Biohydrogen production from wheat straw hydrolysate using Caldicellulosiruptor saccharolyticus followed by biogas production in a two-step uncoupled process

A two-step, un-coupled process producing hydrogen (H2) from wheat straw using Caldicellulosiruptor saccharolyticus in a ‘Continuously stirred tank reactor’ (CSTR) followed by anaerobic digestion of its effluent to produce methane (CH4) was investigated. C. saccharolyticus was able to convert wheat straw hydrolysate to hydrogen at maximum production rate of approximately 5.2 L H2/L/Day. The organic compounds in the effluent collected from the CSTR were successfully converted to CH4 through anaerobic digestion performed in an ‘Up-flow anaerobic sludge bioreactor’ (UASB) reactor at a maximum production rate of 2.6 L CH4/L/day. The maximum energy output of the process (10.9 kJ/g of straw) was about 57% of the total energy, and 67% of the energy contributed by the sugar fraction, contained in the wheat straw. Sparging the hydrogenogenic CSTR with the flue gas of the UASB reactor ((60% v/v) CH4 and (40% v/v) CO2) decreased the H2 production rate by 44%, which was due to the significant presence of CO2. The presence of CH4 alone, like N2, was indifferent to growth and H2 production by C. saccharolyticus. Hence, sparging with upgraded CH4 would guarantee successful hydrogen production from lignocellulosic biomass prior to anaerobic digestion and thus, reasonably high conversion efficiency can be achieved

Anaerobic Digestion – Microbial Ecology, Improved Operational Design and Process Monitoring

The implementation of anaerobic digestion is important in the concept of sustainable development, especially regarding the environmental benefits. Biogas is produced when organic matter is degraded by microorganisms under oxygen-free (anaerobic) conditions. Biogas production occurs in nature where oxygen is absent; in rice fields, landfills, sediments, the intestinal tract of animals, etc. The advantage of degrading organic matter and at the same time producing renewable energy in the form of energy-rich methane, as well as other environmental benefits, has made anaerobic digestion interesting in industrial applications. Anaerobic digestion has been exploited as an effective biotechnological method for organic waste and wastewater treatment. Current national environmental regulations and other policies governing land use and waste disposal have increased interest in anaerobic digestion. However, the anaerobic degradation of organic matter is a complex process involving microorganisms in an advanced interaction. Our knowledge about the anaerobic digestion process is increasing, but to increase the efficiency of the process and to make it more economically beneficial there is a need for improvements in the technology in many areas. Studying the microbial ecology is important for in-depth understanding of the anaerobic degradation process. Fluorescence in situ hybridisation (FISH) was employed to identify microorganisms in the anaerobic process with the focus on methanogens. Probes commonly used in FISH for detecting methanogens were re-evaluated and redesigned, giving better coverage of the methanogens, and the experimental conditions were optimised for use of the probes in FISH. Using FISH, changes in microbial composition could be detected when changing feed composition in anaerobic reactors, which could be correlated to changes in process conditions. A new application for partitioning in aqueous two-phase systems was developed. The mixed culture from an anaerobic digestion process was multi-step partitioned in an aqueous two-phase system in order to obtain a “fingerprint” of the culture. Differences in operational conditions could be reflected in the distribution profiles obtained. Process control and monitoring are of great importance in improving the efficiency of the anaerobic degradation process. Traditional and new methods were evaluated for the monitoring of anaerobic digestion processes. Since the anaerobic process is so complex, one parameter is seldom sufficient to monitor the conditions in a reactor, and a combination of parameters should be used for reliable process monitoring and control. With a good monitoring and control strategy it is possible to run the digesters closer to their maximum capacity thereby improving the treatment capacity and the process economy. The development of process designs and configurations has improved treatment rates making the process more cost-efficient. The successful co-digestion of agricultural waste with sewage sludge and pig manure was reported. Mixing of waste must be done with care as unsuitable mixtures can lead to unstable process conditions resulting in failure of the anaerobic digestion process. The development of new high-rate reactor designs has increased the efficiency and stability of the biogas process compared with the conventional reactor configuration. Three different high-rate reactor designs were evaluated and successfully applied to the treatment of solid agricultural waste

Biogas production from wheat straw in batch and UASB reactors: The roles of pretreatment and seaweed hydrolysate as a co-substrate.

This research evaluated biogas production in batch and UASB reactors from pilot-scale acid catalysed steam pretreated and enzymatic hydrolysed wheat straw. The results showed that the pretreatment was efficient and, a sugar yield of 95% was obtained. The pretreatment improved the methane yield (0.28m(3)/kg VS(added)) by 57% compared to untreated straw. Treatment of the straw hydrolysate with nutrient supplementation in a UASB reactor resulted in a high methane production rate, 2.70m(3)/m(3).d at a sustainable OLR of 10.4kg COD/m(3).d and with a COD reduction of 94%. Alternatively, co-digestion of the straw and seaweed hydrolysates in a UASB reactor also maintained a stable anaerobic process and can thus reduce the cost of nutrients addition. We have shown that biogas production from wheat straw can be competitive by pretreatment, high methane production rate in UASB reactors and also by co-digestion with seaweed hydrolysate

Exploring strategies for seaweed hydrolysis: Effect on methane potential and heavy metal mobilisation

Energy-rich methane can be harnessed from seaweed deposits by anaerobic digestion. However, the high heavy metal content in the seaweed and its digestates limits their use as fertilisers. Heavy metal contaminants from solid seaweed can be removed by, mobilisation into a liquid phase and subsequent metal ions adsorption. In this laboratory-scale study, pretreatment strategies for enhancing seaweed hydrolysis in relation to metal ions. mobilisation were evaluated. Methane potential batch tests were also performed on the resulting treatment leachates. The results show that about 86% of the soluble organic compounds were hydrolysed/solubilised in a leach bed reactor followed by alkaline/autoclave post-treatments. However, Zn ion mobilisation was only 54% from the combined treatments. A 2.8-fold higher methane yield was obtained when the seaweed hydrolysis leachate and the post-treatment leachate were co-digested, compared to raw seaweed. This study demonstrated the efficient utilisation of seaweed for biogas production, and the partial heavy metals mobilisation to enable the metal removal for improved fertiliser quality. (C) 2012 Elsevier Ltd. All rights reserved

Evaluation of biogas production from seaweed in batch tests and in UASB reactors combined with the removal of heavy metals.

Seaweed can be anaerobically digested for the production of energy-rich methane. However, the use of seaweed digestate as a fertilizer may be restricted because of the high heavy metal content especially cadmium. Reducing the concentration of heavy metals in the digestate will enable its use as a fertilizer. In this laboratory-scale study, the potential of seaweed and its leachate in the production of methane were evaluated in batch tests. The effect of removing the heavy metals from seaweed leachate was evaluated in both batch test and treatment in an upflow anaerobic sludge blanket (UASB) reactor. The heavy metals were removed from seaweed leachate using an imminodiacetic acid (IDA) polyacrylamide cryogel carrier. The methane yield obtained in the anaerobic digestion of seaweed was 0.12 N l CH(4)/g VS(added). The same methane yield was obtained when the seaweed leachate was used for methane production. The IDA-cryogel carrier was efficient in removing Cd(2+), Cu(2+), Ni(2+) and Zn(2+) ions from seaweed leachate. The removal of heavy metals in the seaweed leachate led to a decrease in the methane yield. The maximum sustainable organic loading rate (OLR) attained in the UASB reactor was 20.6 g tCOD/l/day corresponding to a hydraulic retention time (HRT) of 12 h and with a total COD removal efficiency of about 81%. Hydrolysis and treatment with IDA cryogel reduced the heavy metals content in the seaweed leachate before methane production. This study also demonstrated the suitability of the treatment of seaweed leachate in a UASB reactor

Two-stage anaerobic dry digestion of blue mussel and reed

Blue mussels and reeds were explored as a new biomass type in the Kalmar County of Sweden to improve renewable transport fuel production in the form of biogas. Anaerobic digestion of blue mussels and reeds was performed at a laboratory-scale to evaluate biogas production in a two-stage dry digestion system. The two-stage system consisted of a leach bed reactor and an upflow anaerobic sludge blanket (UASB) reactor. The two-stage system was efficient for the digestion of blue mussels, including shells, and a methane yield of 0.33 m(3)/kg volatile solids (VS) was obtained. The meat fraction of blue mussels was easily solubilised in the leach bed reactor and the soluble organic materials were rapidly converted in the UASB reactor from which 68% of the methane was produced. However, the digestion of mussels including shells gave low production capacity, which may result in a less economically viable biogas process. A low methane potential, 0.22 m(3)/kg VS, was obtained in the anaerobic two-stage digestion of reeds after 107 days: however, it was comparable to similar types of biomass, such as straw. About 80% of the methane was produced in the leach bed reactor. Hence, only a leach bed reactor (dry digestion) may be needed to digest reed. The two-stage anaerobic digestion of blue mussels and reeds resulted in an energy potential of 16.6 and 10.7 GWh/year, respectively, from the estimated harvest amounts. Two-stage anaerobic digestion of new organic materials such as blue mussels and reeds can be a promising biomass resource as land-based biomass start to be limited and conflict with food resources can be avoided. (C) 2012 Elsevier Ltd. All rights reserved

An update and optimisation of oligonucleotide probes targeting methanogenic Archaea for use in fluorescence in situ hybridisation (FISH)

Fluorescence in situ hybridisation (FISH) is a common and popular method used to investigate microbial populations in natural and engineered environments. DNA oligonucleoticle probes require accurate determination of the optimal experimental conditions for their use in FISH Oligonucleotides targeting the rRNA of methanogenic Archaea at various taxonomic levels have previously been published, although when applied in FISH, no optimisation data has been presented In this study, 3000 Euryarchaeota 16S rRNA gene sequences were phylogenetically analysed and previously published oligonucleoticles were evaluated for target group accuracy. Where necessary, modifications were introduced or new probes were designed. The updated set of probes was optimised for use in FISH for a more accurate detection of methanogenic Archaea. (c) 2005 Elsevier B.V. All rights reserved

Impact of food industrial waste on anaerobic co-digestion of sewage sludge and pig manure

The performance of an anaerobic digestion process is much dependent on the type and the composition of the material to be digested. The effects on the degradation process of co-digesting different types of waste were examined in two laboratory-scale studies. In the first investigation, sewage sludge was co-digested with industrial waste from potato processing. The co-digestion resulted in a low buffered system and when the fraction of starch-rich waste was increased, the result was a more sensitive process, with process overload occurring at a lower organic loading rate (OLR). In the second investigation, pig manure, slaughterhouse waste, vegetable waste and various kinds of industrial waste were digested. This resulted in a highly buffered system as the manure contributed to high amounts of ammonia. However, it is important to note that ammonia might be toxic to the micro-organisms. Although the conversion of volatile fatty acids was incomplete the processes worked well with high gas yields, 0.8-1.0 m(3) kg(-1) VS. (C) 2004 Elsevier Ltd. All rights reserved

Evaluation of parameters for monitoring an anaerobic co-digestion process

The system investigated in this study is an anaerobic digester at a municipal wastewater treatment plant operating on sludge from the wastewater treatment, co-digested with carbohydrate-rich food-processing waste. The digester is run below maximum capacity to prevent overload. Process monitoring at present is not extensive, even for the measurement of on-line gas production rate and off-line pH. Much could be gained if a better program for monitoring and control was developed, so that the full capacity of the system could be utilised without the risk of overload. The only limit presently set for correct process operation is that the pH should be above 6.8. In the present investigation, the pH was compared with alkalinity, gas production rate, gas composition and the concentration of volatile fatty acids (VFA). Changes in organic load were monitored in the full-scale anaerobic digester and in laboratory-scale models of the plant. Gas-phase parameters showed a slow response to changes in load. The VFA concentrations were superior for indicating overload of the microbial system, but alkalinity and pH also proved to be good monitoring parameters. The possibility of using pH as a process indicator is, however, strongly dependent on the buffering capacity. In this study, a minor change in the amount of carbohydrates in the substrate had drastic effects on the buffering effect of the system

Characterisation of anaerobic mixed cultures by partition in an aqueous two-phase system

A method to characterise a dynamic microbial consortium is described. By exploiting differences in surface properties between different cells and between cells of different physiological status, it was possible to develop a partition pattern for a mixed culture under different conditions. The separation method used was partition in aqueous two-phase systems and when using a counter current extraction process one could clearly differentiate the partition profile between resting, active and overloaded biomethanation cultures