Optimizing a Chlorella Vulgaris Wastewater Photobioreactor for Carbon Sequestration

Overview

Microalgal photobioreactors are among the most effective systems for capturing atmospheric CO2. Their capacity to generate massive amounts of hydrocarbon in biomass could be exploited not only to sequester CO2 – the main contributor to global warming – but also to further purify municipal wastewater prior to discharge. Research in this area is primarily focused on thermolytic conversion of the biomass into energy which, in essence, returns CO2 to the atmosphere. Little is equally systematically known about the capacity of microalgae to utilize wastewater as the primary nutrient source of growth, hence reducing the amount of nutrients in wastewater through the process of capturing atmospheric CO2. In this study, the potentials of using Chlorella vulgaris, a species of freshwater microalgae, to store CO2 as biomass while deriving carbon and nutrients from atmospheric CO2 and secondary-treated municipal wastewater (WW), respectively, are combined. Using turbidity as a measure of biomass yield in 310-mL prototypical photobioreactors, results show that the level of wastewater in distilled water (%WW) which supports Chlorella vulgaris culturing optimally is 83%; the lowest level to sustain an appreciable growth rate being 33%. These findings fulfill the need to reduce nutrients in wastewater. Results also show that the incubation time necessary to achieve optimal Chlorella vulgaris yields at any chosen %WW is 29 ± 4 days. An open photobioreactor is found to results in the largest biomass production, especially one in which atmospheric carbon source is augmented by industrial CO2. This latter result fulfills a primary goal of scrubbing atmospheric CO2. Overall, these results demonstrate the use of a microalga species to remove nutrients from secondary-treated municipal wastewater prior to discharge while sequestering atmospheric CO2 simultaneously. Two modular equations for predicting (i) turbidity changes with time, and (ii) pH responses to the metabolic utilization of CO2 with %WW during Chlorella vulgaris cultivation in wastewater are proposed.

Competition history

• AJAS 2019 Category not listed

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