Towards robust partial nitrification in low-ammonia wastewater: Electrospinning nanofiber composite-enhanced hydrogel beads immobilized comammox Nitrospira

Abstract

Stable partial nitrification (PN) in low-ammonia wastewater has been a critical challenge, but comammox Nitrospira shows great potential in PN systems due to unique physiological characteristics. Polyvinyl alcohol/sodium alginate electrospinning nanofiber (PVA/SA-EN) and polyvinylidene fluoride EN (PVDF-EN) were used to construct EN hydrogel beads (ENHB) with sandwich and core–shell structures, respectively. Comammox HB (cHB) and three types of comammox ENHB (cENHB) were assembled by immobilizing comammox sludge and operated for 60 days in low-ammonia wastewater. Results showed a significant correlation between PN performance, HB pore structure, and comammox Nitrospira abundance. With superior pore structure and mechanical strength, PVA/SA-PVDF-cENHB achieved a nitrite accumulation rate of 55.08 %, indicating enhanced PN performance. The contribution of comammox Nitrospira to PN was 73.19 %. Its abundance in PVA/SA-PVDF-cENHB was 5.56 × 10⁶ copies/(g sludge), 1.16–1.95-fold higher than the other three HB. Nanofiber composite-enhanced hydrogel immobilizes comammox Nitrospira provides new ideas for achieving robust PN in low-ammonia wastewater.