Sustainable Use of CO2 and Wastewater from Mushroom Farm for Chlorella vulgaris Cultivation: Experimental and Kinetic Studies on Algal Growth and Pollutant Removal

Abstract

The potential use of carbon dioxide (CO2) and wastewater released from a mushroom farm for the cultivation of Chlorella vulgaris microalga was investigated in this study. For this purpose, a microcontroller-based aided CO2 capture and mixing prototype was constructed for the cultivation of C. vulgaris under varying concentrations of mushroom farm wastewater (0 as control, 50 and 100%). The results showed that the constructed prototype was helpful to maintain desirable CO2 levels (6000 ppm) in the mushroom cultivation chamber with constant CO2 supply to algal culture, i.e., 0.6% at an airflow rate of 50 mL/min. After 16 days of algal cultivation, it was observed that the maximum significant (p < 0.05) algal biomass production of 2.550 ± 0.073 mg/L was recorded in 50% wastewater concentration followed by 100% and control. Also, the maximum removal of selected mushroom farm wastewater pollutants, such as total dissolved solids (84.00 ± 1.37%), biochemical oxygen demand (90.17 ± 2.42%), chemical oxygen demand (91.53 ± 0.97%), total nitrogen (86.27 ± 1.60%) and total phosphorus (94.19 ± 2.33%), was achieved in 50% concentration of wastewater treatment with maximum first-order rate constant (k) values. In addition, the algal growth kinetics results showed that the logistic model fit best compared to the modified Gompertz model, based on selected validation tools, such as experimental vs. predicted values, coefficient of determination (R2 > 0.9938), model efficiency (ME > 0.98) and root mean square error (RMSE < 0.03). The post-harvest characterization of algal biomass revealed that the proximate, biochemical, ultimate elements (carbon, oxygen and nitrogen) and structural properties were significantly higher in 50% treatment than those in 100% and control treatments. Therefore, the findings of this study are novel and provide significant insight into the synergistic use of CO2 and wastewater produced by mushroom farms for algal cultivation and biological wastewater treatment.