Nickel as an accelerator of biogas production in water hyacinth (Eichornia crassipes solms.)

The effect of nickel ions on biogas production has been investigated in 3-litre fermenters. It was observed that nickel is stimulatory up to 5 ppm, with an optimum at 2·5 ppm, in a water hyacinth-bovine excreta substrate. A similar effect with nickel was also observed at 5 ppm in bovine excreta.     

Biotechnological intensification of biogas production

The importance of syntrophic relationships among microorganisms participating in biogas formation has been emphasized, and the regulatory role of in situ hydrogen production has been recognized. It was assumed that the availability of hydrogen may be a limiting factor for hydrogenotrophic methanogens. This hypothesis was tested under laboratory and field conditions by adding a mesophilic (Enterobacter cloacae) or thermophilic hydrogen-producing (Caldicellulosyruptor saccharolyticus) strain to natural biogas-producing consortia. The substrates were waste water sludge, dried plant biomass from Jerusalem artichoke, and pig manure. In all cases, a significant intensification of biogas production was observed. The composition of the generated biogas did not noticeably change. In addition to being a good hydrogen producer, C. saccharolyticus has cellulolytic activity; hence, it is particularly suitable when cellulose-containing biomass is fermented. The process was tested in a 5-m³ thermophilic biogas digester using pig manure slurry as a substrate. Biogas formation increased at least 160–170% upon addition of the hydrogen-producing bacteria as compared to the biogas production of the spontaneously formed microbial consortium. Using the hydrogenase-minus control strain provided evidence that the observed enhancement was due to interspecies hydrogen transfer. The on-going presence of C. saccharolyticus was demonstrated after several months of semicontinuous operation.     

Effect of yeast extract on speciation and bioavailability of nickel and cobalt in anaerobic bioreactors

The speciation of metals plays an important role in their bioavailability. In the case of anaerobic reactors for the treatment of wastewaters, the ubiquitous presence of sulfide leads to extensive precipitation of metals like nickel and cobalt, which are essential for the metabolism of the anaerobic microorganisms that carry out the mineralization of the pollutants present in the wastewater. In practice, nickel, cobalt, and iron are added in excessive amounts to full-scale installations. This study is concerned with the complexation of nickel and cobalt with yeast extract and its effect on the biogas production by methanogenic biomass. Adsorptive stripping voltammetry (AdSV) was used to get information about the stability and complexing capacity of the metal-yeast extract complexes formed. Nickel and cobalt form relatively strong organic complexes with yeast extract. The bioavailability of these essential metals in anaerobic batch reactors was dramatically increased by the addition of yeast extract. This is due to the formation of dissolved bioavailable complexes, which favors the dissolution of metals from their sulfides. Trace doses of yeast extract may be effective in keeping additions of essential metals to anaerobic reactors at a minimum.     

Biogas properties and enzymatic analysis during anaerobic fermentation of <Emphasis Type="Italic">Phragmites australis</Emphasis> straw and cow dung: influence of nickel chloride supplement

The importance of nickel (added as NiCl₂) on mesophilic anaerobic fermentation of Phragmites australis straw and cow dung was demonstrated by investigating the biogas properties, pH values, organic matter degradation [chemical oxygen demand (COD)] and enzyme activities (cellulase, protease and dehydrogenase) during the fermentation process. The results showed that Ni²⁺ addition increased the cumulative biogas yields by >18 % by improving the efficiency of first peak stage and bringing forward the second peak stage. The pH values were not significantly influenced by Ni²⁺ addition (p > 0.05). Biogas yields were associated with variations in COD concentrations rather than momentary concentrations. At the start-up stage of fermentation (4th day), the biogas yields increased gradually together with the increase of dehydrogenase activities at elevated Ni²⁺ concentrations when cellulase and protease activities were similar in all test groups. It is suggested that Ni²⁺ addition was mainly dependent on the methanogenic stage. After the start-up stage, the impact of Ni²⁺ addition on biogas production was mainly dependent on its effect on cellulase activities, rather than protease or dehydrogenase activities.     

Increase of methane formation by ethanol addition during continuous fermentation of biogas sludge

Very recently, it was shown that the addition of acetate or ethanol led to enhanced biogas formation rates during an observation period of 24 h. To determine if increased methane production rates due to ethanol addition can be maintained over longer time periods, continuous reactors filled with biogas sludge were developed which were fed with the same substrates as the full-scale reactor from which the sludge was derived. These reactors are well reflected conditions of a full-scale biogas plant during a period of 14 days. When the fermenters were pulsed with 50–100 mM ethanol, biomethanation increased by 50–150 %, depending on the composition of the biogas sludge. It was also possible to increase methane formation significantly when 10–20 mM pure ethanol or ethanolic solutions (e.g. beer) were added daily. In summary, the experiments revealed that “normal” methane production continued to take place, but ethanol led to production of additional methane.     

Using Contaminated Plants Involved in Phytoremediation for Anaerobic Digestion

This study investigated the anaerobic digestion capability of five plants and the effects of copper (Cu) and S,S’-ethylenediaminedisuccinic acid (EDDS, a chelator widely used in chelant-assisted phytoremediation) on biogas production to determine a feasible disposal method for plants used in remediation. The results showed that in addition to Phytolacca americana L., plants such as Zea mays L., Brassica napus L., Elsholtzia splendens Nakai ex F. Maekawa, and Oenothera biennis L. performed well in biogas production. Among these, O. biennis required the shortest period to finish anaerobic digestion. Compared to normal plants with low Cu content, the plants used in remediation with increased Cu levels (100 mg kg^?1) not only promoted anaerobic digestion and required a shorter anaerobic digestion time, but also increased the methane content in biogas. When the Cu content in plants increased to 500, 1000, and 5000 mg kg^?1, the cumulative biogas production decreased by 12.3%, 14.6%, and 41.2%, respectively. Studies also found that EDDS conspicuously restrained biogas production from anaerobic digestion. The results suggest that anaerobic digestion has great potential for the disposal of contaminated plants and may provide a solution for the resource utilization of plants used in remediation.     

Appropriate technologies for environmental hygiene

Appropriate technologies for environmental hygiene usually centre on the delivery of adequate and accessible water supply, and proper treatment and disposal of excreta and refuse. In the face of the International Drinking Water and Sanitation Decade of 1981-90, several research efforts are under way in the developing countries to develop technologies and approaches for improving environmental hygiene in both rural areas and urban squatter settlements. These are discussed and include the technical development and field testing of infiltration galleries, low-cost slow and fast filtration processes for water treatment, handpumps, on-site excreta disposal using aqua-privy and compost toilets, and excreta treatment and refuse through composting with refuse, biogas generation, fish culture and use of excreta as crop fertilizer. The relevant technology 'hardware' is but one of several components necessary for effective delivery of services. The dearth of qualified manpower at all levels is described as being the major constraint to the Water and Sanitation Decade.     

Anaerobic digestion of animal waste: effect of mixing

Six laboratory scale biogas mixed anaerobic digesters were operated to study the effect of biogas recycling rates and draft tube height on their performance. The digesters produced methane at 0.40-0.45 L per liter of digester volume per day. A higher methane production rate was observed in unmixed digesters, while increased biogas circulation rate reduced methane production. However, different draft tube heights caused no difference in the methane production rate. Air infiltration (up to 15% oxygen in the biogas) was observed in the digesters mixed by biogas recirculation. Slight air permeability of tubing or leakage on the vacuum side of the air pump may have caused the observed air infiltration. The similar performance of the mixed and unmixed digesters might be the result of the low solids concentration (50 g dry solids per liter of slurry) in the fed animal slurry, which could be sufficiently mixed by the naturally produced biogas.     

Advantages of the integrated pig-biogas-vegetable greenhouse system in North China

An integrated pig-biogas-vegetable greenhouse system (PBVGS) was designed and studied in Laiwu, Shandong Province of North China from 2001 to 2002, where 20 groups of PBVGS and their corresponding controls were investigated. The PBVGS involves building a pigsty and a biogas digester in a vegetable greenhouse, putting pig dung into the biogas digester for fermentation, using the biogas for increasing illumination and air temperature in the greenhouse, and using the fermented waste as organic manure. The data indicate that the pig growth, biogas production and vegetable production were effectively improved in PBVGS, and that ecological, economic and social benefits were simultaneously achieved. The average annual net income of a standard PBVGS was 10,900 RMB, with an increase of 58.0% over its traditional non-integrated parts. It could use up 14,000 kg fresh pig dung and produce 10,000 kg organic manure one year for the improvement of soil fertility. The daily net weight increase for a pig in PBVGS averaged 0.82 kg, 227.6% higher than its controls. The average yield per hectare of cucumbers and tomatoes, increased by 18.4 and 17.8% over their controls, respectively. In addition, the biogas produced in the digester increased by 32.4% annually. Based on biogas fermentation, the PBVGS provides a fine ecological cycle from livestock feeding to vegetable production, resulting in a higher conversion efficiency in nutrient cycle and energy flow.     

Phycoremediation coupled production of algal biomass,harvesting and anaerobic digestion: Possibilities and challenges

Biogas produced from anaerobic digestion is a versatile and environment friendly fuel which traditionally utilizes cattle dung as the substrate. In the recent years, owing to its high content of biodegradable compounds, algal biomass has emerged as a potential feedstock for biogas production. Moreover, the ability of algae to treat wastewater and fix CO₂ from waste gas streams makes it an environmental friendly and economically feasible feedstock. The present review focuses on the possibility of utilizing wastewater as the nutrient and waste gases as the CO₂ source for algal biomass production and subsequent biogas generation. Studies describing the various harvesting methods of algal biomass as well as its anaerobic digestion have been compiled and discussed. Studies targeting the most recent advancements on biogas enrichment by algae have been discussed. Apart from highlighting the various advantages of utilizing algal biomass for biogas production, limitations of the process such as cell wall resistivity towards digestion and inhibitions caused due to ammonia toxicity and the possible strategies for overcoming the same have been reviewed. The studies compiled in the present review indicate that if the challenges posed in translating the lab scale studies on phycoremediation and biogas production to pilot scale are overcome, algal biogas could become the sustainable and economically feasible source of renewable energy.     

Biogas production and microbial community change during the Co-digestion of food waste with chinese silver grass in a single-stage anaerobic reactor

Chinese silver grass (CSG), a potential subtropical energy crop, was investigated as a co-substrate to enhance the anaerobic digestion of food waste for municipal solid waste treatment. Results showed that 88.1% of food wastes were degraded using CSG as a co-substrate with 45 days of digestion, where the food waste, CSG, and sludge on VS/TS/working volume was 93.14 g/111.55 g/1 L, in which the average biogas production was at 429.3 L/kg solids, and the average methane content was around 60%. During the digestion, the concentrations of ammonium and free ammonia gradually increased to 1448.2 and 265.2 mg/L respectively, without any significant inhibitory effects on biogas production, which is probably due to the buffering effects of CSG. Microbial community analysis showed that microorganisms from the class of Firmicutes and Bacteroidetes were dominant during digestion, and that the microbial community diversity increased with active methanogenesis, suggesting that the addition of substrates contribute to the increase of microbial diversity, and could be beneficial for biogas production. Therefore, using CSG as a co-substrate in the single-stage food waste anaerobic digestion system is a potential simple method to convert CSG into renewable energy and to simultaneously improve food waste treatment.     

Investigation of factors influencing biogas production in a large-scale thermophilic municipal biogas plant

A continuously operated, thermophilic, municipal biogas plant was observed over 26 months (sampling twice per month) in regard to a number of physicochemical parameters and the biogas production. Biogas yields were put in correlation to parameters such as the volatile fatty acid concentration, the pH and the ammonium concentration. When the residing microbiota was classified via analysis of the 16S rRNA genes, most bacterial sequences matched with unidentified or uncultured bacteria from similar habitats. Of the archaeal sequences, 78.4% were identified as belonging to the genus Methanoculleus, which has not previously been reported for biogas plants, but is known to efficiently use H₂ and CO₂ produced by the degradation of fatty acids by syntrophic microorganisms. In order to further investigate the influence of varied amounts of ammonia (2–8 g/L) and volatile fatty acids on biogas production and composition (methane/CO₂), laboratory scale satellite experiments were performed in parallel to the technical plant. Finally, ammonia stripping of the process water of the technical plant was accomplished, a measure through which the ammonia entering the biogas reactor via the mash could be nearly halved, which increased the energy output of the biogas plant by almost 20%.     

Stirring and biomass starter influences the anaerobic digestion of different substrates for biogas production

Here, we present the results of lab‐scale experiments conducted in a batch mode to determine the biogas yield of lipid‐rich waste and corn silage under the effect of stirring. Further semi‐continuous experiments were carried out for the lipid‐rich waste with/without stirring. Additionally, it was analyzed how the starter used for the batch experiment influences the digestion process. The results showed a significant stirring effect on the anaerobic digestion only when seed sludge from a biogas plant was used as a starter. In this case, the experiments without stirring yielded only about 50% of the expected biogas for the investigated substrates. The addition of manure slurry to the batch reactor as part of the starter improved the biogas production. The more diluted media in the reactor allowed a better contact between the bacteria and the substrates making stirring not necessary.     

Volatile fatty acids (VFAs) and methane from food waste and cow slurry: Comparison of biogas and VFA fermentation processes

The potential of various biomasses for the production of green chemicals is currently one of the key topics in the field of the circular economy. Volatile fatty acids (VFAs) are intermediates in the methane formation pathway of anaerobic digestion and they can be produced in similar reactors as biogas to increase the productivity of a digestion plant, as VFAs have more varying end uses compared to biogas and methane. In this study, the aim was to assess the biogas and VFA production of food waste (FW) and cow slurry (CS) using the anaerobic biogas plant inoculum treating the corresponding substrates. The biogas and VFA production of both biomasses were studied in identical batch scale laboratory conditions while the process performance was assessed with chemical and microbial analyses. As a result, FW and CS were shown to have different chemical performances and microbial dynamics in both VFA and biogas processes. FW as a substrate showed higher yields in both processes (435 ml CH₄/g VS_fed and 434 mg VFA/g VS_fed) due to its characteristics (pH, organic composition, microbial communities), and thus, the vast volume of CS makes it also a relevant substrate for VFA and biogas production. In this study, VFA profiles were highly dependent on the substrate and inoculum characteristics, while orders Clostridiales and Lactobacillales were connected with high VFA and butyric acid production with FW as a substrate. In conclusion, anaerobic digestion supports the implementation of the waste management hierarchy as it enables the production of renewable green chemicals from both urban and rural waste materials.     

Biogas technology in sub-Saharan Africa: status, prospects and constraints

Africa is a continent with abundant, diverse and un-exploited renewable energy resources that are yet to be used for improving the livelihood of the vast majority of the population. The production of biogas via anaerobic digestion of large quantities of agricultural residues, municipal wastes and industrial waste(water) would benefit African society by providing a clean fuel in the form of biogas from renewable feedstocks and help end energy poverty. Biogas technology can serve as a means to overcome energy poverty, which poses a constant barrier to economic development in Africa. Anaerobic digestion of the large quantities of municipal, industrial and agricultural solid waste in developing countries present environmental conditions that make use of anaerobic biotechnology extremely favourable under perspective of sustainable development. However, the use of biogas is not widespread in Africa. There are many reasons of economic, technical and non-technical nature for the marginal use of biogas in Africa. The key issue for biogas technology in Africa is to understand why large scale-up has not occurred despite demonstration by several programmes of the viability and effectiveness of biogas plants. This article provides knowledge-based review of biogas technology status, constraints and prospects in Africa. In addition, recommendations to overcome the technological and non-technological challenges to commercialise biogas are discussed. Recommendations for large scale adoption for biogas technology include establishing national institutional framework, increasing research and development, education and training and providing loans and subsidies and major policy shift in the energy sector. The conclusion is that biogas technology must be encouraged, promoted, invested, researched, demonstrated and implemented in Africa.     

Short-term effect of acetate and ethanol on methane formation in biogas sludge

Biochemical processes in biogas plants are still not fully understood. Especially, the identification of possible bottlenecks in the complex fermentation processes during biogas production might provide potential to increase the performance of biogas plants. To shed light on the question which group of organism constitutes the limiting factor in the anaerobic breakdown of organic material, biogas sludge from different mesophilic biogas plants was examined under various conditions. Therefore, biogas sludge was incubated and analyzed in anaerobic serum flasks under an atmosphere of N₂/CO₂. The batch reactors mirrored the conditions and the performance of the full-scale biogas plants and were suitable test systems for a period of 24 h. Methane production rates were compared after supplementation with substrates for syntrophic bacteria, such as butyrate, propionate, or ethanol, as well as with acetate and H₂+CO₂ as substrates for methanogenic archaea. Methane formation rates increased significantly by 35 to 126 % when sludge from different biogas plants was supplemented with acetate or ethanol. The stability of important process parameters such as concentration of volatile fatty acids and pH indicate that ethanol and acetate increase biogas formation without affecting normally occurring fermentation processes. In contrast to ethanol or acetate, other fermentation products such as propionate, butyrate, or H₂ did not result in increased methane formation rates. These results provide evidence that aceticlastic methanogenesis and ethanol-oxidizing syntrophic bacteria are not the limiting factor during biogas formation, respectively, and that biogas plant optimization is possible with special focus on methanogenesis from acetate.     

Stimulation of biomethanation by Clostridium sp. PXYL1 in coculture with a Methanosarcina strain PMET1 at psychrophilic temperatures

Aim:  Bioaugumentation of low temperature biogas production was attempted by addition of cold-adapted Clostridium and a methanogen.
Methods and Results:  A psychrotrophic xylanolytic acetogenic strain Clostridium sp. PXYL1 growing optimally at 20°C and pH 5·3 and a Methanosarcina strain, PMET1, growing optimally on acetate and producing methane at 15°C were isolated from a cattle manure digester. Anaerobic conversion of xylose at 15°C with the coculture of the two strains was performed, and batch culture methane production characteristics indicated that methanogenesis occurred via acetate through 'acetoclastic' pathway. Stimulation studies were also undertaken to evaluate the effect of exogenous addition of the coculture on biogas yields at 15°C. Addition of 3 ml of PXYL1 at the rate of 12 × 10² CFU ml⁻¹ increased the biogas 1·7-fold (33 l per kg cowdung) when compared to control (19·3 l per kg cowdung) as well as increased the volatile fatty acid (VFA) levels to 3210 mg l⁻¹ when compared to 1140 mg l⁻¹ in controls. Exogenous of addition of 10 ml PMET1 inoculum at the rate of 6·8 ± 10² CFU ml⁻¹ in addition to PXYL1 served to further improve the biogas yields to 46 l kg⁻¹ as well as significantly brought down the VFA levels to 1350 mg l⁻¹.
Conclusions:  Our results suggest that the rate-limiting methanogenic step at low temperatures could be overcome and that biogas yields improved by manipulating the population of the acetoclastic methanogens.
Significance and Impact of the Study:  Stimulation of biomethanation at low temperature by coculture.     

Compact automated displacement gas metering system for measurement of low gas rates from laboratory fermentors

An automated metering system was developed for measuring biogas production from laboratory scale biogas digestors. The gas metering system is based on the principle of liquid displacement with a 100-mL reversible cycle and registration. The gas meter is made entirely of plastic and rubber materials resistant to the corrosive components of biogas (e.g., H(2)S) and requires a 12 to 15 VDC power supply.     

生物燃气技术及工程的发展现状

生物燃气俗称沼气,是微生物群体在厌氧条件下协同发酵可降解有机废弃物的产物,传统能源供应的萎缩和增加可再生能源在能源消费中份额的需求使沼气的重要性越来越突出。经过不断研究与工程实践,已经开发出了不同的发酵工艺处理生活垃圾和工农业生产废弃物等有机质生产生物燃气,其中全混式中温发酵占主导地位,欧洲的技术处于领先水平,特别是德国的沼气发电、热电联产。结合作者多年沼气研究积累的经验,综述了沼气技术的最新进展,包括厌氧发酵菌群、消化反应器结构和发酵工艺,沼气生产和应用等,指出了今后发展的重点和方向。