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Abstract: Mechanisms by which dissolved organic matter (DOM) mediates the photochemical reduction of Hg(II) in aquatic ecosystems are not fully understood, owing to the heterogeneous nature and complex structural properties of DOM. In this work, naturally occurring aromatic compounds including salicylic, 4-hydrobenzoic, anthranilic, 4-aminobenzoic, and phthalic acid were systematically studied as surrogates for DOM in order to gain an improved mechanistic understanding of these compounds in the photoreduction of Hg(II) in water. We show that the photoreduction rates of Hg(II) are influenced not only by the substituent functional groups such as –OH, –NH2 and –COOH on the benzene ring, but also the positioning of these functional groups on the ring structure. The Hg(II) photoreduction rate decreases in the order anthranilic acid>salicylic acid>phthalic acid according to the presence of the –NH2, –OH, –COOH functional groups on benzoic acid. The substitution position of the functional groups affects reduction rates in the order anthranilic acid>4-aminobenzoic acid and salicylic acid>4-hydroxybenzoic acid. Reduction rates correlate strongly with ultraviolet (UV) absorption of these compounds and their concentrations, suggesting that the formation of organic free radicals during photolysis of these compounds is responsible for Hg(II) photoreduction. These results provide insight into the role of low-molecular-weight organic compounds and possibly DOM in Hg photoredox transformation and may thus have important implications for understanding Hg geochemical cycling in the environment. [Copyright &y& Elsevier]

Magnetic carbonaceous adsorbents were synthesized by ball-milling biochar (BC) or activated carbon (AC) with Fe 3 O 4 nanoparticles, and their capacities to sorb methylene blue (MB) from water were evaluated and compared. Ball milling with magnetite not only improved the surface properties of the carbonaceous adsorbents, especially BC, but also introduced magnetic properties through mechanical extrusion. Furthermore, ball-mill extrusion increased the MB adsorption capacity of BC at all pH values by 14-fold, on average, but BC ball milled with magnetite had even greater MB adsorption capacity (27-fold, greater, on average). While ball milling of AC also improved its MB adsorption capacity (by almost 3-fold, on average), ball milling with magnetite did not further improve its MB adsorption capacity. All the magnetic adsorbents showed fast MB adsorption kinetics, reaching equilibrium within about 8 h. The Langmuir maximum MB adsorption capacity of the magnetic ball-milled BC (MBM-BC) was the highest (500.5 mg/g) among all the samples including the ones derived from AC. After five adsorption-desorption cycles, MBM-BC maintained about 80% MB removal capacity. The high MB adsorption capacity of MBM-BC was attributed to its increased surface area, opened pore structure, functional groups and aromatic C C bonds, which promoted π-π and electrostatic interactions. Findings from this study indicate that the magnetic ball-milled BC is a promising adsorbent due to its environmentally friendly synthesis, high efficiency, low cost, and convenience in operation. Unlabelled Image • Ball-mill extrusion magnetic biochar and activated carbon was obtained and compared. • The properties and adsorption mechanism of magnetic absorbents was explored. • Magnetic biochar had higher adsorption capacity than magnetic activated carbon. • The maximum adsorption capacity of methylene blue was 500.5 mg/g. • This approach provided a superior means of removing dye from aqueous solutions. [ABSTRACT FROM AUTHOR]

Abstract Mechanochemically sulfidated microscale zero valent iron (S-mZVIbm) is a promising groundwater remediation material as it has been proven to be not only efficient in dechlorinating chlorinated compounds but also amenable to up-scaling. Yet, its efficiency in treating metal contaminants remains barely studied. In this study, we investigated the mechanism and efficiencies of Cr(VI) removal by S-mZVIbm and its effect on TCE dechlorination as a co-contaminant. The Cr(VI) removal by S-mZVIbm was mainly a chemisorption process and its kinetics was well fitted by a pseudo-second-order model. Alkaline pH inhibited Cr(VI) removal while dissolved oxygen slightly depressed the Cr(VI) removal. The Cr(VI) removal rapidly formed a non-conductive layer on S-mZVIbm surface to hinder further electron transfer from Fe0 core before H+ was able to accept any electrons to produce H 2 , which resulted in 100% electron efficiencies of Cr(VI) removal but <1% of Fe0 utilization efficiency. The presence of Cr(VI) also dramatically inhibited the dechlorination of TCE and its electron efficiency as a co-contaminant by passivating the FeS surface. Therefore, Cr(VI) is likely to be an electron sink if present for remediation of other contaminants in groundwater. Graphical abstract Unlabelled Image Highlights • Cr(VI) removal by S-mZVIbm was mainly a surface reduction and precipitation process. • Mechanochemical sulfidation enhanced Cr(VI) removal by increasing surface area. • Electron efficiency of Cr(VI) removal was 100% but particle efficiency was <1%. • Cr(VI) was an electron sink for TCE dechlorination by S-mZVIbm. [ABSTRACT FROM AUTHOR]

The removal efficiency of sediment phosphorus (P) with the in-situ synergistic effect of modified bentonite granules (MBG) and Vallisneria spiralis ( V. spiralis ) in West Lake, Hangzhou, China was investigated for the first time in the study. CMBG-Na10-450 (nitrification (10% Na 2 CO 3 )-calcination (450 °C) combined modification) was prepared and characterized, and the removal effects of sediment P of all fractions with CMBG-Na10-450 and V. spiralis in combination and separately were evaluated in batch experiments. Results showed that CMBG-Na10-450 could promote the growth of V. spiralis , and the residual P of the sediment not adsorbed on CMBG-Na10-450 was changed through root oxygenation and nutrition allocation, and then enhanced the extra P adsorption on CMBG-Na10-450. The combination of MBG and V. spiralis exhibited a synergistic removal effect higher than the summation of MBG and V. spiralis applied separately. The results of microcosm experiments showed that the combination of CMBG-Na10-450 and V. spiralis enhanced the function of P metabolism by increasing the special genus that belongs to the family Erysipelotrichaceae. [ABSTRACT FROM AUTHOR]

The pond-ditch circulation system (PDCS) is an efficient and economical solution for the restoration of degraded rural water environments. However, little is known about nitrous oxide (N 2 O) and nitric oxide (NO) emissions in the microbial removal process of nitrogen in PDCSs, and their contribution to nitrogen removal. The aim of this study was to quantify N 2 O and NO emissions from the PDCS, evaluate their capacities, and elucidate the key environmental factors controlling them. The results showed that N 2 O and NO fluxes were in the ranges 1.1–2055.1 μg N m − 2 h − 1 and 0.1–6.8 μg N m − 2 h − 1 for the PDCS, respectively. Meanwhile, the N 2 O and NO fluxes from the two ponds in the PDCS were significantly higher than those in the static system. Moreover, the amount of N 2 O and NO emissions in the PDCS accounted for 0.17–4.32% of the total nitrogen (TN) removal. According to the partial least squares (PLS) approach and Pearson's correlation coefficients, nitrate nitrogen in water (W-NO 3 − -N), dissolved oxygen in water (W-DO), dissolved oxygen in sediment (DO), pH in water (W-pH), pH in sediment (pH), total kjeldahl nitrogen (TKN), and soil organic carbon (SOC) significantly affected the N 2 O flux ( p < 0.05), whereas W-NO 3 − -N, DO, and nitrite nitrogen in sediment (NO 2 − -N) significantly affected the NO emission ( p < 0.05). [ABSTRACT FROM AUTHOR]

Hydrated manganese oxide (HMO) nanoparticles were impregnated into a peanut shell-derived biochar (BC) to obtain a remarkable nanocomposite adsorbent, HMO-BC, which overcomes the technical barriers of singly applying either HMO or BC in practical heavy metal-containing wastewater treatment. HMO-BC can effectively sequestrate Pb(II) and Cd(II) in a wide pH range of 3–7 and exhibited more preferable sorption than bare BC in the presence of high-level competing cations. BC also significantly lowered the Mn leaching at acidic pH. Fixed-bed column adsorption tests showed that the effective treatment volume of HMO-BC for a simulated Pb(II)- or Cd(II)-laden wastewater is about 4–6 times higher than that of the BC host. In addition, HMO-BC was effective in removing Pb(II) from a real Pb-containing electroplating wastewater to discharge limit (0.2 mg L − 1 ) with treatable volume of 525 BV, much higher than that of the bare BC (60 BV). More importantly, the saturated HMO-BC can be thoroughly regenerated for repeated uses without any observable capacity loss. Such attractive results of HMO-BC were attributed to the complementary effect of its two components. The embedded HMO nanoparticles provide preferable capture of target cations through specific inner-sphere complexation, as illustrated by XPS spectra of Pb 4f 7/2 and O1s, while the non-diffusive negatively charged oxygen-containing groups bound to BC facilitate the pre-enrichment and permeation of Pb(II) and Cd(II) cations into the pore channels prior to their preferable sorption through the Donnan membrane effect. [ABSTRACT FROM AUTHOR]

Pond-ditch circulation systems (PDCSs) were proved to be an appropriate operation selection in rural wastewater remediation. However, the biological dephosphorization process has not been investigated and quantified in PDCSs. In this study, PDCSs exhibited higher total phosphorus (TP) removal efficiencies (77.8%–97.4%). The activities of polyphosphate kinase (PPK) and exopolyphosphatase (PPX) tightly associated with phosphorus biological removal ranged from 0.356 to 11.844 μmol hydroxamic acid min−1 mg−1 protein, and 0.008 to 0.446 μmol p-nitrophenol min−1 mg−1 protein, respectively. Both PPK and PPX in PDCSs increased with time, peaked at day 30, and then declined, and were negatively correlated with sediment total phosphorus (STP), sediment inorganic phosphorus (SIP), P bound to Al/Fe/Mn oxides and hydroxides (NaOH-P), P associated with Ca (HCl-P), and organic matter (OM) (p < 0.05). Results of high-throughput sequencing suggested that Bacillus (0.46%–19.77%) and Clostridium (0.40%–21.0%) genus might be the predominant groups in phosphorus aerobic biological absorption; while Geobacter (0.15%–4.74%) and Arthrobacter (0.03%–4.01%) genus dominated in anaerobic biological process. The RDA results showed that compared to the ditch, temperature (W-temp), TP, dissolved oxygen (DO), NaOH-P, and OM had stronger effects on microbial community structures in two ponds at day 30 than those at days 14 and 60. Path analysis further indicated that STP could impact PPK and PPX activities in PDCSs both directly and indirectly via altering the relative abundances of bacteria taxa. We found that the indirect effects of W-temp, DO, and OM on PPK and PPX activities mediated through modulating the relative abundances of bacteria taxa and STP. Our findings provide evidences that biological dephosphorization process in PDCSs are jointly modulated by environmental factors and microbial communities. The less-studied W-temp, DO, STP, and OM modulating the relative abundances of bacteria taxa was an existing but previously underestimated indirect pathway influencing on biological dephosphorization process in PDCSs. Unlabelled Image • Biological phosphorus removal in pond-ditch circulation systems was examined. • PPK and PPX activities in PDCSs firstly increased, peaked at day 30 and then declined. • Bacillus and Clostridium were the dominant genus for biological dephosphorization. • STP and microbial diversity were the key determinant of PPK and PPX activities. • W-temp, DO, and OM affected PPK and PPX activities by altering microbial diversity. [ABSTRACT FROM AUTHOR]

Sediment phosphorus (P) is the main source of endogenous P for lake eutrophication. An in-situ combined technology for determination the removal effect of sediment P in all fractions was first developed using the novel modified maifanite (MMF) and submerged macrophytes in this study. MMF was synthesized using an acidification process (2.5 mol/L H 2 SO 4) and then a calcination (400 °C) method. The morphology and structure of MMF were characterized by XRD, SEM, XPS, and BET. We tested the removal effects of sediment P by MMF and submerged macrophytes in combination and separately. The results demonstrated that the synergistic removal capacity of sediment P using MMF coupled with submerged macrophytes was higher than the sum of them applied separately. MMF could promote the submerged macrophytes growth and enhance the adsorption of extra P on MMF through root oxygenation and nutrient allocation. The microcosm experiment results showed that sediment from fMMF+ V. spiralis exhibited the most microbial diversity and abundance among the sediment. The combination of MMF and submerged macrophytes increased the Firmicutes abundance and decreased the Bacteroidetes. These results indicated that adsorption-biological technology can be regarded as a novel and competitive technology to the endogenous pollution control in eutrophic shallow lakes. Unlabelled Image • MMF (acidification-calcination modification) was prepared and characterized. • MMF promotes the growth of submerged macrophytes. • MMF and submerged macrophytes enhanced the microbial diversity and abundance. • MMF and submerged macrophytes exhibited a higher synergistic removal capacity. [ABSTRACT FROM AUTHOR]

Sulfidation can enhance the reactivity and longevity of nanoscale zero-valent iron (nZVI), but little is known about its effect on the fate and transport of nZVI in saturated porous media. This work compared the stability and mobility of carboxymethyl cellulose (CMC) stabilized nZVI (CMC-nZVI) and sulfidated nZVI (CMC-S-nZVI) particles in saturated porous media. After sulfidation, the hydrodynamic size of CMC-S-nZVI was 100–150 nm larger than CMC-nZVI due to enhanced adsorption of CMC onto the S-nZVI surface, which was facilitated by the bidentate bridging interaction between CMC and the FeS x phase on S-nZVI. Of note is that they had a similar core size and zeta potential. In comparison to CMC-nZVI, CMC-S-nZVI exhibited less physical settling (0–5% vs. 5–73%) and chemical dissolution (2–10% vs. 3–27%) within 55 min under the same ionic conditions (Na+, K+ < 200 mM; Al3+ < 0.75 mM). Column breakthrough experiments showed that both CMC-S-nZVI and CMC-nZVI had relatively high mobility in saturated porous media. However, CMC-S-nZVI exhibited greater breakthrough (C/C 0 = 0.57–1.0) and corresponding greater mass recovery rates than the corresponding CMC-nZVI (C/C 0 = 0.44–1.0) under most of the experimental conditions (e.g., different ion type and concentration, flow rate, and input concentration). The fitted colloid filtration theory model was in good agreement with experiments. This work suggests that in addition to the significant reactivity and longevity improvements demonstrated in other studies, CMC-S-nZVI is also more mobile than CMC-nZVI suggesting that CMC-S-nZVI has many of the characteristics favorable for field application. Unlabelled Image • The hydrodynamic size of CMC-S-nZVI particles was 100–150 nm larger than CMC-nZVI. • The stronger interaction between CMC and S-nZVI resulted in its larger size. • CMC-S-nZVI showed less physical settling and chemical dissolution than CMC-nZVI. • CMC-S-nZVI was more mobile than CMC-nZVI in sand column under different conditions. • The fitted colloid filtration theory model agreed well with the breakthrough. [ABSTRACT FROM AUTHOR]

• Hypoxia disturbed GH-IGF axis, causing prolonged negative influences on growth. • Hypoxia caused vitamin D and calcium dyshomeostasis. • Hypoxia resulted in muscle and bone dysfunction. • Hypoxia caused DEGs associated with apoptosis and osteoclast differentiation. Hypoxia generally refers to a dissolved oxygen (DO) level that is less than 2–3 mg/L. With ongoing global warming and environment pollution, environmental or geological studies showed hypoxia frequently occurs in global aquatic systems including ocean, river, estuaries and coasts. A preliminary study was performed to evaluate hypoxia tolerant of rainbow trout (Oncorhynchus mykiss) with parameters of mortality, behavior, endocrine and metabolite, identifying three DO levels including normoxia (Ctrl, 7.0 mg/L), non-lethal hypoxia (NH, 4.5 mg/L) and lethal hypoxia (LH, 3.0 mg/L). Furthermore, trout was treated by Ctrl, NH and LH for six hours to mimic the acute hypoxia in wild and/or farming conditions. A significantly higher mortality was observed in LH group. Trout of NH and LH showed stressful responses with unnormal swimming, increased serum cortisol and up-regulated gill hif1α transcription. Despite trout of NH and LH increased the oxygen delivery abilities by increasing the serum hemoglobin levels, the anerobic metabolism were inevitably observed with increased lactate. This study also showed a prolonged influence of NH and LH on growth after 30-days' recovery. Based on RNA-Seq data, different expression genes (DEGs) associated with stress, apoptosis, antioxidant, chaperone, growth, calcium and vitamin D metabolism were identified. Enrichment analysis showed DEGs were clustered in osteoclast differentiation, apoptosis and intracellular signaling transduction pathways. Results further showed NH and LH significantly decreased bone calcium content and disrupted the growth hormone-insulin-like growth factor (GH-IGF) axis. Our study might contribute to a better understanding of the effects of hypoxia on rainbow trout. [ABSTRACT FROM AUTHOR]