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The influence of aeration on algal growth and gamma-linolenic acid (GLA) production in a bubble column photobioreactor was investigated. Studies were performed in a 20-L reactor at different aeration rates (0.2– 2.5 vvm). Static, continuous, and periodic operation of air resulted in 41.9%, 88.4%, and 108% air saturation of dissolved oxygen, for which the corresponding values of GLA were 2.3, 6.5, and 7.5 mg·g-1 dry cell weight, respectively. An increase in the aeration rate from 0.2 to 2.5 vvm enhanced both the specific growth rate and GLA content under periodic sparging in the bicarbonate medium. With a 6-fold increase in the aeration rate, the GLA content of the alga increased by 69.64% (5.6–9.5 mg· g-1 dry cell weight). In addition, the total fatty acid (TFA) content in dry biomass increased from 2.22% to 4.41%, whereas the algae maintained a constant GLA to TFA ratio within the aeration rate tested. The dependence of GLA production on the aeration rate was explained by interrelating the GLA production rate with the specific growth rate using the Luedeking and Piret mixed growth model.

Switchgrass (SG), corn stover (CS), and prairie cordgrass (PCG) pretreated with ammonia fiber expansion (AFEX) were densified using a novel low-temperature, low-pressure densification method. Simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) were performed with loose and densified AFEX-treated biomass to determine the effect of post-AFEX densification. Biomass particle size reduction before pretreatment increased 144-h SSF ethanol yields from densified material by 8-9 % although no significant differences were seen in the first 72 h. Grinding material after densification had no impact on final ethanol yields but increased production rates in the first 24-48 h. Low-pressure, post-AFEX densification had no adverse effects on SSF ethanol yields from SG or CS but reduced yields from densified PCG by 16 %. Glucose concentrations after hydrolysis (SHF) showed similar trends. Ethanol yields after SHF, however, showed that densification had no significant impact on CS or PCG but reduced final ethanol yields from SG.

Corn stover, switchgrass, and prairie cordgrass were treated with an ammonia fiber expansion (AFEX) process and a novel densification method (ComPAKco). Separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) were used to evaluate impacts of densification. ComPAKco densification is characterized by low-temperature and low-energy requirements, resulting in compacted biomass briquettes (CBB) 1-2 cm square, with a bulk density of 380-460 kg/m(3). Feedstocks were evaluated before and following AFEX pretreatment, after densification, and after storage. Two enzyme doses were tested. The low rate used 5 filter paper units (FPU) of Spezyme CP (cellulase) and 21.3 cellobiase units (CBU) of Novozyme 188 (aka NS50010 [β-glucosidase]) per gram of glucan. The high dosage rate was three times higher and resulted in 40-56 % and 33-82 % higher ethanol yields with SHF and SSF, respectively. Trials revealed no adverse effect on ethanol yield following densification or 6-month storage of densified, AFEX-pretreated feedstocks.

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