Enhancing bioaugmentation in wastewater treatment: the emerging role of aggregating bacteria as mediators in cell immobilization—review

Abstract Bioaugmentation is a promising strategy to enhance biological wastewater treatment by introducing functional microbial strains that improve pollutant degradation and nutrient removal. However, the practical success of bioaugmentation is often limited by the washout of introduced bacteria, low colonization efficiency, and competition with native microbial communities. A key challenge is the lack of natural aggregation or biofilm-forming ability in many functional strains, making them vulnerable to operational stresses and system perturbations. Although conventional immobilization techniques have been applied to improve microbial retention, these approaches can be costly and may reduce microbial activity. Aerobic granules, highly structured microbial aggregates known for their strong settling properties, dense architecture, and intrinsic stability, have recently emerged as a valuable source of naturally aggregating and biofilm-forming bacteria. These granule-derived microorganisms exhibit functional traits that support biological immobilization, enhancing the persistence and performance of introduced strains. Acting as bridging microorganisms, they promote coaggregation and physical integration with functional bacteria, facilitating biofilm formation and supporting community stability. Although several case studies highlight the potential of these bacteria in improving bioaugmentation outcomes, a comprehensive exploration of their functional traits, ecological interactions, and engineering applications remains limited. This review systematically examines recent advances in bioaugmentation strategies using aggregating bacteria, particularly those derived from aerobic granules, elucidating their mechanisms of action and role in supporting microbial persistence and synergy. By focusing on their capacity to promote microbial immobilization and integration in engineered systems, this work highlights a promising direction for improving bioaugmentation performance. The review identifies key research gaps and provides a framework for designing more resilient and effective microbial strategies for wastewater treatment.