Process Intensification of Biological Nutrient Removal Through Spatially Structured Biofilms

Abstract

Excess nitrogen and phosphorus drive algal blooms, and cause oxygen depletion and ecosystem degradation, making nutrient removal a central challenge in modern wastewater treatment. Biological nutrient removal (BNR) relies on microbial processes to transform nutrients into forms that can be removed from water, but achieving high performance within existing infrastructure remains difficult as population growth, urbanization, and increasingly stringent nutrient regulations intensify treatment demands. Process intensification strategies that enhance microbial activity without increasing system footprint are therefore of growing interest. This dissertation investigates how spatially structured biofilms can be leveraged to enhance nitrogen removal, enable phosphorus recovery, and improve process robustness. Across mobile organic biofilms (MOB), aerobic granular sludge (AGS), and hydrogel-encapsulated biomass, a unifying framework is established in which biomass structure governs mass transfer, microbial selection, and the spatial organization of redox conditions. This dissertation first evaluates the MOB process at laboratory scale through the development of a continuous-flow reactor with mobile biofilms grown on kenaf, a lignocellulosic plant-based carrier, and batch experiments designed to assess simultaneous nitrification and denitrification (SND). These experiments showed that kenaf-supported biofilms promoted nitrogen removal and that localized carbon release from the carrier may support denitrification under low-oxygen conditions. The MOB process was then evaluated at pilot scale in a continuous-flow system operated for 288 days at King County West Point Treatment Plant, where nitrogen removal performance, biofilm development, and microbial community differences between mobile biofilms and suspended flocs were examined. Hydrogel encapsulation was subsequently used as a model platform to isolate and examine these mechanisms and was further developed as an engineered system for stable shortcut nitrogen removal using anammox. Finally, AGS was investigated as a platform for phosphorus recovery through controlled phosphate release, demonstrating its potential to generate phosphate-rich streams suitable for struvite precipitation, a commercially valuable slow-release fertilizer. Together, this dissertation shows that spatially structured biofilms and biofilm-like aggregates provide a consistent mechanism for coupling biological processes and improving treatment performance. These findings support practical strategies for next-generation wastewater treatment within existing infrastructure.