SSF Process Research Articles

Heat transfer in citric acid production by solid state fermentation

Different mechanisms of heat removal (conductive, convective and evaporative) were studied in a SSF process using a packed bed reactor with an inert support (Amberlite IRA-900) previously inoculated. The cylindrical bioreactor was incubated in a temperature controlled chamber (30°C). Average temperature gradients obtained during the culture were 1·3 and 0·42°C cm −1 in the radial and axial directions, respectively. During maximal metabolic activity of Aspergillus niger the medium temperature rose from 32 to 48°C, and a maximum radial temperature gradient of 3·1°C cm −1 was achieved. At this stage, the unsteady-heat balances indicated that conductive heat transfer was the least efficient mechanism (8·65%) when compared with convective (26·65%) and evaporative (64·7%) mechanisms. Sugar consumption and glycerol and citric acid production were strongly affected by temperature.

Technoeconomic assessment of biomass to energy

A spreadsheet-based decision support system has been developed that allows easy evaluation of integrated biomass to electricity and biomass to ethanol systems. The Bioenergy Assessment Model (BEAM) has been developed to allow the techno-economic assessment of biomass to electricity and biomass to ethanol schemes, including investigation of the interfacing issues. Technical and economic parameters can be assessed for a variety of feedstocks, conversion technologies and generating cycles. A spreadsheet format has been used to make the model inherently expandable: new system options can be added by adding new spreadsheets and making minor adjustments to the executive program that links the spreadsheets together. Production modules are currently available for biomass supply from short rotation coppice and conventional forestry relevant to conditions and practices in NW Europe. The biomass conversion modules include pre-treatment (reception, storage, handling, comminution, screening and drying); atmospheric gasification (generic gasifier, wet gas scrubbing, dual fuel engine); pressure gasification (generic gasifier, hot gas filtration, gas turbine combined cycle); fast pyrolysis for liquid bio-fuel-oil (pyrolyser, oil storage, pilot-injected diesel engine); combustion (fluid bed combuster steam turbine), conventional acid hydrolysis fermentation and the NREL SSF process to ethanol. In addition there is a further module which can be used to examine the collection, mass burn and generation of electricity from MSW. BEAM has been used, and the results presented in this paper, to determine the costs of generating bio-electricity from short rotation coppice and conventional forestry over a range of power outputs and for each conversion technology. Alternative feedstock supply strategies have been examined and relations drawn between delivered feedstock cost and cost of electricity. Sensitivity analysis reveals that the cost of bio-electricity production from short rotation coppice is highly sensitive to the yield of the crop. BEAM has been shown to work well with the systems under consideration and is capable of further development. The long term aim is to provide a simple model with on-line help and information that will allow biomass systems developers to make initial assessments of the feedstock and technology options that are available and to direct research and development towards the more promising areas.

Sago starch saccharification and simultaneous ethanol fermentation by amyloglucosidase and Zymomonas mobilis

AbstractSimultaneous saccharification and ethanol fermentation (SSF) of sago starch was studied using amyloglucosidase (AMG) and Zymomonas mobilis. The optimal concentration of AMG and operating temperature for the SSF process were found to be 0.5% (v/w) and 35°C, respectively. Under these conditions with 150 g dm−3 sago starch as a substrate, the final ethanol concentration obtained was 69.2 g dm−3 and ethanol yield, YP/S, 0.50 g g−1 (97% of theoretical yield). Sago starch in the concentration range of 100–200 g dm−3 was efficiently converted into ethanol. When compared to a two‐step process involving separate saccharification and fermentation stages, the SSF reduced the total process time by half.