Effects of sludge retention time on sludge reduction by ultrasound treatment: Sludge characteristics, microbial community, and metabolism.

Both ultrasound and sludge retention time (SRT) enable the in-situ sludge reduction during wastewater treatment, but the influence of SRT on ultrasonic lysis - cryptic growth is unclear. This paper researched the influence of different SRTs on sludge lysis - cryptic growth using a sequential bio-reactor (SBR), then explained in details the changes of microorganisms in the SBR. The best SRT for sludge reduction was 30 d, and 47.29% reduction in sludge was achieved. The different SRTs changed the organic matter removal in the wastewater, and the removal rate decreased when SRT exceeded 60 d. The size of the sludge particles varied depending on the SRT, with the smallest size at SRT of 10d being 45.6 µm and the largest size at SRT of 90d being 110.0 µm. SEM showed that the sludge surface changed rough at longer SRT. FTIR and XPS showed notable effect in sludge functional group strength at SRT of 30 d. Extracellular polymeric substance (EPS) reduced the most at SRT of 30 d. The microbial communities of sludge varied with the SRT, and the unique main genus at SRT of 5, 15, 30 and 90 d were C10-SB1A, Lactococcus, Propioniciclava, Lactococcus, respectively. Furthermore, the SRT changed relative abundance of enzymes concerned with metabolism of carbon, nitrogen, and phosphorus. Similarly, SRT changed the metabolic rate, and the metabolic rate of carbon, nitrogen and phosphorus was best at SRT of 30 d.

Structure and composition of dissolved organic matters in sludge by ultrasonic treatment.

The leaching of dissolved organic matter (DOM) from the sludge into the liquid phase is induced by ultrasound. However, there is limited investigation into the structure and molecular composition of sludge DOM in this process. The molecular structure and composition of sludge DOM in ultrasonic treatment were comprehensively elucidated in this study. The sludge dissolved organic carbon (DOC) and three-dimensional fluorescence spectroscopy (3D-EEM) image had most significant change at 15-min ultrasonic time and 1.2 W/mL ultrasonic density, respectively. Gas Chromatography-Mass Spectrometry (GC-MS) analysis indicated that ultrasonic treatment of sludge reduced the macromolecules to small molecules in DOM. Then, electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS) analysis revealed that lignin, tannins, and carbohydrates were the main components of sludge DOMs after ultrasound treatment. analysis revealed that lignin, tannins, and carbohydrates were the main components of sludge DOMs after ultrasound treatment. Furthermore, through the Van Krevelen analysis, the major components were CHO (48.50%) and CHOS (23.20%) in the DOM of ultrasonicated sludge. This research provides the basis for the practical application of ultrasonic treatment of sludge and provides basic information for DOM components.

Recent advances in ultrasound-Fenton/Fenton-like technology for degradation of aqueous organic pollutants.

Organic pollutants in water are a serious problem because of their widespread presence, harming the ecosystem and human health. Of the commonly used advanced oxidation processes, a hybrid of ultrasound and the Fenton/Fenton-like technology has received increasing attention in treatment of aqueous organic pollutants. This hybrid is effective in degradation of organic pollutants, but its application has not been summarised. Herein, first, the application and influencing factors of this hybrid technology for organic pollutants degradation are introduced. Second, the mechanism of its action is discussed. Third, the current challenges and future perspectives associated with this technology are proposed. This review provides valuable information regarding this technology, deepens the understanding of its mechanisms of organic pollutants degradation and provides a reference for its use in treatment of aquatic environments.

Preparation and application of Ag plasmon Bi3O4Cl photocatalyst for removal of emerging contaminants under visible light.

Photocatalytic degradation has been extensively investigated toward the removal emerging contaminants (ECs) from water. In this study, a series of Ag-Bi3O4Cl plasmon photocatalysts were synthesized through the photo-deposition of metallic Ag on the Bi3O4Cl surface. The effects of plasmon modification on the catalytic performance of bismuth oxychlorides were analyzed. Ag addition did not alter the morphology of Bi3O4Cl. With the increasing Ag content, the number of oxygen defects on the catalyst surface first increased and then decreased. Moreover, the surface plasmon resonance effect of Ag suppressed the recombination of electron-hole pairs, promoting the migration and separation of photocarriers and improving the light absorption efficiency. However, the addition of excessive Ag reduced the number of active sites on the Bi3O4Cl surface, hindering the catalytic degradation of pollutants. The optimal Ag-Bi3O4Cl photocatalyst (Ag ratio: 0.025; solution pH: 9; dosage: 0.8 g/L) achieved 93.8 and 94.9% removal of ciprofloxacin and tetrabromobisphenol A, respectively. The physicochemical and photoelectric properties of Ag-Bi3O4Cl were determined through various characterization techniques. This study demonstrates that introducing metallic Ag alters the electron transfer path of the catalyst, reduces the recombination rate of electron-hole pairs, and effectively improves the catalytic efficiency of Bi3O4Cl. Furthermore, the pathways of ciprofloxacin degradation products and their biotoxicity were revealed.

What are the determinants of wastewater discharge reduction in China? Decomposition analysis by LMDI.

Wastewater discharge reduction (WDR) is a key breakthrough point for China's environmental protection. Based on China's 30 provincial data from 2011 to 2017, this paper applied the logarithmic mean Divisia index (LMDI) method to clarify the determinants of WDR at national, regional, and provincial levels. Except for wastewater discharge factor, economic development, and total population, four innovative factors, total water application intensity, water environment cost, water treatment industry development level, and drainage infrastructure investment scale were first proposed in this study. The results indicated that from 2011 to 2017, at the national level, total water application intensity and water treatment industry development level were dominant contributors to WDR, while other factors all inhibited WDR. At the regional level, the results of wastewater discharge factor, economic development, and water environment cost were similar to the national level. The drainage infrastructure investment scale had a positive effect on WDR in Northeast and South China while having a negative effect on other regions. And except for Northeast China, the water treatment industry development level promoted WRD, while the total population inhibited WDR. Finally, the determinants of WDR at the provincial level were investigated. On this basis, targeted corresponding policies were provided in this paper.

Design of choline chloride modified USY zeolites for palladium-catalyzed acetylene hydrochlorination.

USY zeolites (USY) were applied to design and synthesize palladium-based heterogeneous catalysts for exploring an efficient non-mercuric catalyst for acetylene hydrochlorination. Choline chloride (ChCl) was selected as the nitrogen-containing ligand to modify the Pd@USY catalysts and the proposed Pd@15ChCl@USY catalyst exhibited obviously the best catalytic performance with a stable acetylene conversion and vinyl chloride selectivity of over 99.0% for more than 20 h. According to the results of characterization and the density functional theory calculations, it is indicated that the addition of ChCl can significantly inhibit the agglomeration and loss of the Pd active species, prevent carbon deposition and enhance the ability of HCl and C2H2 adsorption and C2H3Cl desorption, resulting in promoting the catalytic performance of Pd@USY catalysts during the acetylene hydrochlorination reaction.

Fabrication of Bi-Bi3O4Cl plasmon photocatalysts for removal of aqueous emerging contaminants under visible light.

Photocatalytic oxidation of emerging contaminants (ECs) in water has recently gained extensive attentions. In this study, bismuth oxychloride-based plasmon photocatalysts (Bi-Bi3O4Cl) exhibiting high performance were successfully developed by reducing Bi3+ on the surface of Bi3O4Cl. Consequently, the photocatalysts were used to remove ECs from water. The effects of developmental process and Bi metal plasmon resonance on the photoelectric performances of Bi-Bi3O4Cl were investigated through a series of characterizations. The UV-vis diffuse reflection and photoluminescence spectra revealed that the light absorption range of the photocatalyst gradually increased and the electron recombination rate gradually decreased with the introduction of Bi metals. The optimal removal rates of ciprofloxacin and tetrabromobisphenol A by Bi-Bi3O4Cl were 93.8% and 96.4%; the respective reaction rate constants were 5.48 and 4.93 times higher than that of Bi3O4Cl. The mechanism study indicated that main reactants in the photocatalytic system were •O2- radicals and photogenerated holes, and the existence of oxygen vacancies and Bi metals promoted electron transfer in photocatalyst. In conclusion, this research produces a novel, green, highly efficient, and stable visible light photocatalyst for the removal of ECs from water.

Di-functional Cu2+-doped BiOCl photocatalyst for degradation of organic pollutant and inhibition of cyanobacterial growth.

Photocatalytic oxidation of contaminants in water has recently gained extensive attentions. In this study, Cu2+-doped BiOCl microsphere photocatalysts were prepared using solvothermal method. The effects of Cu2+ doping ratio on the morphological structures and photoelectric and photocatalytic properties of BiOCl were studied in detail. Results showed that Cu2+ doping affected the particle size of BiOCl microspheres. The introduction of Cu2+ ions gradually increased the light absorption range and decreased the electron recombination rate of photocatalysts as shown by ultraviolet-visible diffuse reflection and photoluminescence spectra. The best doping ratio was 0.25 Cu2+-BiOCl, showing the highest photocatalytic activity for rhodamine B (14.25 time higher than BiOCl) and a good inhibition of algal growth. The main reactants in the photocatalytic system were·OH and h+ (electron holes). Density functional theory (DFT) calculations further demonstrated that the doping of Cu2+ ions made the photogenerated carriers in BiOCl easier to generate and ensured the charge was transferred more rapidly. In conclusion, a novel high-efficiency multifunctional photocatalyst is proposed for the efficient organic pollutants removal and algae growth inhibition from water.

Progress in ultrasound-assisted extraction of the value-added products from microorganisms.

Extracting value-added products from microorganisms is an important research focus for the future. Among the many extraction methods, ultrasound-assisted extraction (UAE) has attracted more attention owing to its advantages in reducing working time, increasing yield, and improving the quality of the extract. This review summarizes the use of UAE value-added products from microorganisms, with the main extracted substances are pigments, lipids, polysaccharides, and proteins. In addition, this work also summarizes the mechanism of UAE and highlights the factors that affect UAE operation, such as ultrasonic power intensity or power density, operation mode, and energy consumption, which need to be considered. All extraction products from microorganisms showed that UAE can effectively improve the extraction yields of value-added products. It also highlights the existing problems of the technology and possible future prospects. In general, the UAE of value-added substances from microorganisms is feasible and has the potential for development.

Functions of constructed wetland animals in water environment protection - A critical review.

Constructed wetlands (CWLs) are widely used for water environment protection. In some cases, CWL animals can help improve CWL treatment efficiency and contribute to CWL maintenance and management. However, while plants, microorganisms, and substrates in CWLs have received much attention, animals have been largely ignored. Therefore, the aims of this review are to determine the roles wetland animals play in the water environmental protection of CWLs. This study introduced species of wetland animals and the main factors that can affect their survival. The way in which CWL animals affect pollutants was discussed in detail from four perspectives: adsorption and bioaccumulation, bioturbation, and the influence of CWL animals on plants and microorganisms. The characteristics of CWL animals that can be used for biological monitoring are summarized, and the use of CWLs for the protection of wetland biodiversity is also discussed. Finally, some prospects are proposed for future research. This study will help researchers better understand the role of CWL animals in CWLs and encourage researchers to focus on studies of wetland animals.

Advanced phosphate and nitrogen removal in water by La-Mg composite.

A novel La-Mg composite was prepared for the removal of low concentration phosphate and ammonium nitrogen to alleviate the eutrophication problem. The composition and morphology of La-Mg composite was characterized; Its surface was composed of La, Mg, C, and O elements, with a specific surface area of 21.92 m2/g. La-Mg composite presented excellent removal of phosphate (100%) and nitrogen (96.8%), and the adsorption capacity reached 49.72 mg-P/g and 159.30 mg-N/g for separated adsorption. The composite also had a wide pH usability range (3-11 for P and 3-9 for N) and the adsorption process was almost not disturbed by coexisting ions. After adsorption, it could be regenerated by Na2CO3 and reused effectively. For actual water treatment, a very low residual P of 0.01 mg/L and N of 0.05 mg/L were achieved. Furthermore, Mechanism analysis showed that P adsorption involved ligand exchange and electrostatic attraction. The potential mechanisms of N adsorption involved electrostatic attraction and ion exchange. The results showed that the La-Mg composite is a novel and efficient adsorbent for actual water treatment to achieve ultra-low nutrients concentration.

Preparation and application of BiOBr-Bi2S3 heterojunctions for efficient photocatalytic removal of Cr(VI).

Recently, the photocatalytic reduction of Cr(VI) has been extensively studied. Herein, we successfully prepared the BiOBr-Bi2S3 heterojunctions with high photocatalytic Cr(VI) reduction performance using an ion exchange method. The optimal BiOBr-Bi2S3 heterojunction (prepared with BiOBr, pH of 6.0, 2 mmol Na2S2O3·5H2O,) achieved 100% removal of Cr(VI) within 12 min. The performance of photo-reduced Cr(VI) was about 28.9 and 184.6 times higher than that of pure Bi2S3 and BiOBr, respectively. Besides, BiOBr-Bi2S3 heterojunctions had a good adsorption efficiency for Cr(III), suggesting that they could be applied as bifunctional photocatalyst. The formation process and photoelectric properties of the BiOBr-Bi2S3 heterojunctions were revealed by a series of characterizations. In conclusion, this work reported the synergistic effect of adsorption and photocatalysis of the BiOBr-Bi2S3 heterojunctions for Cr removal for the first time, suggesting that the BiOBr-Bi2S3 heterojunctions could act as a novel photocatalytic adsorbent to treat the Cr(VI)-containing wastewater.

Ce-based catalysts used in advanced oxidation processes for organic wastewater treatment: A review.

Refractory organic pollutants in water threaten human health and environmental safety, and advanced oxidation processes (AOPs) are effective for the degradation of these pollutants. Catalysts play vital role in AOPs, and Ce-based catalysts have exhibited excellent performance. Recently, the development and application of Ce-based catalysts in various AOPs have been reported. Our study conducts the first review in this rapid growing field. This paper clarifies the variety and properties of Ce-based catalysts. Their applications in different AOP systems (catalytic ozonation, photodegradation, Fenton-like reactions, sulfate radical-based AOPs, and catalytic sonochemistry) are discussed. Different Ce-based catalysts suit different reaction systems and produce different active radicals. Finally, future research directions of Ce-based catalysts in AOP systems are suggested.

Historical development and prospects of photocatalysts for pollutant removal in water.

Photocatalysis, as a low-cost and environment friendly technology, has demonstrated a significant potential for water pollution purification; it has received extensive attention in recent decades. The key is the photocatalyst; a large number of photocatalysts have been developed. To better understand and further develop the photocatalysis technology for water treatment, this review summarizes its development over time. The development period is divided into four stages (1960s-1993, 1994-2000, 2001-2010, and 2011-present) to provide readers with a better understanding of the development characteristics, and causes and consequences of each historical stage. This review expounds the origin and development of photocatalysis and the obstacles encountered and overcome. It describes the development of mechanisms and methods to solve these problems in each time period. Moreover, it reviews the recent development of new photocatalysts, the concept of designing photocatalysts, and photocatalytic-coupling systems. Finally, it enumerates the problems that continue to exist in the application of photocatalysis technology, and highlights the key issues that must be addressed in future research. The review is aimed at providing the researchers with a deeper understanding of photocatalysis technology and encourage further development of the application of photocatalysis to water treatment.

MnCeOX with high efficiency and stability for activating persulfate to degrade AO7 and ofloxacin.

An efficient MnCeOx composite was successfully synthesized for activation of persulfate to degrade acid orange 7 (AO7) and ofloxacin. Pollutants degradation efficiencies with different catalytic systems were investigated. Results showed the performance of MnCeOx was better than MnOx, CeO2 and MnOx + CeO2. Thus, there was a clear synergistic effect (Se) between Mn and Ce in the composite, and the Se was 73.8% for AO7 and 39.6% for ofloxacin. In addition, AO7 removal fitted 1st order reaction while ofloxacin removal fitted 2nd order reaction in MnCeOx/persulfate system. Moreover, MnCeOx/persulfate system showed high efficiency in pH range of 5-9. Mechanism analysis showed that SO4- and OH on the surface of the catalyst were the main active species, and O2- also played an important role in pollutants degradation. Furthermore, MnCeOx showed high activity in actual water. Finally, the possible degradation pathway of ofloxacin was proposed according to the high performance liquid chromatography-mass spectrometry result. Overall, this study provides an efficient and stable catalyst to activate persulfate to degrade refractory pollutants.

MnCeOx/diatomite catalyst for persulfate activation to degrade organic pollutants.

Persulfate (PS)-based oxidation technologies are attracting increasing attentions in water treatment due to their high efficiency and stability. In this study, a novel diatomite supported MnCeOx composite (MnCeOx/diatomite) was prepared and characterized for activation of PS to degrade organic pollutants. Results indicated that diatomite not only dispersed MnCeOx and increased the specific surface area of catalyst, but also improved the low-valence metal site (Mn2+ and Ce3+) and reactive oxygen species site (-OH) of MnCeOx, thus enhancing the activities of MnCeOx. MnCeOx/diatomite/PS showed high efficiency for multiple dyes and pharmaceutical pollutants. Constant rate (k) of MnCeOx/diatomite (kMnCeOx/diatomite) was three times higher than the sum of constant rate of MnCeOx (kMnCeOx) and constant rate of diatomite (kdiatomite). In addition, MnCeOx/diatomite showed wide pH application (5-9). Cl- and NO32- had no effect while SO42- and humid acid had slightly negative effects on MnCeOx/diatomite/PS system. Moreover, MnCeOx/diatomite showed good reusability and stability. Mechanism analyses indicated that electron transfer of Mn and Ce attributed to the activation of PS and oxygen to produce free radicals. SO4-, OH and O2- on the surface of catalyst were the main active free radicals to attack pollutants.

An efficient CuO-γFe2O3 composite activates persulfate for organic pollutants removal: Performance, advantages and mechanism.

CuO-γFe2O3 was fabricated as a novel and effective persulfate (PS) catalyst to remove bio-refractory organic pollutants. Characterization results showed that CuO-γFe2O3 possessed a relatively large surface area among transition metal oxides which provided favorable adsorption and activation sites for PS to degrade pollutants. There was an obvious synergy between CuO and γFe2O3 in the composite, which played 84.7% role in Acid orange 7 (AO7) removal. Under the optimal conditions (CuO-γFe2O3 dosage = 0.6 g L-1, PS dosage = 0.8 g L-1, unadjusted solution pH), almost complete AO7 was rapidly eliminated in 5 min. Moreover, the wide workable pH range (2-13), good stability (0.82 mg L-1 Cu leached, almost no Fe leached) and reusability (4 times) were the significant virtues of CuO-γFe2O3 for wastewater treatment. Besides, the reaction mechanism mainly based on the interaction among Cu(II/III) and Fe(II/III) species for sulfate radical (SO4-) generation was emphatically elucidated by the analyses of radicals, PS utilization, TOC removal and metal chemical states. Finally, CuO-γFe2O3+PS system displayed desirable removal of multiple organic pollutants with different molecular structures. In light of the prominent advantages of CuO-γFe2O3+PS, this work extended activated PS process in treating refractory organic wastewater.