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Activated biochars (AB-0.5, AB-1, AB-1.5, AB-2) prepared under different concentrations of an activating agent were used to manufacturing composites (ABHC-0.5, ABHC-1, ABHC-1.5, ABHC-2) based on high-density polyethylene (HDPE) by compounding and injection molding. Thermal and mechanical properties of the composites were characterized and analyzed. The addition of activated biochars improved the thermal properties of HDPE shown by Differential scanning calorimetry and Thermogravimetric analysis. Additionally, ABHC-0.5 exhibited the best flexural strength (38.66 MPa), flexural modulus (2.46 GPa), tensile strength (32.17 MPa), tensile modulus (1.95 GPa), rigidity, elasticity, creep resistance, and anti-stress relaxation ability due to the best porous structure of AB-0.5. A decrease of mechanical properties was observed in ABHC-1, ABHC-1.5, ABHC-2 compared to ABHC-0.5, which was due to the fact that the porous structure was damaged by an excessive activating agent. The results of this study provided a predictive insight in view of optimizing process parameters and establishing the meaningful relationship between biochar porous structure and its resulting composites. Unlabelled Image • Activated biochars were prepared under different concentrations of an activating agent. • Activated biochars were used to prepare composites. • Pore structures of activated biochars affected the composite properties. • Activated biochars improved the thermal properties of composites. • Activation under low concentration improved mechanical properties of the composites. [ABSTRACT FROM AUTHOR]

Rainfall events have profound influence on the soil carbon release in different forest ecosystems. However, seasonal variations in soil respiration (RS) response to rainfall events and associated regulatory processes are not well documented in riparian forest ecosystems to date. We continuously measured soil respiration in a riparian plantation ecosystem from 2015 to 2018 to explore the relationships between soil respiration and rainfall events. Across the 4 years, 83 individual rainfall events were identified for spring, summer and autumn. We found that mean RS rate after rain (post-RS) was significantly higher than that before rain (pre-RS) (p < 0.05) in spring, and the relative change in soil respiration (RSrc) increased against rainfall size due to the stimulation by the significant increases in soil moisture content (ΔSM). In contrast, mean post-RS was lower than pre-RS and RSrc was significantly decreased with the increasing rainfall size (p < 0.01) in summer and autumn. Reduced changes in soil temperature (ΔTS) and increased soil moisture content after rain (post-SM) contributed to the decreased RS due to frequently occurring heavy rain events in summer. Increased ΔSM following rainfall events coupled with groundwater level increase suppressed RSrc in autumn, even though increased ΔTS could offset the negative effects of SM on RS to some extent. In addition, we found that higher post-SM after large rainfall events (>10 mm day−1) changed the response of RS to soil temperature (TS) by reducing the temperature sensitivity (Q 10) even in this riparian plantation ecosystem. Our study highlights the importance of integrating seasonal difference in soil respiration response to rainfall events and the impact of large rainfall events on soil C release for estimating forest soil carbon cycling at multiple scales. Relationship between the relative change in soil respiration (RSrc) and rainfall event sizes. Rainfall size classes were calculated per event in each season: light (<10 mm day−1), moderate (10–25 mm day−1), heavy (>25 mm day−1). Spring: April and May; Summer: June, July and August; Autumn: September and October. Unlabelled Image • Soil respiration response to rainfall events varied seasonally. • Soil respiration increased after rainfall in spring. • Soil respiration decreased after heavy rainfall in summer/autumn. • Heavy rainfall altered the soil respiration response to soil temperature. • Rainfall size and groundwater fluctuation reinforced the seasonality. [ABSTRACT FROM AUTHOR]

The formation of emerging nitrogenous disinfection by-products (N-DBPs) from the chlorination of aspartic acid (Asp) was investigated. The yield of dichloroacetonitrile (DCAN) was higher than other N-DBPs, such as dichloroacetamide(DCAcAm) and chloropicrin (TCNM) during the chlorination of Asp. The formation of DCAN, DCAcAm, and TCNM all showed a trend of first increasing and then decreasing during the chlorination of Asp with increasing contact time. The dosage of chlorine had an impact on the formation of DCAN, DCAcAm, and TCNM. The highest yields of DCAN and DCAcAm appeared when the Cl 2 /Asp molar ratio was about 20, the yield of TCNM increased with increasing the Cl 2 /Asp molar ratio from 5 to 30 and TCNM was not produced when the ratio was less than 5. Cyanogen chloride (CNCl) was detected when the Cl 2 /Asp molar ratio was lower than 5. N-DBPs formation was influenced by pH. DCAN formation increased with increasing pH from 5 to 6 and then decreased with increasing pH from 6 to 9, but DCAcAm and TCNM increased with increasing pH from 5 to 8 and then decreased. Higher temperatures reduced the formation of DCAN and DCAcAm, but increased TCNM formation. DCAN and DCAcAm formation decreased, and relatively stable TCNM formation increased, with increasing free chlorine contact time during chloramination. N -nitrosodimethylamine (NDMA) was produced during chloramination of Asp and increased with prolonged chloramination contact time. The presence of bromide ions enhanced the yields of haloacetonitriles and shifted N-DBPs to more brominated species. [ABSTRACT FROM AUTHOR]

2,5-Dimethyl-p-phenylenediamine–1,3,5-triformylphloroglucinol covalent organic frameworks (PATP COF) were prepared and used as novel adsorbent for controlling the formation potential (FP) and reducing the toxic potential of both carbonaceous disinfection by-products (C-DBPs) and nitrogenous DBPs (N-DBPs) during their subsequent chlorination. During the PATP COF adsorption pretreatment process, the FP of C-DBPs, N-DBPs and total organic halogen (TOX) were reduced by 86.5, 75.4 and 81.1%, respectively. These removal efficiencies were significantly higher when compared with those obtained using a traditional activated carbon (AC) adsorption pretreatment process (42.7, 19.4 and 28.7%, respectively). By comprehensive toxicity calculations, a significant reduction in both the acute and chronic toxic potential of C-DBPs and N-DBPs were observed during the PATP COF adsorption process (with reduction rates of ~85 and ~ 75% observed for the C-DBPs and N-DBPs, respectively), which were comparable to the removal efficiencies observed for C-DBPs FP and N-DBPs FP by weight, suggesting the simultaneous and effective control of DBPs FP and their toxic potential. Cycling tests and stability trial also showed the excellent reusability, wide pH adaptability, and high stability of PATP COF, demonstrating its great potential application to the treatment of drinking water. Unlabelled Image • PATP COF adsorption simultaneously decreased C-DBPs and N-DBPs during chlorination. • PATP COF adsorption simultaneously controlled DBPs FP and their toxic potential. • PATP COF adsorption showed superior performance in controlling DBPs FP than AC did. • PATP COF showed good reusability, wide pH adaptability and high stability. [ABSTRACT FROM AUTHOR]

The emergence of nitrogenous disinfection byproducts (N-DBPs) in drinking water has become a widespread concern. In this study, dichloroacetonitrile (DCAN), dicholoacetamide (DCAcAm) and trichloronitromethane (TCNM) were chosen as representatives to clarify the characteristics of N-DBP precursors in the raw waters of Taihu Lake, the Yangtze River, and Gaoyou Lake. Removal of DCAN and DCAcAm precursors must focus on nonpolar and positively charged organics, but more attention should be paid to micromolecular, polar and non-positively charged organics as TCNM precursors. Compared to molecular weight (MW) and hydrophilicity fractionation, polarity and electrical classification have higher selectivity to intercept N-DBP precursors. The properties of N-DBP precursors are relatively fixed and traceable in water systems, which could contribute to their targeted removal. Based on investigation of their characteristics, the removal efficiency and preferences of organic precursors under different processes were studied in three drinking water treatment plants (DWTPs). The TCNM precursors produced in preozonation can be effectively removed during coagulation. The cumulative removal efficiency of conventional processes on N-DBP precursors was approximately 20–30%, but O 3 /BAC process improved removal by about 40%. The key to improving the removal efficiency of N-DBP precursors by O 3 /BAC is that it can significantly remove low-MW, nonpolar, positively charged, hydrophilic and transphilic organics. In combined toxicity trials, both cytotoxicity and genotoxicity showed a synergistic effect when DCAN, DCAcAm, and TCNM coexisted, which means that low-level toxicity enhancement in the actual water merits attention. DCAN precursors dominated in the toxicity formation potential (TFP), followed by TCNM precursors. In addition, the removal rate of total N-DBP precursors may be higher than that of TFP, leading to overly optimistic evaluation of precursor removal in water treatment practice. Therefore, the removal effect on TFP must also be considered. Unlabelled Image • Polarity and electrical classification of organics were used for N-DBP precursors. • O 3 /BAC process effectively removed nonpolar and positively charged precursors. • Toxicity showed a synergistic effect when DCAN, DCAcAm and TCNM coexisted in water. • Improving the removal rate of DCAN precursors is the key to reducing toxicity risk. • Toxicity formation potential was significantly reduced by preozonation and O 3 /BAC. [ABSTRACT FROM AUTHOR]

The novelty of this study is to explore the effect of temperature varied biochar on the properties of biochar/polymers composites. Rice husk biochar (RB) samples were prepared at different pyrolysis temperatures and injection molding was used to prepare RB/high-density polyethylene (HDPE) composites. Additionally, ultimate analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), pore structure characteristics, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile properties, and dynamic mechanical analysis (DMA) were used to characterize these RB and RB/HDPE composites samples. The results validated that RB obtained at 600 °C showed the highest carbon content, the most complete pore structure, and the largest specific surface area. Moreover, the thermal studies revealed that the addition of RB improved the thermal stability of HDPE. The best tensile strength (26.25 MPa) and Young's modulus (1.87 GPa) were obtained in 500 °C RB/HDPE composites and 600 °C RB/HDPE composites due to their good physical/mechanical interlocking structures shown in SEM. DMA revealed that the stiffness, elasticity, creep resistance and stress relaxation of the composites were improved by the addition of RB. The utilization of temperature varied biochars in biocomposites is important to manage wastes and optimize the properties of biocomposites in terms of reducing production cost and ensuring environmental safety. Unlabelled Image • Temperature varied rice husk biochars were used to prepare composites. • Thermal and mechanical properties of high-density polyethylene were improved. • The 500 and 600 °C biochar composites showed better properties. [ABSTRACT FROM AUTHOR]

The main purpose of this study was to control membrane fouling by degrading natural organic matter, mainly based on free radicals, with a dead-end ultrafiltration system integrated with pretreatment. Four advanced oxidation processes, namely, ultraviolet (UV)/Fe(II), UV/persulfate (PS), Fe(II)/PS and UV/Fe(II)/PS, were used to pretreat raw water prior to ultrafiltration. The priority of the pretreatment effect followed the order of UV/Fe(II)/PS > Fe(II)/PS > UV/PS > UV/Fe(II). In the UV/Fe(II)/PS pretreatment (Fe(II) = 100 μM and PS = 400 μM), the removal rates of UV 254 with a UV irradiation time of 60 min reached 93.07%. Degradation experiments of free-radical probes (carbamazepine) and free-radical scavenger addition (sodium hyposulfite or tert-butanol) showed that the sulfate radical (SO 4 −) was dominant in degrading organic compounds. The specific flow rate (J / J 0) increased by 139.13% and the irreversible fouling resistance was reduced by 69.94%. The total interfacial energy of the colloid-membrane interaction decreased by 84.42% and the separation distance was shortened to ~2 nm. The release of Fe(III) from water under UV radiation and its possible conversion to Fe(II) were observed on the surface of the fouled membranes. After UV/Fe(II)/PS pretreatment, bulky and rough pollutant particles were transformed into a slew of sheet-contaminated layer with the appearance of numerous permeable holes, and the average surface roughness was reduced to 38.1 nm according to atomic-force-microscopy characterization. Unlabelled Image • Surface water was pretreated by UV/Fe(II)/PS and filtered by UF membrane. • UV/Fe(II)/PS pretreatment reduced the self-loss of Fe(II). • The degradation of NOM is mainly mediated by SO 4 − radicals, not by OH. • Fe(II) regeneration increased the utilization rate of PS. • The release of iron from foulants was observed on the fouled membrane surface. [ABSTRACT FROM AUTHOR]

Soluble microbial products (SMPs), as precursors of disinfection byproducts (DBPs) in water treatment, are composed of polysaccharides, humic acid, proteins and DNA, and have caused widespread concerned. Pyrimidine bases (cytosine and thymine) are significant nitrogenous constituents of DNA, which could pose an adverse impact on water quality during chlorination. This study focused on the correlation between relative reactivity, formation of DBPs and combined toxicity in the chlorination of a binary pyrimidine base mixture. The relative reactivities of cytosine and thymine were quite different at a low disinfectant concentration; cytosine reacted more actively with chlorine than thymine did, at the chlorine/total pyrimidine bases molar ratio = 10. The chlorination of binary pyrimidine bases can produce both carbonous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs). In particular, the total yields of trichloromethane (TCM) and trichloronitromethane (TCNM) were lower than the additive yields of monadic cytosine and monadic thymine ("monadic" refers to "separate"), whereas the total yields of haloacetic acids (HAAs) and haloacetonitriles (HANs) were promoted evidently. High reactivity of cytosine with chlorine, greater potential of cytosine to produce specific DBPs and the alkylation of transformation products of thymine may synthetically account for the diversity in total DBPs yields, especially the increased formation of HAAs and HANs. In our toxicity trial, even though the antagonistic effect predominated at f a > 0.4 (f a refers to the affected fraction), the synergism at low concentration levels could enhance the combined toxicity by promoting the yields of N-DBPs. Unlabelled Image • Total yields of HAAs and HANs were enhanced in chlorination of binary combinations. • The alkylation of TPs produced from thymine may affect intermediate reactions. • The toxicity emerged synergism and additive effect at low effect levels in water. • Total HANs yields were regarded as a key factor in determining combined toxicity. [ABSTRACT FROM AUTHOR]