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

Two-Stage Conversion of Land and Marine Biomass for Biogas and Biohydrogen Production

The replacement of fossil fuels by renewable fuels such as biogas and biohydrogen will require efficient and economically competitive process technologies together with new kinds of biomass. A two-stage system for biogas production has several advantages over the widely used one-stage continuous stirred tank reactor (CSTR). However, it has not yet been widely implemented on a large scale. Biohydrogen can be produced in the anaerobic two-stage system. It is considered to be a useful fuel for the future due to its high energy density and clean combustion with the emission of only water vapour. Anaerobic digestion can be used to treat wastewater and for energy production, leading to a reduction in eutrophication and greenhouse gases. The material remaining after treatment can also be used as a fertiliser as long as certain standards are met. The production of biogas and biohydrogen from a range of land and marine biomasses was studied in this work. The reduction of the heavy metal content of seaweed was also studied in order to improve fertiliser quality. Two-stage, dry anaerobic digestion of mussels, reeds, seaweed, solid cow manure, and a mixture of seaweed and manure was studied. The system consisted of a leach bed reactor for hydrolysis and an upflow anaerobic sludge blanket (UASB) reactor for methane production. The results showed that mussels with shells, seaweed, and the seaweed and manure mixture were efficiently digested in the two-stage system; 68 to 83% of the methane being produced in the UASB reactor. The manure by itself, and reeds, which are slowly degradable, were efficiently digested in the one-stage dry leach bed process, in which most of the biogas was produced. Seaweed and manure can also be co-digested in the one-stage dry digestion process, since methano¬genic conditions prevailed in the leach bed reactor, thus reducing the cost of operating two biogas reactors. Technically, both the new feedstocks and the one- and two-stage dry anaerobic systems have great potential for biogas production. However, economic evaluations are needed to validate practical applicability. The removal of heavy metals from seaweed hydrolysate was studied in the two-stage system. The heavy metals Cd, Cu, Ni and Zn were adsorbed using iminodiacetic acid Cryogel® carriers. However, removal of the heavy metals resulted in low methane yields, possibly due to the removal of micro¬nutrients needed for anaerobic digestion. It is therefore suggested that the metals be removed after methane production in a UASB reactor. Alkaline and autoclave post-treatment of the seaweed digestate resulted in 86% organic matter solubilisation and the leachate may be treated in a UASB reactor, providing a means of handling digestate with high heavy metal content. Co-digestion of leachates from the leach bed reactor and the post-treatment resulted in a high methane yield, 0.34 l/gVSadded in a batch test. Subsequent treatment of the leachate from the leach bed reactor resulted in a high methane productivity at a loading rate of 20.6 g COD/l.day in a UASB reactor. Treatment of the seaweed leachate in the UASB reactor resulted in a stable process without the need for additional nutrients or buffer. As the seaweed leachate was rich in nutrients and buffer capacity, its co-digestion with wheat straw hydrolysate in the UASB reactor resulted in a stable process. Biohydrogen and biogas were co-produced from wheat straw hydrolysate in a two-stage system consisting of a CSTR and a UASB reactor, employing the thermophile, Caldicellulosiruptor saccharolyticus in the first H2 reactor. Straw hydrolysate was efficiently produced by acid-catalysed steam and enzyme pretreatment, giving a 95% sugar yield of the theoretical yield. High biofuel production rates of 1.8 to 3.5 l H2/l.day and 2.6 to 4.0 l CH4/l.day were obtained under stable operational conditions and treatment efficiencies. However, the cost of nutrient supplementation was high, and cheaper nutrient sources will be required to make the production cost economically competitive. This research has demonstrated the versatility of a two-stage system that allowed the digestion of new kinds of biomass such as seaweed with sand, mussels with shells, reeds, manure and wheat straw. It has also been shown to be possible to remove heavy metal from seaweed to improve fertiliser quality. High hydrogen and methane production rates were also demonstrated, and the two-stage anaerobic system is thus, technically, a promising reactor configuration for the production of biofuels

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

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

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

Design of a novel biohythane process with high H2 and CH4 production rates

A biohythane process based on wheat straw including: i) pretreatment, ii) H2 production using Caldicellulosiruptor saccharolyticus, iii) CH4 production using an undefined consortium, and iv) gas upgrading using an amine solution, was assessed through process modelling including cost and energy analysis. According to simulations, a biohythane gas with the composition 46–57% H2, 43–54% CH4 and 0.4% CO2, could be produced at high production rates (2.8–6.1 L/L/d), with 93% chemical oxygen demand (COD) reduction, and a net energy yield of 7.4–7.7 kJ/g dry straw. The model was calibrated and verified using experimental data from dark fermentation (DF) of wheat straw hydrolysate, and anaerobic digestion of DF effluent. In addition, the effect of gas recirculation was investigated by both wet experiments and simulation. Sparging improved H2 productivities and yields, but negatively affected the net energy gain and cost of the overall process