Browsing by Author "Demirkaya, Cigdem"

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    Autofermentation of alkaline cyanobacterial biomass to enable biorefinery approach
    (2023-04-08) Demirkaya, Cigdem; Vadlamani, Agasteswar; Tervahauta, Taina; Strous, Marc; De la Hoz Siegler, Hector
    Abstract Background Carbon capture using alkaliphilic cyanobacteria can be an energy-efficient and environmentally friendly process for producing bioenergy and bioproducts. The inefficiency of current harvesting and downstream processes, however, hinders large-scale feasibility. The high alkalinity of the biomass also introduces extra challenges, such as potential corrosion, inhibitory effects, or contamination of the final products. Thus, it is critical to identify low cost and energy-efficient downstream processes. Results Autofermentation was investigated as an energy-efficient and low-cost biomass pre-treatment method to reduce pH to levels suitable for downstream processes, enabling the conversion of cyanobacterial biomass into hydrogen and organic acids using cyanobacteria’s own fermentative pathways. Temperature, initial biomass concentration, and oxygen presence were found to affect yield and distribution of organic acids. Autofermentation of alkaline cyanobacterial biomass was found to be a viable approach to produce hydrogen and organic acids simultaneously, while enabling the successful conversion of biomass to biogas. Between 5.8 and 60% of the initial carbon was converted into organic acids, 8.7–25% was obtained as soluble protein, and 16–72% stayed in the biomass. Interestingly, we found that extensive dewatering is not needed to effectively process the alkaline cyanobacterial biomass. Using natural settling as the only harvesting and dewatering method resulted in a slurry with relatively low biomass concentration. Nevertheless, autofermentation of this slurry led to the maximum total organic acid yield (60% C mol/C mol biomass) and hydrogen yield (326.1 µmol/g AFDM). Conclusion Autofermentation is a simple, but highly effective pretreatment that can play a significant role within a cyanobacterial-based biorefinery platform by enabling the conversion of alkaline cyanobacterial biomass into organic acids, hydrogen, and methane via anaerobic digestion without the addition of energy or chemicals.
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    Development of a Cyanobacterial Biorefinery:Integration of Autofermentation and AnaerobicDigestion for Maximal Value Generation and Reduced Energy Inputs
    (2023-01-25) Demirkaya, Cigdem; De la Hoz Siegler, Hector; Bassi, Amarjeet; Nowicki, Edwin; Mahinpey, Nader; Hu, Jinguang; De la Hoz Siegler, Hector
    Cyanobacteria are ideal bio-factories for diverse biotechnological applications owing to their capacity to use solar energy and fix carbon dioxide into valuable bioactive compounds such as proteins and pigments. However, the economic viability of large-scale cyanobacteria cultivation is hindered by low volumetric productivity due to the slow mass transfer rate of CO2 into the culture media and significant CO2 losses. High pH (>10) and high alkalinity (>>10000 ?Eq L-1) can be used to improve CO2 delivery efficiency, as alkalinity enhances buffering capacity and improves CO2 mass transfer rates. Another important factor is the high cost associated with harvesting and energy intensive downstream processing methods. Thus, there is a need to develop integrated biorefinery strategies to maximize product recovery and value creation. To develop an economically viable cyanobacterial biorefinery, an alkaline cyanobacterial biomass production system was integrated with an autofermentation step, and a low temperature anaerobic digestion. Integration of these processes increase biomass productivity, trigger the release of valuable products, and enable multiple product recovery, nutrient recycling, and maximum energy production.Autofermentation was investigated as an energy-efficient and low-cost method to reduce pH to an optimal level (6.8–7.2) for the successful conversion of biomass to biogas and enable the production of hydrogen and organic acids simultaneously. High value-added products, hydrogen, and phycocyanin were also recovered from the process. Maximum total organic acid yield (60 % C mol/ C mol biomass) and hydrogen yield (326.1 ?mol/g AFDM) were obtained at the lowest biomass concentration after natural settling with no additional energy requirement.Three different inocula including digested manure, digested sewage sludge, and soda lake sediment were evaluated for energy efficient anaerobic digestion of cyanobacterial biomass at a low temperature (21 °C). Low temperature semi-continuous anaerobic digestion of fermented cyanobacterial biomass was carried successfully over 800 days with an average methane yield of 476 ml/ g VS by using soda lake sediment in duplicate 2 L digesters operating at 21 °C. Techno-economic assessment of the integrated process showed that phycocyanin is an important parameter for the economic value of this proposed alkaline cyanobacterial based biorefinery.