Enhancement of UV-assisted TiO_2 degradation of ibuprofen using Fenton hybrid process at circumneutral pH

A synergistic UV/TiO2/Fenton(PCF)process is investigated for the degradation of ibuprofen(IBP)at circumneutral pH.The IBP decay in the PCF process is much faster than that with the conventional UV,UV/H2O2,Fenton,photo‐Fenton,and photocatalysis processes.The kinetics analysis showed that the IBP decay follows a two‐stage pseudo‐first order profile,that is,a fast IBP decay(k1)followed by a slow decay(k2).The effects of various parameters,including initial pH level,dosage of Fenton’s reagent and TiO2,wavelength of UV irradiation,and initial IBP concentration,are evaluated.The optimum pH level,[Fe2+]0,[Fe2+]0/[H2O2]0 molar ratio,and[TiO2]0 are determined to be approximately 4.22,0.20 mmol/L,1/40,and 1.0 g/L,respectively.The IBP decay at circumneutral pH(i.e.,6.0–8.0 for wastewater)shows the same IBP decay efficiency as that at the optimum pH of 4.22 after 30 min,which suggests that the PCF process is applicable for the treatment of wastewater in the circumneutral pH range.The lnk1 and lnk2 are observed to be linearly correlated to 1/pH0,[IBP]0,[H2O2]0,[H2O2]0/[Fe2+]0 and ln[TiO2]0.Mathematical models are therefore derived to predict the IBP decay.

Stability of potentially toxic elements in municipal sludge biochars modified by MgCl2 and phosphate

Municipal wastewater sludge can be pyrolyzed as biochars to better use nutrients and stabilize carbon compared with other typical technologies,such as landfill and incineration.However,sludge-derived biochars might contain large amounts of potentially toxic elements(PTEs),such as Zn,Cu,Cr,Ni,Pb,and As.The stability of PTEs in biochars might be improved by higher pyrolytic temperatures,which can be further improved by different modifications.Herein,PO4-modification at 300°C and Cl-modification at 700°C were carried out,respectively,to enhance the stability of PTEs.Various leaching tests have been performed to assess the stability of PTEs in biochars,including the synthetic precipitation leaching procedure(SPLP),toxicity characteristic leaching procedure(TCLP),diethylenetriamine pentaacetate(DTPA)extraction,and in vitro simple bioaccessibility extraction test(SBET).The morphological structure,elemental mapping,and mineral formation of the pristine and modified biochars were studied by scanning electron microscopy–energy-dispersive X-ray spectroscopy(SEM–EDS)and X-ray diffraction(XRD).Our results suggested that the leachability,mobility,plant-availability,and bioaccessibility of most PTEs were decreased by pyrolysis,yet the total contents of PTEs were elevated,especially at 700°C.Generally,modification by phosphates and MgCl2 enhanced the stability of PTEs in biochars.Nevertheless,it should be noted that higher bioaccessibility of PTEs was observed in biochars of P-modification than Cl-modification,which is associated with the dissolution of phosphate precipitates under acidic conditions(pH<2).Additionally,Cl-modification leads to higher plant-available Zn and Cu and bioaccessible Zn compared with the unmodified biochar produced at 700°C.

Heavy metal pollution increases soil microbial carbon limitation:Evidence from ecological enzyme stoichiometry

Heavy metals can exist in soil for a long time and seriously affect soil quality.The coexistence of various heavy metal pollutants leads to biotoxicity and alters the activity of microorganisms.Soil microbial metabolism plays an important role in nutrient cycling and biochemical processes of soil ecosystem.However,the effects of heavy metal contamination on microbial metabolism in soil are still unclear.This study aims to reveal the responses of microbial metabolic limitation to heavy metals using extracellular enzyme stoichiometry,and further to evaluate the potential impacts of heavy metal pollution on soil nutrient cycle.The results showed that soil microbial metabolism reflected by the ecoenzymatic activities had a significant response to soil heavy metals pollution.The metabolism was limited by soil carbon(C)and phosphorus(P)under varied heavy metal levels,and the increase of heavy metal concentration significantly increased the microbial C limitation,while had no effect on microbial P limitation.Microorganisms may increase the energy investment in metabolism to resist heavy metal stress and thus induce C release.The results suggest that energy metabolism selected by microorganisms in response to long-term heavy metal stress could increase soil C release,which is not conducive to the soil C sequestration.Our study emphasizes that ecoenzymatic stoichiometry could be a promising methodology for evaluating the toxicity of heavy metal pollution and its ecological effects on nutrient cycling.