Towards robust partial nitrification in low-ammonia wastewater: Electrospinning nanofiber composite-enhanced hydrogel...

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.