Project summary. Global concern over water availability has highlighted the importance of developing effective water reuse programs to alleviate current and future needs. Water reuse refers to the utilization of wastewater as an additional source for both potable and non-potable water applications. However, reusing water requires additional treatment, as compared to traditional wastewater handling, in order to reduce risks associated with organic contaminants and pathogens. In the case of wastewater organic contaminants, several processes are currently used to reduce them to acceptable levels, notably the utilization of advanced oxidation processes (AOPs). AOPs are based on the activity of highly reactive species, typically hydroxyl radicals (OH), which are generated directly in the water and then react to destroy organic contaminants of concern. While AOPs have significant advantages in their ability to non-selectively destroy contaminants, one of the most important factors in their application is the decrease in the available OH due to side reactions (scavenging) with other water quality components, most importantly effluent organic matter (EfOM). EfOM is the organic carbon unique to human derived wastewater, in contrast to natural organic matter (NOM), which is derived from plant and soil based sources. A detailed understanding of the reactivity of EfOM, including specific sub-components within this material, would result in targeted pre-treatment of EfOM to remove high scavenging components before they cold impact the efficiency of AOP treatment systems. In this study a detailed evaluation of the chemistry between EfOM and OH is proposed by quantitatively determining the reactivity of different EfOM sub-components and to evaluate potential treatment options that could be applied to reduce overall EfOM reactivity.
Intellectual merit. The application of AOPs to reduce levels of organic contaminants in water reuse operations is feasible under optimal conditions. A detailed understanding of the reactivity of EfOM is important, as this species will dominate OH scavenging reactions. However, a detailed, quantitative, study of EfOM chemistry is hindered by the inability to define its specific chemical structure. This project will conduct a detailed characterization of the reactivity of EfOM towards ?OH; specifically correlating how different sub-components (fractions) relate to its reactivity through quantitative measurement of reaction rate constants and correlation to EfOM bulk properties. Knowledge of specific EfOM reactivity will guide evaluation of existing treatment processes that could decrease its overall reactivity, therefore making the application of AOPs for water reuse more efficient and thus feasible.
Broader impacts. A better understanding of the effect of EfOM on AOP applications will lead to the optimization of AOPs for water reuse applications both nationally and internationally. Furthermore, participation in this project will allow students to be exposed to the complex topic of water reuse, which is important to sustained growth and environmental health in many areas throughout the world. The proposed project is also designed to promote undergraduate and graduate student involvement and interaction in this vital area, particularly under-represented students in engineering and science at participating institutions. Students will be involved in all aspects of the project, performing the characterization and kinetics experiments, analyzing data, and correlating the findings of this work. The involved students will utilize state-of-the-art facilities to perform the required measurements, and ultimately present their findings at national and international meetings and workshops. Moreover, it is expected that all the results of this study will provide material to be incorporated in environmental engineering courses at CU Boulder and chemistry/ environmental science courses at CSULB.
As part of this project ("BRIGE: Reactivity of effluent organic matter (EfOM) towards hydroxyl radical and its effects on the application of advanced oxidation processes for water reuse applications". PI: Fernando Rosario-Ortiz), the PI studied the reactivity of EfOM towards the hydroxyl radical (HO•) by measuring the second order reaction rate constant (kEfOM?HO•), and how this rate its impacted by the apparent molecular weight (AMW) of the EfOM. The measured values for kEfOM-HO• increased as the AMW decreased and were also generally higher than for dissolved organic matter (DOM) samples (average kDOM?HO• ~ 3 × 108 M-1 s-1). The variability of the values of kEfOM-HO• also suggests that significant differences could be observed as a function of physicochemical properties of EfOM, originating from different wastewater treatment facilities. This interpretation was supported by analysis of two samples collected at a single wastewater treatment facility that included two different treatment trains (sites C1 and C2) where differences in kEfOM-HO• were observed. As a follow up to this portion of the work, the temperature dependence for the value of the reaction rate constant between HO• and a series of EfOM samples and DOM isolates was evaluated. The results indicated that both materials followed the expected Arrhenius behavior for the temperature dependence, although the EfOM samples somewhat deviated from linearity, suggesting also the potential role of the physical heterogeneity on the chemical properties. A second aspect of the chemistry of EfOM also evaluated was the decomposition of ozone as a function of different AMW fractions of EfOM. The results from this study also suggest that different AMW fractions of the EfOM behave differently with regards ozone decomposition and long term (times > 5 seconds) HO• formation. Lastly, the role of enhanced coagulation on the performance of ozone for the oxidation of trace organic contaminants in wastewater was evaluated by focusing on the targeted removal of EfOM. In 2010, the PI was awarded a Graduate Research Supplement to expand the scope of the original BRIGE award and bring a female PhD student into the project. The objective for this supplement was to expand the work and evaluate the photochemical formation of HO• in wastewater-impacted streams. The PI and one graduate student have conducted preliminary studies evaluating the formation of HO• from irradiation of EfOM (collected from four different wastewater facilities) and DOM isolates commercially obtained. These experiments were performed using bulk wastewaters from which the contribution of nitrate to the formation rate of HO• was quantified as 2.92 × 10-7 MHO MNO3-1 s-1 and was factored out. Following irradiations with a solar simulator, the apparent quantum yield for the formation of HO• from EfOM and DOM isolates (ΦHO,EfOM, ΦHO,DOM) were obtained (the term apparent quantum yield is used as these values were determined for the 290-400 nm range as opposed to at single wavelengths). The values for the ΦHO,DOM were in agreement with values reported by others for DOM isolates. For EfOM, the values for ΦHO,EfOM were in general higher than for ΦHO,DOM, and also generally higher than values for ΦHO,DOM observed for natural waters. Taken together, these prior results indicate that once released into the environment, wastewater discharges will in general have higher formation rates for HO• both due to higher nitrate concentrations and relatively high ΦHO,EfOM.
