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PARAFAC modeling of irradiation- and oxidation-induced changes in fluorescent dissolved organic matter extracted from poultry litter Kiranmayi P Mangalgiri, Stephen Andrew Timko, Michael Gonsior, and Lee Blaney Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b06589 • Publication Date (Web): 12 Jun 2017 Downloaded from http://pubs.acs.org on June 15, 2017

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Environmental Science & Technology

PARAFAC modeling of irradiation- and oxidation-induced changes in fluorescent dissolved organic matter extracted from poultry litter Kiranmayi P. Mangalgiri 1, Stephen A. Timko 2, Michael Gonsior 3, and Lee Blaney 1* 1:

University of Maryland Baltimore County Department of Chemical, Biochemical and Environmental Engineering 1000 Hilltop Circle, ECS 314 Baltimore, MD 21250 USA

2:

Kennedy/Jenks Consultants 1191 2nd Avenue, Suite 630 Seattle, WA 98101

3:

University of Maryland Center for Environmental Science Chesapeake Biological Laboratory 146 Williams Street, P.O. Box 38 Solomons, MD 20688

* Corresponding author: Lee Blaney, PhD University of Maryland Baltimore County Department of Chemical, Biochemical and Environmental Engineering 1000 Hilltop Circle, ECS 314 Baltimore, MD 21250 USA Tel: +1-410-455-8608 Fax: +1-410-455-1049 Email: [email protected]

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TABLE OF CONTENTS GRAPHIC

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ABSTRACT

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Parallel factor analysis (PARAFAC) applied to fluorescence excitation emission matrices

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(EEMs) allows quantitative assessment of the composition of fluorescent dissolved organic

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matter (DOM). In this study, we fit a four-component EEM-PARAFAC model to characterize

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DOM extracted from poultry litter. The dataset included fluorescence EEMs from 291 untreated,

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irradiated (253.7 nm, 310 – 410 nm), and oxidized (UV-H2O2, ozone) poultry litter extracts. The

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four components were identified as microbial humic-, terrestrial humic-, tyrosine-, and

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tryptophan-like fluorescent signatures. The Tucker’s congruence coefficients for components

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from the global (i.e., aggregated sample set) model and local (i.e., single poultry litter source)

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models were greater than 0.99, suggesting that the global EEM-PARAFAC model may be

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suitable to study poultry litter DOM from individual sources. In general, the transformation

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trends of the four fluorescence components were comparable for all poultry litter sources tested.

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For irradiation at 253.7 nm, ozonation, and UV-H2O2 advanced oxidation, transformation of the

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humic-like components was slower than that of the tryptophan-like component. The opposite

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trend was observed for irradiation at 310 – 410 nm, due to differences in UV absorbance

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properties of components. Compared to the other EEM-PARAFAC components, the tyrosine-

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like component was fairly recalcitrant in irradiation and oxidation processes. This novel

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application of EEM-PARAFAC modeling provides insight into the composition and fate of

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agricultural DOM in natural and engineered systems.

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1. INTRODUCTION

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Parallel factor analysis (PARAFAC) is a mathematical tool that models the fluorescence

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excitation emission matrices (EEM) of dissolved organic matter (DOM) using a finite number of

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components 1-3. These components are described by their characteristic excitation and emission

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spectra, and are associated with a pool of organic molecules and/or moieties that contribute to the

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overall fluorescence signature of the bulk DOM matrix. EEM-PARAFAC models can be

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employed to study environmental or experimental samples using component scores that are

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analogous to concentrations, although these scores cannot be compared between different

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components due to differences in quantum yield; furthermore, solution pH and temperature also

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affect comparison of component scores 4. Regardless, changes in DOM fluorescence spectra can

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be described by component scores along a gradient corresponding to time, space, or extent of

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treatment.

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In the last decade, EEM-PARAFAC has been widely used to characterize the composition,

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biodegradability, and photolability of DOM in natural systems (e.g., rivers, oceans, lakes,

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wetlands, groundwater, soil, and sediments) 5-13 and to study the effects of hydrological events

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and biogeochemical cycles 14-16. DOM matrices from water and wastewater treatment plants

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have also been analyzed by EEM-PARAFAC to determine the fate of DOM through biological,

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physical, and chemical treatment processes, such as conventional activated sludge, filtration,

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coagulation, and disinfection 17-20. Recently, EEM-PARAFAC models have been used to

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describe DOM reactivity in bench-scale advanced oxidation processes, specifically, UV-TiO2,

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UV-Fenton, UV-chlorine, and UV-persulfate 21-24.


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The ability of EEM-PARAFAC to deconvolute DOM signatures has allowed for contaminant

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source tracking, which can be used to analyze the effects of anthropogenic activities on the

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environment. While several reports tie the DOM signatures of downstream natural systems to

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changes in upstream land use patterns 25-27 from industry, agriculture, and forestry, a limited

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number of models 28-30 have been developed using DOM derived from agricultural waste. Using

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an EEM-PARAFAC model constructed for DOM from plant chaff (e.g., oat, millet, soybean,

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corn, wheat, and canola) and animal biomass (i.e., dairy, swine, and poultry manure), Hunt and

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Ohno 28 reported that while decomposition of plant-based DOM showed similar behavior across

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species, degradation of animal-derived DOM was dependent on the type of animal manure. Yu

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et al. 29 developed an EEM-PARAFAC model for commercial compost generated from

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agricultural and industrial organic waste; however, the DOM sources were not separately

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assessed to determine agriculture- and industry-specific components. For these reasons, studies

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comprising DOM from specific animal manures are necessary to better understand the

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composition and fate of organic molecules in manure management processes.

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With the introduction of concentrated animal feeding operations in the United States (US) in the

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mid-20th century, five states (i.e., Alabama, Arkansas, Georgia, Mississippi, and North Carolina)

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account for 60% of the country’s total production 31 of broilers (chicken raised for consumption

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of meat). Poultry is the most widely available meat in the US 32 and the second most consumed

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meat worldwide 33. However, intensive poultry farming has been associated with the

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introduction of antibiotics, hormones, nutrients, and pathogens to the environment, ultimately

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affecting water quality 34. As DOM leaches from poultry litter, and affects the fate of other

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poultry litter-derived contaminants 35-37, an EEM-PARAFAC model to describe changes in DOM



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composition may offer additional insight into the fate and transport of other agricultural

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contaminants.

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The overall objective of this work was to characterize DOM in treated and untreated poultry

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litter-impacted water using EEM-PARAFAC. In this study, we investigated DOM

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transformation through UV irradiation at 253.7 nm, simulated sunlight photolysis at 310 – 410

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nm, UV-H2O2 advanced oxidation, and ozonation. Irradiation at 253.7 nm, advanced oxidation,

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and ozonation were performed to analyze changes in poultry litter-derived DOM fluorescence in

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engineered systems for agricultural waste management and treatment. These treatment processes

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are of increasing interest to the agricultural industry. UV irradiation (253.7 nm) and ozonation

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have been employed for disinfection and odor control 38-42. Adak et al. 36 proposed the UV-H2O2

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system for treatment of organoarsenicals, which are predominantly used in the poultry industry

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and present in poultry litter-impacted waters. Photolysis at 310 – 410 nm was chosen to simulate

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solar photodegradation, which occurs in storage lagoons, constructed wetlands, and surface water

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systems. Studying the wavelength-dependent phototransformation of DOM allows for

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comparison of UV-based engineered processes and sunlight photolysis, ultimately providing a

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better understanding of the reactivity of agricultural DOM in intentional waste management

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systems. As DOM significantly impacts the treatment efficiency of oxidation systems, EEM-

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PARAFAC modeling offers the ability to characterize compositional changes in the poultry

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litter-derived DOM matrix during UV-H2O2 and ozone treatment.

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2. EXPERIMENTAL

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2.1 Poultry Litter Extracts

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Poultry litter samples (i.e., PL1, PL2, and PL3) were acquired from three anonymous

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conventional and organic broiler operations in the Chesapeake Bay watershed following “crust

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out” of poultry houses. These operations produce poultry meat for consumption. During crust

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out, the top layer of poultry litter is collected, but the lower bedding material is left behind to be

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used by the next flock 43. The litter is then piled, but not actively composted. The time that litter

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spent in the pile before collection was designated as the litter age. At each farm, litter was

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collected from multiple points within a pile to obtain a representative sample.

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Upon receipt, the moisture content of poultry litter was determined by gravimetric methods. The

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poultry litter was then oven-dried for five days at 40 °C, homogenized, and sieved (1.19 mm).

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The total organic carbon (TOC) content of the poultry litter was measured with a Shimadzu TOC

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analyzer (TOC-5000A; Columbia, MD) equipped with a solids analysis module (SSM-5000A).

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Stock poultry litter extracts (stock-PLEs) were prepared by adding one gram of the processed

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litter to 25 mL of deionized water (DI; Neu-Ion; Windsor Mill, MD), based on the solids loading

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of a previously reported nutrient recovery process 44. The solutions were shaken at 250 rpm for

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40 minutes, centrifuged at 14,000 g, filtered with 1.2 µm glass fiber pre-filters (Millipore) and

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0.45 µm glass micro-fiber syringe filters (Whatman), and stored in the dark at -20 °C. The stock-

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PLEs were generated just before experimentation, and approximately one week before

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fluorescence analysis commenced. The dissolved organic carbon (DOC) content (see Table 1)

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was determined with a Shimadzu TOC analyzer (TOC-LCPH; Columbia, MD). The pH values

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of the three stock-PLEs were in the range 6.8-6.9. 7 ACS Paragon Plus Environment


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Insert Table 1

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2.2 Photodegradation and Oxidation Experiments

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A merry-go-round type photoreactor (Rayonet RPR600, Southern New England Ultraviolet Inc.;

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Branford, CT), equipped with eight exchangeable bulbs, was used for irradiation experiments.

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The effective photon flux, measured by ferrioxalate actinometry 45, was 1.22×10-5 Ein/L-s for the

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253.7 nm bulbs and 3.52×10-5 Ein/L-s for the 310 – 410 nm bulbs. Experimental solutions,

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consisting of 9.5 mL DI and 0.5 mL stock-PLE (i.e., 20× diluted stock-PLE, to match the DOC

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of agricultural runoff following manure application 46), were irradiated for 24 hours in quartz

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tubes. A 200 µL aliquot was extracted at 0, 6, 12, 18, and 24 hours.

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UV-H2O2 advanced oxidation was conducted using light at 253.7 nm. Hydrogen peroxide (30%

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H2O2) was purchased from Fisher Scientific (Pittsburgh, PA). Samples (10 mL) containing 9.5

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mL of DI and 0.5 mL of stock-PLE were irradiated for 90 minutes in the presence of a gradient

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of H2O2 concentrations, namely 0, 5, 25, and 50 mg/L. At 0, 15, 30, 60, and 90 min, 200 µL of

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the irradiated solution was withdrawn.

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A high-strength aqueous ozone solution was generated by bubbling ozone gas from a Del Ozone

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generator (LG-7; San Luis Obispo, CA) into DI as previously reported 47. The ozone

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concentration was approximately 12 mg O3/L, as determined by the indigo method 48. The high-

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strength aqueous ozone was added to 10 mL samples, which contained 0.5 mL stock-PLE, at

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doses of 0, 1, 2, 4, and 6 mg O3/L. Specific ozone doses were calculated as the mass of dosed

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ozone to the initial mass of organic carbon. Samples were allowed to react at room temperature

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in the dark for 20 hours, at which time a 200 µL aliquot was collected for analysis. Absorbance


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and fluorescence data were corrected for dilution caused by the addition of the high-strength

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ozone solution.

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For all experiments, the 200 µL sample aliquots were diluted with DI to a volume of 10 mL to

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limit inner-filter effects and prevent detector overload. All data were, therefore, collected and

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reported for samples with an effective dilution factor of 1000, with respect to the stock-PLEs.

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Below, the 1000× diluted stock-PLE solutions are labeled as “PLEs” for brevity. Solution pH

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was not adjusted; all samples were naturally buffered in the pH 6.7 ± 0.2 range. The irradiation

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and oxidation experiments were performed in triplicate, and all data are reported as mean ± 95%

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confidence interval.

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2.3 PARAFAC Modeling

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Fluorescence EEMs and UV-visible absorbance spectra (Figure 1) were recorded for the PLEs

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using a 1-cm quartz cuvette in an Aqualog fluorometer (Horiba Scientific; Edison, NJ). The

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excitation and emission wavelength ranges were 210 – 620 nm and 240 – 600 nm, respectively;

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these ranges were restricted to 240 – 520 nm for excitation and 240 – 600 nm for emission

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during PARAFAC analysis. In all cases, the wavelength step was 3 nm. Inner-filter corrections,

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blank corrections, and conversion to Raman Units (RU) using water peaks at an excitation

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wavelength of 350 nm (emission range 381 – 441 nm) were performed as described in Timko et

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al. 4. Best practices, as described in Murphy et al. 3, were used for preprocessing corrections and

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exploratory analyses.

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A “global” EEM-PARAFAC model was developed with the drEEM 1.0 toolbox 3 in MATLAB

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(MathWorks; Natick, MA) using 291 untreated and treated PLE solutions. The input data was

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normalized during preliminary analysis. Preliminary models with 3-13 components were tested 9 ACS Paragon Plus Environment


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for all poultry litter samples, and a four-component model was found to best describe the

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fluorescence patterns in the associated EEMs (see Text S1 and Figure S1 in the Supporting

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Information). The five-component model did not significantly reduce the residuals (see Figure

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S2 in the Supporting Information). A convergence criterion of 10-10 was used, and 50 iterations

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with random initialization were run to check model convergence and confirm the global

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minimum. The four-component EEM-PARAFAC model had a core consistency of greater than

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80% (see Table S3 in the Supporting Information) and acceptable residual errors (see Figure S2

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of the Supporting Information). The data was reverse-normalized at the end of the analysis, as

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per Murphy et al. 3. Rigorous validation tests were performed using six fluorescence data splits

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with alternate sample distributions, and the model was found to be robust as determined by split-

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half analysis.

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To ensure the suitability of the global EEM-PARAFAC model to study DOM from three

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different sources, local 3-13 component EEM-PARAFAC models were tested to examine the

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presence of potentially unique DOM characteristics in the individual poultry litter sources. The

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same standards and protocols were used for preprocessing and exploratory analysis of ‘global’

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and ‘local’ models. As with the global model, four-component models were found to best

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describe the fluorescence data of the individual PLEs. The local EEM-PARAFAC models were

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validated using best practices 3, and the excitation and emission loadings were compared to those

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of the global model in Figure 2b-e. The Tucker’s congruence coefficient was greater than 0.99

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for all components, suggesting that the global EEM-PARAFAC model can be used to analyze

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DOM changes resulting from irradiation and oxidation experiments for all poultry litter sources.

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The Fmax values (i.e., the component scores multiplied by the maximum fluorescence intensities)


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for the PLE solutions are reported in RU, and were used to compare the fluorescence of a single

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component across the treated and untreated PLEs.

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Insert Figure 1

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3. RESULTS AND DISCUSSION

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3.1 Poultry Litter Characterization

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As indicated in Table 1, poultry litter from the three commercial farms exhibited a comparable

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TOC content of approximately 30%, while the DOC for the stock-PLE solutions varied from 1.9

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to 4.2 g C/L. The specific UV absorbance (SUVA254), which is calculated as the UV absorbance

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at 254 nm (UV254) divided by the DOC concentration, suggested that PLE1 contained more

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aromatic moieties compared to PLE2 and PLE3. The E2/E3 ratios (i.e., the UV absorbance at

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250 nm divided by the absorbance at 365 nm) for PLE1, PLE2, and PLE3 were 6.2 (±1.2), 3.8

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(±1.3), and 5.3 (±0.2), respectively, suggesting that the water extractable DOM had dissimilar

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molecular weight distributions 49. A similar conclusion can be made from the spectral slope

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values calculated for 275 – 295 nm (S275-295) which ranged from 0.9 to 1.4×10-2. For context, a

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lower S275-295 and E2/E3 reflects that the DOM matrix has a higher average molecular weight 50.

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The apparently conflicting trends of molecular size and aromaticity from the UV-based

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parameters that are typically used to characterize surface water DOM requires further vetting

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with other analytical techniques to provide additional insight into agricultural DOM

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characterization. Below, we use EEM-PARAFAC to analyze DOM content and reactivity.

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Insert Table 2



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The fluorescence signatures in the EEMs (Figure 1) were tentatively characterized by Coble’s

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peak picking method and the descriptors used for regional analysis reported by Chen et al. 51

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(Table 2). The water content of the poultry litters varied with age. PL1 and PL2 were relatively

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fresh (i.e., 0-6 months) and, unsurprisingly, contained more water than PL3, which had been

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aged for 12 months in an unmanaged pile. The impacts of litter age on DOM composition were

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also apparent from the higher fluorescence intensity associated with soluble microbial products

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at excitation wavelengths greater than 250 nm and emission wavelengths less than 380 nm

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(Figure 1) in PLE1 and PLE2. The process of composting poultry litter involves elevated

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microbial activity and temperature, resulting in the breakdown of carbon sources, accompanied

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by the formation of humic-like fluorophores from protein-like molecular pools 52. Hence, the

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intensity of peaks corresponding to humic-like fluorescence is higher in PLE3 compared to those

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for PLE1 and PLE2. Similar changes in fluorescence signature have been reported in other

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composted organic matter 29. These fluorescence differences in poultry litter-derived DOM were

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further elucidated using EEM-PARAFAC.

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3.2 Global and Local PARAFAC Models

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Recent studies have demonstrated that fluorescence peaks in EEM datasets are a result of

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complex combinations of multiple fluorescent molecules 6, 25. These findings suggest that EEM-

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PARAFAC components are useful descriptors of fluorophores in DOM samples as these

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components facilitate deconvolution of the bulk fluorescence data. The excitation and emission

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patterns of the four components from the global EEM-PARAFAC model (Figure 2) were

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examined in the online OpenFluor 53 database and identified as microbial humic- 54, 55

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(Component 1 or C1), terrestrial humic- 56, 57 (Component 2 or C2), tyrosine- 18 (Component 3 or


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C3), and tryptophan-like 58 (Component 4 or C4) fluorophores, based on Tucker’s congruence

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coefficients greater than 0.97.

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Insert Figure 2

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The large spectral overlap (68 nm and 130 nm) in the excitation and emission loadings of C1 and

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C2 is indicative of a complex DOM composition 3, 59; furthermore, the red shift of the

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fluorophores is likely associated with higher aromaticity 60, 61. The sources of the fluorophores

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identified from the OpenFluor database closely matched those indicated by Coble’s peak-picking

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technique 62 and regional analysis descriptors 51 (see Table 2). The terrestrial humic-like

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component (C1) is one of the most frequently reported EEM-PARAFAC components in

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OpenFluor 53, particularly for surface water and wastewater. Previous studies 54, 55 have also

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reported the presence of the microbial humic-like fluorescence component (C2) in wastewater

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and marine environments, indicating that these fluorophores are autochthonous in nature. The

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C3 and C4 protein-like fluorophores are typically present at lower levels than humic substances

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in surface waters. For poultry manures, which exhibit a higher ratio of protein-like molecules to

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humic substances compared to surface waters, further description of the changes in the

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concentrations of these components during natural and engineered processes is important to fully

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understand the fate of agricultural DOM.

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The differences in the fluorescence EEMs for the three DOM sources (Figure 1) suggest the

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presence of a variety of fluorophores. The relative abundance of each component in the

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untreated samples were similar for PLE1 and PLE2, but different for PLE3. For example, the

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relative abundance of humic-like C1 was about 30% in both PLE1 and PLE2, but much higher

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(44%) in PLE3. Similarly, C4 represented 43% and 50% of the total fluorescence intensity in 13 ACS Paragon Plus Environment


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untreated PLE1 and PLE2, but contributed only 27% of the total fluorescence for PLE3.

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Regardless of these differences, the local and global EEM-PARAFAC models exhibited a high

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degree of similarity (see Figure 2b-e). Furthermore, a comparison of the Fmax values for all

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components from the global model shows a high degree of correlation (R2 > 0.99) with

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components from the local models (see Figure S3 in the Supporting Information). For these

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reasons, the global model was used to analyze all experimental samples. Full excitation and

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emission loadings for the global fluorescence components are provided in Tables S1 and S2 of

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the Supporting Information. The core consistency and explained variance of the global and local

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models are presented in Table S3 in the Supporting Information.

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3.3 Irradiation of Poultry Litter-Derived DOM

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EEMs showing the change in fluorescent DOM during irradiation are shown in Figure 3a-b for

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select treatment times. The complete suite of EEMs for irradiated PLE1, PLE2, and PLE3

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samples are shown in Figures S4 – S6 (see Supporting Information), respectively. For all PLE

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sources, irradiation at 253.7 nm and 310 – 410 nm resulted in an overall loss of fluorescence.

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The corresponding changes in DOC were less than 8% and 4% for the 253.7 and 310 – 410 nm

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treatments, respectively. The Fmax value was used to study the degradation of individual

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fluorescence components. The degradation trends showed a rapid change for C1, C2, and C4

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(Figure 4) in the first six hours of irradiation, corresponding to a fluence of 3.95×10-4 Ein/cm2 for

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253.7 nm and 1.14×10-3 Ein/cm2 for 310 – 410 nm. For C3, the overall trend varied by

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wavelength; these trends are discussed in more detail below. The loss of fluorescence agrees

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with previous studies of aquatic humic substances that have reported photobleaching (i.e., loss of

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UV absorbance) 63, 64. A similar loss in Fmax has also been reported for sunlight photolysis of

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Suwannee River natural organic matter 4. 14 ACS Paragon Plus Environment

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Insert Figure 3

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Insert Figure 4

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The degradation kinetics varied with the light source due to wavelength-dependent absorbance

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(Figure 2) and photoreactivity, as previously reported 21, 65. The reactivity trends encompassed

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by the data in Figure 4 demonstrate that the fate of poultry litter DOM in natural systems (solar-

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based irradiation) is markedly different than in treatment processes (irradiation with 253.7 nm).

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Although the higher photon flux at 310 – 410 nm partially accounts for the increased

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degradation, a comparison of the Fmax loss for similar fluence at the two irradiation wavelengths

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highlights the role of the absorbance spectra of the fluorophores. For example, a fluence of

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1.19×10-3 Ein/cm2 at 253.7 nm results in 60.1% loss in Fmax for C1 in PLE3; the corresponding

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loss at 310 – 410 nm was greater (68.2%) due to the higher UV-A absorbance of C1. The

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differences in characteristic absorbance spectra are also exhibited by the excitation loading of

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C1: 0.125 at 253.7 nm and 0.208 at 315 nm (see Figure 2b). Hence, the excitation loading was

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used to further examine the effects of irradiation on individual components. Degradation of C2

305

was similar at both irradiation wavelengths, reflecting the similar UV absorbance at 253.7 nm

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and 310 – 410 nm (see Figure 2c). On the contrary, C4 absorbed more light at 253.7 nm (Figure

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2e), resulting in faster degradation (see Figure 4g-h). The observations for C4 degradation at

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310 – 410 nm are in agreement with previous literature suggesting that protein-like fluorophores

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are less photolabile than humic acid-like molecules 21, 66.

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Overall, the trends in the degradation of C1, C2, and C4 were similar for all three poultry litter

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sources. During irradiation, the component scores decreased quickly within the first six hours,

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followed by a slower kinetic regime through 24 hours. After 6 hours of irradiation at 310 – 410 15 ACS Paragon Plus Environment


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nm, the Fmax values for C1, C2, and C4 in PLE1 were 40, 37, and 33%, respectively, of the initial

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values. C3 was an exception (see Figure 4e-f). The fluorescence signal associated with C3 was

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fairly constant for PLE1 and PLE2 during irradiation at 253.7 nm, but increased for PLE3

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initially, before plateauing near the levels observed for PLE1 and PLE2. PLE3 exhibited low

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protein fluorescence prior to irradiation, suggesting that irradiation decreased the inherent

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fluorescence quenching in the sample 67 (i.e., the loss of fluorescence of tryptophan due to the

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presence of tyrosine) 68 or generated fluorescent tyrosine-like species through unknown

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mechanisms due to photodegradation of other DOM molecules 69, 70. In sunlight photolysis, the

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Fmax for C3 increased for all three PLEs. These findings indicate that either the rate of C3

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formation was greater for 310 – 410 nm or the rate of C3 degradation was faster at 253.7 nm.

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Due to the higher absorbance of C3 at 253.7 nm compared to 310 – 410 nm (Figure 2d), we

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attribute these trends to the higher rate of C3 photodegradation at 253.7 nm. Similar

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wavelength-dependent photodegradation was reported by Phong and Hur 21 for a tryptophan-like

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component.

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The photodegradation trends observed for C1-C4 at 253.7 nm and 310 – 410 nm are important in

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understanding the fate of agricultural DOM. These findings suggest that the global EEM-

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PARAFAC model proposed above may be used to provide accurate estimates of the

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photoreactivity of poultry litter-derived DOM in natural and engineered systems. Furthermore,

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these trends may also extend to other organic contaminants present in agricultural waste.

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3.4 Oxidation of DOM from Poultry Litter

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The reactivity of DOM with several oxidants has been well documented in terms of bulk

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parameters, such as DOC, SUVA254, and spectral slopes 71-73. In general, ozonation of DOM is a 16 ACS Paragon Plus Environment

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fast reaction that occurs at electron-rich groups 71 and generates smaller, more polar molecules 74.

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The ozone reaction rate constant with DOM is source dependent 75, indicating that standard

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DOM surrogates cannot be used to predict the reactivity of DOM from wastewater or agricultural

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sources. Liu et al. 76 reported the loss of UV254 and the formation of aldehydes for ozonated

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surface waters and wastewaters. Furthermore, Li et al. 77 showed that changes in DOM

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composition were directly associated with oxidant exposure (i.e., ∫[oxidant]dt) in advanced

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oxidation processes. However, few studies 78 have described the degradation of EEM-

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PARAFAC components as a function of ozone treatment.

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Select fluorescence EEMs for ozone treatment of PLE3 are shown in Figure 3c; furthermore, the

344

EEMs for PLE1, PLE2, and PLE3 at all treatment levels are shown in Figures S4, S5, and S6,

345

respectively (see Supporting Information). Ozonation of the PLEs resulted in fluorescence loss

346

at relatively low specific ozone doses (i.e., < 100 mg O3 /g DOC). Minimal changes (i.e., less

347

than 3%) in DOC were observed for the ozone treatments. For most EEM-PARAFAC

348

components, an increase in O3 dose resulted in greater loss of fluorescence (see Figure 5). In

349

PLE1 and PLE2, the transformation of C4 was faster than that of C1, C2, and C3. This

350

observation corroborates previous studies reporting that ozone preferentially reacts with

351

molecules that have high electron density 79. For PLE1 and PLE2, C3 exhibited slow

352

degradation; furthermore, C3 levels in PLE3 increased slightly during ozone treatment,

353

indicating that while tyrosine degrades due to reaction with ozone 80 , the suite of molecules

354

demonstrating tyrosine-like fluorescence may behave differently.

355

Insert Figure 5



Page 18 of 43

356

Reaction of DOM with hydroxyl radicals generated by the UV-H2O2 system resulted in

357

significant fluorescence losses (see Figure 3d); however, changes in DOC concentration were

358

less than 3%. Previous literature has reported that UV-H2O2 process generates hydroxyl radicals

359

with an approximate yield of 1 mol HO• / mol H2O2 at 253.7 nm 81. Three H2O2 doses, namely

360

5, 25, and 50 mg/L, were employed in this study to study the effect of increasing HO• exposure.

361

The corresponding specific H2O2 doses (i.e., the mass of dosed H2O2 per mass of initial DOC)

362

are reported in the legend of Figure 6. Previous studies have shown that an increase in the H2O2

363

concentration results in greater transformation of organic molecules, although high H2O2

364

concentrations can result in HO• scavenging and no net benefit. For example, Adak et al. 36

365

showed that for a H2O2 dose of greater than 50 mg/L, no significant increase in transformation

366

was observed for the poultry feed additive, roxarsone.

367

Addition of H2O2 to the PLE resulted in an increase in the Fmax value for C3 prior to irradiation.

368

These observations may be associated with reaction of H2O2 with DOM or other dissolved

369

species to form C3-like fluorescent molecules. The impacts of UV-H2O2 treatment on

370

fluorescence in PLE1, PLE2, and PLE3 are shown for all three H2O2 doses after irradiation in

371

Figure S4 – S6 (see Supporting Information). For all poultry litter sources, the loss of

372

fluorescence at a fluence of 1.65×10-5 Ein/cm2 and an H2O2 dose of 50 mg/L (i.e., the highest

373

H2O2 dose and lowest irradiation time) was greater than the transformation at an H2O2 dose of 5

374

mg/L and fluence of 9.88×10-5 Ein/cm2 (i.e., the lowest H2O2 dose and highest irradiation time).

375

Accordingly, the overall loss of fluorescence was significantly lower for 253.7 nm irradiation

376

alone, even for a fluence that was two orders of magnitude greater. These observations highlight

377

the role of HO•-mediated reactions during transformation of DOM. Hydroxyl radicals are non-

378

selective oxidants with a high oxidation potential (2.7 eV) 82. Westerhoff et al. 71 found that the 18 ACS Paragon Plus Environment

Page 19 of 43


379

rate constant for reaction of DOM with HO• was dependent on molecular weight and

380

aromaticity. While a representative second-order rate constant for reaction of DOM with HO•

381

has been proposed 83, EEM-PARAFAC component-specific behavior has not been reported and

382

may be more representative, as it better encompasses the reactivity of different DOM

383

components.

384

For C1, C2, and C4, the transformation efficiency increased with H2O2 dose (Figure 6); however,

385

the extent of increase in efficiency varied between the components. For example, the

386

degradation of C4 over 90 minutes of irradiation was consistently high (> 88%) for all H2O2

387

doses and poultry litter sources. After 90 minutes of irradiation, the transformation of C1 and C2

388

ranged from 10 to 80%, depending on H2O2 dose and poultry litter source. The greater reactivity

389

of C4 compared to C1 and C2 is in agreement with previous studies reporting the degradation of

390

tryptophan- and humic-like components in hydroxyl radical-mediated photocatalysis 21. Like

391

irradiation with 253.7 nm in the absence of H2O2 (Figure 4e), the fluorescence intensity of C3

392

remained relatively stable throughout treatment regardless of the H2O2 dose, indicating that this

393

component was recalcitrant during UV-H2O2 advanced oxidation. The relative pseudo-stability

394

of this component is also noticeable in the full set of EEMs for the three poultry litter sources in

395

Figures S4 – S6 (see Supporting Information). For UV-H2O2 treatment (5 mg/L H2O2, 90

396

minutes of irradiation), the change in fluorescence associated with C1 was greatest for PLE3

397

(55%) and lowest for PLE1 (15%), suggesting that litter age, and the associated biochemical

398

processes, may influence the reactivity of the DOM matrix. Thus, the fluorescence signatures

399

associated with C1 in PLE1 and PLE3 may stem from similar fluorescent moieties present in

400

different molecular compositions, although no significant trends of component reactivity with

401

initial SUVA254 and E2/E3 were observed. 19 ACS Paragon Plus Environment


402

Page 20 of 43

Insert Figure 6

403

3.5 Environmental Significance

404

EEM-PARAFAC models provide a quantitative approach to study changes in fluorescent DOM

405

composition during natural and engineered processes. The global model developed here for

406

three poultry litter sources was found to be robust and suitable for analysis of the changes in four

407

fluorescence EEM-PARAFAC components during irradiation and oxidation. The excitation and

408

emission loadings of C1-C4 were used to identify the nature and source of fluorophores in

409

poultry litter. Here, we have validated an EEM-PARAFAC model for poultry litter-derived

410

DOM that satisfactorily describes the fluorescence patterns from three sources. Although the

411

number of litter sources used in this study is low, our model successfully captures the differences

412

in the fluorescent signatures associated with litter source, age, and treatment. The EEMs

413

highlight the similarity in DOM signatures originating from conventional and organic farms,

414

which may be associated with the dietary consistency for broilers and uniformity of waste

415

management practices. However, we note that poultry species and type (i.e., broiler, layer, etc.),

416

bedding material, environmental factors, climate, and waste management practices (i.e., active or

417

passive) may affect DOM composition; therefore, several factors affecting EEM-PARAFAC

418

components must be further evaluated to construct a more complete understanding of DOM

419

degradation in agricultural waste.

420

The EEM-PARAFAC model was successfully employed to identify changes in fluorescent DOM

421

during irradiation and oxidation processes relevant to four waste management strategies. These

422

results provide the first comparison of changes to fluorescence components in poultry litter-

423

derived DOM during abiotic transformation-based processes, and facilitate characterization of 20 ACS Paragon Plus Environment

Page 21 of 43


424

other animal manures using similar techniques. The results from this study indicate that

425

tryptophan-like protein fluorescence was fairly labile across the various treatments, whereas the

426

tyrosine-like fluorescence was recalcitrant for most treatments. As such, these two components

427

may be useful in benchmarking changes in DOM during treatment of agricultural waste,

428

although it should be noted that fluorescent DOM may not be representative of the total DOM 84.

429

While the UV-H2O2 system (at the highest H2O2 dose) performed best in this study, further

430

analysis is required to better understand the operating costs and energy demands of each system

431

for treatment of agricultural waste.

432

Our findings establish a groundwork for continued investigation into the fate of animal manure

433

fluorescence components during abiotic treatment. Additional studies should be performed to

434

comprehensively understand the fate of DOM in agricultural waste. Given the high nutrient

435

content in agricultural waste, specific changes in the dissolved organic nitrogen content are also

436

of interest; these measurements may provide additional insight to the protein-like fluorescence

437

components identified in this study. More specific identification of fluorescent DOM

438

components and better understanding of their reactivity in other treatment processes, including

439

composting, lagooning, and anaerobic digestion, will prove useful to continuing efforts to

440

manage agricultural waste and ensure environmental protection.

441

4. SUPPORTING INFORMATION

442

Analysis and validation of the EEM-PARAFAC model; representative EEMs for all treatments



Page 22 of 43

443

5. ACKNOWLEDGEMENTS

444

We thank four anonymous reviewers for their helpful suggestions. We gratefully acknowledge

445

funding from NSF CHE 1508090. This is contribution (xxxx, to be filled in after acceptance of

446

manuscript) of the University of Maryland Center for Environmental Science, Chesapeake

447

Biological Laboratory.


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699 700

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Table 1. Physicochemical characteristics of poultry litter samples and extracts. Data are reported as mean ± 95% confidence interval (n = 3). PL1

PL2

PL3

Farm type

Conventional, commercial

Organic, commercial

Organic, commercial

Litter age a

0-3

0-6

>12

Water content (% H2O) of

31.5 ± 0.4

45.7 ± 1.1

19.1 ± 1.5

TOC (% C) of poultry litter

31.8 ± 1.1

32.6 ± 0.6

29.3 ± 0.5

DOC of stock-PLE (g C/L)

1.9 ± 0.3

3.3 ± 0.1

4.2 ± 0.1

SUVA254 of PLE (L/(mg C m)) b

2.30 ± 0.40

1.10 ± 0.01

1.20 ± 0.04

E2/E3 of PLE c

6.2 ± 1.2

3.8 ± 1.3

5.3 ± 0.2

Spectral slope (S275-295) of PLE d

0.9 (± 0.1)×10-2

1.4 (±0.1)×10-2

1.2 (± 0.3)×10-2

Relative abundance (%) of C1 in untreated PLE

30.2

30.1

44.4


20.9

15.4

28.8


5.4

4.3

0.2

poultry litter

701 702 703 704

43.4 50.2 26.5 Relative abundance (%) of C4 in untreated PLE a approximate time that litter has been piled at the poultry farm b defined as the UV absorbance of sample at 254 nm normalized to DOC c determined as at the ratio of UV absorbance at 250 nm to that of 365 nm d calculated for the UV range of 275 – 295 nm


Page 37 of 43

705


Table 2.

a

Description of components in the global EEM-PARAFAC model for DOM extracted from poultry litter.

Component

Exmax (nm) a

Emmax (nm) b

Source from OpenFluor database 53

C1

240 (310) c

405

Microbial humic-like

C2

240 (365) c

470

Terrestrial humic-like

C3 C4

250 270

300 333

Tyrosine-like Tryptophan-like

Description from Chen et al. Soluble microbial product-like Humic acid-like Soluble microbial product-like Humic acid-like Fulvic acid-like Tyrosine-, protein-like Tryptophan-, protein-like Fulvic acid-like

51

Fluorescence peak association from Coble 62 (Exmax/Emmax) (nm/nm) M (300/390) A (260/450), C (340/440) B (270/306) T (270/340)

Maximum excitation wavelength Maximum emission wavelength c Secondary fluorescence peaks in parentheses b

706



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707 708 709 710

Figure 1. (a-c) Fluorescence EEMs and (d) UV-visible absorbance spectra for untreated PLEs (1000× dilution). The DOC concentrations for the PLE1, PLE2, and PLE3 data shown here were 1.87, 3.31, and 4.17 mg C/L, respectively.


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711 712 713 714 715

Figure 2. (a) Fluorescence fingerprints of the four components in the global EEM-PARAFAC model; (b-e) excitation (Ex, dashed line) and emission (Em, dashed and dotted lines) spectra for all four components in the global (black) and local models for PLE1 (blue), PLE2 (red), and PLE3 (green). The legend in (d) also applies to (b), (c), and (e). Note that the similarity of spectra from the global and local models reinforces the suitability of the global model.



716 717 718 719 720 721 722 723

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Figure 3. Fluorescence EEMs for treated PLE3 for (row a) irradiation with 253.7 nm, (row b) photolysis at 310-410 nm, (row c) ozonation, and (row d) advanced oxidation by UV-H2O2. This figure shows the initial, first, and final samples for each treatment type. Full EEM datasets for treated PLE1 (Figure S4), treated PLE2 (Figure S5), and treated PLE3 (Figure S6) can be found in the Supporting Information.


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724 725 726 727


Figure 4. Loss of fluorescence for all components (rows a-d) for irradiation of the treated PLEs at 253.7 nm (solid symbols, left column) and 310 – 410 nm (open symbols, right column).



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728 729 730 731

Figure 5. Change in Fmax of C1, C2, C3, and C4 during ozonation for (a) PLE1, (b) PLE2, and (c) PLE3 as a function of the specific ozone dose (mg O3 added / g of initial DOC).


Page 43 of 43


732 733 734 735 736 737

Figure 6. Change in fluorescence intensity of Components 1 - 4 for all three DOM sources during UV-H2O2 treatment as a function of irradiation time and the specific H2O2 dose (corresponding to H2O2 concentrations of 5, 25, and 50 mg/L). Individual plots are shown for (a) C1 in PLE1, (b) C2 in PLE1, (c) C3 in PLE1, (d) C4 in PLE 1, (e) C1 in PLE2, (f) C2 in PLE2, (g) C3 in PLE2, (h) C4 in PLE2, (i) C1 in PLE3, (j) C2 in PLE3, (k) C3 in PLE3, and (l) C4 in PLE3. The legends in (d), (h), and (l) correspond to PLE1, PLE2, and PLE3 measurements, respectively. 43 ACS Paragon Plus Environment

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