Display omitted
•IOM chemical structure was rich in aromatic and aliphatic protein-like materials.•EOM contained humic and fulvic-like substances with high carboxylic content.•Chemical structure of ...IOM had high reactivity to substitute with chlorine.•IOM was a higher-yielding precursor of THMs and HAAs than EOM.
Algal eutrophication in reservoirs is frequently accompanied by a remarkable increase in the concentration of algogenic organic matter (AOM). Because AOM is well-known as an important precursor to disinfection byproducts (DBPs) in drinking water, algal eutrophication poses severe concerns for public health. This study aimed to characterize the chemical properties of AOM from two major origins, i.e. extra- (EOM) and intra-cellular organic matter (IOM), of a commonly found green alga Chlorella sp. as precursors to trihalomethanes (THMs) and haloacetic acids (HAAs). Particularly, the corresponding relation between the chemical functional structure of EOM and IOM and their THM and HAA formation potential (THMFP and HAAFP) was comprehensively investigated. Results show that IOM chiefly comprised of aromatic and other aliphatic protein-like materials (high organic nitrogen content) those have high activity for chlorine substitution (high UV253/UV203 value) due to the high hydroxyl and amide contents in its chemical structures. EOM alternatively exhibited the characteristics of humic- and fulvic-like materials accompanying with high DOC/DON ratio and aromaticity. However, the chemical structure of EOM had a low tendency for chlorine substitution (low UV253/UV203 value); it was also accompanied by a considerable content of carboxylic moisture, which likely resulted in an unfavorable substitution reaction of EOM with chlorine. As a result, the carbonaceous DBP formation potential (C-DBPFP) showed that IOM yielded higher levels of both THMFP and HAAFP than that yielded by EOM.
The hydrolysis of Al-based coagulants in acidic conditions is necessary for the removal of organic matter by the coagulation/sedimentation process. However, interactions between hydrolyzed Al species ...and organic matter are complicated and this makes it difficult to optimize coagulant dosing for organics removal. The goal of this study was to investigate the reactions of hydrolyzed Al species in the coagulation of organic matter. Two polyaluminum chloride (PACl) coagulants, a commercial product with sulfate (PACl-C) and lab-prepared material (PACl-Al13) containing 7% and 96% of total Al as Al13, respectively, have been applied to investigate the coagulation of humic acid (HA). At pH 6, a lower dosage of PACl-Al13 than of PACl-C was required for optimized HA removal through coagulation/sedimentation due to the strong complexation and charge neutralization by Al13. Observation of the coagulation process using wet scanning electron microscopy showed that PACl-C produced both clustered flocs and linear precipitates in the presence of sulfate while PACl-Al13 produced curled precipitates due to the formation of intermolecular complex, when both coagulants were added at the optimum doses. Investigation of Al–HA floc by 27Al-NMR and Al 2p XPS suggested that monomeric Al (Alm) was hydrolyzed into Al(OH)3 with tetrahedron for PACl-C coagulation while a half of Al13 slowly decomposed into octahedral Al–HA precipitates for PACl-Al13 coagulation. Meanwhile, C ls XPS indicated that aromatic CC of HA was preferentially removed from solution to Al–HA flocs for both PACl-C and PACl-Al13 coagulation. It was concluded that Al–HA complexation strongly affects the reaction pathways for Al hydrolysis and the final nature of the precipitates during PACl coagulation of HA and that the hydrolysis products are also strongly affected by the characteristics of the PACl coagulant.
Display omitted
•A lower dosage of PACl-Al13 than of PACl-C was required for optimized HA removal.•PACl-C produced clustered and linear flocs while PACl-Al13 produced curled flocs.•Monomeric Al in PACl-C substantially hydrolyzed into Al(OH)3 with tetrahedron.•A half of Al13 in PACl-Al13 slowly decomposed into octahedral Al–HA precipitates.•Aromatic CC of HA was preferentially removed from solution to Al–HA flocs.
Display omitted
•A CuCo/NF electrode was used for the electrooxidation (EO) of ammonia.•EO with a Cu0.5Co0.5/NF anode achieved 93% removal of ammonia within 5 h.•Active NiOOH and CoOOH were formed ...after EO of ammonia by CuCo/NF.•The Cu/Co ratio on NF affects current efficiency and energy consumption for ammonia EO.
As part of ongoing efforts to effectively remove ammonia from industrial wastewater, electrochemical oxidation has become an alternative to conventional biological treatment due to its easier operation and better tolerance of toxic pollutants. This study aims to prepare CuCo/nickel foam (CuCo/NF) electrodes by depositing different ratios of Cu and Co as catalysts and investigate their performance for ammonia electrooxidation (EO). Under optimum conditions (pH 11 and applied voltage of 1.1 V vs Ag/AgCl), excellent ammonia removal was obtained using the Cu0.5Co0.5/NF electrode system, with 93% removal after 5 h for a low level of ammonia loading (50 mg-N/L), which was superior to the performance of the bare NF electrode (only 54%). The Cu0.5Co0.5/NF electrode also had a higher current efficiency of 34% and lower energy consumption of 0.11 kWh g−1 compared to the bare NF and single metal Cu (Cu1Co0/NF) or Co (Cu0Co1/NF) electrodes. The high catalytic performance of the Cu0.5Co0.5/NF electrode towards ammonia indicates that a CuCo bimetallic catalyst on a NF substrate is a promising solution for effective removal of ammonia from industrial wastewater.
Biofouling is one the most critical problems in seawater desalination plants and science has not yet found effective ways to control it. Silver compounds and ions are historically recognized for ...their effective antimicrobial activity. Nanosilver particles have been applied as a biocide in many aspects of disinfection, including healthcare products and water treatment. This study proposes an innovative biofouling control approach by surface modification of the RO membrane and spacer with nanosilver coating. A chemical reduction method was used for directly coating nanosilver particles on the membrane sheet and spacer. The surface-modified membrane and spacer were tested for their antifouling performance in a cross-flow flat-sheet membrane cell, which is a part of a pilot plant in Wukan desalination plant. The silver-coating membranes and spacers, along with an unmodified membrane sheet, were tested in the membrane cell and compared on the basis of their antifouling performance. Permeate flux decline and salt rejection was continuously monitored through the testing period. Meanwhile regrowth of microbial populations on the membrane cell was quantified by a unique microbial counting every three to four days.
The results showed that both silver-coated membrane (Ag-cM) with uncoated spacer and silver-coated spacer (Ag-cS) with uncoated membrane perforemed better than the unmodified membrane and spacer (Un-MS), in terms of much slower decrease in permeate flux and TDS rejection. However, the effect of silver-coated spacer on antimicrobial activity was more lasting. In the silver-coated spacer test, there was almost no multiplication of cells detected on the membrane during the whole testing period. Besides, the cells adhering to the membrane seemed to lose their activity quickly. According to the RO performance and microbial growth morphology, the nanosilver coating technology is valuable for use in biofouling control in seawater desalination.
This study aimed to investigate the transformation of copper oxide nanoparticles (CuO NPs) in aquatic environments under different ionic strength and further examine its effects on copper toxicity ...and bioaccumulation by monitoring the responses and uptake behaviours of zebrafish embryo. Ionic strength (IS) was simulated according to surface water (1.5 mM), groundwater (15 mM), and wastewater (54 mM), representing low-, mid-, and high-IS water, respectively. At the highest exposure of 10 mg CuO/L, zebrafish larvae mortality was increased from 21.3% to 33.3%, when IS decreased from 54 to 1.5 mM. Low-IS solution also caused the highest numbers of delayed hatching embryo (81.3%) and opaque yolk deformation (36.3%). Copper bioaccumulation markedly increased when larvae were exposed to low-IS water (35%) relative to high-IS water (15%). Exposing to low-IS particularly enhanced copper uptake (~15 ng Cu/g inside embryo), facilitating the copper accumulation in the heart of larvae, whereas aggregated CuO NPs (>500 nm) in mid- and high-IS water were blocked from the embryo and found abundantly in the body axis and tail. Results indicate that CuO NPs in low-IS solutions rapidly form the relatively small CuO NP aggregates with a high copper dissolution, which would pose great concern for aquatic organisms.
Display omitted
•CuO NPs in low-IS solution induced the highest mortality and sublethal responses.•Low-IS solution facilitated the uptake of CuO NPs and copper ion into embryo.•Death and delayed hatching of embryo were induced by ionic Cu(II) of CuO NPs.•Particle-form of CuO NPs mainly caused a slow heartbeat in larvae.•CuO NPs in low-IS solution distributed to the cardiac area of the embryo.
The effect of noise on the human body has attracted increasing research attention. In particular, many factories generate motor noise pollution, which exposes general workers to noise for extended ...periods. To solve this problem, masks made of different materials are used for reducing the noise generated by motors. In this study, we attempted to predict the acoustic sound of masked motors. We collected noise level data in decibels for different operation frequencies of motors used at National Synchrotron Radiation Research Center (NSRRC) and developed a machine learning model according to the characteristics of the collected data to simulate the effect of masks on the motor sound. We use the Gradient Boost Model (GBM) as the main learning method because the model is suitable for predicting noise from comparison results of the five models are very common predictive models and may performed as compare method to predict acoustic noise. The results indicated that the prediction accuracy of the GBM was considerably higher than other four traditional machine learning methods (random forests, support vector machine, gaussian processes regression model and multiple linear regression models). Moreover, we used a general multiple linear regression method as the worst method of comparison and conducted time-frequency visualization of the sound for analysis. At NSRRC, we examined the effects of three observation locations and three mask materials, namely wood, metal, and acrylic, on the sound prediction accuracy achieved with the developed model. The highest sound prediction accuracy was obtained behind the motor and under an acrylic mask.
The cyanobacteria-bloom in raw waters frequently causes an unpredictable chemical dosing of preoxidation and coagulation for an effective removal of algal cells in water treatment plants. This study ...investigated the effects of preoxidation with NaOCl and ClO_2 on the coagulation-flotation effectiveness in the removal of two commonly blooming cyanobacteria species, Microcystis aeruginosa（MA） and Cylindrospermopsis raciborskii（CR）, and their corresponding trihalomethane（THM） formation potential. The results showed that dual dosing with NaOCl plus ClO_2 was more effective in enhancing the deformation of cyanobacterial cells compared to single dosing with Na OCl, especially for CR-rich water.Both preoxidation approaches for CR-rich water effectively reduced the CR cell count with less remained dissolved organic carbon（DOC）, which benefited subsequent coagulation–flotation. However, preoxidation led to an adverse release of algogenic organic matter（AOM） in the case of MA-rich water. The release of AOM resulted in a poor removal in MA cells and a large amount of THM formation after oxidation-assisted coagulation-flotation process. The reduction in THM formation potential of CR-rich waters is responsible for effective algae and DOC removal by alum coagulation. It is concluded that the species-specific characteristic of cyanobacteria and their AOM released during chlorination significantly influences the performance of coagulation–flotation for AOM removal and corresponding THM formation.
Complex organics contained in dye wastewater are difficult to degrade and often require electrochemical advanced oxidation processes（EAOPs） to treat it. Surface activation of the electrode used in ...such treatment is an important factor determining the success of the process.The performance of boron-doped nanocrystalline diamond（BD-NCD） film electrode for decolorization of Acid Yellow（AY-36） azo dye with respect to the surface activation by electrochemical polarization was studied. Anodic polarization found to be more suitable as electrode pretreatment compared to cathodic one. After anodic polarization, the originally H-terminated surface of BD-NCD was changed into O-terminated, making it more hydrophilic.Due to the oxidation of surface functional groups and some portion of sp2 carbon in the BD-NCD film during anodic polarization, the electrode was successfully being activated showing lower background current, wider potential window and considerably less surface activity compared to the non-polarized one. Consequently, electrooxidation（EO） capability of the anodically-polarized BD-NCD to degrade AY-36 dye was significantly enhanced, capable of nearly total decolorization and chemical oxygen demand（COD） removal even after several times of re-using. The BD-NCD film electrode favored acidic condition for the dye degradation; and the presence of chloride ion in the solution was found to be more advantageous than sulfate active species.
In recent years there has been an increasing interest in the use of autohydrogenotrophic bacteria to treat nitrate from wastewater. However, our knowledge about the characteristics of extracellular ...polymeric substances（EPS） releasing by these activities is not yet very advanced. This study aimed to investigate the change in EPS compositions under various p H values and hydrogen flow rates, taking into consideration nitrogen removal. Results showed that p H 7.5 and a hydrogen flow rate of 90 m L/min were the optimal operating conditions, resulting in 100% nitrogen removal after 6 hr of operation. Soluble and bound polysaccharides decreased, while bound proteins increased with increasing p H. Polysaccharides increased with increasing hydrogen flow rate. No significant change of bound proteins was observed at various hydrogen flow rates.
PDF
