Polylactic acid-based slow-release carbon source composite kaolin with modified biochar: Synergistic co-removal of nitrate, Cd(II), and diclofenac through manganese redox-coupled denitrification.

The problem of mixed pollution resulting from nitrate (NO3--N), cadmium(II), and diclofenac (DCF) due to incorrect discharge of industrial and agricultural wastewater has garnered significant attention. This study utilized polylactic acid (PLA) as a controlled-release carbon source, combined with kaolin and modified biochar, with the Pseudomonas sp. XFQ, to develop the manganese redox reactor G1, thereby improving denitrification efficiency and electron transfer capacity. This reactor was designed to synergistically remove NO3--N, Cd(II), and DCF. PLA in the composite carriers served as a stable sustained-release carbon source, continuously supplying bioavailable organic carbon to fuel microbial metabolism. When influent NO3--N concentration was 16.5 mg L-1, pH was 6.8, HRT was 8.0 h, bioreactor G1 demonstrated removal efficiencies of 99.8% for NO3--N, 91.0% for Cd(II), and 96.5% for DCF. Analysis demonstrated that manganese (Mn) modification improved the redox activity of biochar (BC), subsequently enhanced bacterial denitrification ability and resistance to Cd(II) and DCF. Additionally, microbial metabolism functions as a crucial mechanism for the removal of pollutants in fixed biofilm reactors (FBRs). The microbial community, primarily composed of Pseudomonadota, actively modulated its structure and gene expression associated with microbial metabolism to respond to the combined stress of Cd(II) and DCF. This research is of considerable importance for the treatment of mixed-pollutant wastewater.