Advancing the Chemistry of Solid Waste Leachate Treatment: Novel Integrated Photocatalytic-Bioelectrochemical System Development for Municipal Landfill Sites in South West Nigeria

Landfill leachate is one of the most complex and recalcitrant industrial wastewater types, containing refractory organic compounds, ammonium, heavy metals, and emerging contaminants at concentrations that defeat conventional treatment approaches at municipal landfill sites in rapidly urbanising South West Nigeria. This dissertation advances the chemistry of leachate treatment through the original development and optimisation of a novel integrated photocatalytic-bioelectrochemical system combining solar-driven persulphate activation on a composite manganese dioxide-graphene oxide electrode with a microbial fuel cell-based polishing stage. Leachate samples were obtained from three municipal landfill sites in Lagos, Ogun, and Oyo States over eight months, characterised for dissolved organic carbon, biochemical oxygen demand, chemical oxygen demand, specific ultraviolet absorbance at 254 nanometres, heavy metals, ammonium, and a panel of 28 pharmaceutical and personal care product micropollutants by LC-MS-MS. The photocatalytic electrode was synthesised, characterised by XPS, HRTEM, and photoelectrochemical measurements, and evaluated for persulphate activation kinetics. Microbial community analysis of the bioelectrochemical unit was performed by 16S rRNA amplicon sequencing. Integrated system optimisation was conducted by response surface methodology with dissolved organic carbon removal as the primary response. The integrated system achieved 94 percent dissolved organic carbon removal from mature leachate, compared to 62 percent for photocatalysis alone, with simultaneous electricity generation of 0.38 watts per square metre in the bioelectrochemical stage. Pharmaceutical micropollutant removal exceeded 99 percent for 24 of 28 target compounds. Original kinetic models for persulphate-advanced oxidation of leachate organic matter are derived. Keywords: landfill leachate, photocatalysis, bioelectrochemical system, advanced oxidation, South West Nigeria