Showing papers on "Biogas published in 1997"

Renewable methane from anaerobic digestion of biomass.

Abstract: Production of methane via anaerobic digestion of energy crops and organic wastes would benefit society by providing a clean fuel from renewable feedstocks. This would replace fossil fuel-derived energy and reduce environmental impacts including global warming and acid rain. Although biomass energy is more costly than fossil fuel-derived energy, trends to limit carbon dioxide and other emissions through emission regulations, carbon taxes, and subsidies of biomass energy would make it cost competitive. Methane derived from anaerobic digestion is competitive in eAciencies and costs to other biomass energy forms including heat, synthesis gases, and ethanol. 7 2000 Elsevier Science Ltd. All rights reserved.

Bioconversion of waste biomass to useful products

Abstract: A process is provided for converting waste biomass to useful products by gasifying the biomass to produce synthesis gas and converting the synthesis gas substrate to one or more useful products. The present invention is directed to the conversion of biomass wastes including municipal solid waste, sewage sludge, plastic, tires, agricultural residues and the like, as well as coal, to useful products such as hydrogen, ethanol and acetic acid. The overall process includes the steps of gasifying the waste biomass to produce raw synthesis gas, cooling the synthesis gas, converting the synthesis gas to the desired product or products using anaerobic bioconversion, and then recovering the product or products. In accordance with a particular embodiment of the present invention, waste biomass is converted to synthesis gas containing carbon monoxide and, then, the carbon monoxide is converted to hydrogen by an anaerobic microorganism ERIH2, bacillus smithii ATCC No. 55404.

Mesophilic and thermophilic anaerobic digestion of source-sorted organic wastes: effect of ammonia on glucose degradation and methane production

Abstract: The wet organic fraction of household wastes was digested anaerobically at 37 °C and 55 °C. At both temperatures the volatile solids loading was increased from 1 g l−1 day−1 to 9.65 g l−1 day−1, by reducing the nominal hydraulic retention time from 93 days to 19 days. The volatile solids removal in the reactors at both temperatures for the same loading rates was in a similar range and was still 65% at 19 days hydraulic retention time. Although more biogas was produced in the thermophilic reactor, the energy conservation in methane was slightly lower, because of a lower methane content, compared to the biogas of the mesophilic reactor. The slightly lower amount of energy conserved in the methane of the thermophilic digester was presumably balanced by the hydrogen that escaped into the gas phase and thus was no longer available for methanogenesis. In the thermophilic process, 1.4 g/l ammonia was released, whereas in the mesophilic process only 1 g/l ammonia was generated, presumably from protein degradation. Inhibition studies of methane production and glucose fermentation revealed a Ki (50%) of 3 g/l and 3.7 g/l ammonia (equivalent to 0.22 g/l and 0.28 g/l free NH3) at 37 °C and a Ki (50%) of 3.5 g/l and 3.4 g/l ammonia (equivalent to 0.69 g/l and 0.68 g/l free NH3) at 55 °C. This indicated that the thermophilic flora tolerated at least twice as much of free NH3 than the mesophilic flora and, furthermore, that the thermophilic flora was able to degrade more protein. The apparent ammonia concentrations in the mesophilic and in the thermophilic biowaste reactor were low enough not to inhibit glucose fermentation and methane production of either process significantly, but may have been high enough to inhibit protein degradation. The data indicated either that the mesophilic and thermophilic protein degraders revealed a different sensitivity towards free ammonia or that the mesophilic population contained less versatile protein degraders, leaving more protein undegraded.

Anaerobic digestion of Ulva sp. 1. Relationship between Ulva composition and methanisation

Abstract: Ulva often represents the main component of mass algal growths, and its composition and degradability make it a relatively good methanisation substrate. In ‘green tides’ Ulva sp. from Brittany, the low content oflignin-type components (polyphloroglucinols: 1.3% dry weight), and the large hemicellulosic fraction (9% dry weight) favour the substrate's accessibility to enzymes. Anaerobic degradation with a batch orcompletely stirred system is technically possible. However, the methane yield reached only 0.20 m3 kg−1 volatile solids and the epuration rate 50% volatile solids in experiments in batch or completely stirred reactors. More generally, methanisation comes up against various practical obstacles: seasonal growth of Ulva, low density of alga in suspension for loading the digester, high S concentration leading to the production of a biogas with a high H2S content, and, finally, the existence of a refractory or slowly degradable part, which requires a compromise between productivity and biological yield.

Inhibition of mesophilic solid-substrate anaerobic digestion by ammonia nitrogen

Abstract: This work focused on determining the effects of ammonia-nitrogen supplementation on the mesophilic solid-substrate anaerobic digestion of municipal wastes and waste activated sludge (biosolids). Bench-scale, semi-continuous, mesophilic reactors were operated with a 21-day mass-retention time and dosed with NH4Cl, such that the corresponding chemical O2 demand (COD)/N ratios in their feeds were 90, 80, 65 and 50 (reactors R1 or control, R2, R3 and R4 respectively). Reactor performance was evaluated in terms of the efficiency of volatile solid removal (efficiency for short), biogas productivity, methane content in the biogas, pH and volatile organic acid contents, among other monitoring and analytical parameters. The feedstock was a mixture of urban wastes with biosolids. It was found that the process performance deteriorated at increasing dosages of ammonia N, the process practically ceasing at COD/N = 50 (R4). Inhibition was characterized by efficiency and biogas productivity decreases and a more sudden drop of methane content in biogas and pH. A significant rise of propionic, butyric and valeric acid was found in reactors receiving the highest doses of ammonia N (R3 and R4). This suggested that inhibition of the syntrophic bacteria present in the anaerobic consortia also occurred. Luong and Pearson inhibition models were fitted to the data. Both models represented very well the acute effects of N supplementation on solid-substrate anaerobic digestion. However, the Luong model could also represent the process ceasing at a critical ammonia N concentration of 2800 mg/kg mixed solids.

Codigestion of olive oil mill wastewaters with manure, household waste or sewage sludge

Abstract: Large amounts of organic waste are generated from household, agriculture and industry today. The major part of the waste from industry and households is deposited in landfills, an undesirable solution, because landfills fill up landscapes and leach pollutants into the groundwater. Furthermore, special wastes, such as wastewaters from olive oil processing, are produced in large amounts in concentrated areas mainly in Mediterranean countries. Treatment of oil mill effluent (OME) still presents a problem, which has not been solved to date. If not treated, this waste imposes a great environmental hazard, due to the very high organic chemical oxygen demand (COD) loads. Anaerobic treatment of organic wastes is the most optimal treatment system, reducing the organic content, destructing toxicants and, at the same time, yielding energy in the form of biogas which can be used for heating and electricity production. Several investigators have studied anaerobic degradation of OME and obtained COD-reductions up to approx. 80% [4, 5, 6, 13]. However, especially at high feed concentrations, the process proved probably unstable due to the inhibitory effect of phenols, lack of ammonia and due to the low alkalinity of OME. In order to overcome the above problems, the OME was diluted with water, and urea was added as nitrogen supplement [7, 12]. Furthermore, the alkalinity of the reactor content was often adjusted by NaHCO3, NaOH or Ca(OH)2 [6, 7]. However, dilution of OME with water results in unnecessary large effluent volumes, and additions of chemicals is not economically and environ-mentally desirable.

Laboratory studies on the temperature‐phased anaerobic digestion of domestic primary sludge

Abstract: The temperature-phased anaerobic process involves a two-stage reactor system with the first stage operated at a thermophilic temperature (typically 55°C) and the second stage operated at a mesophilic temperature (typically 35°C). The purpose of this laboratory study was to compare the performance of the temperature-phased system with the conventional single-stage mesophilic system for treating domestic wastewater sludge. Of particular interest in the research was a comparison of the two systems from the standpoint of coliform reduction, volatile solids destruction, and biogas production. The temperature-phased system achieved almost complete destruction of total and fecal coliforms over a range of solids retention times (SRTs) from 10 to 15 days. The concentration of fecal coliforms in the effluent from the temperature-phased system never exceeded 1 000 MPN/g total solids, which can meet the U.S. federal fecal coliform requirements for Class A biosolids. At SRTs ranging from 10 to 15 days, the temperature-phased system achieved an 18% higher destruction of volatile solids and 16% more methane production than was possible with the single-stage mesophilic process.

Studies on Anaerobic Digestion Mechanism: Influence of Pretreatment Temperature on Biodegradation of Waste Activated Sludge

Abstract: The effect of thermal pretreatment on hydrolysis, acidogenesis and methanogenesis during anaerobic digestion of waste activated sludge (WAS) was investigated. Pretreatment temperature of WAS ranged from 60°C to 120°C and the holding times were 5, 10, 20, 30 and 60 minutes. WAS was fed into the laboratory-scale anaerobic digesters, after thermal pretreatment. The preliminary conversion step (such as death/lysis of cell and hydrolysis of WAS) was promoted through thermal pretreatment, and consequently efficiencies of acidogenic and methanogenic steps were also markedly enhanced. Thermal pretreatment at lower temperature resulted in a significant increase in methane generation and destruction of organic matter. At 60°C, when hydraulic retention time (HRT) was 8 days, an increase in approximately 52.1 % in methane generation (ml. l−1. d−1) and 26.6% in organic matter destruction was achieved (Series-I). In addition, HRT necessary for anaerobic digestion could be reduced by thermal pretreatment.

Biogas production from Jatropha curcas press-cake.

Abstract: Seeds of the tropical plant Jatropha curcas (purge nut, physic nut) are used for the production of oil. Several methods for oil extraction have been developed. In all processes, about 50% of the weight of the seeds remain as a press cake containing mainly protein and carbohydrates. Investigations have shown that this residue contains toxic compounds and cannot be used as animal feed without further processing. Preliminary experiments have shown that the residue is a good substrate for biogas production. Biogas formation was studied using a semicontinous upflow anaerobic sludge blanket (UASB) reactor; a contact-process and an anaerobic filter each reactor having a total volume of 110 L. A maximum production rate of 3.5 m3 m-3 d-1 was obtained in the anaerobic filter with a loading rate of 13 kg COD m-3 d-1. However, the UASB reactor and the contact-process were not suitable for using this substrate. When using an anaerobic filter with Jatropha curcas seed cake as a substrate, 76% of the COD was degraded and 1 kg degraded COD yielded 355 L of biogas containing 70% methane.

Anaerobic treatment of swine waste by the anaerobic sequencing batch reactor

Abstract: Anaerobic sequencing batch reactor (ASBR) uses a high-rate anaerobic bioconversion process to stabilize organic wastes for odor control and generate biogas for energy use. It is well suited for treating animal wastes. This article reviews previous research on the ASBR and reported a laboratory study to evaluate the ASBR with swine waste at short hydraulic retention times (HRTs) (two, three, and six days), over a wide range of volatile solids loading rate (0.9 to 5.5 g/L/day) and at 25°C. The ASBR demonstrated satisfactory performance at all three HRTs. The three-day HRT reactor showed the best overall performance in terms of biomass settleability, biogas production rate, and reductions of volatile solids and biochemical oxygen demand in the manure after the treatment. In the intermediate range of VS loading rate (1.6-4.5 g/L/day), the VS reduction was 55 to 61%, BOD5 reduction was 81 to 86% and biogas production rate was 0.9 to 1.8 L/L/day. It was found that ammonia did not adversely affect the performance of the ASBR at a concentration as high as 2470 mg/L in a pH range of 6.8 to 7.4. The ASBR can be easily integrated into a waste management system on a swine farm. The conceptual designs for the configurations and operational schemes of the ASBR system for working with swine confinement operations using flushing, scraping, or gravity draining (pull-plug) systems are presented.

High-Solids Anaerobic Digestion of Mixed Municipal and Industrial Waste

Abstract: Laboratory studies on dry anaerobic digestion of mixture of paper, kitchen food waste, and sewage sludge have demonstrated the optimum performance at total solids (TS) at the range of 30--35% TS. The thermophilic process (at 55 C) was found to be superior to a mesophilic (35 C) one, both in terms of volatile solid (VS) reduction and specific gas production, but was somewhat less stable at short mass retention times (MRT). The efficiency of total volatile solids destruction and the decrease in the oxygen demand were found to be proportional to the product of the mass retention time and temperature (d {center_dot} C). Pilot studies, conducted on a mixture of sewage sludge, mixed paper, food waste, and solids from a potato processing conducted on site in Portage la Prairie, Manitoba, Canada, have demonstrated the feasibility of running the process at loads exceeding 9 kg TS/m{sup 3} {center_dot} d and producing biogas at 140 m{sup 3} of wet solids fed to the composter. The residual oxygen demand per unit mass of the dry compost was 20 mg O{sub 2}/g {center_dot} h, which indicated a need for aerobic postcuring of the anaerobically produced compost.

Co-digestion of municipal sewage sludges and pre-hydrolysed woody agricultural wastes.

Abstract: Material balance has been used to evaluate the COD behaviour and the time required for fed-batch digestion of mixtures of domestic sludges and pre-hydrolysed agricultural wastes. Pre-hydrolysis of the feed materials has been used to penetrate the strong lignocellulosic structure of these wastes as well as to increase the fraction of soluble organic substances in the mixture. The influence of the organic loading rate on the main process parameters (methane, carbon dioxide, total biogas productions and their respective conversion yields) has also been investigated. The organic load has been varied from 0.8 up to 6.1 g COD dm -3 day -1 , corresponding to a range of volatile solids load of 0.6-4.5 g vs dm -3 day -1 for the material under consideration. These values are slightly higher than those usually employed in conventional digester for domestic sewage sludges. However, methane production reached a maximum rate of only 5.6 mmol dm -3 day -1 at an organic loading rate of 4.6 g COD dm -3 day -1 , while both CH 4 content and production of biogas rapidly fell over 2.2 g COD dm -3 day -1 . On the whole, these results suggest that removal of lignin is necessary in order to carry out the continuous anaerobic digestion of pre-hydrolysed agricultural wastes rich in woody materials.

Potential for the psychrophilic anaerobic treatment of swine manure using a sequencing batch reactor.

Abstract: Masse, 0.1., R.L. Droste, Kennedy, K.J., Patni, N.K. and Munroe, J.A. 1997. Potential for the psychrophilic anaerobic treatment of swine manure using a sequencing batch reactor. Can. Agric. Eng. 39:025-034. The feasibility of psychrophilic anaerobic digestion (PAD) in intermittently fed sequencing batch reactors (SBR) was investigated during the start-up run of an ongoing laboratory study. The start-up run results indicated that PAD in SBRs was efficient in stabilizing and deodorizing swine manure slurry. The digester effluents had little odour when compared to the raw manure. Total chemical oxygen demand (COD) was reduced by 58 to 73% and soluble COD (SCOD) by 85 to 96%. Methane production varied from 0.30 to 0.66 L CH4/g volatile solids added and methane concentration in the biogas ranged from 50 to 80%. The biog

Tracer Studies in a Laboratory and Pilot Scale UASB Reactor

Abstract: Residence time distribution studies on laboratory and pilot scale upflow anaerobic sludge blanket reactors (UASB) were carried out in order to measure and evaluate the influence, on the reactor's hydraulic performance, of the biogas collection device position (gas-liquid-solid separator), of the presence of granular sludge and of the arrangement of the influent distribution system within the reactor The main purpose of the pilot scale experiment was to assess the influence of the biogas collection device on the reactor hydraulic performance accurately The results show that if the biogas collector system is located in a lower position (nearer to the sludge bed), the dead volume fraction decreases and a better performance of the settler could be obtained In addition, it can be appreciated that the mixed flow pattern has more dead volume fraction than a plug flow hydraulic pattern