Development of a Novel Mass-Energy-Water Nexus Optimisation Framework for Industrial Parks in Nigeria with Application to the Onne Free Trade Zone, Rivers State

Industrial ecology principles suggest that the simultaneous optimisation of mass, energy, and water exchanges among co-located industries in a park framework can dramatically reduce individual plant environmental footprints and operating costs, yet no rigorous nexus optimisation framework has been developed for and applied to Nigerian industrial park conditions. This study develops a novel mass-energy-water nexus optimisation framework for Nigerian industrial parks and applies it to the Onne Oil and Gas Free Trade Zone, Rivers State, which hosts petroleum services, chemical processing, power generation, and cold storage enterprises. A comprehensive plant-level input-output characterisation was conducted for 12 major enterprises in the zone, covering process streams, waste heat grades and quantities, wastewater volumes and compositions, cooling water cycles, and solid waste categories. An original mixed integer linear programming optimisation model was formulated to identify optimal heat integration, water cascade reuse, and material symbiosis networks, incorporating distance-dependent cost penalties for inter-plant connections, regulatory constraints on waste stream co-processing, and safety separation requirements. The model was solved using CPLEX in the GAMS environment. Optimal nexus solutions reduced aggregate external energy demand by 31%, freshwater withdrawal by 44%, and solid waste to landfill by 57% relative to the current independent operation baseline, translating to estimated annual cost savings of 1.8 billion Naira for the twelve-enterprise cluster. An original environmental synergy metric, the Nexus Co-benefit Coefficient, is introduced to quantify the environmental co-benefits of multi-resource integration relative to single-resource optimisation. The framework provides a replicable methodology for nexus optimisation of all Nigerian industrial zones. Keywords: mass-energy-water nexus, industrial ecology, MILP, Onne Free Trade Zone, Rivers State