Citation: Širi´ c, I.; Abou Fayssal, S.; Adelodun, B.; Mioˇ c, B.; Andabaka, Ž.; Bachheti, A.; Goala, M.; Kumar, P.; AL-Huqail, A.A.; Taher, M.A.; et al. Sustainable Use of CO 2 and Wastewater from Mushroom Farm for Chlorella vulgaris Cultivation: Experimental and Kinetic Studies on Algal Growth and Pollutant Removal. Horticulturae 2023, 9, 308. https:// doi.org/10.3390/horticulturae9030308 Academic Editor: Agnieszka Jasi ´ nska Received: 31 January 2023 Revised: 13 February 2023 Accepted: 20 February 2023 Published: 24 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). horticulturae Article Sustainable Use of CO 2 and Wastewater from Mushroom Farm for Chlorella vulgaris Cultivation: Experimental and Kinetic Studies on Algal Growth and Pollutant Removal Ivan Širi´ c 1 , Sami Abou Fayssal 2,3 , Bashir Adelodun 4,5 , Boro Mioˇ c 1 , Željko Andabaka 1 , Archana Bachheti 6 , Madhumita Goala 6 , Pankaj Kumar 7, * , Arwa A. AL-Huqail 8 , Mostafa A. Taher 9,10 and Ebrahem M. Eid 11,12, * 1 University of Zagreb, Faculty of Agriculture, Svetosimunska 25, 10000 Zagreb, Croatia 2 Department of Agronomy, Faculty of Agronomy, University of Forestry, 10 Kliment Ohridski Blvd, 1797 Sofia, Bulgaria 3 Department of Plant Production, Faculty of Agriculture, Lebanese University, Beirut 1302, Lebanon 4 Department of Agricultural and Biosystems Engineering, University of Ilorin, PMB 1515, Ilorin 240003, Nigeria 5 Department of Agricultural Civil Engineering, Kyungpook National University, Daegu 41566, Republic of Korea 6 Department of Environment Science, Graphic Era (Deemed to be University), Dehradun 248002, India 7 Agro-Ecology and Pollution Research Laboratory, Department of Zoology and Environmental Science, Gurukula Kangri (Deemed to Be University), Haridwar 249404, India 8 Departmentof Biology, College of Science, Princess Nourah bint Abdulrahman University, P.O. Box 84428, Riyadh 11671, Saudi Arabia 9 Biology Department, Faculty of Science and Arts, King Khalid University, Mohail Assir 61321, Saudi Arabia 10 Botany Department, Faculty of Science, Aswan University, Aswan 81528, Egypt 11 Biology Department, College of Science, King Khalid University, Abha 61321, Saudi Arabia 12 Botany Department, Faculty of Science, Kafrelsheikh University, Kafr El-Sheikh 33516, Egypt * Correspondence: rs.pankajkumar@gkv.ac.in (P.K.); ebrahem.eid@sci.kfs.edu.eg (E.M.E.) Abstract: The potential use of carbon dioxide (CO 2 ) 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 CO 2 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 CO 2 levels (6000 ppm) in the mushroom cultivation chamber with constant CO 2 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 maxi- mum 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 (R 2 > 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 CO 2 and wastewater produced by mushroom farms for algal cultivation and biological wastewater treatment. Keywords: climate change; CO 2 capture; greenhouse; mathematical modeling; phycoremediation; zero waste mushroom farm Horticulturae 2023, 9, 308. https://doi.org/10.3390/horticulturae9030308 https://www.mdpi.com/journal/horticulturae