gg methane emission which is equal to 43.8 Gg of CO₂.     

Solar greenhouse assisted biogas plant in hilly region – A field study

The present study was undertaken with the objective of evaluating plastic as an alternative material for biogas plant on a par with conventional brick material. The field study was carried out for one year (October, 2005–September, 2006) in a small hamlet at Nilgiris incorporating solar energy to study its influence on biogas production. During summer (April–June) the temperature reaches to the maximum of 21–25 °C and the minimum of 10–12 °C. During winter (October–December), the temperature available is maximum of 16–21 °C and minimum of 2 °C. The solar insolation in the study area ranges from 250 to 600 W/m². This study involves the control conventional Deenabandhu model (Indian standard model prevailing in most part of India made of masonry structure only) and the experimental plastic tank with greenhouse canopy of similar capacity. Our previous work [Vinoth Kumar, K., Kasturi Bai, R., 2005. Plastic biodigesters – a systematic study. Energy for Sustainable Development 9 (4), 40–49] on lab scale digester made from plastic material was compared over other materials and the results gave us much confidence to carry out further study on pilot scale. In continuation, a semi-continuous study was conducted for one year with the retention time of 55 days. The gas generated from the biogas plants was utilized for cooking (burner) and lighting (lamp) purposes. The yearly average slurry temperatures recorded during the study period was 26.3 and 22.4 °C in experimental and control biogas plants against ambient temperature of 17.0 °C. The yearly average greenhouse chamber temperature recorded was 29.1 °C in the experimental biogas plant. The yearly average gas yield from the experimental and control biogas plants were 39.1 and 34.6 l kg^?1 day^?1 respectively. Gas productions in the winter season registered lower than other months. It can be concluded that the solar greenhouse assisted plastic biogas plant can be efficiently adopted with minor modifications in hilly regions since the temperature profile plays a major role in biogas production.     

Anaerobic digestion of slaughterhouse by-products

Anaerobic digestion of animal by-products was investigated in batch and semi-continuously fed, reactor experiments at 55 °C and for some experiments also at 37 °C. Separate or mixed by-products from pigs were tested. The methane potential measured by batch assays for meat- and bone flour, fat, blood, hair, meat, ribs, raw waste were: 225, 497, 487, 561, 582, 575, 359, 619 dm³ kg^?1 respectively, corresponding to 50–100% of the calculated theoretical methane potential. Dilution of the by-products had a positive effect on the specific methane yield with the highest dilutions giving the best results. High concentrations of long-chain fatty acids and ammonia in the by-products were found to inhibit the biogas process at concentrations higher than 5 g lipids dm^?3 and 7 g N dm^?3 respectively. Pretreatment (pasteurization: 70 °C, sterilization: 133 °C, and alkali hydrolysis (NaOH) had no effect on achieved methane yields. Mesophilic digestion was more stable than thermophilic digestion, and higher methane yield was noticed at high waste concentrations. The lower yield at thermophilic temperature and high waste concentration was due to ammonia inhibition. Co-digestion of 5% pork by-products mixed with pig manure at 37 °C showed 40% higher methane production compared to digestion of manure alone.     

Enhanced biohydrogen production from cornstalk wastes with acidification pretreatment by mixed anaerobic cultures

Biohydrogen production from the cornstalk wastes with acidification pretreatment was reported in this paper. Batch tests were carried out to analyze influences of several environmental factors on biohydrogen production from cornstalk wastes. Two predominant bacterial morphologies, namely spore-forming rod shape bacteria and micrococcus were screened, purified, and identified after enriched from a hydrogen-producing fermentor with cow dung composts. The maximum cumulative H₂ yield of 149.69 ml H₂ g⁻¹ TVS was obtained at initial pH 7.0 and substrate concentration 15 g l⁻¹, the value is about 46-fold as compared with that of raw cornstalk wastes. The maximum hydrogen production rate was 7.6 ml H2 h⁻¹. The hydrogen concentration in biogas was 45–56% (v/v) and there was no significant methane observed in the biogas throughout this study. In addition, biodegradation characteristics of the substrate by microorganisms were also discussed. During the conversion of cornstalk wastes into hydrogen, the acetate, propionate, butyrate, and the ethanol were main by-products in the metabolism of hydrogen fermentation. The test results showed that the acidification pretreatment of the substrate plays a crucial role in conversion of the cornstalk wastes into biohydrogen gas by the cow dung composts generating hydrogen.     

Photofermentative hydrogen production using purple non-sulfur bacteria Rhodobacter sphaeroides O.U.001 in an annular photobioreactor: A case study

For meeting the increasing demand of energy, biohydrogen production is to be considered in higher yield. Biohydrogen can be produced both by dark and photofermentative process. In this study, the photofermentative pathway is followed by using dl malic acid (IUPAC name: 2-hydroxybutanedioic acid, molecular weight: 134.08744 g mol^?1, molecular formula: C₄H₆O₅) as carbon source. Pure strain of purple non-sulfur (PNS) bacteria: Rhodobacter sphaeroides strain O.U.001 was studied to produce biohydrogen using the photobioreactor. The photobioreactor was constructed aiming the uniform light distribution. The objective of this study was to investigate the performance of 1 L annular photobioreactor operating in indoor conditions. The highest rate of hydrogen production was obtained at 92 h. In the designed photobioreactor, using Rhodobacter sphaeroides strain O.U.001 (initial dl malic acid concentration of 2.01 g L^?1) at an initial pH of 6.8 ± 0.2, temperature 32 ± 2 °C, inoculum volume 10% (v/v), inoculum age of 48 h, 250 rpm (rotation per minute) stirring and light intensity of 15 ± 1.1 W m^?2, the average H₂ production rate was about 6.5 ± 0.1 mL H₂ h^?1 L^?1 media and yield 4.5 ± 0.05 mol of H₂ mol^?1 of dl malic acid. Luedeking–Piret model was applied for the data fitting to determine the relationship between the cell growth and photofermentative hydrogen production. The photofermentative hydrogen production by this PNS bacterium was found to be microbial mixed growth associated function.     

Productive use of bioenergy for rural household in ecological fragile area,Panam County,Tibet in China: The case of the residential biogas model

Bioenergy is the major domestic energy for rural households in developing countries due to its cheap or easy-getting characteristics. Productive use of bioenergy is an important strategy for rural households to improve not only their income, but also their health, living environment and so on. In Tibet of China, which is rich in cattle dung and firewood as the major energy sources for rural households, the efficiency of energy utilization is just about 10%. In order to improve energy utilization efficiency and the living conditions for rural residents, the Tibet Autonomous Region government introduced residential biogas model (RBM) to local households, which was a comprehensive utilization system of energy integrated with residential biogas digester, vegetable greenhouse and livestock shed. This paper aims to show the productive use of the bioenergy by the RBM, which could be depicted as the feasibility and the benefits on economic, eco-environmental and social aspects of biogas utilization, based on household questionnaires in Panam County. In RBM, biogas digester works as the biomass material supplement loop to transform originally biomass flow from single-direction to recycling-direction. The results indicate that the output of unit biogas digester could replace 1.44 t of firewood, 1.65 t of agricultural residues and 1.75 t of cattle dung, respectively. The net incremental benefit of RBM could reach 5550.72 Yuan in 15 years. The reduced amount of CO₂ emission when substituted by biogas in other agricultural areas and the areas of semi-agricultural and semi-husbandry in Tibet could be (76.66–79.89) × 10⁴ t/year and the capability for nitrogen storage could achieve (0.39–0.99) × 10⁴ t/year. The amount of cattle dung replaced by biogas could reach 78.29 × 10⁴ t/year; this means that the saved cattle dung, 3.51 t/hm², could be reallocated back to cultivated land to improve the soil fertility and to keep the balance of nutrient elements in cultivated land. Biogas utilization reduces the labor opportunity costs of women compared to use of traditional bioenergy sources. It could be concluded that the productive use of bioenergy through RBM in this area has its capability to release the current pressures on biomass sources by adjusting patterns of rural energy consumption, and to improve the conditions of health, environment, economy and energy conservation.     

Optimization of conditions for the extraction of phorbol esters from Jatropha oil

The production of Jatropha curcas seeds as a biodiesel feedstock is expected to reach 160 Mt by 2017. The present study aims at extracting phorbol esters (PEs) as a co-product from Jatropha oil before processing it to biodiesel. The conditions were optimized for extraction of PEs in organic solvents by using a magnetic stirrer and an Ultra turrax. The extent of reduction in PEs was >99.4% in methanol using any of the stirring tools. However, the extraction using Ultra turrax affected considerably the colour of the remaining oil. Therefore, further solvent:oil ratio, time and temperature were optimized using a magnetic stirrer to get PE rich fraction-I (48.4 mg PEs g^?1) and virtually PE-free oil. PEs were 14 fold higher in this fraction than the control oil. PEs, extracted in methanol from the untreated Jatropha oil, at 1 mg L^?1 produced 100% mortality in snails (Physa fontinalis). The methanol extract from virtually PE-free oil when concentrated 20 and 25 time the untreated Jatropha oil (equivalent of 20 mg L^?1 and 25 mg L^?1 PEs in the control oil) was nontoxic to snails. PE rich fraction-I, obtained as a co-product, can be used in agricultural, medicinal and pharmaceutical applications and the remaining oil can be used for biodiesel preparation. The remaining oil will be friendly to the environment and workers.