Synthesis And Characterization of Coconut Husk Biochar–Chitosan Composite Adsorbent and Evaluation of Its Efficacy for Salinity Removal from Borehole Drinking Water in Chamwino District, Central Tanzania

Abstract

In many semi-arid regions of sub-Saharan Africa, safe drinking water is unavailable because borehole water is often highly saline. In Chamwino District, central Tanzania, electrical conductivity (EC) and total dissolved solids (TDS) in borehole water frequently exceed World Health Organization (WHO) drinking water guidelines. This study evaluated the synthesis and characterisation of a coconut husk biochar–chitosan (CC-CH) composite adsorbent and its efficacy for salinity removal from borehole drinking water using appropriate standard methods. Biochar was produced by slow pyrolysis at 400°C, 500°C, and 600°C and combined with chitosan at mass ratios of 1:1, 1:2, and 2:1. Composites were characterised by BET surface area analysis, FTIR spectroscopy, XRD, and nitrogen adsorption–desorption analysis. Batch adsorption experiments optimised adsorbent dose, solution pH, and contact time. The 2:1 biochar-to-chitosan ratio pyrolysed at 600°C exhibited the best physicochemical properties (surface area 318.88 m²/g; pore volume 0.375 cc/g; BET C = 17.424 ± 0.00) and achieved a maximum salinity removal of 22% ± 0.00 at a dose of 5.0 g, with optimal performance at pH 6–7 and a contact time of 45 minutes. Post-treatment TDS of approximately 1,100 mg/L still exceeded the WHO guideline of 1,000 mg/L, indicating that integration with complementary technologies is necessary. The Freundlich isotherm model best described adsorption equilibrium, confirming heterogeneous multilayer adsorption. This low-cost composite from locally sourced materials offers significant potential for integrated salinity remediation in rural semi-arid sub-Saharan Africa.