Development of Novel Humic Acid Coagulant Aids from Nigerian Peat and Lignite Sources for Removing Cyanotoxins and Taste-and-Odour Compounds from Drinking Water in North Central Nigeria

Cyanobacterial blooms in Nigerian reservoirs used for drinking water supply are increasing in frequency due to nutrient enrichment and climate-driven thermal stratification, releasing cyanotoxins and taste-and-odour compounds that challenge conventional treatment processes. This dissertation develops novel humic acid-derived coagulant aids extracted from peat and lignite deposits in Kogi and Benue States for enhanced removal of microcystin-LR, geosmin, and 2-methylisoborneol from water treatment plant influents in North Central Nigeria. Humic acids were extracted from peat and lignite by standard alkaline-acid procedure, characterised by elemental analysis, fluorescence spectroscopy, size-exclusion chromatography, and 13C NMR. Chemical modification by carboxymethylation and graft copolymerisation with polyacrylamide was conducted to enhance functional group density and flocculation activity. Coagulation-flocculation performance for cyanotoxin and taste-and-odour compound removal was evaluated in jar tests using raw water from Kainji Reservoir and two Benue State water treatment plant intakes. Microcystin-LR was quantified by enzyme-linked immunosorbent assay and confirmed by liquid chromatography-tandem mass spectrometry. Geosmin and 2-methylisoborneol were determined by purge-and-trap GC-MS. Optimised modified humic acid coagulant at 25 milligrams per litre achieved 88 percent microcystin-LR removal and 73 percent geosmin reduction compared to 45 and 28 percent for conventional alum alone. Mechanism elucidation using zeta potential, floc characteristics, and competitive adsorption experiments identifies charge neutralisation and hydrophobic interaction as primary removal pathways. This dissertation presents original contributions in functional material development from Nigerian natural organic matter for solving emerging drinking water quality challenges. Keywords: humic acid, cyanotoxins, coagulation, drinking water treatment, North Central Nigeria