Multi-pollutant grey water footprint of a paper recycling industry considering conventional and emerging contaminants

The paper recycling industry, despite its environmental benefits, discharges wastewater with considerable pollution loads, including both conventional and emerging contaminants. This study evaluated the multi-pollutant grey water footprint (GWF) of this industry with its ecological risks based on experimental data obtained from the raw and treated wastewater of a large paper recycling facility using A2/O system in northern Iran. Over a one-year monitoring period (October 2024–October 2025), eight pollutants: COD, BOD, TSS, TDS, TP, TN, PFOA, and detergents were analyzed by sampling. Results showed that the monthly average GWF of this industry based on raw and treated wastewater were 1017 and 36 m 3 /ton, respectively. They mostly relied on COD and TDS. However, detecting PFOA changed the leading pollutant and dramatically increased the monthly GWF to 31007 and 6367 m 3 /ton, respectively. Despite the effectiveness of the wastewater treatment system on reducing the monthly GWF based on conventional (96%) and emerging (80%) contaminants, the monthly average risk of this effluent by RQ values only reduced from 1326 to 272 by wastewater treatment, indicating severe ecological risk (RQ > 1) due to PFOA emissions. These findings firstly imply that GWF could simultaneously include both conventional and emerging pollutants in calculations for an industry. Secondly, they demonstrate that while conventional treatment effectively reduces organic loads, emerging contaminants, e.g., PFOA, can excessively affect environmental indicators and change their final values.