Unlocking the potential of down-flow hanging sponge reactors for integrated nutrient management

Abstract

Downflow Hanging Sponge (DHS) reactor has emerged as a promising attached-growth process for sustainable wastewater treatment, offering energy-efficient and low-sludge solutions for organic carbon and nutrient removal. This review critically evaluates the applications of the DHS process for nitrogen and phosphorus management in both domestic and industrial wastewater. Emphasis is placed on recent advances that enhance nutrient removal efficiency, including bioaugmentation, integration with conventional activated sludge systems, and the use of complete ammonia oxidation (Comammox) microorganisms. Additional innovations involve the functionalization of sponge materials with catalytic or adsorptive properties and the design of redox-stratified reactor configuration to facilitate simultaneous nitrification-denitrification and phosphorus removal. Key challenges, such as treating high-strength wastewaters, adapting to seasonal variability, and advancing kinetic modeling, are critically assessed. Full-scale implementations like up-flow anaerobic sludge blanket (UASB)-DHS and anaerobic baffled reactor (ABR)-DHS demonstrate the system’s versatility under varying loading rates and environmental conditions. The DHS process has also shown potential in aquaculture applications by efficiently managing nitrogenous compounds and maintaining effluent quality. Despite its advantages, challenges remain in treating high-strength wastewaters, optimizing performance under seasonal variability, and developing predictive models for process control. This review outlines key research directions to advance DHS technology focusing on advancing material properties, refining operational designs, and developing robust models to establish DHS as a viable and scalable solution in sustainable wastewater management.