Nitrate concentrations exceed standards in many drinking water sources. Solid carbon source (SCS) is usually used to increase the biological denitrification in waters with a low carbon‑nitrogen ratio. However, there is a lack of research on the enhanced denitrification in drinking water sources with nitrate exceeding limits by the introduction of SCS. In this study, a SCS composite was prepared using agricultural waste corncob and polybutylene succinate and the SCS carbon release performance, denitrification effect and potential chemical and biological risks were investigated via a series of batch and column experiments. The SCS composite presented a long-term, stable carbon release performance and good microbial utilization capability for denitrification: SCS composite has a sustained release capacity for over 28 days in dynamic waters. Short-chain fatty acids accounted for over 60 % of the released carbon, and predominant fluorescence compounds were protein organic compounds and soluble microbial metabolites. The introduction of SCS composite evidently improved bio-rope biomass and its denitrification effect. The removal percentage of NO₃⁻ by SCS reactor pretreatment reached 90.9 %, remaining stable within 28 days. The SCS pretreatment increased formation potentials of trihalomethanes, but formation potentials of haloacetonitriles with higher toxicity were effectively reduced, so the comprehensive toxicity risk of disinfection by-products was reduced. The SCS pretreatment has slight negative impact on drinking water biological stability only during the first 10 days, which needs attention. This study demonstrated that the prepared SCS composite has excellent carbon release performance and denitrification effect, and its chemical and biological risks were controllable.

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In drinking water treatment plants (DWTPs), the widely used biological activated carbon filters (BACFs), as the last barrier before disinfection, can remove dissolved organic matter (DOM) known as precursors of disinfection by-products (DBPs). Whether phosphate addition can improve water purification and DBP control of BACFs is still controversial. This study investigated short-term and long-term effects of phosphate addition on controlling DBP formation potentials (FPs) by BACFs via column and batch experiments. The BAC columns presented good water purification performance: they removed around 50 % DOM, nearly all fulvic acid-likes and humic acid-likes as well as 5 %–70 % chlor(am)innated THM4, HAA9 and HAN4 FPs (except chloraminated THM4 FPs)， which was mainly contributed by aerobic bacteria not anoxic bacteria. Phosphate addition within 7–14 days further improved removals of DOM, aromatic organics, fluorescence fractions in DOM as well as HAA9 and HAN4 FPs (especially TCAA FP and TCAN FP) to different extent. However, this improvement did not last longer, and removals of DOM, aromatic organics, two fluorescence fractions (soluble microbial byproduct-likes and humic acid-likes) and DBP FPs decreased despite long-term phosphate addition. Oxic and anoxic batch experiments showed that the positive response of water purification to short-term phosphate addition was also mainly attributed to aerobic bacteria and not to anoxic bacteria. For example, the former decreased DOM and DBP FPs, while the latter increased protein- and tryptophan-like substances as well as chloraminated THM4 FPs. Phosphate addition resulted in EPS increase in anoxic reactors and decrease in oxic reactors. These results indicated that a high dissolved oxygen in BACFs may be helpful for water purification and DBP control. Overall, short-term phosphate addition into phosphorus-limited water is beneficial for BACFs to control DBPs while long-term addition has no effect. Therefore, an intermittent phosphate addition into BACFs is suggested to control DBPs in DWTPs.@en

The illicit connection of sewage pipes to stormwater pipes commonly occurs in urban stormwater systems. This brings problems that sewage might be directly discharges into natural water and even drinking water sources without treatment, posing risks to ecological safety. Sewage contains various unknown dissolved organic matter (DOM), which could react with disinfectants and lead to the formation of carcinogenic disinfection byproducts (DBPs). Thus, understanding the impacts of illicit connections on downstream water quality is of significance. This study firstly investigated the characteristics of DOM using fluorescence spectroscopy and the formation of DBPs after chlorination in an urban stormwater drainage system in the case of illicit connections. The results found that the concentrations of dissolved organic carbon and dissolved organic nitrogen ranged from 2.6 to 14.9 mg/L and from 1.8 to 12.6 mg/L, respectively, with the highest levels occurring at the illicit connection points. Concerning DBP precursors, pipe illicit connections introduced considerable precursors of highly toxic haloacetaldehydes and haloacetonitriles into the stormwater pipes. Furthermore, illicit connections introduced more contents of tyrosine-like and tryptophan-like aromatic proteins, which may be related to foods, nutrients, personal care products, etc. in the untreated sewage. This indicated that the urban stormwater drainage system was a significant input source of DOM and DBP precursors to natural water. The results of this study are of great significance for protecting the security of water sources and promoting the sustainability of urban water environment.@en

Biological activated carbon (BAC) filtration is usually considered to be able to decrease formation potentials (FPs) of disinfection by-products (DBPs) in drinking water treatment plant (DWTP). However, BAC filters with long running time may release microbial metabolites to effluents and therefore increase FPs of nitrogenous DBPs with high toxicity. To verify this hypothesis, this study continuously tracked BAC filters in a DWTP for one year, and assessed effects of old (running time 8–9 years) and new (running time 0–13 months) BAC filters on FPs of 15 regulated and unregulated DBPs. Results revealed that dissolved organic carbon (DOC) removal was slightly higher in the new BAC than the old one. All fluorescent components of dissolved organic matter evidently declined after new BAC filtration, but fulvic acid-like and soluble microbial product-like substances increased after old BAC filtration, which could be caused by microbial leakage. Correspondingly, new BAC filter generally removed more DBP FPs than the old one. 46.5% HAA7 FPs from chlorination and 44.3% THM4 FPs from chloramination were removed by new BAC filter. However, some DBP FPs, especially HAN FPs, were poorly removed or even increased by the old BAC filter. Proteobacteria could be a main contributor for DBP precursor removal in BAC filters. Herminiimonas, most abundant genera in new BAC filter, may explain its better DOC and UV254 removal performance and lower DBP FPs, while Bradyrhizobium, most abundant genera in old BAC filter, might produce more extracellular polymeric substances and therefore increased N-DBP FPs in old BAC effluent. This study provided insight into variations of DBP FPs and microbial communities in the new and old BAC filters, and will be helpful for the optimization of DWTP design and operation for public health.@en

Light scattering by biological tissues sets a limit to the penetration depth of high-resolution optical microscopy imaging of live mammals in vivo. An effective approach to reduce light scattering and increase imaging depth is to extend the excitation and emission wavelengths to the second near-infrared window (NIR-II) at >1,000 nm, also called the short-wavelength infrared window. Here we show biocompatible core–shell lead sulfide/cadmium sulfide quantum dots emitting at ~1,880 nm and superconducting nanowire single-photon detectors for single-photon detection up to 2,000 nm, enabling a one-photon excitation fluorescence imaging window in the 1,700–2,000 nm (NIR-IIc) range with 1,650 nm excitation—the longest one-photon excitation and emission for in vivo mouse imaging so far. Confocal fluorescence imaging in NIR-IIc reached an imaging depth of ~1,100 μm through an intact mouse head, and enabled non-invasive cellular-resolution imaging in the inguinal lymph nodes of mice without any surgery. We achieve in vivo molecular imaging of high endothelial venules with diameters as small as ~6.6 μm, as well as CD169 + macrophages and CD3 + T cells in the lymph nodes, opening the possibility of non-invasive intravital imaging of immune trafficking in lymph nodes at the single-cell/vessel-level longitudinally.

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Natural organic matter in waters varies in different fractions. To better understand the removal of different fractions by a magnetic ion exchange (MIEX) resin and the mechanism behind it, this study investigated adsorption kinetics, equilibrium and thermodynamics of humic acid (HA) fractions with different hydrophilic-hydrophobic properties and molecular weights on MIEX resin through a series of batch experiments. MIEX resin can effectively remove approximately 40% of hydrophilic and 30% of hydrophobic HA components, as well as approximately 44% of molecular weight (MW) ,10 kDa to some degree. The removal efficiency of HA fractions by MIEX resin reduced with the increase of pH from 6 to 9. Adsorption kinetics of different HA fractions on MIEX resin fitted the pseudo-second-order model well. With the increase of MW of HA from ,1 kDa to .10 kDa, the time to reach adsorption equilibrium reduced from 180 to 120 min. It took more time for the hydrophilic fractions (140 min) to reach the equilibrium than for hydrophobic HA fractions (120 min). The Sips model fitted the adsorption equilibrium data of HA fractions on MIEX resin well. It was revealed that the adsorption of HA fractions on MIEX resin was spontaneous, endothermic and an entropy driven process, and the chemisorption might dominate the adsorption of HA components on MIEX resin. This study is of great significance to the design of magnetic ion exchange resin reactors and the optimization of operational parameters for the removal of natural organic matter with different hydrophilic-hydrophobic properties and molecular weights in different water sources.

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The high chlorine dosages in wastewater treatment plants during the COVID-19 pandemic may result in increased formation of disinfection by-products (DBPs), posing great threat to the aquatic ecosystem of the receiving water body and the public health in the downstream area. However, limited information is available on the effect of biological wastewater treatment processes on the formation of CX3R-type DBPs. This study investigated the effect of oxidation ditch (OD) and anaerobic-anoxic-oxic (AAO), two widely used biological wastewater treatment processes, on the formation of five classes of CX3R-type DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetaldehydes (HALs), haloacetonitriles (HANs) and halonitromethanes (HNMs), during chlorination. Experimental results showed that biological treatment effectively reduced the dissolved organic carbon (DOC) and UV254, while it increased the dissolved organic nitrogen (DON), and therefore the ratio of DON/DOC. In addition, increases in the contents of soluble microbial product- and humic acid-like matters, and the transformation of high molecular weight (MW) fractions in the dissolved organic matter into low MW fractions were observed after OD and AAO processes. Although biological treatment effectively decreased the formation of Cl-THMs, Cl-HAAs, Cl-HANs and Cl-HNMs, the formation of DBCM, DBAA, BDCAA, DBCAA, DCAL, TCAL and DBAN (where C = chloro, B = bromo, D = di, T = tri) all increased significantly, due to the increased formation reactivity. Moreover, biological treatment increased the ratio of bromide/DOC and bromine incorporation into THMs, HAAs and DHANs except for HALs and THANs. Different from previous studies, this study revealed that biological treatment increased the formation of some DBPs, especially brominated DBPs, despite the efficient removal of organic matters. It provides insights into the DBP risk control in wastewater treatment, particularly during the COVID-19 pandemic.@en