Abstract
The two-step photosynthetic biogas upgrading process, which combines CO2 capture by carbonate solution and carbonate regeneration by using aquatic microbial oxygenic photoautotrophs (i.e., cyanobacteria, algae, and diatoms), may provide a potential alternative to the commercial routes used for gaseous biofuel upgrading. Such a process not only provides a green and low energy intensive biogas upgrading pathway but also converts CO2 in biogas into high value biomass. To improve the upgrading performance, the effects of light intensity and NaHCO3 concentration on the growth and the HCO3- transformation characteristics of halophilic and alkaliphilic Spirulina platensis were investigated in this study. Experimental results showed that the light attenuation of S. platensis culture was significant. Increasing light intensity up to 210 μmol m-2 s-1 effectively improved the S. platensis growth and photosynthetic pigment accumulation. S. platensis could grow in the range of 0.05 to 0.6 M NaHCO3, and a maximum biomass concentration of 1.46 g L-1 was achieved under an optimal growth condition of 0.1 M NaHCO3, which was 65.9% higher than at 0.05 M NaHCO3. Moreover, the bicarbonate utilization efficiency reached 42.0%. Finally, in a case study, a biogas stream at a flow rate of 800 m3 h-1 could generate biomass up to 344 kg h-1, corresponding an energy value of 5591 MJ h-1.
Highlights
Have focused on the impacts of environmental parameters on carbon utilization and AMOPs growth during the two-step photosynthetic biogas upgrading process
When the incident light intensity was 210 μmol m-2 s-1 and the distance from light incident surface was 1 cm, as biomass concentration increased from 0.05 to 0.8 g L-1, the light intensity significantly decreased by 29.2% to 93.9%
The results showed that the maximum biomass concentration of 1.46 g L-1 was observed on the 8th day under an optimal growth condition of 0.1 M NaHCO3, which was 65.9% higher than 0.05 M NaHCO3
Summary
Have focused on the impacts of environmental parameters on carbon utilization and AMOPs growth during the two-step photosynthetic biogas upgrading process. Gas spargers may not be required in such AMOPs systems, thereby leading to different growth and carbon fixation behaviours for AMOPs. The cyanobacteria ( known as blue green microalgae) Spirulina platensis is tolerant to high alkalinity and high salinity conditions and is considered as a candidate for photosynthetic biogas upgrading (Xia et al, 2015). The innovation of this study is that it comprehensively investigates the effect of environmental parameters on the growth and bicarbonate transformation characteristics of halophilic and alkaliphilic S. platensis for photosynthetic biogas upgrading. The objectives are to investigate the light transmission characteristics in S. platensis culture, to assess the effects of light intensity and NaHCO3 concentration on bicarbonate utilization and cyanobacteria growth, and to discuss the design and application of the photosynthetic biogas upgrading system
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