Journal of the Faculty of Engineering and Architecture of Gazi University 38:2 (2023) 1013-1025 Influence of different operating conditions on the performance of upflow anaerobic filter reactor: PHREEQCI-ADM1 model comparison Sevgi Tokgöz Güneş 1 * , Ezgi Özgünerge Falay 2 1 Department of Environmental Engineering, Faculty Engineering, Dokuz Eylül University, 35390, Buca, İzmir, Türkiye 2 Arnes Mechanic Machinery Industry and Trade Ltd. Co., 129/7, Street No:12, 4. Industrial Site, 35040, Bornova, İzmir, Türkiye Highlights: Graphical/Tabular Abstract  Influence of the operating conditions on the performance of AF  The Anaerobic Digestion Model No.1 (ADM1) and PHREEQCI  The effect of denitrification and sulfate reduction on methanogenesis While there were high COD treatment efficiencies in the ADM1 model results, high losses were observed in wastewater treatment efficiencies in the experimental study. The model simulation of nitrate and sulfate reduction process and redox potential (EH) change, driven by organic carbon degradation, in conditions closed to the atmosphere is given in Figure A. In Zones 1 and 2, the attainment of the EH required for metagenesis is controlled by the NO3 - and SO4 2- concentration and the reducing biomass. Figure A. Effect of nitrate and sulfate reduction on EH potential driven by dissolved organic carbon degradation (PHREEQCI model) Purpose: The treatability of synthetic molasses wastewater with the upflow anaerobic filter system in different filter material packing ratios, operation modes, and organic loading rates was investigated. In addition, a modeling study was carried out to analyzed anaerobic degradation proseses for AF100 continuous mode experimental operating parameters by implement the ADM1 directly in PHREEQCI. Theory and Methods: Reactors with different filter material packing ratios were operated at OLRs of 0.5-2 kgCOD/m³.day, 2 days of HRT. Experimental data were compared with ADM1 based PHREEQC model results in order to investigate anaerobic digestion mechanism in filter system. Results: According to experimental study results, while OLR increased, treatment efficiency decreased. Acceptable removal efficiencies were achieved in anaerobic treatment of wastewater for continuous operating mode and filter material packing ratio greater than 75%. Conclusion: In the combination of ADM1 model and PHREEQCI software is a powerful tool that can provide crucial decision support in understanding and solving problems in laboratory and industrial scale anaerobic treatment systems. Keywords:  Anaerobic degradation  Anaerobic filter  Molasses wastewater  ADM1  PHREEQCI Article Info: Research Article Received: 03.12.2021 Accepted: 01.05.2022 DOI: 10.17341/gazimmfd.1031991 Acknowledgment: The authors thank Pakmaya Bakery Yeast Factory (İzmir, Turkey) for their support Correspondence: Author: Sevgi Tokgöz Güneş e-mail: sevgi.tokgoz@deu.edu.tr phone: +90 232 301 7128