Enhanced remediation of monosodium glutamate wastewater using the microalgae Phaeodactylum tricornutum: Integrating strain selection, process optimization and adaptive laboratory evolution

Abstract

This study aimed to create an efficient and sustainable treatment for high-salinity monosodium glutamate wastewater (MSGW) by assessing the algal marine diatom Phaeodactylum tricornutum. A systematic approach involving clonal screening, process optimization, and adaptive laboratory evolution (ALE) was employed. The optimal initial chemical oxygen demand (COD) for algal growth was found to be 412 mg L⁻¹. Among 60 monocultures, strain No. 41 isolated by monoclonal screening showed the best removal efficiencies for COD, total nitrogen (TN), and total phosphorus (TP). Using Box-Behnken response surface methodology, optimal cultivation conditions were identified: light intensity of 110.31 μmol m⁻² s⁻¹, temperature of 20.98 °C, ferric ion concentration of 265.41 μmol L⁻¹, and trace elements at 264.41% of f/2 medium. Validation tests achieved removal rates of 82.46% (COD), 73.43% (TN), and 83.45% (TP), with an optical density (OD₇₅₀) of 0.891 and a relative error under 6%. Furthermore, ALE-driven adaptation produced a robust strain capable of thriving in 1099 mg L⁻¹ COD—a concentration lethal to the wild-type strain. This evolved strain demonstrated enhanced growth rates and pollutant degradation efficiency, with total lipid content reaching 0.43 g g⁻¹ dry weight, underpinned by favorable modifications in morphology and ultrastructure. This study provides both theoretical insights and technical frameworks for the large-scale application of P. tricornutum in MSGW treatment.