Audenaert, Wim

Chys, Michael

Demeestere, Kristof

Dutoit, Dennis

Nopens, Ingmar

Van Hulle, Stijn

English

Ghent University Academic Bibliography

UV-VIS spectral analysis as process tool to assess ozone reactivity for secondary effluent M. Chys*,**, D. Dutoit*, W.T.M. Audenaert*,**, K. Demeestere***, I. Nopens**, S.W.H. Van Hulle*,** * LIWET, Department of Industrial Biological Sciences, Ghent University, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium (Corresponding author: M. Chys, Michael.Chys@UGent.be, Tel.: +32 56 24 12 11, Fax.: +32 56 24 12 24) ** BIOMATH, Department of Mathematical Modelling, Statistics and Bioinformatics, Ghent University, Coupure Links 653, B-9000 Gent, Belgium *** EnVOC, Department of Sustainable Organic Chemistry and Technology, Ghent University, Coupure Links 653, B-9000 Gent, Belgium  Keywords: ozonation; on-line UV-VIS; micropollutants; effluent organic matter   INTRODUCTION Due to upcoming (European) legislation, operators of municipal wastewater treatment plants (MWWTPs) are preparing for plant upgrades with advanced technologies to remove organic micropollutants (MPs) from secondary effluent. Ozonation has shown to be a promising technology for MP removal (Oneby et al. 2011, Gerrity & Snyder 2011) but the basic control strategies currently applied (e.g. constant dose, flow based) prevent cost-effective operation due to sub-optimal ozone dosing. Additionally, MP analyses are time, cost and labour intensive which enhances the need for more readily available (online) and less expensive measurement techniques (e.g. UV-VIS). Although the potential value of simple surrogate models, correlating the removal of UV254 absorbance (UVA254) to MP removal, has been indicated (Bahr et al. 2007, Wert et al. 2009, Dickenson et al. 2009, Audenaert et al. 2013) significant research is still required to further establish and validate this type of surrogate models. Furthermore, multi-wavelength (i.e. full UV-VIS spectrum) approaches are scarcely used while the robustness and predictive power of such models might potentially be higher. This work aimed to assess real-time UV-VIS spectra to quantify the degradation kinetics of ozone and effluent organic matter (EfOM). These insights can potentially be the basis for further research towards the use of these spectra in on-line monitoring strategies to obtain a fast pre-assessment of MP removal during ozonation of secondary MWWTP effluent.  METHODS Secondary effluent was collected from the WWTP in Harelbeke (Belgium) operated by Aquafin. After collection, but prior to any experimentation, effluent samples were passed through a rapid sand filter to remove suspended solids. Subsequently, batch ozonation experiments were conducted by adding specific amounts of freshly prepared ozone stock solution to the effluent samples. The ozone concentration of the stock solution (± 100 ppm O3) was determined using the indigo method (Bader & Hoigne, 1981). The effluent used was collected on two different dates and experiments were performed at different temperatures (10 & 20 °C) to assess the influence on the reaction mechanisms. In total 8 experiments were conducted, relating to different effluent samples, initial ozone doses and temperatures. Online and offline UV-VIS spectra (200-800 nm) were recorded and remaining ozone concentrations at different time intervals (ranging from 20 s until 30 min) were analyzed.   RESULTS AND DISCUSSION An assessment was made of the reactivity of ozone towards the effluent organic matter based on the method developed by Puxty et al. (2006). For this, only an online UV-VIS profile was used. The decay of the remaining ozone concentration and EfOM is represented by two differential equations, given below. The evolution of UVA254 is presented in Figure 1.        ⁄                            ⁄                          with CO3 = ozone concentration; CEfOM = effluent organic matter concentration; kO3 = reaction rate of ozone; ϒEfOM = yield factor of EfOM  A unity spectrum for EfOM (200–800 nm; relative to UVA254 = 1 cm-1) is retrieved from the online UV-VIS measurements before dosage. A unity spectrum for ozone (200-800 nm; related to 1 mg l-1) was readily available. Multiplying the unity spectrum with the concentrations retrieved by the differential equations above, a full spectrum is determined at each time interval. Both spectra can thus be used to determine a composed UV-VIS spectrum in time, containing both the absorption by ozone and EfOM itself. Detailed explanation about this general calculation procedure can be found in Puxty et al. (2006). By minimizing the error between the calculated spectrum and the actual measured spectrum, kO3 and ϒEfOM were estimated. The goodness-of-fit between experimental and simulated values was quantified by calculating the Theil’s inequality coefficient (TIC) according to Audenaert et al. (2010). Using the online UV-VIS measurements (e.g. Figure 2 with a measurement frequency of 1 s-1) of in total eight different experimental runs, a single value of kO3 and one for ϒEfOM could be estimated. This resulted to a good agreement (all individual TIC values < 0.3) between the measured and calculated UV-VIS spectrum (200-800 nm) for all eight experiments, independent of variations in sample conditions (Figure 3). A comparison between the modeled and measured profile at e.g. 254 nm is displayed in Figure 1. Determining the goodness-of-fit between the offline measured ozone concentration and the estimated concentration showed an overall TIC of 0.22 (< 0.3), indicating a good agreement with the independent measured values (see e.g. Figure 4).  CONCLUSION UV-VIS measurements show great potential to be key input for control strategies of effluent ozonation processes. Current research already indicated the relationship between UVA254 removal and micropollutant removal. The usage of the complete UV-VIS profile, used in the presented model, can be the start of a further development towards a reliable control strategy for ozonation of secondary effluent treatment. A profound linking with micropollutant removal, possibly using some data-driven modeling (e.g. PCA), is of great importance.  REFERENCES Audenaert, W.T.M., Callewaert, M., Nopens, I., Cromphout, J., Vanhoucke, R., Dumoulin, A., Dejans, P. & Van Hulle, S.W.H. 2010 Full-scale modelling of an ozone reactor for drinking water treatment. Chem. Eng. J. 157, 551-557. Audenaert, W.T.M., Vandierendonck, D., Van Hulle, S.W.H. & Nopens, I. 2013 Comparison of Ozone and HO˙ Induced Conversion of Effluent Organic Matter (EfOM) Using Ozonation and UV/H2O2 Treatment. Water Res. 47(7), 2387–2398. Bahr, C., Schumacher, J., Ernst, M., Luck, F. & Heinzmann, B. 2007 SUVA as control parameter for the effective ozonation of organic pollutants in secondary effluent. Water Sci. Technol. 55(12), 267-274. Bader, H. & Hoigne, J. 1981 Determination of Ozone in Water by the Indigo Method. Water Res. 15, 449–456. Dickenson, E.R., Drewes, J.E., Sedlak, D.L., Wert, E.C. & Snyder, S.A. 2009 Applying surrogates and indicators to assess removal efficiency of trace organic chemicals during chemical oxidation of wastewaters. Environ Sci Technol. 43(16), 6242-6247. Gerrity, D. & Snyder, S.A. 2011 Review of Ozone for Water Reuse Applications: Toxicity, Regulations, and Trace Organic Contaminant Oxidation. Ozone Sci. Eng. 33(4), 253-266. Oneby, M.A., Bromley, C.O. Borchardt, J.H. & Harrison, D.S. 2010 Ozone Treatment of Secondary Effluent at U.S. Municipal Wastewater Treatment Plants, Ozone Sci. Eng. 32(1), 43-55. Puxty, G., Maeder, M. & Hungerbühler, K. 2006 Tutorial on the fitting of kinetics models to multivariate spectroscopic measurements with non-linear least-squares regression, Chemom. Intell. Lab. Syst., 81, 149-164. Wert, E.C., Rosario-Ortiz, F.L. & Snyder, S.A. 2009 Using ultraviolet absorbance and color to assess pharmaceutical oxidation during ozonation of wastewater. Environ Sci Technol. 43(13), 4858-4863.    FIGURES   Figure 1: Lay-out of measured changes in UVA254 before and during the first 6 minutes of reaction time after ozone dosing (± 5 mg O3/L; T = 10 °C) compared to the modeled profile  00.020.040.060.080.10.120.140 50 100 150 200 250 300 350UVA254 (cm-1) Time (s) model measuredO3 dosing Effluent before O3 dosing O3 decay and EfOM conversion  Figure 2: Online UV-VIS profile during the first 10 minutes of reaction time after ozone dosing (± 9 mg O3/L; T = 10 °C)   Figure 3: Goodness-of-fit (TIC) for the modeled UV-VIS spectra of 8 different experiments   Figure 4: Comparison between measured and modeled ozone concentrations (± 5 mg O3/L; T = 10 °C) 0.000.020.040.060.080.100.120.140.161 2 3 4 5 6 7 8TIC calculated Experiment no. 0.00.51.01.52.02.53.03.54.04.55.00 50 100 150 200 250 300 350 400Ozone concentration (mg L-1) Time (s) measured model

UV-VIS spectral analysis as process tool to assess ozone reactivity for secondary effluent

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UV-VIS spectral analysis as process tool to assess ozone reactivity for secondary effluent

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