Integration of microbial bioreactors and Lemna minor cultivation for sustainable treatment of dairy processing wastewater

A novel technological approach for dairy processing wastewater remediation is presented. This approach combines microbial bioreactor systems with Lemna minor plant biomass cultivation is presented. Sequential anaerobic and aerobic microbial batch reactors achieved wastewater remediation efficiencies of 97.5 %, 83 % and 58.5 %, for chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), respectively. Molecular profiling of the bioreactor communities indicated that phylum Pseudomonadota dominated nitrification/denitrification metabolism. TP removal was largely correlated with PO₄³⁻-P uptake, with significant redundancy observed among bacterial genera contributing ppK and ppX-gppA phosphate metabolism genes. Novel dominant roles for members of the genus Macellibacteriales and Rikenellacea in phosphate uptake are proposed. Integration of Lemna cultivation increased wastewater TN and TP remediation efficiencies to 96.5 % and 73 %, respectively. However, relative growth rates of Lemna were found to be critically dependent on pH adjustment of effluents from pH 8.9 to pH 4.9–5.1. Phytotoxicity under alkaline conditions was correlated with wastewater NH₃-N concentration (p < 0.001). Elevated wastewater sodium and chloride levels did not appear to induce plant stress, with no statistical difference in photosynthetic activity. This study provides valuable, practical insights into the integration of microbial and phyto-remediation technologies, coupling wastewater treatment with opportunities for valorisation.