Insight into enrichment of anammox bacteria by a polyurethane sponge carrier coupled with iron-carbon micro-electrolysis under no strict anaerobic condition

A novel composite carrier (ICME-PS) was formed by coupling polyurethane sponge carriers (PS) with different pore sizes (15, 25, 40 ppi) and iron-carbon micro-electrolysis (ICME), which was used for enrichment of anammox bacteria and stable operation under no strict anaerobic condition. An increase of 5.67%-38.55% in specific anammox activity (SAA), an significant enhancement of biofilm stability and an improvement of 14.61%-42.38% in Ca.Brocadia were observed in ICME-PS, compared to PS carriers. ICME played a dual role: 1) contributed to the formation of an anaerobic microenvironment; 2) used for nitrogen cycle reactions. Additionally, small-pore carriers with highest biofilm stability can be used in high shear environments, while medium-pore carriers achieved the highest SAA in stable environments. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) analysis indicated that ICME application reduced the energy barrier and improved aggregation performance. This study designed a novel composite carrier to broaden the application of anammox under no strict anaerobic condition.