The following sections highlight the various process developments proposed by our team that may convert both processes from conceptual designs with dubious economic potential to economically viable processes that can be utilized within rural areas that are currently producing high volumes of waste biomass. These rural areas in Mississippi can be transformed from areas undergoing public debate over waste disposal issues to economic development zones producing ethanol as a product.

Commercialization of the fermentation of syngas has been hindered by a variety of technical and economic shortcomings. Significant work is on-going on the improvement of syngas production from waste products step because this step contributes to the overall economics of ethanol production. Currently, DOE and MSU are both working on optimized syngas production reactor designs for increasing the carbon monoxide yield of the syngas process. With regard to the fermentation (bioprocessing) system, several issues require further development to improve the economic outlook of this process and improve the performance and stability of the system. One particularly attractive aspect is the high capture efficiency of the carbon and hydrogen within the waste products during syngas generation as opposed to significant carbon and hydrogen losses via carbon dioxide and water evolution experienced by the other ethanol production techniques.

The microorganisms that have been utilized in past DOE research have been almost exclusively derived from a discovery of a bacterial isolate from a chicken processing sludge. Optimization of this isolate into new, more productive strains has been successful using forced molecular evolution techniques (advanced acclimation). It is believed that continued bacterial discovery efforts may lend to the development of even more efficient microorganism than the currently used isolates. Various anaerobes have shown promise for acetate production using syngas constituents. It is postulated that these organisms and others of similar physiological character may serve as organisms that with careful manipulation may produce even greater yields of ethanol. Many of these organisms can function at high CO levels with relatively short doubling times indicating the great untapped potential of these organisms for producing carboxylic salts and/or primary alcohols. Past work in the environmental bioremediation field indicates that comprehensive searches of a wide variety of microbial ecosystems often result in the discovery of new isolates that have increased degradation capabilities over what had previously been considered "optimal" isolates. It is proposed that continued screening of various other anaerobic ecological sources may lead to the discovery of improved isolates as wilds. This effort will then be followed by attempts at optimization, hopefully resulting in the discovery of improved strains via forced molecular evolution techniques which may lead to gene discovery efforts in the future. Additionally, there are a variety of fermenter ecosystem manipulation techniques that may result in further optimization of the microorganisms discovered during this effort and those from the past DOE efforts. Investigations into reformulation of fermenter nutrient solutions, pH adjustments, manipulation of electron streams, and evaluation of off-line feeder fermenters may greatly improve performance and reactor stability.

Another key issue that will challenge the stability of the fermenter is the maintenance of isolate purity within industrial-scale fermenters. From a microbiological standpoint, the ecosystem provided by fermenters used for producing ethanol from syngas may be conducive to the establishment of microbial contaminants (i.e. organisms that establish themselves within the fermenter that compete for nutrients and eventually inhibit or completely disrupt ethanol production). For example, given the presence of sufficent nutrients under the REDOX conditions used within syngas fermenters there is a good potential for the establishment of methanogens which produce methane using the scheme below:

CO₂ + 4H₂ –> CH₄ + 2H₂O

The establishment of methanogens is problematic because they convert the gas constituents that would have produced ethanol into a product of limited value compared to ethanol and acetic acid. Additionally, these organisms compete for nutrients which are intentionally maintained at near stressed levels (results in higher ethanol yields); thereby, scavenging the limited nutrients present, possibly, to the extent of adversely affecting ethanol production. The currently subscribed technique for preventing establishment of methanogens is the presence of the carbon monoxide within the syngas feed, which is toxic to methanogens; however, as discussed above, it is hoped that increased utilization of carbon monoxide can be obtained for maximizing ethanol production, thus increasing the potential for methanogen establishment. Outside of evaluating the growth potential of methanogens, a screening of other potential biological contaminants needs to be initiated in order to determine what other bacterial contaminants may be problematic during full-scale application (under less than ideal sterility conditions). This effort should provide insight into potential preventive protocols that may have to be initiated to preserve isolate integrity.

Another tool that is proposed for development is the use of phospho-lipid, fatty acid (PLFA) finger-printing of the selected isolate(s) for ethanol production within the fermenter. This gas chromatography based analytical procedure has become the state-of-the-art for evaluating reactor biomass stability and assessing stress levels within bioreactors. A database of key isolates with proven value for ethanol production will be developed as well as data generated for typing selected bacterial contaminants. This approach will allow process engineers to accurately evaluate functional biomass density (as opposed to gravimetric techniques), evaluate isolate integrity, and assess biomass stress levels (especially useful for those systems targeting microstressed environments for maximizing ethanol production) within a reasonable time-frame. Additionally, this technique will utilize GC instrumentation that is commonly used at ethanol production facilities for analyzing ethanol content. Plus, the PLFA assay can be programmed and stored within a commercially available GC software operation and data evaluation package.

Attached growth fermenters (aka. trickle-bed) have been found during waste treatment to provide a more stable bioreactor than a suspended growth units. Albeit not with fermentation of syngas, some research with fermentation-produced ethanol within attached/immobilized growth reactors has yielded very positive results. Another benefit to the use of attached growth bioreactors is that cell separation techniques are not required down-stream which eliminates the need for membrane cell separators. The membrane separation step represents approximately 25% of total capital construction costs of plant construction (based on a recent design evaluation by MSU). Additionally, improved mass transfer of the syngas constituents into the fementation broth may be realized using a counter-current flow trickle bed fermentation column. Various configurations are possible that may increase production efficiency through increased biomass levels and stability within the fermenter. Several designs, including both flow configuration and structural substrate selection, need evaluation. One particularly innovative concept that will be evaluated involves the use of membrane bacterial supports that provide a growth medium for the organisms to attach; while, through development of ethanol permeable materials, allowing the ethanol to be directly extracted from the fermenter (i.e. production and separation within the same unit). This concept has been proposed by others for removing ethanol/water solutions to be removed from direct fermentation units.

Another intriguing research issue that addresses a very practical problem facing potential commercial development is the management of the acetic acid formed as a secondary fermentation by-product (see above discussions). The management of acetic acid was evaluated in the past DOE funded effort. Recirculation of the distillation bottoms to the head of the plant was studied with little or no success noted. Currently, most facilities under consideration are planning to treat the distillation bottoms as a process wastewater. It is believed that treating an acetic acid laden wastewater (estimated to be approximately 5,000 mg/l) containing this high BOD is an expensive option and a waste of valuable carbon source that may be used for secondary production of a potentially beneficial product. Various extraction/recovery techniques are believed to be technically and, possibly, economically feasible for recovering the acetic acid as a secondary product. Examples of potential processes to be evaluated include advanced distillation, liquid-liquid extraction, membranes, or a combination of these.

The application of synthetic ionomeric membranes in a number of industrially important technologies is now widespread. Based on the ability to easily control the ionic composition of ionomers, the hydrophobic/hydrophilic character of the resulting membranes has been tailored using a wide range of polymers for the efficient separation of ethanol/water mixtures. Of particular importance to this work, the ionic functionality in ionomers is known to greatly enhance the transport of water and other polar organic solvents, increase physical strength and durability in thin films, and yield a complex morphology of phase separated ionic domains that can effectively reject the transport of ionic species by Donnan exclusion. These desirable characteristics of ionomers will be exploited in the preparation of new membranes for the separation of products from fermentation aqueous streams and possibly distillation bottoms.

Another proposed management option for the acetic acid in the waste stream from ethanol separation is the anaerobic digestion of the process wastewater to produce methane (via decarboxylation which can be used as an energy source for firing the distillation secondary burner or used as a fuel within the syngas facility. Numerous isolates are very capable of efficiently producing methane from acetate/acetic acid. Numerous sources report successful production of fuel-grade methane from the anaerobic degradation of a methanol (8 g/l) and acetic acid (1.5 g/l) influent. Several industrial aqueous waste streams have been converted to recovered biogas leading to the construction of full-scale systems. Germany has implemented a massive biogas production effort (greater than 400 plants) from agricultural manure treating facilities which is reported successful in terms of methane recovery and utilization. Anheuser-Bush is currently feeding brewery wastewaters into an anaerobic digestor that is producing methane from an estimated 90,000 pounds of BOD yielding a reported fuel cost savings of $485,000.

Aerobic biotreatment is the most popular waste treatment technique for industrial wastewaters. However, unpublished studies at MSU indicates a high BOD mass conversion rate from sodium acetate which represents a relatively high organic loading that will make aerobic biotreatment too costly for the management of the wastewaters produced by the current designs for ethanol-from-syngas facilities. Therefore, it likely some form of anaerobic treatment must be implemented; however, from an economic standpoint, this approach is best when coupled with methane recovery. Therefore, a high potential does exist for taking the process acetate wastestream and converting it into a source of additional energy in the form of biogas. Utilizing this acetic acid will greatly reduce the organic loading of down-stream wastewater treatment processes. At worst, if sufficient methane cannot be produced, this effort will provide an evaluation of the potential for using an anaerobic bioreactor system for treatment of the acetate laden stream, which is considered an economically more attractive waste treatment option than aerobic biotreatment for this type of wastewater.

Acid hydrolysis of a hardwood cellulose structure is expected to be more difficult than hydrolysis of the cellulose found in cotton waste. Cotton waste has more surface area for acid decrystallization and depolymerization of its cellulose structure than that found in sawdust. Thus, acid impregnation of the cotton waste may not require the high surface shearing forces or acid amounts needed to impregnate sawdust. In addition, ethanol yields from cotton waste will exceed that for hardwood because cotton waste contains a higher amount of cellulose than sawdust. Still, the potential for producing by-products that are toxic and/or inhibitory to fermentation must be evaluated; however, base on cotton waste composition, it is believed that lower yields of these problem by-products will be observed.

The benefits of acid recovery and reuse in the conversion process are both economic and environmental. The present technique for acid/sugar separation uses a continuous ion exclusion chromatography system. This provides effective recovery of the acid and sugars. However, the ion exclusion separation process, while effective, requires complex equipment and control systems to achieve high efficiency. A review of available literature indicates the feasibility of using a less expensive membrane based separation system. Thus, research is needed to investigate the membrane micro-architecture required to separate hydrolyzate into its components, acid and sugar.

The chromatography system used successfully by TVA/USM to separate hydrolyzate components made use of sulfonated polystyrene materials. The membranes proposed to be developed in this study for extracting sugars from the acid hydrolyzate will also be fabricated from the same type polymeric materials. However, because it is not possible to predict the necessary degree of sulfonation for successful sugar separation, a range of degrees of sulfonation in the membrane will have to be explored. This will involve two membrane formation approaches: post-polymerization sulfonation and co-polymerization.

Post-polymerization techniques may be applied to solvated polymers or pre-fabricated porous membranes. This will allow a study of the differences in membrane formation as a function of ionic group content and the effect of the sulfonation reaction on the membrane. Secondly, it is possible to create copolymers from styrene and styrene sulfonate. These copolymers allow a much larger variation in sulfonate group content in the polymer than is obtainable via post-polymerization reactions. Also as an alternative membrane material, the use of a more conventional polysulfone matrix will be evaluated. These materials may be sulfonated using procedures similar to that used in the preparation of sulfonated polystyrene. Manufacturing processes can be customized to produce asymmetric membranes with a "swiss cheese" or fingered morphology. Asymmetric fingered membranes can be visualized by imagining a porous material with conical pores. The excluded material is larger than the narrow inlet channel opening, and is therefore prevented from entering the membrane. However, once the permeate passes through the narrow inlet opening, flow is unrestricted by the ever widening channel passage. This feature of an asymmetric membrane eliminates the problem of blocked pores inherent to symmetric membranes. Experimental and predictive models, already developed by USM will be employed, because of the number of experimental variations, to narrow the range of possible membrane structures, including porosity of the membrane, degree of sulfonation, and pre- versus post-polymerization sulfonation. The use of statistical experimental design techniques will allow a large number of membranes to be evaluated and direct the research to a micro-architecture that gives optimum acid separation.

Currently, the most important polymeric membranes for separation processes are those made by a phase inversion technique. The phase inversion technique is based upon the addition of a non-solvent to a thin layer of solvated polymer and can result in the formation of microporous membranes with variable morphologies. The mechanism of formation is a complicated combination of mass transport and thermodynamic phase separation phenomena. The non-solvent induced phase inversion (NIPI) can be accomplished in a variety of ways. Another process of interest for membrane fabrication is thermally induced phase separation (TIPS). In this process, both metastable and unstable phase regions are first identified. Of the three possible morphologies that can be developed, those derived from the unstable regions are of the most interest. Phase separation through an unstable region can result in membranes that have both uniform interconnected pores and good mechanical strength.

Phase change separation processes will also be evaluated because of the importance of developing an energy efficient acid concentration process for minimizing operational cost. Sulfuric acid concentration by multi-effect evaporation will be investigated. Multi-effect evaporation is a process whereby the dilute acid solution from acid recovery can be concentrated in several stages or effects with the vapor generated in each effect being used as a heat source in each succeeding effect. This process allows heat efficiencies of five or six times greater than single stage evaporation. This method of concentration by multi-effect evaporation is used extensively in the desalinization of sea water and in paper mill black liquor recovery processes. However because of corrosion difficulties, its application to sulfuric acid concentration will present a unique set of challenges to be addressed.

Adequate removal of acid from the sugar feed stream to fermentation is critical to the survival of the fermenting organisms. However as acid levels are reduced in the sugar stream output, all separation processes become less economical. Thus, the development of acid tolerant sugar fermenting organisms would reduce the demands on any acid/sugar separation process and also provide increased robustness to any variability occurring in the acid-sugar separation system.

The chemical conversion of agricultural waste to ethanol via acid hydrolysis could be made more efficient if it were supplemented with enzymes which by their nature have a high turnover. Although it would be desirable to augment acid hydrolysis with an efficient enzyme, the technical drawback is that most biochemical systems are inactivated by the harsh acidic conditions found in an industrial process. Therefore, an effort to identify enzymes that might be of potential use in supplementing the acid hydrolysis of cellulose will be initiated. As a source of these enzymes, the examination of microorganisms that grow in environments of low pH will be performed (an extremophile termed an acidiphile). The rationale being that if the organisms are normally found growing in an acidic niche, their proteins, enzymes etc. should be more stable under low pH conditions.