Hydrothermal Carbonisation of Market Organic Waste for Hydrochar Production and Application as a Soil Amendment in Plateau State

Rapid urbanisation in Jos, Plateau State, North Central Nigeria, generates large volumes of organic market waste including vegetable trimmings, food spoilage, and fruit peels that currently overload municipal solid waste collection infrastructure. This study investigates hydrothermal carbonisation of mixed market organic waste from the Jos main market as a waste valorisation strategy, producing hydrochar for application as a soil amendment for vegetable production. Organic market waste was characterised by elemental analysis, proximate analysis, and calorific value measurement. Hydrothermal carbonisation was conducted at temperatures of 180, 220, and 260 degrees Celsius at a residence time of 4 hours with a biomass-to-water ratio of 1:6. Hydrochar products were characterised for yield, elemental composition, pH, surface functional groups by FTIR, BET surface area, and cation exchange capacity. Pot experiments were conducted using degraded farm soils from Barkin Ladi district amended with hydrochar at rates of 1, 2, and 4% by weight, with conventional compost and unfertilised controls. Hydrochar produced at 220 degrees Celsius exhibited an energy density of 22.8 MJ/kg, high carbon content (62.4%), and stable surface functional groups indicative of recalcitrant carbon. Amendment at 2% hydrochar improved soil water retention by 29%, available phosphorus by 42%, and tomato yield by 38% relative to the unfertilised control, with performance comparable to conventional compost. The study supports hydrothermal carbonisation as an integrated waste management and soil restoration strategy in Jos. Keywords: hydrothermal carbonisation, hydrochar, soil amendment, market waste, Plateau State