A multi-dimensional AHP comprehensive evaluation of zero liquid discharge systems: A case study of chemical...

Facing increasing global water scarcity and stringent environmental pressures, the chemical industry urgently requires sustainable wastewater management strategies. Zero Liquid Discharge (ZLD) systems offer a promising solution, however, a comprehensive framework for evaluating their multi-dimensional performance is lacking. This study applies an integrated Analytic Hierarchy Process(AHP) model to holistically assess the performance of the ZLD retrofit in a coal chemical enterprise, considering the critical nexus of water quality, water volume, and energy consumption. A three-level AHP model (goal, criteria, indicators) was constructed. Pairwise comparison matrices using a 1-9 scale established indicator weights, with consistency ratios (CR < 0.1) confirming model reliability. The enterprise's performance was quantitatively scored before and after the ZLD retrofit using a 5-point scale and weighted summation. AHP results indicated that water quality emerged as the core dimension(50% weight), with the reuse water quality compliance rate (31.6%) being identified as the pivotal ZLD factor. The ZLD retrofit significantly improved the enterprise's comprehensive performance score from 3.188(average) to 4.291(good-to-excellent). The retrofit achieved zero external wastewater discharge, reduced freshwater consumption by 58.8%, and enhanced energy consumption stability, despite a moderate increase in specific energy use for water treatment. The AHP model proved effective for the comprehensive evaluation of ZLD systems. The findings demonstrate that ZLD can simultaneously enhance water-use efficiency, eliminate environmental pollution, and maintain economic viability, providing a scientific basis for the green transformation of the chemical industry.