Identifying the fate of dissolved organic matter in wastewater treatment plant effluent-dominated urban river based on fluorescence fingerprinting and flux budget approach.

Effluent organic matter from wastewater treatment plants (WWTPs) is an important source of dissolved organic matter (DOM) in urban rivers worldwide and is an important water quality factor. Identifying the fate of DOM in urban river is crucial for water quality management. To address this concern, a fluorescent flux budget approach was conducted to probe the fate of DOM in WWTP effluent-dominated urban river, in combination with field measurement and fluorescence fingerprinting. An urban river receiving two WWTP effluents in Hefei City, China was chosen as the study site, where longitudinal measurements of river hydrology and water quality were performed. The fluorescence fingerprinting revealed the presence of two humic-like components (C1, C4), one fulvic-like component (C2) and one protein-like component (C3) in this investigated river, among which C2 and C4 were indicative of anthropogenic influences, closely associated with treated effluents. For each fluorescent component, the WWTP effluent contributed over 80 % of the total fluorescent dissolved organic matter (FDOM) input in this river. Using the developed FDOM flux budget model, it was found that the C1 and C3 were almost conserved within the waterbody, while the C2 and C4 experienced losses due to biogeochemical reactions. The decay rates of C2 and C4 were estimated to be 0.109-0.174 d-1 and 0.096-0.320 d-1, respectively. Spatial heterogeneity of decay rates for C2 and C4 were associated with the varied chemistries of the lateral input sources including two treated effluents and one tributary flow. Our study highlights that after treated effluent is released into the receiving waterbody, the FDOM would undergo loss from the waters particularly for anthropogenic fulvic-like substance C2 and humic-like substance C4. Additionally, the quantified FDOM decay rate in actual urban water environment provides insights for river water quality management, especially when using DOM as the surrogate indicator of organic pollutants.

Yeast Metabolic Engineering for Biosynthesis of Caffeic Acid-Derived Phenethyl Ester and Phenethyl Amide.

Caffeic acid (CA)-derived phenethyl ester (CAPE) and phenethyl amide (CAPA) are extensively investigated bioactive compounds with therapeutic applications such as antioxidant, anti-inflammatory, and anticarcinogenic properties. To construct microbial cell factories for production of CAPE or CAPA is a promising option given the limitation of natural sources for product extraction and the environmental toxicity of the agents used in chemical synthesis. We reported the successful biosynthesis of caffeic acid in yeast previously. Here in this work, we further constructed the downstream synthetic pathways in yeast for biosynthesis of CAPE and CAPA. After combinatorial engineering of yeast chassis based on the rational pathway engineering method and library-based SCRaMbLE method, we finally obtained the optimal strains that respectively produced 417 µg/L CAPE and 1081 µg/L CAPA. Two screened gene targets of ΔHAM1 and ΔYJL028W were discovered to help improve the product synthesis capacity. This is the first report of the de novo synthesis of CAPA from glucose in an engineered yeast chassis. Future work on enzyme and chassis engineering will further support improving the microbial cell factories for the production of CA derivatives.

Mechanically Robust, Recyclable, and Self-Healing Polyimine Networks.

To achieve energy saving and emission reduction goals, recyclable and healable thermoset materials are highly attractive. Polymer copolymerization has been proven to be a critical strategy for preparing high-performance polymeric materials. However, it remains a huge challenge to develop high-performance recyclable and healable thermoset materials. Here, polyimine dynamic networks based on two monomers with bulky pendant groups, which not only displayed mechanical properties higher than the strong and tough polymers, e.g., polycarbonate, but also excellent self-repairing capability and recyclability as thermosets are developed. Owing to the stability of conjugation effect by aromatic benzene rings, the final polyimine networks are far more stable than the reported counterparts, exhibiting excellent hydrolysis resistance under both alkaline condition and most organic solvents. These polyimine materials with conjugation structure can be completely depolymerized into monomers recovery in an acidic aqueous solution at ambient temperature. Resulting from the bulky pendant units, this method allows the exchange reactions of conjugation polyimine vitrimer easily within minutes for self-healing function. Moreover, the introduction of trifluoromethyl diphenoxybenzene backbones significantly increases tensile properties of polyimine materials. This work provides an effective strategy for fabricating high-performance polymer materials with multiple functions.

PMo12 as a redox mediator for bio-reduction of Cr(VI): Promotor or inhibitor?

Slow reduction rate and low reduction ability were the main limitations of bio-reduction of Cr(VI). As an efficient redox mediator, how phosphomolybdic acid (PMo12) affected bio-reduction of Cr(VI) was worthy of exploration. In this study, short-term and long-term effects of PMo12 on Cr(VI) reduction were investigated to reveal the relevant mechanism. After evaluating the short-term effect of PMo12 concentration from 0.05 to 1.00 mM on Cr(VI) bio-reduction, 0.50 mM was found to be optimum by improving Cr(VI) reduction rate by 16.3 % and microbial electron transport system activity (ETSA) by 43.0 % with Cr(VI) reduction efficiency of 100 % in short-term (22 h) batch experiments. By contrast, in long-term (28 days) continuous flow experiments, 0.50 mM PMo12 exhibited serious inhibition on Cr(VI) bio-reduction. The cumulative toxicity of Mo, strong oxidative stress (reactive oxygen species increased by 16.5 %), the inhibition of extracellular polymeric substances production and the reduction of microbial activity were proved to be the main inhibition mechanism. In terms of microbial electron transport system, the main electron carriers including flavin mononucleotide (FMN), nitrate reductase (NAR), nitrite reductase (NIR) were seriously inhibited. BugBase analysis confirmed that the relative abundance of biofilm forming bacteria decreased after PMo12 addition, and the relative abundance of oxidative stress tolerance bacteria continued to increase.

Aggregation kinetics of coalescing polymer colloids.

The aggregation behavior of a soft, rubbery colloidal system with a relatively low glass transition temperature, T(g) approximately -20 degrees C, has been investigated. It is found that the average gyration and hydrodynamic radii, R(g) and R(h), measured by light scattering techniques, evolve in time in parallel, without exhibiting the crossover typical of rigid particle aggregation. Cryogenic scanning electron microscopy (cryo-SEM) images reveal sphere-like clusters, indicating that complete coalescence between particles occurs during aggregation. Since coalescence leads to a reduction in the total colloidal surface area, the surfactant adsorption equilibrium, and thus the colloidal stability, change in the course of aggregation. It is found that to simulate the observed kinetic behavior based on the population balance equations, it is necessary to assume that all the clusters are spherical and to account for variations in the colloidal stability of each aggregating particle pair with time. This indicates that, for the given system, the coalescence is very fast, i.e., its time scale is much smaller than that of the aggregation.

Role of counterion association in colloidal stability.

A generalized model for colloidal stability has been validated against experimentally measured values of Fuchs stability ratio and critical coagulation concentration (ccc) for electrolytes with mono- or divalent cation, i.e., potassium chloride and magnesium chloride, respectively. Besides the classical DLVO theory, the generalized model accounts for the interplay between colloidal interactions and the association of cations with the particles surface charge groups. The model parameters are either obtained or estimated purely on the basis of independent information available in the literature. For the monovalent salt, the predictions agree well with literature experimental data, forecasting both the ccc values and stability ratios quantitatively. For the divalent salt the predictions for large values of the stability ratio tend to deviate from the experimental data produced in this work, but it is noted that the onset of stability, i.e., the ccc, and small stability ratios are correctly predicted. Moreover, a comparison of the above results with those neglecting the effect of counterion association with the particles surface charge groups indicates that the latter substantially overestimates stability ratios in the presence of high salt concentration in the case of the monovalent salt, and leads to unrealistic large values of the ccc for the divalent salt. Including the association of cations with the particles surface charge groups can explain the relatively low values of experimental ccc for divalent salts compared to the theoretical predictions by the classical DLVO theory neglecting ion association, which is apoint of interest in industrial coagulation processes.

Effect of temperature and surfactant type on the stability and aggregation behavior of styrene-acrylate copolymer colloids.

The colloidal stability, aggregation kinetics, and cluster structure of two styrene-acrylate copolymer latexes, stabilized with an aliphatic sulfonate and an aliphatic carboxylate surfactant, respectively, have been investigated experimentally in the temperature range between 283 and 323 K. The main objective of this study is to investigate the role of temperature and surfactant type on the aggregation kinetics and cluster structure. For this, the values of the Fuchs stability ratio and the time evolutions of the average radius of gyration, hydrodynamic radius, and structure factor of the clusters have been determined using static and dynamic light scattering techniques at different temperatures. It is found that although the two latexes exhibit a somewhat different dependence of the colloidal stability on temperature, all of the values of the average radius of gyration (or hydrodynamic radius) measured at different temperatures and surfactant types, which are plotted as a function of a properly defined dimensionless time, collapse to form a single master curve. Similarly, all of the measured average structure factors also collapse to form a single master curve when they are plotted as a function of the wavevector normalized using the average radius of gyration. These results indicate that, at least for the conditions investigated in this work, the aggregation mechanism and cluster structure are independent of temperature and surfactant type.

Thermal restructuring of fractal clusters: the case of a strawberry-like core-shell polymer colloid.

Thermal restructuring of fractal styrene-acrylate copolymer clusters dispersed in water has been investigated experimentally in the temperature range between 313 and 363 K. The particles constituting the clusters are of strawberry-like core-shell structure with a soft core and a rigid shell grafted on the core polymer chains. Due to the incomplete coverage of the core, the rather soft core may "flow out" through the open areas of the shell, leading to coalescence with the neighboring particles. The clusters were generated under diffusion-limited cluster aggregation conditions, and the restructuring kinetics was monitored by small-angle light scattering. Two sets of thermal restructuring experiments have been performed at various temperatures: (1) restructuring of growing clusters during aggregation and (2) restructuring of preformed clusters in the absence of aggregation. It is found that restructuring occurs only at temperature values above 323 K. In the absence of aggregation, restructuring leads to an increase of the fractal dimension and a decrease of the radius of gyration of the clusters. At sufficiently long times, both quantities reach a plateau value due to the presence of the grafted rigid shell, which constrains the coalescence of the soft core. A simple model, based on coalescence theory of liquid droplets and accounting for the incomplete coalescence and its dependence on temperature, has been developed to interpret the restructuring kinetics in the absence of aggregation. It is found that the proposed model can represent the measured experimental data well.

A generalized model for the stability of polymer colloids.

A generalized model has been proposed to describe the stability of polymer colloids stabilized with ionic surfactants by accounting simultaneously for the interactions among three important physicochemical processes: colloidal interactions, surfactant adsorption equilibrium, and association equilibria of surface charge groups with counterions at the particle-liquid interface. A few Fuchs stability ratio values, determined experimentally for various salt types and concentrations through measurements of the doublet formation kinetics, are used to estimate the model parameters, such as the surfactant adsorption and counterion association parameters. With the estimated model parameters, the generalized model allows one to monitor the dynamics of surfactant partitioning between the particle surface and the disperse medium, to analyze the variation of surface charge density and potential as a function of the electrolyte type and concentration, and to predict the critical coagulant concentration for fast coagulation. Three fluorinated polymer colloids, stabilized by perfluoropolyether-based carboxylate surfactant, have been used to demonstrate the feasibility of the proposed colloidal stability model.