Biopolymer treatment of ammonium-rich industrial effluents for the mass cultivation of microalgae

Abstract

Although wastewater reutilization for microalgae culturing can meet the dual goals of wastewater treatment and biomass production, some effluents with high contaminant concentrations are toxic to microalgae, necessitating pretreatment protocols to lower the toxicity before bioremediation. The present study aimed to bioremediate the industrial effluents of El Delta Co. for Fertilizers and Chemical Industries (Mansoura, Egypt), using sodium alginate as a pretreatment to enable reuse as a growth medium for microalgae culturing. Various water quality parameters signified the inferior state of the effluent with an ammonia-N concentration of 185.76 mg L−1. Toxicity investigations of the raw industrial effluents revealed toxicity to Chlorella sorokiniana, Scenedesmus vacuolatus and Pseudokirchneriella subcapitata. Effluent bioremediation was adopted using different concentrations of the biopolymer sodium alginate, and 1.0 g L−1 sodium alginate resulted in the highest removal of both ammonia-N and heavy metals. Chlorella sorokiniana and S. vacuolatus successfully grew in the 1.0 g L−1 alginate-treated effluent. Chlorella sorokiniana removed 87.8% of the ammonia-N, 75% of the copper, and 100% of the phosphorus. Scenedesmus vacuolatus consumed 85.7% of the ammonia-N, 66.7% of the copper, and 100% of the phosphorus. Adjusting the N:P mass ratio to 9.9 resulted in high tolerance of C. sorokiniana and S. vacuolatus to the effluent toxicity, with an EC50 > 100%. The 1.0 g L−1 sodium alginate-treated effluent stimulated C. sorokiniana and S. vacuolatus growth relative to the control. Additionally, C. sorokiniana and S. vacuolatus had the highest biomass production and protein content, reaching 1.42 and 0.74 g L−1 and 57.04 ± 0.04% and 52.19 ± 0.02%, respectively, in the treated effluent. Therefore, it was concluded that this bioremediation approach using the 1.0 g L−1 alginate pretreatment followed by microalgal cultivation (C. sorokiniana and S. vacuolatus) successfully treated the industrial effluent, representing a promising protocol for bioremediation practices.