Fermentation liquid as a carbon source for wastewater nitrogen removal reduced nitrogenous disinfection byproduct formation potentials of the effluent

Sludge alkaline fermentation liquid (SAFL) is an alternative to sodium acetate (NaAc) in enhancing wastewater nitrogen removal. Upon SAFL addition, dissolved organic nitrogen (DON) can be externally introduced or biologically synthesized during nitrogen removal, which is an important precursor to toxic nitrogenous disinfection by-products (N-DBPs). This study aims to evaluate the effects of different carbon source addition on effluent DON concentration, composition, and N-DBP formation potentials. A lab-scale A2O system treating real municipal wastewater was operated with NaAc or SAFL as external carbon sources. DON molecules and potential N-DBP precursors were identified by Orbitrap mass spectrometry. Subsequently, major microorganisms contributing to DON biosynthesis were suggested based on metagenomics. It was found that effluent DON was higher with SAFL as the carbon source than NaAc (1.51 ± 0.24 v.s. 0.56 ± 0.08 mg N/L, p < 0.05). Nevertheless, dichloroacetonitrile and nitrosamine formation potentials (7.14 ± 1.02 and 1.57 ± 0.07 μg/mg DON-N, respectively) of the effluent with SAFL addition were 42.79 ± 2.42% and 54.89 ± 1.70% lower than those of NaAc. Protein- and lignin-like compounds were the most abundant DON molecules in the effluent, where alanine, glycine and tyrosine were important precursors to N-DBPs. Azonexus and Flavobacterium spp. were positively correlated with these precursors, and possessed key genes involved in precursor synthesis. SAFL is a promising carbon source, not only for achieving efficient inorganic nitrogen and DON removals, but also for reducing N-DBP formation potentials of chlorinated effluent. [Display omitted] •SAFL as a carbon source induced higher effluent DON than acetate in wastewater BNR.•Effluent DON was mainly comprised by microorganism-derived proteins and lignins.•SAFL led to 42.8–54.9% lower N-DBP formation potentials of the effluent than acetate.•Alanine, glycine and tyrosine were important precursors to N-DBPs.•Azonexus and Flavobacterium were major synthesizers of N-DBP precursors.