Municipal landfill leachate (MLL) contamination in surface water is a critical global issue due to the high concentration of toxic organics and recalcitrants. The biological treatment of MLL is ineffective due to an elevated concentration of ammoniacal nitrogen, which restricts the production of the recalcitrant degrading laccase enzyme. In this context, integrating an external laccase-anchored carbon catalyst (LACC) matrix system with the microbial system could be an efficient strategy to overcome the drawbacks of conventional biological MLL treatment technologies. In the present study, the LACC matrix was synthesized by utilizing nanoporous activated carbon (NAC) functionalized ethylene diamine (EDA) and glutaraldehyde (GA) (GA/EDA/NAC) matrix for the anchoring of laccase. The maximum anchoring capacity of laccase onto GA/EDA/ NAC was achieved to be 139.65 U/g GA/EDA/NAC at the optimized anchoring time, 60 min; pH, 5; temperature, 30 °C, and mass of GA/EDA/NAC, 300 mg and was confirmed by Fourier transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope (SEM), and X-ray Diffraction (XRD) analyses. Further, the mechanistic study revealed the involvement of covalent bonding in the anchoring of laccase onto the functionalized surface of the GA/EDA/NAC matrix. The adsorption isotherm and kinetics of laccase anchoring onto the GA/EDA/NAC matrix were performed to evaluate its field-level application. Subsequently, the sequential microbial system (I-stage bacterial treatment followed by II-stage fungal treatment) and III-stage LACC matrix system could effectively reduce the COD by 94.2% and phenol by 92.36%. Furthermore, the Gas Chromatography-Mass Spectrophotometry (GC–MS) and FT-IR analyses confirmed the effective degradation of organic compounds and recalcitrants by the integrated microbial and LACC matrix system. The study suggested that the application of the LACC matrix system has resulted in the complete treatment of real-time MLL by overcoming the negative interference of elevated ammoniacal nitrogen concentration. Thus, the integrated microbial and LACC matrix approach could be considered to effectively treat the MLL without any secondary pollution generation.

A novel integrated microbial and laccase-anchored carbon catalyst system for the effective treatment of toxic organic and recalcitrant-rich municipal landfill leachate
    Abstract
        Graphical abstract
    1 Introduction
    2 Materials and methods
        2.1 Materials and methods
        2.2 Isolation, screening and identification of toxic organics degrading microorganisms
        2.3 Optimization of first stage culture conditions for the efficient degradation of toxic organics in MLL by variable at a time method
        2.4 MLL color estimation
        2.5 Sequential second stage treatment of MLL using P. chrysosporium
        2.6 Surface functionalization of nanoporous activated carbon (NAC)
        2.7 Studies on the optimization of parameters for the synthesis of LACC matrix
        2.8 Instrumental characterization of LACC matrix
        2.9 Sequential third stage treatment of MLL using LACC matrix
        2.10 Instrumental characterization of raw and treated MLL by sequential microbial and LACC matrix system
    3 Result and discussion
        3.1 Isolation, screening and identification of toxic organics degrading microorganisms
        3.2 Optimization of first stage culture conditions for the efficient degradation of toxic organics present in MLL by variable at a time method
            3.2.1 Effect of biomass size on COD removal
            3.2.2 Effect of pH on COD removal
            3.2.3 Effect of temperature on COD removal
        3.3 Sequential second stage treatment of MLL using P. chrysosporium
        3.4 Studies on the optimization of parameters for the synthesis of LACC matrix
            3.4.1 Effect of time on anchoring of laccase on NAC and GAEDANAC
            3.4.2 Effect of pH on anchoring of laccase on NAC and GAEDANAC
            3.4.3 Effect of temperature on anchoring of laccase on NAC and GAEDANAC
            3.4.4 Effect of mass of carrier matrices on anchoring of NAC and GAEDANAC
        3.5 Confirmation of LACC matrix synthesis
        3.6 Sequential third stage treatment of MLL using LACC matrix
        3.7 Confirmation of MLL treatment by sequential microbial and LACC matrix system
    4 Conclusion
    Acknowledgements 
    References

• Maseed Uddin(Industrial and Environmental Sustainability Laboratory, Department of Biotechnology, School of Bioengineering, SRM Institute of Science and Technology, Kattankulathur, Tamil Nadu 603203, India)
• Sri Swarna Sriram(Industrial and Environmental Sustainability Laboratory, Department of Biotechnology, School of Bioengineering, SRM Institute of Science and Technology, Kattankulathur, Tamil Nadu 603203, India)
• Kishore Krishna(Industrial and Environmental Sustainability Laboratory, Department of Biotechnology, School of Bioengineering, SRM Institute of Science and Technology, Kattankulathur, Tamil Nadu 603203, India)
• Karthikeyan Sekar(Sustainable Energy and Environmental Research Laboratory, Department of Chemistry, SRM Institute of Science and Technology, Kattankulathur, Tamil Nadu 603203, India)
• Ramani Kandasamy(Industrial and Environmental Sustainability Laboratory, Department of Biotechnology, School of Bioengineering, SRM Institute of Science and Technology, Kattankulathur, Tamil Nadu 603203, India)