No abstract

In the present study, the responses of microbial products in the biosorption process of Cu(II) onto aerobic granular sludge were evaluated by using batch and spectroscopic approaches. Batch experimental data showed that extracellular polymeric substances (EPSs) contributed to Cu(II) removal from an aqueous solution, especially when treating low metal concentrations, whereas soluble microbial products (SMPs) were released under the metal stress during biosorption process. A three-dimensional excitation-emission matrix (3D-EEM) identified four main fluorescence peaks in the EPS, i.e., tryptophan protein-like, aromatic protein-like, humic-like and fulvic acid-like substances, and their fluorescence intensities decreased gradually in the presence of Cu(II) during the sorption process. Particularly, tryptophan protein-like substances quenched the Cu(II) binding to a much higher extent through a static quenching process with less than one class of binding sites. According to the synchronous fluorescence spectra, the whole fluorescence intensity of released SMP samples expressed an increased trend with different degrees along with contact time. Two-dimensional correlation spectroscopy (2D-COS) suggested that the fulvic-like fluorescence fraction might be more susceptible to metal exposure than other fractions. The result of molecular weight distribution demonstrated that the SMPs released from the biosorption process differed significantly according to contact time. The result obtained could provide new insights into the responses of microbial products from aerobic granular sludge with heavy metal treatment.

Denitrification coupled with anammox is an effective approach to improve total nitrogen removal from wastewater, especially by reducing the nitrate produced by anammox. Nevertheless, the behavior of dissolved organic nitrogen (DON) is commonly ignored in this process. In the present study, poly(butylene succinate) (PBS), an alternative solid carbon source, was coupled with simultaneous partial nitrification, anammox, and denitrification (SNAD) to achieve complete nitrogen removal in a single reactor. After 90 days of continuous operation, dissolved inorganic nitrogen (DIN) removal efficiencies were 80.7 ± 1.0% without PBS and 97.4 ± 3.5% with PBS. Correspondingly, the effluent DON was reduced from 1.0 to 0.6 mg/L when PBS was provided. Fourier transform ion cyclotron resonance mass spectrometry revealed that DON molecules with large, unsaturated and aromatic structures were preferentially transformed in SNAD when PBS was provided. Microbial analysis indicated that Candidatus_Jettenia (22.0%−17.7%) and Nitrosomonas (3.8%− 2.6%) were the predominant functional bacteria for anammox and nitrification, regardless of whether PBS was provided or not. Meanwhile, increased abundances of denitrifying bacteria, such as Denitratisoma (2.9%−4.0%) and Thauera (2.2%−3.3%), were observed and assumed to improve nitrate reduction. The results provide a practical alternative for nitrogen removal by coupling solid denitrification with anammox, and also reveals novel insights about DON characteristics at the molecular level.