Zhanyou Chi

Bicarbonate produced from carbon capture for algae culture

Using captured CO(2) to grow microalgae is limited by the high cost of CO(2) capture and transportation, as well as significant CO(2) loss during algae culture. Moreover, algae grow poorly at night, but CO(2) cannot be temporarily stored until sunrise. To address these challenges, we discuss a process where CO(2) is captured as bicarbonate and used as feedstock for algae culture, and the carbonate regenerated by the culture process is used as an absorbent to capture more CO(2). This process would significantly reduce carbon capture costs because it does not require additional energy for carbonate regeneration. Furthermore, not only would transport of the aqueous bicarbonate solution cost less than for that of compressed CO(2), but using bicarbonate would also provide a superior alternative for CO(2) delivery to an algae culture system.

Two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production.

A two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production was studied, wherein high density heterotrophic cultures of Chlorellasorokiniana serve as seed for subsequent phototrophic growth. The data showed growth rate, cell density and productivity of heterotrophic C.sorokiniana were 3.0, 3.3 and 7.4 times higher than phototrophic counterpart, respectively. Hetero- and phototrophic algal seeds had similar biomass/lipid production and fatty acid profile when inoculated into phototrophic culture system. To expand the application, food waste and wastewater were tested as feedstock for heterotrophic growth, and supported cell growth successfully. These results demonstrated the advantages of using heterotrophic algae cells as seeds for open algae culture system. Additionally, high inoculation rate of heterotrophic algal seed can be utilized as an effective method for contamination control. This two-stage heterotrophic phototrophic process is promising to provide a more efficient way for large scale production of algal biomass and biofuels.

Bicarbonate-based Integrated Carbon Capture and Algae Production System with alkalihalophilic cyanobacterium

An extremely alkalihalophilic cyanobacteria Euhalothece ZM001 was tested in the Bicarbonate-based Integrated Carbon Capture and Algae Production System (BICCAPS), which utilize bicarbonate as carbon source for algae culture and use the regenerated carbonate to absorb CO2. Culture conditions including temperature, inoculation rate, medium composition, pH, and light intensity were investigated. A final biomass concentration of 4.79 g/L was reached in tissue flask culture with 1.0 M NaHCO3/Na2CO3. The biomass productivity of 1.21 g/L/day was achieved under optimal conditions. When pH increased from 9.55 to 10.51, 0.256 M of inorganic carbon was consumed during the culture process. This indicated sufficient carbon can be supplied as bicarbonate to the culture. This study proved that a high biomass production rate can be achieved in a BICCAPS. This strategy can also lead to new design of photobioreactors that provides an alternative supply of CO2 to sparging.

Sequential hydrothermal fractionation of yeast Cryptococcus curvatus biomass.

A sequential hydrothermal liquefaction (SEQHTL) process was evaluated in this work for fractionating different component of yeast biomass. Sugar and protein were separated first at a lower temperature, and the remaining biomass was then converted to bio-oil at a higher temperature. The separated aqueous products were investigated to be recycled as a carbon and nitrogen sources for the yeast culture. In the first step of SEQHTL, the temperature effect on the yield of sugar/protein and inhibitory compounds (acetic acid and 5-hydroxymethyl furfural (5HMF)) was investigated. The highest yields of sugar and protein and a minimal level of inhibitory compounds were obtained at 180°C. At the second step of SEQHTL, the highest bio-oil yield was achieved at 240°C. In comparison to the one-step hydrothermal liquefaction process, SEQHTL produced a higher quality bio-oil with higher fatty acid and lower nitrogen contents.

Production of ω-3 Polyunsaturated Fatty Acids From Cull Potato Using an Algae Culture Process

Algal cultivation for converting cull potato to docosahexaenoic acid (DHA) was studied. Schizochytrium limacinum SR21 was selected as the better producing strain, compared with Thraustochytrium aureum because of higher cell density and DHA content. Used as both carbon and nitrogen source, an optimal ratio of hydrolyzed potato broth in the culture medium was determined as 50%, with which the highest production of 21.7 g/L dry algae biomass and 5.35 g/L DHA was obtained, with extra glucose supplemented. Repeat culture further improved the cell density but not fed batch culture, suggesting limited growth was most likely caused by metabolites inhibition.

System integration for producing microalgae as biofuel feedstock.

Although a promising technology, using microalgae as feedstock for biofuel production faces a broad range of grand challenges to become technologically and economically viable. Growing algae for fuel production involves altering the culture conditions and processes toward maximum accumulation of biomass, especially lipid. Commercial success of such targeted use requires optimal combination of processes and culture environments so that maximum value from algae biomass will be achieved with high productivity, minimal inputs, sustainable resources and lowest possible costs. A systematic approach and process integration are critical factors in a successful future for algal biorefineries. This article presents opinions and supporting literature on: employing physiological characteristics of algae for increasing biomass productivity and lipid accumulation, opportunities for producing co-products, water resource conservation, nutrient recycling, CO2 capture and delivery and process integration with downstream processing. While various information gaps still need to be filled, the available knowledge base clearly demonstrates the need for system integration.

Biological Hydrogen Production via Bacteria Immobilized in Calcium Alginate Gel Beads

Hydrogen can be biologically produced by fermenting sugars in a mixed bacterial culture under anaerobic conditions. However, the slow growth rate of hydrogen-producing bacteria limits the productivity of a suspended-growth reactor due to the requirement for long hydraulic resident time in order to maintain adequate bacteria population. Calcium alginate gel entrapment was studied in this research as a possible method for enhancing biomass density through bacteria immobilization. Sewage sludge was used as the source for the hydrogen-producing bacteria, after pretreatment using acid to eliminate the methanogenic archaea. Experimental results indicated that these hydrogen-producing bacteria maintained high activity within a range of pH, i.e., from 5 to 8. Calcium alginate gel beads effectively entrapped the hydrogen-producing bacteria, resulting in significantly increased hydrogen production rates. The immobilized hydrogen-producing bacteria with 30% inocula increased the hydrogen production over 50% when compared to the production from 15% inocula. Four repeated cultures were used to determine the effective life of the calcium alginate gel beads. The gel collapsed after 22 days, but during this time the hydrogen production held relatively constant. Cheese whey was used in this study as the nutrient for hydrogen production. The results showed that dilution was required for the suspended fermentation to obtain maximum hydrogen production yield. However, for the immobilized hydrogen fermentation, undiluted raw cheese whey could be directly used to produce hydrogen with maximum yield, probably because substrate inhibition was alleviated with the diffusion barrier provided by the immobilization matrix.