The important role of high sludge concentration in anaerobic biological systems with low COD/SO42- sulfate-containing wastewater predicted by machine learning: Insights from microbial community and metabolic pathways

Abstract

In anaerobic biological systems, sulfate reduction efficiency is influenced by multiple factors synergistically, particularly under low chemical oxygen demand-to-sulfate ratio (COD/SO42-) conditions. Enhancing sulfate reduction efficiency under low COD/SO42- conditions is challenging due to the deficiency of electron donors. In this study, two anaerobic systems were operated with a gradual decrease in COD/SO42-. The primary objective was to investigate the correlations among various influential factors, the efficacy of sulfate reduction, and the progression of microbial communities. The results showed that even with a decrease in COD/SO42- to 0.1, the sulfate reduction efficiency could reach 70% under high sludge concentration. Machine learning predictions identified sludge concentration as the most influential factor under low COD/SO42- conditions. The functional gene analysis confirmed that the sulfate reduction under high sludge concentration was primarily governed by the dissimilatory pathway and exhibited minimal reliance on COD/SO42-. These findings provide theoretical support and a novel approach for the anaerobic biological treatment of sulfate-containing wastewater under low COD/SO42- conditions.