Exploring the Circular Reuse Potential of Wastewater and Scrap Metal in Crop Irrigation at Urban-Rural Intersections...

Wastewater treatment by electrocoagulation (EC) using waste-derived electrodes is a promising solution, but its viability in irrigation reuse remains unclear. This work presents a quantitative framework integrating agrometeorological analysis (FAO-56 method) and waste information into energy and electrochemical models (Faraday's laws of dissolution) for viability assessment. The circular reuse framework was evaluated at a study site comprising a large institution surrounded by irrigated trees. Onsite experiments showed that electrochemical dosages as low as 20 g/m³ of aluminum (Al) scrap, or 60 g/m³ for iron (Fe) scrap, achieved significant removals (75%-94%) of COD, BOD, TSS, and turbidity. Onsite metal waste generation (593 kg/month) could accommodate ~98,000 m² of surrounding irrigated lands. Crop production capacities of scrap metals (food per scrap) were estimated to reach 23.3 kg/kg using Al scrap. Based on crop water dynamics, theoretical fixed energy demand for renewable energy integration was calculated to be 0.58 kWh/m³. Validation of model components revealed that modeling scrap electrode consumption comprised minimal uncertainty compared with other components like crop water demand. The reuse framework shows promising potential as a WEFE nexus application but raised some socioeconomic concerns such as impacts on scrap scavengers' livelihoods. Prior to wider adoption, qualitative assessments are necessary to address heavy metals removal, soil contamination, nutrient content, and microbial indicators. Pilot-scale experiments are also encouraged to gain improved insights.