Mechanisms of Signaling Molecules Regulating Microbial Community Succession and Metabolic Pathways in a Mainstream Partial Nitrification System of a Novel Composite Zeolite-Biofilm Under Limited Salinity

Abstract

The substitution of seawater and the excessive use of deicing salt hinder the treatment of mainstream low salinity wastewater by traditional nitrogen removal process. However, the salinity (>1.0%) required for the operation of partial nitrification was too high, the actual sewage was difficult to meet the requirements, and there were some problems such as corrosion of sewage pipes and scaling in high salinity. In this experiment, a new composite zeolite (NCZ) biofilm was used to for the first time to realize the start-up and stable operation of partial nitrification at low salinity. The biomass, adhesion and resistance of biofilm were enhanced while a high NO2--N accumulation efficiency (94.1 %) was obtained at 0.6% salinity. C6-HSL and C8-HSL in the sludge phase of NCZ biofilm promoted gene expression and increased nitrate reductase (Nar) to stabilize the supply of NO2--N. The enhanced release of C8-HSL from the aqueous phase of the NCZ system increased the oxygen transfer resistance of the sludge layer, thus reducing the oxygen mass transfer efficiency of the sludge layer and inhibiting NOB more effectively. The enhanced release of C6-HSL and C12-HSL in the NCZ biofilm enhanced the membrane surface proteins from inside and outside the cell, respectively, making the "eggshell" structure more stable. Meanwhile, NCZ biofilm enhanced the microbial impact resistance by enhancing the TCA cycle, and important gene (nrfA) with DNRA function are awakened to ensure the ratio of NH4+-N to NO2--N in the effluent, which was conducive to the subsequent anammox process. Finally, NCZ biofilm could effectively elute Nitrospira out of the system and increase the relative abundance of Nitrosomonas to 12.8 % at 0.6 % salinity.

Keywords: Partial nitrification, Low salinity, Signal molecule, Oxygen transfer resistance