Methane production/emission in storages for animal manure

Results of extended research on laboratory scale have shown that relatively high gas productions can occur at digestion of animal manure in fed-batch (=Storage)- systems at ambient temperatures. High gas productions are also reported at on-farm storage of animal manure.In order to predict the gas production during the storage of animal manure at different conditions, a model is developed based on first order kinetics for the hydrolysis and on Monod kinetics for methanogenesis. Results of anaerobic digestion of manure in both CSTR- and fed-batch systems have been used for the estimation of constants. The model predicts that, when continuously 15% of the storage is filled, no gas production is produced, at a temperature of 15°C and a storage capacity 100 days and at a temperature of 10°C and a storage capacity 150 days. At higher temperatures and longer storage capacities methane gas is always produced.     

Greenhouse gas emissions from animal houses and manure stores

In contrast to ammonia few data about the emissions of CH₄, N₂O and CO₂ from animal houses are yet available. To be reliable, such data should derive from investigations meeting the following minimum requirements: (1) continuous measurement of ventilation rates and gas concentrations; (2) long-term experiments, to cover diurnal and seasonal effects; (3) use of extremely exact measuring equipment. A literature review has shown that reliable data about CH₄ emissions are basically only available for cattle housing systems. Data about N₂O emissions from animal houses are lacking, because of the difficulties in measuring very low N₂O concentrations. However, the results of existing investigations are not comparable and most of them do not meet the minimum requirements mentioned above. Our own experiments have been carried out for dairy cows in loose housing with natural ventilation. The amount of CH₄ originating from cows' digestion is about 223 g per livestock unit (1 LU = 500 kg live-weight) per day and varies between 200 and 250 g per LU per day. It mainly depends on the feed intake, which is positively related to animal size, growth rate and production. There is practically no influence of outside conditions on the emission rate. N₂O was emitted at about 1.6 g per LU per day. This revised version was published online in August 2006 with corrections to the Cover Date.     

Catalytic decomposition of methane and methane/CO2 mixtures to produce synthesis gas and nanostructured carbonaceous material

Methane and CO₂ are the main components of biogas; therefore its direct conversion into a higher added value gas as syn-gas (mixture of CO and H₂) is a very interesting alternative for the valorisation of such renewable resource. In this work, firstly a thermodynamic analysis of the decomposition of CH₄:CO₂ mixtures at different temperatures and CH₄:CO₂ ratios simulating the biogas composition, has been carried out. Secondly, the decomposition of a mixture with a molar ratio of 1:1 has been studied in a fixed-bed reactor by using a Ni/Al₂O₃ based catalyst, at the temperature range in which according to the thermodynamic study, carbon formation is favoured. Results obtained have been compared to those of methane decomposition carried out under the same experimental conditions. Co-feeding of CO₂ and CH₄ avoids catalyst deactivation substantially, allowing to obtain a syn-gas with H₂:CO ratio close to 1. Moreover, the carbon obtained from mixtures of CH₄ and CO₂ is deposited as fishbone carbon nanofibres at 600 °C and ribbon carbon nanofibers at 700 °C, both being materials with high added value which can be used in multiple applications.     

厌氧/好氧/缺氧模式的SBR处理生活污水

采用厌氧/好氧/缺氧SBR处理生活污水,研究了泥龄、温度、曝气量对处理效果的影响,确定了特定水质条件下的最佳运行工况:污泥龄25 d,温度25℃,曝气量64 L/h。在此工况下,该系统对COD、NH4+-N、TN、TP的去除率较高,分别为92.9%、90.8%、82.9%、97.8%,出水中的COD、NH4+-N、TN、TP均可以达到《城镇污水处理厂污染物排放标准》的一级A标准。通过连续培养运行,系统中存在反硝化除磷现象。     

去除牛粪厌氧生物转化过程中的H2S

The main aim of this research was the experimental study at lab scale to check the absorption technolOgytor the in situ removal of H2S from biogas during anaerobic digestion process.The reagent FeCll was used to check the removal efficiency of H,S produced from dairy manure during anaerobic bioconversion process.The expenments werc conducted under mesophilic conditions.Thc composition of biogas was analyzed by gas chromatography analyzer equipped with flame photometer and thermal conductivity detectors.Experimental results under the same conditions demonstrate that high concentration of HES in the form of FeS can be removed totally from the biogas using FeCl3 dosing with in anaerobic batch digester.     

厌氧/好氧/缺氧模式运行SBR工艺的影响因素

采用厌氧/好氧/缺氧模式运行的SBR工艺处理人工配水模拟生活污水,分析了泥龄、温度、曝气量对反硝化除磷过程的影响。结果表明:温度为30℃、SRT为25 d、曝气量在64 L/h时,发生明显的反硝化除磷现象,缺氧段吸磷速率可达到0.054 0 mg/(g·h)。     

Simulation and performance evaluation of the anoxic/anaerobic/aerobic process for biological nutrient removal

As a modified configuration of the conventional anaerobic/anoxic/aerobic (AAO) process, a novel anoxic/anaerobic/aerobic (Reversed AAO, RAAO) process has been extensively applied in domestic wastewater treatment plants (WWTP). In this study, the Activated Sludge Model No. 2d (ASM2d) and a secondary clarifier model were calibrated and applied to simulate a pilot-scale RAAO test and evaluate the operational performance of the RAAO process. For calibration of the biological model ASM2d, only four kinetic parameters were adjusted to accurately simulate in-process variations of ammonium, nitrate and phosphate. Simulation results by the calibrated model demonstrated that phosphorus accumulating organisms (PAO) in the RAAO process (0.243 gP·(gCOD)⁻¹) contains less poly-phosphate than the AAO process (0.266 gP·(gCOD)⁻¹). With the increasing mixed liquor recirculation ratio in the RAAO process, the fraction of heterotrophic biomass and autotrophic biomass both increased, whereas the PAO decreased owing to adverse effects of electron acceptors on phosphorus release and poly-hydroxy-alkanoates synthesis.     

Optimisation of methane production and refuse decomposition in landfills by temperature control

The major contributions to the thermal regime of an anaerobic domestic refuse landfill are identified and quantified. These are heat of reaction, specific heat of water/refuse mixtures, heats of neutralisation, heat losses to air and soil, solar radiation and aerobic metabolism. It is shown that even in temperate climates, landfill temperatures can rise to 45°C and above under anaerobic conditions with the concomitant reduction in fatty acid concentrations in leachate. This has been confirmed with field observations. Management requirements for establishing and maintaining temperatures of about 45°C in an anaerobic landfill are identified. Principally these involve allowing water into the site from the bottom and maintaining an insulating layer of refuse of about 4 m above the water-table in the landfill. The advantages of a bioreactive landfill are briefly discussed.     

The influence of ammonium and methods for removal during the anaerobic treatment of poultry manure

The addition of exogenous NH₄Cl to poultry manure and synthetic medium was used to study the effect of ammonia-nitrogen on the activity and composition of a methanogenic consortium. Results indicated that the production of biogas and methane was not affected by the variation in NH₄Cl concentration within the range 2–10 g dm⁻³ (0·5–2·6 g N-NH₄ dm⁻³). At higher values of ammonium (10–30 g dm⁻³ or 2–8 g N-NH₄ dm⁻³) a significant decline in both parameters (by 50–60% for biogas and 80–90% for methane) was observed. A significant decrease in the numbers of bacteria of all physiological groups (especially proteolytic and methanogenic) was observed when more than 30 g NH₄Cl dm⁻³ (7·8 g N-NH₄ dm⁻³) was added to the fermentation medium. The addition of 10% (w/v) of powdered phosphorite ore enhanced the production of biogas and methane at NH₄Cl concentrations up to 30 g dm⁻³, and also changed the composition of the methanogenic consortium. A partial recovery in the numbers of proteolytic and methanogenic bacteria coupled with the decrease in the density of sulphate-reducers was observed. High concentrations (more than 50 g dm⁻³) of NH₄Cl seemed to cause irreversible inhibition of methanogenesis which could not be eliminated by the addition of phosphorites. ©1997 SCI     

Hydrogen production by decomposition of ethane-containing methane over carbon black catalysts

Mixtures of methane and small amounts of ethane were decomposed in the presence of carbon black (CB) catalysts at 1,073–1,223 K for hydrogen production. Although most of the added ethane was first decomposed to ethylene and hydrogen predominantly by non-catalytic reaction, subsequent decomposition of ethylene was effectively facilitated by the CB catalysts. Because some methane was produced from ethane, the net methane conversion decreased as the added ethane increased. The rate of hydrogen production from methane was decreased by the added ethane. A reason for this is that adsorption of methane on the active sites is inhibited by more easily adsorbing ethylene. In spite of this, the hydrogen yield increased with an increase of the added ethane because the contribution of ethane and ethylene decomposition to the hydrogen production was dominant over methane decomposition. A higher hydrogen yield was obtained in the presence of a higher-surface-area CB catalyst.     

Hydrogen production by the thermocatalytic decomposition of methane in a fluidized bed reactor

CO₂-free production of hydrogen via thermocatalytic decomposition of methane in a fluidized bed reactor (FBR) was studied. The technical approach is based on a single-step decomposition of methane over carbon catalyst in air/water vapor free environment. The factors affecting Fe catalyst (Iron powder activity in methane decomposition reactions were examined. Carbon species produced in the process were characterized by SEM methods. The fluidization quality in a gas-fluidized bed of Fe (Iron powder) and Fe/Al₂O₃ catalyst was determined by the analysis of pressure fluctuation properties, and the results were confirmed with characteristics of methane decomposition. The effect of parameters on the H₂ yield was examined. Fibrous carbon formed over Fe catalyst surface. The hydrogen yield increased with increasing reactor temperature, and decreased with increasing superficial velocity of methane inlet stream. The conversion rate of methane is maintained by attrition of produced carbon on Fe catalyst surface in a FBR.     

Formation of filamentous carbon during methane decomposition over Co-MgO catalysts

The carbon formation during methane decomposition was investigated at 900 °C over the 48 wt% Co-MgO catalysts as a function of the calcination temperature T_c used in their preparation. Examination of the carbonaceous deposits by transmission electron microscopy revealed three kinds of structures: shapeless tangles, shell-like materials, and carbon filaments. In another set of experiments, the structural characteristics of the calcined catalysts were investigated using temperature-programmed reduction (TPR) and X-ray diffraction (XRD). Co₃O₄, Co₂MgO₄, and (Co, Mg)O (solid solution of CoO and MgO) were identified for T_c≤700 °C, Co₃O₄ and (Co, Mg)O for T_c=800 °C and only (Co, Mg)O for T_c=900 °C. It was found that the metal particles originated from the reduction of the solid solution favored the formation of filamentous carbon. A possible explanation is proposed.     

Hydrogen production during the anaerobic acidogenic conversion of glucose

Experiments on hydrogen production using chemostat‐type anaerobic digesters were conducted. The results indicate that the anaerobic acidogenic conversion of glucose can produce hydrogen. The hydrogenic activity of acclimated anaerobic sewage sludge is high at a short solids retention time (SRT) and low pH. At pH 5.7, SRT 0.25 days and an organic loading rate of 416 mmol‐glucose dm⁻³ day⁻¹, each mole of glucose in the mesophilic acidogenic reactor can produce 1.7 mol of hydrogen; each gram of biomass produces 0.456 mole of hydrogen per day. Moreover, the hydrogen productivity of the sludge is comparable to that of an enrichment culture. © 1999 Society of Chemical Industry     

Greenhouse gas emissions during co-composting of cattle mortalities with manure

Following outbreaks of bovine spongiform encephalopathy (BSE), fewer cattle mortalities are being rendered. Composting may be a viable on-farm alternative for disposal of cattle carcasses. A study was conducted to assess feasibility and greenhouse gas (GHG) emissions during co-composting of cattle mortalities and manure. Using a tractor-mounted front-end loader, windrows were constructed containing manure + straw (control; CK) or manure + straw + cattle mortalities (cattle mortality; CM). The composting process lasted 310 d. The windrows were turned twice, at days 93 and 211, using either a tractor-mounted front-end loader or a specialized shredder bucket. Maximum windrow temperatures were >50 °C for 36 out of 92 d (before first turning) and 142 out of 208 d (after first turning) for the CM treatment and cattle mortalities were completely decomposed except for a few large bones. The cumulative CO₂ and CH₄ emissions were significantly affected by the mortality treatment, but not by the turning technology or their interactions. Significantly higher CO₂ (53.6 g d⁻¹ m⁻²) and CH₄ (2.204 g d⁻¹m⁻²) emissions were observed during the co-composting of cattle mortalities than manure composted with straw (23.0 and 0.742 g d⁻¹m⁻² for CO₂ and CH₄, respectively). Similarly, N₂O emissions were higher with mortalities than without and, for the CM treatment only, higher with shredder bucket than front-end loader turning. In the final compost, CM had higher TN and NH₄⁺-N contents than CK while TC and the C/N ratio were higher with compost turned with the front-end loader than with the shredder bucket. In conclusion, composting was an effective means of disposing of cattle mortalities, but did increase GHG emissions and the N content in the final compost. It is not known if GHG emissions are different than those that would be released from natural decomposition of carcasses. The higher N content in compost containing mortalities would increase its agronomic value.     

残留兽药添加剂磺胺喹噁啉钠和3,5-二硝基苯甲酰胺对畜禽粪便中温厌氧消化的影响

为研究饲料添加剂磺胺喹噁啉钠和3,5-二硝基苯甲酰胺对畜禽粪便中温厌氧消化的影响,以模拟畜禽粪便为对象,在中温(35℃)厌氧发酵条件下,考察了磺胺喹噁啉钠和3,5-二硝基苯甲酰胺的添加量对VFAs的生成、累积产气量和累积甲烷产量的影响。试验结果表明:在厌氧发酵过程中,产生的VFAs以乙酸和正丁酸为主,产甲烷菌对VFAs的利用顺序为乙酸正丁酸丙酸。2种兽药添加剂均抑制VFAs的生成,但添加剂浓度的增加对抑制效果影响不明显。2种兽药添加剂对产甲烷均没有抑制作用,反而具有一定的促进作用。含有残留磺胺喹噁啉钠和3,5-二硝基苯甲酰胺的养殖废水和畜禽粪便可以进行厌氧消化处理。     

Hydrogen production by methane decomposition: Origin of the catalytic activity of carbon materials

A wide variety of carbon materials (ordered mesoporous carbons, carbon blacks, activated carbon, carbon nanotubes, coke and graphite) have been investigated as catalysts for hydrogen production by methane decomposition, with the aims of identifying the carbon properties which control in a greater extension the catalytic activity and determine the nature of the active sites involved in the reaction.The catalytic activity of the different carbon materials was determined and compared using temperature-programmed experiments in a thermobalance. The initial activity was followed through the threshold temperature, defined as the temperature at which hydrogen production starts being detected, whereas the average reaction rate was also calculated and compared. The lowest threshold temperature was observed with ordered mesoporous carbons (CMK materials), followed by activated carbon and carbon blacks. On the other hand, at long reaction times activated carbon was quickly deactivated yielding a relatively low average reaction rate. The deactivation process seems to be greatly linked to the presence of micropores while the long-term activity is retained in those materials with ordered mesoporosity (CMKs) or formed by nanoparticles (carbon blacks), which make them more resistant to deactivation by the formation of carbonaceous deposits.Whereas no clear dependence is observed between the threshold temperature and the surface area neither with the presence of polar groups in the carbon catalysts, characterization of these materials by XPS shows that a direct relationship exists with the amount of defects present on the graphene layers. This fact strongly supports that these defects are the main active sites for methane decomposition over carbon catalysts.     

Stability of acetylene/methane and acetylene/hydrogen/methane gas mixtures at elevated temperatures and pressures

Hydrogen-enriched natural gas (HENG) containing a mixture of acetylene, hydrogen, and methane is produced from natural gas feedstock in our plasma dissociation process. Storage of this HENG fuel at pressures up to 4000 psig is required for rapid vehicle refueling. Little information on the stability of acetylene mixtures at elevated pressures is presently available; therefore we have performed stability testing on gas mixtures that simulate our HENG fuel. This report describes the stability testing of binary gas mixtures of acetylene and methane containing up to 10%(v) acetylene, and a ternary gas mixture of 4%(v) acetylene, 20%(v) hydrogen, and 76%(v) methane, at pressures up to 3600 psig and temperatures up to 200 °C. The mixtures tested were found to be stable to rapid spontaneous decomposition at all test conditions; however, some degree of hydrogenation of acetylene to ethylene may have occurred in an intermediate mixture of acetylene and hydrogen while preparing the highest pressure ternary test mixture.     

Catalytic characteristics of specialty carbon blacks in decomposition of methane for hydrogen production

Catalytic characteristics of specialty (color and conductive) carbon blacks (CBs) for methane decomposition were investigated and compared with those of rubber blacks. The catalytic characteristics of the color blacks were more similar to those of the rubber blacks, in such that both blacks exhibited very stable activity, a positive correlation of the activity with increasing specific surface area, and higher activation energies. However, the conductive blacks showed quasi-stable behavior, leveling-off of the activity at a somewhat higher value despite their specific surface areas being several times higher than the most active color black, and significantly lower activation energies. These differences were attributed to their morphology differences: the color and rubber blacks were nonporous, whereas the conductive blacks were highly porous. Particularly, the conductive blacks had many dented corners at the pore wall with a highly active armchair structure, resulting in the lower activation energies. Meanwhile, the reaction orders over all the specialty and rubber blacks lay between ca. 0.7 and 1, but no obvious trend in the reaction order was discernible with respect to the surface area or type of CBs.     

Hydrogen production by catalytic decomposition of methane over activated carbons: Deactivation study

The amount of deposited carbon on activated carbons was adjusted by varying the space time and the time on stream. Carbon nuclei formation appeared to occur initially but was terminated soon and then the carbon crystallite growth became dominant. The methane decomposition rate over activated carbons had a nearly linear relationship with the amount of carbon deposited. This suggests that the carbon deposition occurs uniformly and the activity decreases due to pore blocking, resulting in loss of accessibility to the active sites. The rate was also nearly proportional to the surface area for the same kind of activated carbon, which is contrasted with the previous finding that no discernible trend was observed between the initial activity and the surface area among different kinds of the activated carbons.