Development, dilemma and potential strategies for the application of nanocatalysts in wastewater catalytic ozonation: A review

With the continuous development of nanomaterials in recent years,the application of nanocatalysts in catalytic ozone oxidation has attracted more and more researchers’attention due to their excellent catalytic properties.In this review,we systematically summarized the current research status of nanocatalysts mainly involving material categories,mechanisms and catalytic efficiency.Based on summary and analysis,we found most of the reported nanocatalysts were in the stage of laboratory research,which was caused by the nanocatalysts defects such as easy aggregation,difficult separation,and easy leakage.These defects might result in severe resource waste,economic loss and potentially adverse effects imposed on the ecosystem and human health.Aiming at solving these defects,we further analyzed the reasons and the existing reports,and revealed that coupling nano-catalyst and membrane,supported nanocatalysts and magnetic nanocatalysts had promising potential in solving these problems and promoting the actual application of nanocatalysts in wastewater treatment.Furthermore,the advantages,shortages and our perspectives of these methods are summarized and discussed.

A tailored and rapid approach for ozonation catalyst design

Catalytic ozonation is widely employed in advanced wastewater treatment owing to its high mineralization of refractory organics.The key to high mineralization is the compatibility between catalyst formulation and wastewater quality.Machine learning can greatly improve experimental efficiency,while fluorescence data can provide additional wastewater quality information on the composition and concentration of organics,which is conducive to optimizing catalyst formulation.In this study,machine learning combined with fluorescence spectroscopy was applied to develop ozonation catalysts(Mn/g-Al_(2)O_(3)catalyst was used as an example).Based on the data collected from 52 different catalysts,a machine-learning model was established to predict catalyst performance.The correlation coefficient between the experimental and model-predicted values was 0.9659,demonstrating the robustness and good generalization ability of the model.The range of the catalyst formulations was preliminarily screened by fluorescence spectroscopy.When the wastewater was dominated by tryptophan-like and soluble microbial products,the impregnation concentration and time of Mn(NO_(3))_(2) were less than 0.3 mol L^(-1)and 10 h,respectively.Furthermore,the optimized Mn/g-Al_(2)O_(3)formulation obtained by the model was impregnation with 0.155 mol L^(-1)Mn(NO_(3))_(2)solution for 8.5 h and calcination at 600℃ for 3.5 h.The model-predicted and experimental values for total organic carbon removal were 54.48% and 53.96%,respectively.Finally,the improved catalytic performance was attributed to the synergistic effect of oxidation(·OH and ^(1)O_(2))and the Mn/g-Al_(2)O_(3) catalyst.This study provides a rapid approach to catalyst design based on the characteristics of wastewater quality using machine learning combined with fluorescence spectroscopy.

Effect of short-term atrazine addition on the performance of an anaerobic/anoxic/oxic process

In this study,an anaerobic/anoxic/oxic(A^(2)O)wastewater treatment process was implemented to treat domestic wastewater with short-term atrazine addition.The results provided an evaluation on the effects of an accidental pollution on the operation of a wastewater treatment plant(WWTP)in relation to Chemical Oxygen Demand(COD)and biological nutrient removal.Domestic wastewater with atrazine addition in 3 continuous days was treated when steady biological nutrient removal was achieved in the A^(2)O process.The concentrations of atrazine were 15,10,and 5 mg%L–1 on days 1,2 and 3,respectively.The results showed that atrazine addition did not affect the removal of COD.The specific NH4þoxidation rate and NO3–reduction rate decreased slightly due to the short-term atrazine addition.However,it did not affect the nitrogen removal due to the high nitrification and denitrification capacity of the system.Total nitrogen(TN)removal was steady,and more than 70%was removed during the period studied.The phosphorus removal rate was not affected by the short-term addition of atrazine under the applied experimental conditions.However,more poly-hydroxy-alkanoate(PHA)was generated and utilized during atrazine addition.The results of the oxygen uptake rate(OUR)showed that the respiration of nitrifiers decreased significantly,while the activity of carbon utilizers had no obvious change with the atrazine addition.Atrazine was not removed with the A^(2)O process,even via absorption by the activated sludge in the process of the short-term addition of atrazine.

A magnetic-void-porous MnFe_(2)O_(4)/carbon microspheres nano-catalyst for catalytic ozonation:Preparation,performance and mechanism

Wastewater treatment is essential to guarantee human health and ecological security.Catalytic ozonation with nanocatalysts is a widely studied and efficient treatment technology.However,this method has always been limited by nanocatalysts disadvantages such as easily loss,difficult to separate and reuse,and catalytic ability decay caused by aggregation,which could cause severe resources waste and potential risk to human health and ecosystem.To remedy these challenges,a magnetic-void-porous MnFe_(2)O_(4)/carbon microsphere shell nanocatalyst(CMS-MnFe_(2)O_(4))was successfully synthesized using renewable natural microalgae.The separation test showed CMS-MnFe_(2)O_(4) was rapidly separated within 2 min under an external magnetic field.In catalytic ozonation of oxalic acid(OA),CMS-MnFe_(2)O_(4) showed efficient and stable catalytic efficiency,reaching a maximum total organic carbon removal efficiency of 96.59% and maintained a 93.88% efficiency after 4 cycles.The stable catalytic efficiency was due to the supporting effects of the carbon microsphere shell,which significantly enhanced CMS-MnFe_(2)O_(4) chemical stability and reduced the metal ions leaching to 10-20% of MnFe_(2)O_(4) through electron transfer.To explore the catalytic mechanism,radical experiments were conducted and a new degradation pathway of OA involving superoxide anions rather than hydroxyl radicals was proposed.Consequently,this study suggests that an efficient,recyclable,stable,and durable catalyst for catalytic ozonation could be prepared.