Showing papers on "Biogas published in 1993"

Methane fermentation of energy crops: maximum conversion kinetics and in situ biogas purification.

Abstract: A seven-year study addressed both the limitations on the rate and efficiency of biomass conversion, and the enrichment of biogas methane content. Energy crops examined included sorghum ( Sorghum bicolor ), napiergrass ( Pennisetum purpureum ), corn ( Zea mays ), and a sorghum/α-cellulose mix. High solids digestion work (25–30% effluent total solids (TS)) showed the need to address ammonia toxicity and trace nutrient limitations. Trace nutrient supplementation and control of the feedstock C/N ratio enabled stable operation of digesters at volatile solids (VS) loading rates up to 24 grams per kilogram reactor wet mass per day (gVS kg −1 day −1 ), with mean methane production rates of 7.5 L kg −1 day −1 . Acid-extractable metal concentrations were used as an indicator of bioavailable metals. Initial work with low solids digestion (8–10% TS) resulted in efficient VS conversion but low methane production rates. Subsequent work using trace nutrient supplementation enabled stable operation of intermittently-fed (three times per week) digesters at loading rates up to 12 gVS kg −1 day −1 , resulting in methane production rates up to 3.3 L kg −1 day −1 . Continuous feeding of corn at rates up to 18 gVS kg −1 day t-1 resulted in a mean methane production rate of 5.4 L kg−1 day-' with a 67% VS conversion efficiency. The maximum methane production rates for both the high solids and low solids systems are among the highest observed for biomass conversion. An in situ technique to enrich digester offgas was developed to take advantage of the differing solubilities of C0 2 and CH 4 , in which dissolved C0 2 was removed from the reactor in a recycled leachate stream and gas-stripped in an external stripper. Such a system easily enriched the remaining digester offgas to over 90% methane, and contents in excess of 98% were achieved. Quantitative evaluation of system variables defined the effects of leachate recycle rates, leachate alkalinity, and pH on the resulting offgas methane contents.

Anaerobic digestion : modern theory and practice

Abstract: Part 1 The microbiology and biochemistry of anaerobic digestion: general considerations substrate degradations physical factors enumerating the bacteria the breakdown of carbohydrates. Part 2 Mathematical models: the economic and engineering model the biological model general considerations the stirred-tank digester steady-state models. Part 3 Types of digesters and their construction: design and operation sludge and slurry digesters the contact digester anaerobic filters the upflow sludge blanket (UASB) digester. Part 4 Pretreatment of feedstocks: physical pretreatments removal of digestible solids, or of liquids removal of non-biodegradable solids mainly biological pretreatments particle-size reduction. Part 5 Digestion of high-solids feedstocks: simple and modified batch digesters fed-batch digesters continuous-flow stirred tanks the climatically-heated, small-farm digester the "standard" stirred-tank sewage digester. Part 6 Digestion of low-solids feedstocks: the "feedback" or "contact" digester the anaerobic filter the expanded- or fluidized-bed digester baffled and similar upflow sludge-blanket digester baffled and similar digesters. Part 7 Uses of digester products: use as fertilizer animal feedstuffs indirect use to produce animal or human feeds biogas. Part 8 Running and control of digesters: safety physical control systems analytical control systems. Appendix: glossary of terms types of digester terms used in digester running terms used in descriptions of wastes and their treatment.

Anaerobic digestion of Chlorella vulgaris for energy production

Abstract: The anaerobic digestion of Chlorella vulgaris was studied using batch digesters. Standard analysis of chemical oxygen demand (COD), solids, pH, acidity, alkalinity and chlorophyll were done. Biogas composition and production were also determined. The conversion of biomass to biogas ranged from 70–90% in COD. This implies that C. vulgaris could constitute a valuable method of bioconversion of sun energy to biogas.

Dry anaerobic digestion of the organic fraction of municipal solid waste

Abstract: Anaerobic digestion is an attractive technology for solid waste management This thesis describes the technological potentials of dry anaerobic digestion of the organic fraction of Municipal Solid Waste (MSW) using batch systems In 1985 a research programme was started to develop the so- called BIOCEL system based on batchwise anaerobic digestion yielding biogas and compost The research programme was financially supported by the Dutch National Programme for reuse of Waste (NOH), which is coordinated by NOVEM, the Dutch Organization for Energy and the Environment and RIVM, the Dutch Institute for Public Health and the Environment The research was carried out on laboratory scale as well as on pilot-plant scale This study presents the results of the experimental work For start-up of the dry digestion of the organic fraction of MSW, the addition of a methanogenic inoculum appears to be essential The best results are obtained with the digested residue as the methanogenic inoculum at start-up Start-up of dry anaerobic digestion of Vegetable Fruit and Yard (VFY) waste, the source-separated organic fraction of Municipal Solid Waste, is also investigated The total solids retention time (SRT) at an inoculum factor of 050 is 28 days The influence of temperature and the total solids (TS) concentration on the rate of the anaerobic digestion process was investigated Depending on the start-up procedure, anaerobic digestion proceeds in the range of 10 to 50 % T S at similar rate The optimum temperature of the process is 40 °C The acid formation rate shows less response to a temperature increase then does the methanogenesis The effect of suboptimal transport of free liquid phase in the solid waste bed of solid waste digesters was studied It has been found that dry anaerobic batch digestion of solid organic wastes can proceed at pH values as low as 52 and organic acid concentrations of 40-50 g CODA in the digester environment Methanogenesis takes place in zones that are formed in the solid waste bed due to heterogenous mixing characteristics of the reactor contents The phenomenon of methanogenesis in dry anaerobic digestion of solid wastes under extreme conditions, such as pH values below 6, and volatile fatty acid concentrations up to 40 g/I was studied Methanogenesis is possible at an initial acetate concentration as high as 583 mM (38 g/1) and at pH = 70 Microscopic observations of enriched cultures show that the predominant organisms resemble the genus Methanosarcina sp Pilot-scale experiments (5 m 3 , 450 m 3 ) illustrated the technological potentials of the BIOCEL process Based on the results of the experiments on several scales it can be concluded that the process is ready for full-scale application Future research should deal with the microbial and kinetic aspects of the hydrolysis of particulate organic matter present in the organic fraction of Municipal Solid Waste

High efficiency energy conversion and treatment of organic waste

Abstract: A system and method for converting organic material to electricity includes the steps of collecting a quantity of organic material, generating biogas from the material, and passing the biogas through an energy converter. Biogas is generated from the organic material by an anaerobic filter, and electricity is converted from the biogas by an energy converter, such as a high efficiency solid oxide fuel cell. To further increase the efficiency of the system, an anaerobic digester is used for treating a solid or sludge component of the organic material to generate additional biogas. In one embodiment of the invention, solar energy is used to maintain the anaerobic digester at an elevated temperature. Further efficiency enhancing measures include the recirculation of both the sludge and liquid components of the organic material to obtain additional biogas. After all of the biogas generating potential of the organic material has been utilized, the liquid component thereof is suitable for irrigation or discharge, while the solid component thereof is suitable for use as soil conditioner.

Kinetic and performance study of a batch two-phase anaerobic digestion of fruit and vegetable wastes

Abstract: Anaerobic digestion of a simulated organic fraction of the waste of a central market selling fruit and vegetables was carried out in two-phase digesters in the mesophilic range of temperatures. Batch digestion was prolonged until no biogas was produced (33 days). With digested pig manure as inoculum, maximum biogas production was obtained around day 10, and within 3 weeks the digestion was almost complete. A kinetic analysis was carried out using first-order, Monod and Chen-Hashimoto models. The Chen-Hashimoto model represents the best fit, whereas a first-order model was not consistent with the experimental results.

Biogas electricity -- The Pura village case study

Abstract: A potentially useful decentralized source of energy is biogas, which is an approximately 60:40 mixture of methane (CH{sub 4}) and carbon dioxide (CO{sub 2}), produced by the anaerobic fermentation of cellulosic biomass materials such as bovine wastes. Since 1987, the traditional system of obtaining water, illumination, and fertilizer in Pura village in south India has been replaced with a community biogas plant electricity-generation system. The technical, managerial, and economical aspects of this system are the subject manner of the present paper. Various subsystems are described, and the problems of operation and maintenance under field conditions are also discussed. A comparison of Pura`s present community biogas system with its traditional means for obtaining water, illumination, and fertilizer shows that the households are winners on all counts, having obtained such benefits as improved hygiene and convenience at relatively low cost. The Pura community biogas plant is held together and sustained by the convergence of individual and collective interests. Noncooperation with the community biogas plant results in a heavy individual price (access to water and light being cut off by the village), which is too great a personal loss to compensate for the minor advantages of noncooperation and noncontribution to collective interests.

Treatment of detoxified olive mill wastewaters by anaerobic filter and aerobic fluidized bed processes

Abstract: Anaerobic filter (AF) was compared with aerobic fluidized bed fermentor (AFBF) for treating detoxified Olive Mill Wastewaters by Aspergillus niger. The behaviour of AFBF is more difficult than AF. The AFBF removes 57% of total COD after elimination of TSS which correspond to sludge. The treatment of detoxified OMW by AF reduces the total COD and soluble COD at 67 and 68.1% respectively. As regard to double role of AF, physical retention and anaerobic mineralization, the reduction of TSS was 62.9%. AFBF is less economic than AF because of consumption of aeration energy and of the very high production of secondary sludge. Moreover, AF produces biogas at 80% of methane. The black colour of OMW is weakly reduced only by AF.

Biogas purification process using intensive microalgae cultures

Abstract: The main contaminants (CO2 and H2S) in biogas produced by anaerobic digestion can be removed by an intensive mass culture of microalgae.

Effect of metals on anaerobic digestion of water hyacinth-cattle dung

Abstract: The effect of several salts, FeCl3, NiCl2, CoCl2, CuCl2, and ZnCl2, on anaerobic digestion of water hyacinth-cattle dung was examined. Among the salts studied, FeCl3 caused a more than 60% increase in gas production with a high methane content.

Arthospira sp. intensive cultures for food and biogas purification.

Abstract: The main contaminants (CO2 and H2S) in biogas produced by anaerooic digestion can be removed by an intensive mass culture of Arthospira sp.. At the same time productivities of 26–34 g dry mass/m2 -d were reached.