Aiming for Efficiency

University researcher designs efficient, sustainable biorefinery systems
By Erin Voegele | April 27, 2012

The biorefining industry has made great strides in technology development, but as the industry begins to scale-up production, a strong technology platform in and of itself may not be enough to ensure that commercial operations are as economically competitive as possible. It will also be important that biorefining companies find ways to leverage the production of coproducts while reducing energy use and waste.

A researcher at North Carolina A&T State University is developing biorefining models that can help make biorefinery operations as efficient as possible. Lijun Wang, an associate projector of chemical, biological and bioengineering, is developing such models for lignocellulosic biofuel production, algae cultivation and thermochemical conversion of waste biomass into bio-oil. “I think the big issue of the moment within the industry,” he says, “is the need to improve process efficiency while bringing costs down so biobased products can be competitive in the market.”

For cellulosic ethanol production, Wang has developed an innovative model that involves the coproduction of acetic acid and activated carbon, which are recycled back into the process to increase efficiencies. Wang says only the cellulosic component of lignocellulosic biomass can be effectively converted into ethanol. As a result, the hemicellulose and lignin fractions of the feedstock are wasted in a typical fermentation operation.

In Wang’s design, cellulosic (C6) sugars are converted into ethanol via a yeast fermentation process, while the hemicellulosic (C5) sugars are used to produce acetic acid. Although the commonly used commodity chemical could be sold into the market as a coproduct, Wang’s biorefinery design calls for it to be recycled back into the plant’s operation where it is used to pretreat lignocellulosic biomass and help separate the C5 and C6 sugars. The design could help reduce operational costs, as a plant effectively produces its own feedstock pretreatment solution.

Wang’s design also incorporates the processing of fermentation residue into activated carbon, which can be used to treat wastewater coming out of the fermentation process. The activated carbon can then be burned onsite in a cogeneration facility to produce heat and electricity to power the facility and its biorefinery operations.

Wang, however, hasn’t focused exclusively on the cellulosic biofuels sector; he is also leading an ongoing algae project. Under Wang’s algae production model, wastewater treatment would be combined with algae cultivation. The challenge, he says, is to design an algae production system that can operate economically and efficiently year-round. The project contains several components including biological and computer modeling work to select the most appropriate algae strain for use in a specific wastewater treatment operation, and testing it in a photobioreactor system.

 As part of the project, Wang is also designing a method to use carbon dioxide gas produced via an anaerobic digestion system using biological matter found in wastewater to bubble through the algae solution serving as an agitator. The agitation process has typically been done using energy-intensive pump systems. Wang says his method would have the additional benefit of increasing the amount of carbon dioxide circulating within the solution, helping to promote algae growth. The project will also seek to develop ways to help increase the amount of sunlight that can penetrate the algae solution.

—Erin Voegele