Development of comammox-active sponge-based bioreactor

Abstract

Rapid urbanization and increasing wastewater generation challenge conventional treatment technologies, such as the conventional activated sludge process, owing to high land and energy demands. Downflow hanging sponge (DHS) reactors offer a compact and energy-efficient alternative with minimal sludge production. However, achieving effective total nitrogen removal remains a challenge. Researchers have explored the integration of single-stage partial nitritation-denitrification and anaerobic ammonia oxidation (anammox) using dissolved oxygen gradients in sponge biomass carriers. The discovery of complete ammonia-oxidizing (comammox) bacteria that convert ammonia to nitrate within a single microorganism presents new opportunities for nitrogen removal in DHS reactors. Microbial studies have suggested that comammox bacteria contribute to nitrogen transformation in low-strength wastewater environments. This chapter reviews the nitrification mechanisms in DHS reactors, the role of comammox bacteria, and advancements in comammox-activated DHS systems, supporting their potential for sustainable and efficient wastewater treatment in urban and resource-limited settings.