UV-LED/P25-based photocatalysis for effective degradation of isothiazolone biocide

In this work,LED-based photocatalysis using mixed rutile and anatase phase TiO_(2)(P25)as the photocatalyst could effectively remove 5-chloro-2-methyl-4-isothiazolin-3-one(CMIT)and methylisothiazolone(MIT)simultaneously,with removal efficiencies above 80%within 20 min.The photocatalytic degradation of both CMIT and MIT could be modeled using a pseudo-first-order rate equation.The photocatalytic degradation rates of CMIT and MIT under LED280 illumination were higher than under LED310 or LED360 illumination.At concentrations below 100 mg/L,the degradation rate of CMIT and MIT under LED illumination significantly increased with increasing catalyst dosage.Additionally,the effects of the chloride ion concentration,alkalinity and dissolved organic matter on the photocatalytic degradation reaction were also investigated.The·OH free radicals were determined to play the primary role in the photocatalytic degradation reaction,with a degradation contribution of>95%.The photocatalytic degradation of CMIT and MIT mainly occurred via oxidation,hydrolysis,and chain growth reactions.Finally,the possible photocatalytic degradation pathways of CMIT and MIT over LED/P25 are proposed.

Inhibition of bromate formation by reduced graphene oxide supported cerium dioxide during ozonation of bromidecontaining water

Ozone(O3)is widely used in drinking water disinfection and wastewater treatment.However,when applied to bromide-containing water,ozone induces the formation of bromate,which is carcinogenic.Our previous study found±at graphene oxide(GO)can enhance the degradation efficiency of micropollutants during ozonation.However,in this study,GO was found to promote bromate formation during ozonation of bromide-containing waters,with bromate yields from the O3/GO process more than twice those obtained using ozone alone.The promoted bromate formation was attributed to increased hydroxyl radical production,as confirmed by the significant reduction(almost 75%)in bromate yield after adding t-butanol(TBA).Cerium oxide(less tfian 5 mg/L)supported on reduced GO(xCeO2/RGO)significantly inhibited bromate formation during ozonation compared with reduced GO alone,and the optimal Ce atomic percentage(x)was determined to be 0.36%,achieving an inhibition rate of approximately 73%.Fourier transform infrared(FT-IR)spectra indicated the transformation of GO into RGO after hydrothermal treatment,and transmission electron microscope(TEM)results showed that CeO2 nanoparticles were well dispersed on the RGO surface.The X-ray photoelectron spectroscopy(XPS)spectra results demonstrated that the Ce^3+/Ce^4+ratio in xCeO2/RGO was almost 3-4 times higher than that in pure CeO2,which might be attributed to the charge transfer effect from GO to CeO2.Furthermore,Ce+on thexCeO2/RGO surface could quench Br-and BrO-to further inhibit bromate formation.Meanwhile,0.36CeO2/RGO could also enhance the degradation efficiency of N,N-diethyl-zn-toluamide(DEET)in synthetic and reclaimed water during ozonation.

Removal of C.I.Reactive Red 2 by low pressure UV/chlorine advanced oxidation

Azo dyes are commonly found as pollutants in wastewater from the textile industry,and can cause environmental problems because of their color and toxicity.The removal of a typical azo dye named C.I.Reactive Red 2（RR2） during low pressure ultraviolet（UV）/chlorine oxidation was investigated in this study.UV irradiation at 254 nm and addition of free chlorine provided much higher removal rates of RR2 and color than UV irradiation or chlorination alone.Increasing the free chlorine dose enhanced the removal efficiency of RR2 and color by UV/chlorine oxidation.Experiments performed with nitrobenzene（NB）or benzoic acid（BA） as scavengers showed that radicals（especially OH） formed during UV/chlorine oxidation are important in the RR2 removal.Addition of HCO_3^- and Cl^- to the RR2 solution did not inhibit the removal of RR2 during UV/chlorine oxidation.

Improvement of detection method of Cryptosporidium and Giardia in reclaimed water

Cryptosporidium and Giardia are two typical species of pathogenic protozoans that seriously endanger water quality.Previous works indicated that detection of Cryptosporidium and Giardia with modified United States Environmental Protection Agency(USEPA)method-1623 using a membrane filtration-elution for sample concentration attained better recovery and lower cost compared to the USEPA method-1623.Several improvements of membrane filtration-elution step as well as immunomagnetic separation(IMS)steps were investigated and an optimized method for detection of Cryptosporidium and Giardia in wastewater reclamation system was recommended in this paper.The experimental results show that an overnight soak of the membrane after scraping and vortex agitation before elution could enhance and stabilize the recovery.Increasing turbidity to 4 NTU by adding kaolin clay before filtration could effectively improve the recovery of low-turbidity water.Washing the concentrate after centrifugation and twice acid dissociation both reduced the impact of water quality to protozoan recovery.Protozoans in different water samples were determined by this optimized method,and the recovery of Cryptosporidium and Giardia were above 70% and 80%respectively,much higher than the acceptance of method-1623.

Genotoxicity removal of reclaimed water during ozonation

Genotoxicity in wastewater and reclaimed water now is gaining increased attention because of genotoxins＇ potential damage to the ecosystem and human health. The effect of ozonation on genotoxicity in reclaimed water was investigated. It was found that ozonation decreased the genotoxicy dramatically in three tertiary treatment plants. In the further batch ozonation experiment in laboratory, secondary effluent sample used exhibited the genotoxicity of （41.1 ± 4.1） μg 4NQO/L. Ozonation with a dose of 10 mg O3/L completely removed the genotoxicity in secondary effluent. However, after ozonation, the dissolved organic carbonvalue of the sample didn＇t change much but the specific ultraviolet absorbance （SUVA） value dropped sharply. With the help of Fourier transform infrared spectroscopy, ozonation was found to change chemical aliphatic carbon and C-O of the dissolved arganic matter, which might be the reason of the significant decreases of SUVA and genotoxicity.

Removal of fluorescence and ultraviolet absorbance of dissolved organic matter in reclaimed water by solar light

Storing reclaimed water in lakes is a widely used method of accommodating changes in the consumption of reclaimed water during wastewater reclamation and reuse. Solar light serves as an important function in degrading pollutants during storage, and its effect on dissolved organic matter（DOM） was investigated in this study. Solar light significantly decreased the UV_（254） absorbance and fluorescence（FLU） intensity of reclaimed water.However, its effect on the dissolved organic carbon（DOC） value of reclaimed water was very limited. The decrease in the UV_（254） absorbance intensity and FLU excitation–emission matrix regional integration volume（FLU volume） of reclaimed water during solar light irradiation was fit with pseudo-first order reaction kinetics. The decrease of UV_（254） absorbance was much slower than that of the FLU volume. Ultraviolet light in solar light had a key role in decreasing the UV_（254） absorbance and FLU intensity during solar light irradiation. The light fluence-based removal kinetic constants of the UV_（254） and FLU intensity were independent of light intensity. The peaks of the UV_（254） absorbance and FLU intensity with an apparent molecular weight（AMW） of 100 Da to 2000 Da decreased after solar irradiation, whereas the DOC value of the major peaks did not significantly change.