Enhance adhesion of ammonia-oxidizing bacteria on biocarriers based on surface free energy characteristics

Sustainable wastewater management increasingly depends on biofilm-based treatment technologies for pollutant removal, particularly in nitrogen-rich wastewater. However, high density polyethylene (HDPE) biocarriers often show poor bacterial adhesion due to surface energy differences with autotrophic nitrifying bacteria, such as ammonia-oxidizing bacteria (AOB). Polyvinyl alcohol (PVA) has emerged as a promising biocarrier material due to its hydrophilicity, abundance of hydroxyl groups, and ease of chemical modification. This study introduces a modified PVA biocarrier designed to enhance microbial adhesion by minimizing surface energy differences. The modified PVA biocarrier achieved a surface energy difference of 7.7 mJ m ⁻² and adhesion of 6.3 nN, outperforming those of HDPE (1.2 nN). Over 50-d operation, the modified PVA reactor demonstrated superior nitrogen removal efficiencies, achieving 91, 81, and 57% for ammonia, nitrite, and total nitrogen, respectively. Compared to the HDPE reactor, which achieved 76, 61, and 42%, respectively. Real-time PCR revealed a 60-fold increase in AOB adhesion on the modified PVA biocarrier, which was significantly higher than that on HDPE. This innovation accelerates biofilm formation and enhances nitrogen removal, offering significant benefits for wastewater treatment.