Abstract
Production and enhancement of high value phycocyanin pigment from microalgae biofilms cultured on oilfield and natural gas produced wastewater were investigated. Cyanobacteria isolated from Logan City, Utah, wastewater treatment Lagoons (LLC2) was cultured in produced water using rotating algal biofilm reactors (RABRs). The RABRs were operated under “low” and “high” light conditions and biomass and phycocyanin content were compared. Phycocyanin content was enhanced by growth under low light conditions to a maximum yield of 31.7 mg/g ash-free dry weight (AFDW) biomass for an 87.6% increase in phycocyanin yield. Phycocyanin productivity was equivalent for both the low and high light treatments (327 ± 81 and 305 ± 39 mg/m2/day, respectively), due to the significantly lower AFDW biomass productivity of the low light treatment (2.7 ± 0.4 g/m2-day). An indoor laboratory evaluation of 14 substrata for biofilm growth showed that cotton rope and cotton belt material provided the highest biomass yields. Further evaluation in a pilot-scale outdoor produced wastewater pond showed that the biomass characteristics from the two substrata differed. The corrugated surface area of the cotton rope cultured a biofilm with a large community of non-photosynthetic organisms with an autotrophic index of 507 and a low phycocyanin yield of 3.4 mg/g AFDW. However, the cotton belt substratum cultured a healthy photosynthetic biofilm with an autotrophic index of 127 and a phycocyanin yield of 47.0 mg/g AFDW. These results demonstrate the cultivation of microalgae biomass and valorization of oilfield and natural gas produced wastewater through the design and management of algal-based biofilm photobioreactors.
Highlights
“Produced wastewater” disposal from oil and natural gas extraction is a growing problem in the United States and around the world
The increase in phycocyanin yield during low light treatment was accompanied by an increase in crude extract purity, to just above the benchmark standard for food grade quality phycocyanin (Figure 2) (Eriksen, 2008; Rito-Palomares et al, 2001)
These results highlight the malleability of the phycobilisome apparatus to respond to different light intensities that may be configured or controlled at large scale by the rotating algal biofilm reactors (RABRs) photobioreactor design and operation
Summary
“Produced wastewater” disposal from oil and natural gas extraction is a growing problem in the United States and around the world. Sullivan Graham et al (2017) conducted a thorough review on produced water as a growth medium for microalgal cultivation for nutrient recycling. They found that produced water can have high salinity ranges and organic chemical constituents detrimental to growth of microalgae, it has the advantage of containing inorganic nutrients needed for microalgal growth. The indicate that microalgal cultivation in produced water represents an opportunity for wastewater treatment and biofuels generation (Sullivan Graham, et al, 2017). High value bioproduct side streams can be integrated into a microalgal biorefinery to potentially improve the economics of produced water treatment using microalgal biomass and derived biofuels to offset capital costs (Chew et al, 2017). Therapeutic compositions of phycocyanobilin have been reported to be effective at low micromolar concentrations, making them potent antioxidants (Hirata et al, 2000)
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