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The long-term abuse of antibiotics such as norfloxacin (NOR) poses a significant threat to aquatic environments. The development of efficient and economical treatments is still a pain point in the industry. Herein, we reported a directly robust carbonization-pyrolysis method to synthesize iron and nitrogen co-doped biochar material (Fe@N co-doped biochar) that was first applied to NOR removal through persulfate (PS) activation. The catalytic performance and operating factors were systematically investigated. It was found that 10 mg/L NOR achieved 95% degradation within 20 min under optimal reaction conditions. The removal rate of NOR could still achieve 80% and almost 50% of NOR was completely mineralized after five cycles. Through combined electron-paramagnetic-resonance analysis, quenching experiments, and X-ray-photoelectron-spectroscopy tests, •OH, •SO4−, and 1O2 were confirmed as reactive oxygen species in catalytic reaction. Iron activated PS to produce •OH and •SO4− through electron transfer and nitrogen-containing functional groups (graphitic N, C-OH/C = N) accepted electrons from PS to generate 1O2. The radical pathway involving hydroxyl radicals and the nonradical pathways involving singlet oxygen together accounted for the rapid degradation of NOR. The degradation pathways were comprehensively established, including defluorination, decarboxylation, piperazine ring breakage and nalidixic ring transformation. This study shed light on a new mechanism of radical and nonradical co-dominated PS activation and proposed a simple and inexpensive antibiotic wastewater treatment system.

The visible light sensitive metal-free mesoporous graphitic carbon nitride (mpg-CN) was fabricated for photodegradation of atenolol (ATN), a widely used drug for cardiovascular diseases. Peroxydisulfate (PDS) as an electron acceptor as well as a radical origin was introduced to enhance the catalytic performance, and retaining the nature of metal-free and mesoporous of mpg-CN. The photo-induced holes, SO4 − and O2 − were identified as the active species. Integrated with density functional theory (DFT) calculations and photoelectrochemical experiments, the interaction among PDS, catalyst, and ATN is unveiled. PDS can obtain an electron from the catalyst, hence to improve the separation of electron-hole pairs and activates itself. ATN has stable chemical adsorption states on catalyst surface. Then the electron-deficient catalysts can acquire electrons from ATN. In addition, primary degradation sites of ATN and following possible degradation pathways were explored with DFT calculations and mass spectrometry analysis.

The construction of heterogeneous Fenton-like catalyst with high efficiency is crucial for wastewater treatment. In this study, magnetite nanoparticles were successfully embedded into chitosan beads to form a porous structure (Fe3O4-Cs) by in-situ or two-step method, and it was put forward as a kind of Fenton-like catalyst to degrade tetracyclines for the first time. SEM, TEM, XRD, FT-IR, XPS, TG and BET technologies were used to characterize its properties. After comparing the tetracycline hydrochloride (TC) degradation efficiencies of two prepared beads, the in-situ method was selected for subsequent studies. The influential factors of TC degradation efficiency were investigated, including iron content, pH value, the amount of H2O2, reaction temperature, catalyst dosage and initial TC concentration. The results showed that under the optimal conditions, about 96.0% of TC (48.09 mg/L) and 68.3% of total organic carbon (TOC) were degraded within 20 min and 120 min, respectively. The degradation efficiencies for the other two tetracyclines: oxytetracycline (OTC) and doxycycline hyclate (DOTC), have been explored as well. And the degradation process followed pseudo first order kinetic equation. In addition, these Fe3O4-Cs beads with saturated magnetization could be easily reused for 6 cycles without significantly reducing catalytic activity. High degradation performance of beads was attributed to the stable porous structure, abundant active sites and possible synergistic effects between two components, which promoted the formation of hydroxyl radicals (HO ) for TC degradation. The possible reaction pathways and mechanism on TC degradation were discussed technically. In short, these results indicated that macroscopic Fe3O4-Cs beads (3–4 mm) with high efficiency, excellent stability and reusability exhibited a superior Fenton-like process on the removal of tetracyclines for future application.

Struvite crystallization has been so far proved to be a potential technology for nitrogen and phosphorus recovery from nutrient-rich wastewater. However, humic acid (HA) among organic matters in nutrient-rich wastewaters would inevitably exert an adverse impact on the crystallization. Therefore, in the present study, we innovatively propose a process monitor chart to accurately differentiate and quantify the nucleation and crystal growth of struvite crystallization by means of constant composition technique, thereby probing the effect of HA on the nucleation and growth kinetics of struvite. Moreover, the mechanism underlying the interaction between HA and struvite crystals was also explored by FTIR and XPS analysis. The results indicated that HA not only significantly prolonged the induction time, but also decreased the growth rate of struvite crystals. This can be explained by the fact that HA is prone to complex with the reactant, and its subsequent adsorption on the surface of struvite crystals performs during the crystallization process. Consequently, the crystal morphology initially varied from rod-like shape to trapezoidal prism, and ultimately to triangular prism, as HA concentration gradually increased from 0 to 100 mg/L. Interestingly, the interaction between HA and struvite crystals is likely to be triggered by the formation of amide, HA-Mg2+ complex and phosphate ester on the crystal surface. These findings herein put forward an innovate method to elucidate the inhibitory effect of organic matter on the nucleation and growth kinetics of struvite, which can provide a theoretical basis for understanding the interference of organic pollutants with struvite crystallization.

A granular form of a layered double hydroxide (LDH) material was used as an anionic adsorbent in packed column and slurry experiments to remove endocrine active compounds (EACs) from river water downstream from wastewater treatment plants and from laboratory water spiked with 17β-estradiol (E2). The estrogenic activity of the samples was estimated using the biological yeast estrogen screen (YES) assay and the E2 concentrations were analyzed using radioimmunoassay techniques. The LDH in a packed column significantly (p < 0.05) decreased the estrogenic activity of the river water from 519 to 387 ng E2 equiv./L after one pass through the column. The LDH packed column reduced the E2 concentration in a different river water sample from 12 ng/L to below detection limit (1.8 ng/L) with minimal retention time. Finally, LDH in a slurry treatment reduced the E2 concentration in water from 317 ng/L to below detection limit. The results of these experiments suggests that LDH may be used to treat waste or drinking water for estrogenic endocrine disrupting components (EDCs) such as E2 and possibly other anionic compounds that affect the endocrine system.