Comparison of UVC/S₂O₈ ^2- with UVC/H₂O₂ in terms of efficiency and cost for the removal of micropollutants from groundwater

This study compared the UVC/S2O82- system with the more commonly used AOP in water industry, UVC/H2O2, and examined whether the first one can be an economically feasible alternative technology. Atrazine and 4 volatile compounds (methyl tert-butyl ether, cis-dichlorethen, 1,4-dioxane and 1,1,1-trichloroethane) were chosen as model contaminants because they exhibit different susceptibility to UVC photolysis and AOPs. A collimated beam apparatus was utilized for the majority of the experiments (controlled environment, without mass transfer phenomena), while selected experiments were performed in a flow-through reactor to simulate industrial applications. Initial experiments on the activation of oxidants with a LP lamp indicated that S2O82- is photolysed about 2.3times faster than H2O2 and that the applied treatment times were not sufficient to utilize the majority of the oxidant. The effect of oxidants' concentrations were tested with atrazine alone and in the micropollutants' mixture and it was decided to use 11.8mgL-1 S2O82- and 14.9mgL-1 H2O2 for further testing since is closer to industrial applications and to minimize the residual oxidant concentration. Changes of the matrix composition of the treated water were investigated with the addition of chloride, bicarbonate and humic acids at concentrations relevant to a well-water-sample, the results showed that the system least affected was UVC/H2O2. Only when bicarbonate was used, UVC/S2O82- performed better. Overall, testing these systems with the mixture of micropollutants gave better insights to their efficiency than atrazine alone and UVC/S2O82- is recommended for selective oxidation of challenging matrices

Greywater treatment by Fenton, Photo-Fenton and UVC/H2O2 processes

Advanced oxidation processes (AOPs) have been used to treat drinking water and wastewater but their application to greywater is limited to photocatalysis. Therefore, three homogeneous AOPs were investigated in this project: Fenton, photo-Fenton, and UVC/H2O2 processes. Alum and ferrous sulphate coagulation were also compared and their supernatants were treated by UVC/H2O2. The process comparisons were based on the removal of chemical oxygen demand (COD), treatment type (physical separation versus chemical oxidation), sludge formation, complexity in operation, required pH, visual aesthetic of effluent and energy requirement. Treating greywaters collected from the researcher's home or laboratory, alum coagulation achieved 73% COD removal and was more effective than ferrous sulphate coagulation (49%) and the Fenton process (45%). The photo-Fenton process removed 83% COD, compared with 87% by overnight settlement and subsequent UVC/H2O2 treatment. Using ferrous sulphate and alum, sequential coagulation and UVC/H2O2 treatment removed 91% and 98% COD, respectively. Overnight settlement generated little sludge and the subsequent UVC/H2O2 treatment removed most organic contaminants by oxidation. All other processes produced a large quantity of chemical sludge from coagulation which requires appropriate disposal. Also, the residual iron in some treated water was not aesthetically desirable. The Fenton and photo-Fenton processes were complex and involved the optimisation of multiple parameters. Their requirement for different procedures according to the greywater type presents a major challenge to process design and operation. Due to the non-selectivity of the hydroxyl radicals (●OH), the UVC/H2O2 process was capable of treating all greywaters collected by the researcher, and its operation was moderate in complexity. The COD removal was modelled as a pseudo first-order reaction in terms of H2O2 dosage: The rate constant (k´) increased linearly up to 10 mM H2O2, above which the excess H2O2 scavenged the ●OH and reduced the rate. The overall kinetics of COD removal followed a second-order equation of r = 0.0637 [COD][H2O2]. In contrast to the literature, operation of UVC/H2O2 in acidic conditions was not required and the enhanced COD removal at the initial pH of 10 was attributed to the dissociation of H2O2 to O2H-. Maintaining the pH at 10 or higher resulted in poorer COD removal due to the increased decomposition rate of H2O2 to O2 and H2O. The performance of the UVC/H2O2 treatment was unaffected for initial pH 3 - 10 with the initial total carbonate concentration (cT) of 3 mM. For initial cT ≥ 10 mM, operating between pH 3 and 5 was essential. After 3 hours of the UVC/H2O2 treatment, the effluent met the requirement of Class B reclaimed water specified by the Environment Protection Authority of Victoria, and less than 1 org/100 mL of Escherichia coli survived. A subsequent treatment such as filtration may be required to meet more requirements for biochemical oxygen demand (BOD5), turbidity and total suspended solids. Since the biodegradability (as BOD5:COD) of the greywater was increased from 0.22 to 0.41 with 2 hours of UVC/H2O2 treatment, its integration with a subsequent biological treatment may be viable to reduce the costs and energy consumption associated with the UVC/H2O2 process

Two-step persulfate and Fenton oxidation of naphthenic acids in water

WILEY: "This is the peer reviewed version of the following article: Journal of Chemical Technology and Biotechnology 93 (2018): 2262-2270, which has been published in final form at http://doi.org/10.1002/jctb.5569. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions."BACKGROUD: In the current study, two-step persulfate and Fenton oxidation has been investigated for the mineralization of naphthenic acids at 80 °C and initial pH ≈ 8. This pH evolves during the persulfate oxidation step towards the optimum for Fenton oxidation (≈ 3). The effects of persulfate and H2O2doses, iron concentration, duration of the persulfate oxidation step and operating temperature have been assessed. RESULTS: The combined treatment allowed up to ≈ 80% mineralization of cyclohexanoic acid using fairly low relative amounts of reagents (20 and 30% of the stoichiometric for persulfate and H2O2, respectively). For mineralization of cyclohexanoic acid, 115 and 87 kJ mol-1were obtained as representative values of the apparent activation energy for the persulfate and Fenton oxidation steps, respectively. The system was also successfully tested with other naphthenic acids, including cyclohexanebutyric acid, 2-naphthoic acid and 1,2,3,4-tetrahydro-2-naphthoic acid. Treatment of the naphthenic acids tested by this system gave rise to easily biodegradable effluents consisting mainly of short-chain organic acids. The biodegradability was confirmed by the BOD5/COD ratio and respirometric tests. CONCLUSION: The results show the potential application of this approach as a promising cost-effective solution for the treatment of naphthenic acids-bearing aqueous wastes. This approach has significant advantage compared with the single thermally-activated persulfate or Fenton oxidation, since it allows a high mineralization at reduced reagent cost upon replacing part of the persulfate by less expensive H2O2.We are grateful to the Chinese Scholarship Council (CSC) for supporting the Ph.D. program of Xiyan Xu (CSC, File No. 201308410047). Spanish MINECO is also gratefully acknowledged for the financial support through the project CTQ2013-41963-

Advanced Oxidation Processes for the Treatment of Real Slaughterhouse Wastewater After a Biological Treatment

Water shortage is increasing worldwide and becoming a social and environmental problem. To address the increasing need of water human population is currently facing, the use of advanced oxidation processes (AOPs) after a biological treatment seem to be a right approach for the treatment of industrial wastewaters. AOPs such as ozone (O3), ultrasound (US), ultraviolet light (UV) or electrochemical oxidation produce in situ powerful oxidants (i.e. OH radicals) that can easily degrade recalcitrant organic matter and inactivate microorganisms. Among different industries, current industrialised livestock agriculture has one of the highest consumptions of water and produces up to ten times more polluted wastewaters in comparison to domestic sewage. Therefore, the present study looks into the use of single and combined AOPs for the treatment of real slaughterhouse wastewaters. O3 proved to be a powerful oxidant, reducing significantly chemical oxygen demand (COD) and biological oxygen demand (BOD), as well as lowering colour and total suspended solids (TSS) to minimum values. O3 also acted as a strong disinfectant, inactivating most of the microorganisms present in the wastewater. After an activated sludge process, a complete inactivation of total coliforms (TC) was obtained with 17 min of ozonation at an O3 inlet concentration of 71 mg O3/Lgas. For total viable counts (TVC), a drastic reduction was observed after 30 min of ozonation (5 log inactivation). The addition of US only increased ozonation performance slightly (44% COD and 74% BOD reduction), principally due to the high inlet O3 concentration supplied to the system. US alone showed a modest effect in organic matter removal, reducing 18% COD, 50% BOD and 25% TSS with 300 kHz at an applied power of 40 W. A minor removal was achieved for TC (< 1 log), while an insignificant reduction in TVC was measured. The application of UVC light (254 nm) and hydrogen peroxide (H2O2) individually did not reduce any dissolved organic carbon (DOC), while the combination of UVC and H2O2 led to a large synergy. The coupled system reached 26% DOC abatement with an optimised H2O2 concentration after 3 h of treatment, principally due to the attack of OH radicals formed through the cleavage of H2O2 molecules by UVC. DOC removal was further increased to 41% when O3 was used as a pre-treatment. This was attributed to the reduction in colour, turbidity and TSS by O3 pre-treatment, which lowered UV inner filtering effects and hence, increased the performance of the subsequent UVC/H2O2 process. The application of a pre-ozonation step also improved organics removal by converting original organic compounds into easily oxidisable compounds. O3, UVC and H2O2 were later combined in a single process, but no synergy was observed with a DOC reduction of 43% and the COD was reduced down to 61 mg O2/L. However, less O3 (mg O3/Lwastewater) was used with the combined O3/UVC/H2O2 system compared to that supplied during O3 pre-treatment (O3+UVC/H2O2), increasing O3 performance. Electrochemical oxidation alone reduced DOC values by 15%, while the use of an electrochemical cell along with UVC and H2O2 led to a DOC removal of ~81%. The significant production of OH radicals and electrochemically generated oxidants during the combined process would be responsible for such a high removal. A similar removal percentage was achieved when O3 was used as a pre-treatment prior to EO and UVC combined. Colour values below 25 mg Pt-Co/L were achieved, typical acceptable colour limit values for treated wastewaters leaving wastewater treatment plants. O3 pre-treatment also reduced the production of hazardous compounds such as ClO4- in subsequent treatments. The individual application of AOPs did not show high efficiency in organic matter removal, while the combination of different AOPs reached direct discharge limits set by the European Union and showed potential to be used for water treatment intended for agricultural irrigation. Particularly, the coupling of UVC and H2O2 showed a high synergy, with and without O3 pre-treatment, as well as the combination of EO, UVC and H2O2, where the highest DOC removal was observed

Photo driven homogeneous advanced oxidation coupled to adsorption process for an effective arsenic removal from drinking water

The presence of arsenic (As) in drinking water is a major concern for human health. As(III) is the most toxic water-soluble form and it is hard to remove by separation methods, including adsorption, while As(V) is less toxic and easily removable by adsorption. In this work homogenous photo driven advanced oxidation processes (HP-AOPs), namely UVC/H2O2 and UVC/NaOCl, have been investigated in the oxidation of As(III) (initial concentration of 0.1&nbsp;mg/L) to As(V) and commercial available adsorbents (γ-Al2O3, Bayoxide E33, MgAl-LDHs and ZnAl-LDHs) were tested for subsequent As(V) removal. UVC/H2O2 (99% of As removal, 19&nbsp;mg/L of H2O2, 2&nbsp;min of treatment time) and UVC/NaOCl (99% of As removal, 5.1&nbsp;mg/L of NaOCl, 2&nbsp;min of treatment time) were found to be more effective than H2O2 (2% of As removal in the same condition of UVC/H2O2) and NaOCl (6% of As removal in the same condition of UVC/NaOCl), respectively and the optimum operation conditions were identified by response surface methodology (RSM) in distilled water and subsequently confirmed in real drinking water (with differences of less than 1%). UVC/NaOCl was the most suitable process being a good compromise among oxidation efficiency, oxidant dose and treatment time. The best results in terms of subsequent removal of As(V) by adsorption were obtained using ZnAl-LDH (88% in both distilled and drinking water). Accordingly, UVC/NaOCl advanced oxidation coupled to ZnAl-LDH adsorption is the best combination for an effective removal of arsenic from drinking water

Performance of hybrid systems coupling advanced oxidation processes and ultrafiltration for oxytetracycline removal

In this study, the efficiency of three different hybrid systems coupling ultrafiltration (UF) with (i) UVC/H2O2, (ii) UVC/TiO2, and (iii) UVC was evaluated for the treatment of a secondary effluent (SE) from a municipal wastewater treatment plant and a surface water (SW) from Miedwie Lake, both spiked with 5 mg L-1 of oxytetracycline (OTC). A ceramic membrane made of TiO2 was tested. The effect of H2O2 concentration (30 to 120 mg L-1) on the UVC/H2O2-UF system and of P25-TiO2 loading (0.5 to 1.5 g L-1) in suspension on the photocatalytic UVC/TiO2-UF system were investigated. A photonic flux of 5.1 J s(-1) was provided in all systems. The maximum pure water flux (PWF) was 111 L m(-2) h(-1). Adsorption on the photocatalyst particles and/or on the membrane surface was found to be an important contribution for the removal of OTC and dissolved organic carbon (DOC). The UF membrane contributed significantly to photocatalyst and pollutants rejection in the photocatalytic membrane reactor (PMR) with the UVC/TiO2 system; whereas when using the UVC/H2O2 process, with the highest H2O2 dose, the membrane effect was negligible. Using SE as reaction matrix in the UVC/ TiO2-UF system with 1.0 g L-1 of TiO2, the complete OTC removal was achieved in 5 h with a mineralization of 49%. For the same reaction period, a DOC removal of 52% was achieved with the UVC/H2O2-UF system (120 mg H2O2 L-1). A similar permeate flux decrease (ca. 40%) was observed in both cases. Furthermore, the highest reduction of permeate flux (60%) was observed when using the UVC-UF system. Using SW as reaction matrix, higher OTC degradation rates and percentage of mineralization were reached for the same reaction period, when compared with SE, due to the lower COD and inorganic salts concentration present in the surface water

Photo driven homogeneous advanced oxidation coupled to adsorption process for an effective arsenic removal from drinking water

The presence of arsenic (As) in drinking water is a major concern for human health. As(III) is the most toxic water-soluble form and it is hard to remove by separation methods, including adsorption, while As(V) is less toxic and easily removable by adsorption. In this work homogenous photo driven advanced oxidation processes (HP-AOPs), namely UVC/H2O2 and UVC/NaOCl, have been investigated in the oxidation of As(III) (initial concentration of 0.1 mg/L) to As(V) and commercial available adsorbents (γ-Al2O3, Bayoxide E33, MgAl-LDHs and ZnAl-LDHs) were tested for subsequent As(V) removal. UVC/H2O2 (99% of As removal, 19 mg/L of H2O2, 2 min of treatment time) and UVC/NaOCl (99% of As removal, 5.1 mg/L of NaOCl, 2 min of treatment time) were found to be more effective than H2O2 (2% of As removal in the same condition of UVC/H2O2) and NaOCl (6% of As removal in the same condition of UVC/NaOCl), respectively and the optimum operation conditions were identified by response surface methodology (RSM) in distilled water and subsequently confirmed in real drinking water (with differences of less than 1%). UVC/NaOCl was the most suitable process being a good compromise among oxidation efficiency, oxidant dose and treatment time. The best results in terms of subsequent removal of As(V) by adsorption were obtained using ZnAl-LDH (88% in both distilled and drinking water). Accordingly, UVC/NaOCl advanced oxidation coupled to ZnAl-LDH adsorption is the best combination for an effective removal of arsenic from drinking water

An Innovative Photoreactor, FluHelik, To Promote UVC/H2O2 Photochemical Reactions: Tertiary Treatment of an Urban Wastewater

This is the accepted manuscript of the following article: Espíndola et al. Science of the Total Environment, 2019, 667, 197-207. https://doi.org/10.1016/j.scitotenv.2019.02.335An innovative photoreactor, FluHelik, was used to promote the degradation of contaminants of emerging concern (CECs) by a photochemical UVC/H2O2 process. First, the system was optimized for the oxidation of a model antibiotic, oxytetracycline (OTC), using both ultrapure water (UPW) and a real urban wastewater (UWW) (collected after secondary treatment) as solution matrices. Following, the process was evaluated for the treatment of a UWW spiked with a mixture of OTC and 10 different pharmaceuticals established by the Swiss legislation at residual concentrations (∑CECs <660 μg L−1). The performance of the FluHelik reactor was analyzed both at lab and pre-pilot scale in multiple and single pass flow modes. The efficiency of the FluHelik photoreactor, at lab-scale, was evaluated at different operational conditions (H2O2 concentration, UVC lamp power (4, 6 and 11 W) and flow rate) and further compared with a conventional Jets photoreactor. Both photoreactors exhibited similar OTC removal efficiencies at the best conditions; however, the FluHelik reactor showed to be more efficient (1.3 times) in terms of mineralization when compared with the Jets reactor. Additionally, the efficiency of the UVC/H2O2 photochemical system using the FluHelik photoreactor in reducing the toxicity of the real effluent containing 11 pharmaceuticals was evaluated through zebrafish (Danio rerio) embryo toxicity bioassays. FluHelik scale-up from laboratory to pre-pilot to promote UVC/H2O2 photochemical process proved to be feasibleThis work was financially supported by: Associate Laboratory LSRE-LCM - UID/EQU/50020/2019 - funded by national funds through FCT/MCTES (PIDDAC). V.J.P. Vilar acknowledges the FCT Investigator 2013 Programme (IF/00273/2013). J.C.A. Espíndola acknowledges CNPq (Brazil) for his scholarship (205781/2014-4). R. Montes, R. Rodil and J.B. Quintana acknowledge the financial support of Spanish "Agencia Estatal de Investigación" (ref. CTM2017-84763-C3-R-2) and Xunta de Galicia (ref. ED431C2017/36), both confounded by FEDER/ERDFS