Dissolved oxygen dependence of Microbe-Derived dissolved organic nitrogen dynamics during membrane biofilm-based linear alkylbenzene sulfonate mineralization

Abstract

Oxygen-based membrane biofilm reactor (O2-MBfR) can achieve bubble-free efficient linear alkylbenzene sulfonate (LAS) mineralization. However, effluent microbially derived dissolved organic nitrogen (mDON) reduces recycled water quality and induces water eutrophication. How dissolved oxygen (DO) impacts the dynamics of mDON during LAS biodegradation is unknown. Here, we explored the fate of mDON releasing, molecular characteristics and formation metabolisms in the O2-MBfR responding to DO dynamics using Fourier transform ion cyclotron resonance mass spectrometry and metagenomic analyses. Results showed that DO presents a negative impact (λ = -0.242, P < 0.001) on mDON production, but can positively influence mDON reduction through influencing total organic nitrogen (TDN) removal. DO of 0.3 mg/L led to the lowest concentration of mDON with the least number of organic molecular formulas and high proportion of stable N2– and N3-containing organics. Much lower (0.0 mg/L) or higher (0.6 mg/L) DO concentrations favored dissimilatory-based ammonia formation and assimilatory nitrogen fixation that enhancing mDON formation. Firmocutes were the dominant bacteria that contributing to mDON formation. TDN (λ = 0.844, P < 0.001) and pH (λ = 0.248, P < 0.01) directly affected the effluent mDON concentration. The relatively low effluent mDON under anoxic condition suggested that DO controlling can be an effective strategy to minimize bioavailable mDON discharges in the O2-MBfR, which showed great implication potential for high-quality reclaimed water production and eutrophication control.