Synergistic utilization of inherent halides and alcohols in hydraulic fracturing wastewater for radical-based treatment: A case study of di-(2-ethylhexyl) phthalate removal

Degradation of dibutyl phthalate by ozonation in the ultrasonic cavitation-rotational flow interaction coupled-field: performance and mechanism

Dibutyl phthalate (DBP) is present in hydraulic fracturing flowback and produced water. Degradation of DBP in aqueous by means of ozonation in ultrasonic cavitation-rotational flow interaction coupled-field (UC-RF coupled-field) was studied. The effect of ozone dosage, ozone intake flow, operating temperature, initial pH, DBP initial concentration, liquid flow rate, and ultrasonic power on the DBP removal was investigated. Results indicated that the DBP degradation rate was strongly influenced by the liquid flow rate and the ultrasonic power over the range investigated. HCO₃^- and Cl^- revealed an inhibitory effect on the DBP removal. SO₄^2- seemed to have no effect on DBP removal. The ozone utilization efficiencies in the UC-RF coupled-field were 2.77 and 1.13 times higher than those in the conventional microporous aeration (CMA) and rotating-flow microbubble aeration (RFMA), respectively. The DBP degradation rate was diminished in the presence of tert-butyl alcohol. Cavitation bubbles are considered as innumerable microreactors. Degradation of DBP by direct ozonation, hydroxyl radical (·OH) oxidation, high pressure, and high-temperature pyrolysis was demonstrated. Finally, a possible degradation pathway of DBP is obtained on the basis of the main reaction intermediates.

Iron-based materials for simultaneous removal of heavy metal(loid)s and emerging organic contaminants from the aquatic environment: Recent advances and perspectives

The existence of heavy metals and emerging organic contaminants in wastewater produces serious toxic residues to the environment. Developing cheap and efficient materials to remove these persistent pollutants is crucial. Iron-based materials are cost-effective and environmentally friendly catalysts, and their applications in the environmental field deserve attention. This paper critically reviewed the removal mechanisms of heavy metals and emerging organic pollutants by different influencing factors. The removal of pollutants (heavy metals and emerging organic pollutants) in a multi-component system was analyzed in detail. The mechanisms of synergism, antagonism and non-interference were discussed. This paper had a certain reference value for the research of wastewater remediation technology which could simultaneously remove various pollutants by iron-based materials.

Enhancement of urea removal from reclaimed water using thermally modified spent coffee ground biochar activated by adding peroxymonosulfate for ultrapure water production

To enhance the degradation of urea in reclaimed water for producing ultrapure water (UPW), thermally modified biochar (TBC) was prepared by secondary pyrolysis using spent coffee biochar with the function as an activator of peroxymonosulfate (PMS). Results showed that 94.4% of urea can be degraded effectively by the TBC-PMS system at the dosage of 0.4 g/L TBC and 2 g/L PMS under neutral and weak acid conditions. Moreover, urea removal mainly depended on the free radical pathway (SO₄^{• -} and OH^•), especially OH^•. The inorganic anions of TBC increased via secondary pyrolysis, especially carbonate and phosphate, resulting in higher electrical conductance (EC) value than the original biochar. It was conducive to activating PMS. As well, C-O, -OH worked as an active site in the TBC-PMS system, providing electrons and activating PMS. This work provides a novel strategy for UPW production using TBC-PMS system.

Polyoxometalates for bifunctional applications: Catalytic dye degradation and anticancer activity

Improving the efficiencies of organic compound degradations by catalytic materials is a challenging materials research field. In our research, we successfully synthesized cobalt-based polyoxometalates (CoV-POMs) via a simple crystallization-driven self-assembly method. The incorporation of the newly synthesized CoV-POMs into peroxymonosulphate (PMS), forming a mixture, greatly enhancing the catalytic activation for a complete degradation of dye solution. The positive synergic effect between CoV-POMs and PMS was substantiated by a relatively meager degradation of less than 10% in the system without CoV-POMs, in which CoV-POMs played a vital role to activate PMS towards free radicals generation for dye degradation. Methylene blue (MB) and rhodamine B (RB) dyes were completely decolorized under 60 min with the presence of 40 mg/L CoV-POMs and 150 mg/L PMS. The CoV-POMs/PMS system was pH dependance with a lower dye degradation efficiency at elevated pH. The effect of pH was more prominent in RB dye, in which the degradation efficiency dropped drastically from 93.3% to 41.12% with the increase in the solution pH from 7 to 11. The quenching tests suggested that sulfate radicals were the dominant active species involving in the dye degradation reaction. Besides MB and RB dyes, CoV-POMs/PMS system also showed significant activity towards the degradation of phenol red (PR) and methyl orange (MO) dyes. In the biological test, CoV-POMs exhibited non-toxic behavior towards normal cells that reduced safety concern for the large-scale wastewater treatment application. In addition, the testing divulged the anticancer property of CoV-POMs with more than 35 % of A549 lung adenocarcinoma and MDA-MB-231 breast adenocarcinoma were killed with 250 mg/L CoV-POMs. The selective lethality of CoV-POMs towards cancer cells was found to be caused by different extents of cellular apoptosis. In overall, the synthesized bifunctional CoV-POMs manifested superior activities in the examined applications, specifically dye degradation and anticancer.

Comparison of the Hydraulic Fracturing Water Cycle in China and North America: A Critical Review

There is considerable debate about the sustainability of the hydraulic fracturing (HF) water cycle in North America. Recently, this debate has expanded to China, where HF activities continue to grow. Here, we provide a critical review of the HF water cycle in China, including water withdrawal practices and flowback and produced water (FPW) management and their environmental impacts, with a comprehensive comparison to the U.S. and Canada (North America). Water stress in arid regions, as well as water management challenges, FPW contamination of aquatic and soil systems, and induced seismicity are all impacts of the HF water cycle in China, the U.S., and Canada. In light of experience gained in North America, standardized practices for analyzing and reporting FPW chemistry and microbiology in China are needed to inform its efficient and safe treatment, discharge and reuse, and identification of potential contaminants. Additionally, conducting ecotoxicological studies is an essential next step to fully reveal the impacts of accidental FPW releases into aquatic and soil ecosystems in China. From a policy perspective, the development of China's unconventional resources lags behind North America's in terms of overall regulation, especially with regard to water withdrawal, FPW management, and routine monitoring. Our study suggests that common environmental risks exist within the world's two largest HF regions, and practices used in North America may help prevent or mitigate adverse effects in China.

Selective removal of phenanthrene for the recovery of sodium dodecyl sulfate by UV-C and UV-C/PDS processes: Performance, mechanism and soil washing recycling

Soil washing is commonly used to remediate PAHs contaminated sites. However, the effluent after washing containing PAHs and surfactant may cause secondary pollution and remediation cost is still high, unless PAHs are selectively removed from the effluent and the surfactant is recovered and recycled. Herein, ultraviolet irradiation (254 nm, UV-C) and its combination with peroxydisulfate (UV-C/PDS) were applied to selectively degrade PHE in the synthetic soil washing effluent. At natural pH of 8.6, 98.2 % of PHE was removed within 30 min under 6 W UV-C irradiation. After adding 2 mM PDS, the time was shortened to 8 min but still achieving 98.7 % PHE removal and less toxic treated effluent than UV-C alone. The ¹O₂ was the main oxidizing species in UV-C alone system, while ¹O₂ as well OH and SO₄^- were responsible for PHE removal in the UV-C/PDS system. The possible intermediates of PHE degradation were recognized using liquid chromatography-mass spectrometry technique and the degradation pathways in both systems were proposed. Soil washing recycling experiments verified the recovered SDS could be reused directly without surfactant supplement and the soil washing efficiency changed insignificantly during three cycles. It indicates UV-C/PDS coupled with soil washing is a promising remediation technology.

Ball milled Fe0@FeS hybrids coupled with peroxydisulfate for Cr(VI) and phenol removal: Novel surface reduction and activation mechanisms

Fe⁰@FeS hybrids were synthesized by ball milling and applied to couple with peroxydisulfate (PS) for Cr(VI) reduction and phenol oxidation. A synergistic effect between Fe⁰ and FeS for contaminants removal was found in experimental results. The removal rates of Cr(VI) and phenol by ball milled Fe⁰@FeS hybrids coupled with PS were 97% and 88.7% (initial concentrations of Cr(VI) and phenol are 35 and 40 mg/L, respectively), indicating a successful treatment method for industrial wastewater containing metals, metalloids and organic pollutants. Concentrations of Cr(VI) lower than 45 mg/L could promote the degradation of phenol, while high concentration of Cr(VI) inhibited phenol degradation. Acidic conditions were beneficial to Cr(VI) and phenol removal. Scan electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analysis suggested that surface morphology and element valence of ball milled Fe⁰@FeS hybrids changed after reaction. Radicals quenching experiment and EPR (electron paramagnetic resonance) results illustrated that SO₄•^- and HO• were major free radical species for phenol degradation. Fe(II) quenching experiment revealed that surface-bound Fe(II) instead of dissolved Fe(II) mainly participated in Cr(VI) reduction and PS activation. This study illustrated novel surface reduction of Cr(VI) and surface activation of PS by ball milled Fe⁰@FeS hybrids, providing useful perspective for applying ball milled Fe⁰@FeS hybrids for complex wastewater treatment.

A novel Fe2+/persulfate/tannic acid process with strengthened efficacy on enhancing waste activated sludge dewaterability and mechanism insight

As an essential section before final sludge disposal, sludge dewatering has currently been one of the focus issues. In this study, an innovative Fe²⁺/persulfate/tannic acid (TA) process was verified to further strengthen systemic efficacy on enhancing sludge dewaterability, compared with the conventional Fe²⁺/persulfate process. With the efficient TA/Fe²⁺ (molar ratio) of 0.25 added in Fe²⁺ (0.3 mmol/gTS (total solid))/persulfate (0.6 mmol/gTS) process, sludge dewaterability was enhanced remarkably. Capillary suction time, specific resistance to filtration, and water content of dewatered sludge cake were further reduced by 61.5%, 35.3%, and 6.4% than these in Fe²⁺/persulfate. Sludge supernatant viscosity was further reduced by 86.7% due to the more removal of extracellular polymeric substances (EPS). The secondary structure of EPS protein changed apparently and fluorescent components of EPS decreased distinctly. Sludge functional group contents were observed to be lower. TA effectually increased sludge particle size and heightened sludge flocculability, rendering the large and compact aggregations. Moreover, TA accelerated the recovery of Fe²⁺, facilitating persulfate activation to generate more SO₄^·- and ^·OH for EPS disruption and cell lysis in the conditioning system. These findings provided a novel approach based on the Fe²⁺/persulfate process in sludge treatment for desirable dewaterability.