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Quantitative Characterization of Aqueous Byproducts from Hydrothermal Liquefaction of Municipal Wastes, Food Industry Wastes, and Biomass Grown on Waste Balakrishna Maddi, Ellen A. Panisko, Thomas Wietsma, Teresa Lemmon, Marie Swita, Karl Albrecht, and Daniel Trusler Howe ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02367 • Publication Date (Web): 09 Jan 2017 Downloaded from http://pubs.acs.org on January 14, 2017

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ACS Sustainable Chemistry & Engineering

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Quantitative Characterization of Aqueous Byproducts from Hydrothermal Liquefaction of Municipal Wastes, Food Industry Wastes, and Biomass Grown on Waste

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Balakrishna Maddi,a* Ellen Panisko,a Thomas Wietsma,a Teresa Lemmon,a Marie Swita,a Karl Albrecht,a and Daniel Howea

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Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA

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*Corresponding author

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Post Doctorate Research Associate

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Pacific Northwest National Laboratory, P.O. Box 99352, Richland, WA 99352, USA

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e-mail: [email protected]

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Phone: 1-509-375-6491

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Fax: 1-509-372-1861

Balakrishna Maddi

ACS Paragon Plus Environment


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Highlights •

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The total carbon yield in the aqueous fraction from hydrothermal liquefaction (HTL) of municipal/food industry waste was 20 to 55 wt%.

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40 to 70% of the total carbon in the aqueous fraction was identified and quantified.

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50 to 90% of the total nitrogen in aqueous byproducts produced from HTL of municipal

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waste and algae grown on municipal waste is ammonia. •

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The aqueous stream generated from HTL of grape pomace primarily consists of ethanol, acetone, acetic acid and 2-butanone.

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High-value organic species (such as acetone, acetic acid, ethanol, N-methylsuccinimide,

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etc.), alkaline salts, sulfur, and phosphorous should be utilized/recycled from these

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aqueous streams for the overall sustainability of a biorefinery.

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Abstract

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Hydrothermal liquefaction (HTL) is a viable thermochemical process for converting wet

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solid wastes into biocrude which can be hydroprocessed to liquid transportation fuel blendstocks

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and specialty chemicals. The aqueous byproduct from HTL contains significant amounts (20 to

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50%) of the biogenic feed carbon, which must be valorized to enhance economic sustainability

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of the process on an industrial scale. In this study, aqueous fractions produced from HTL of food

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industry wastes, municipal wastes and biomass cultivated on wastewater were characterized

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using a wide variety of analytical approaches. Organic species present in these aqueous fractions

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were identified using two-dimensional gas chromatography equipped with time-of-flight mass

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spectrometry. Identified compounds include organic acids, nitrogen compounds, alcohols,

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aldehydes, and ketones. Conventional gas chromatography coupled with flame ionization

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detection and liquid chromatography utilizing refractive index detection were employed to

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quantify the identified compounds. Inorganic species in the aqueous streams were also were

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quantified using ion chromatography and inductively coupled plasma optical emission

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spectroscopy. The concentrations of organic compounds and inorganic species are reported, and

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the significance of these results are discussed in detail.

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Keywords: Municipal waste, Hydrothermal liquefaction, Food industry waste, Aqueous

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byproduct, Biorefinery, Biofuels, Biocrude.



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1.

Introduction

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Based on a recent survey of fossil energy resources, energy security and independence are

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challenges encountered by the United States as well as developing countries 1-3. Therefore, there

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is an incentive to explore renewable energy resources that have potential for use in producing

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liquid transportation fuels (especially jet fuel and diesel) and/or fuel additives. Conventional

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biomass, which includes lignocellulosic and aquatic feedstocks, has the potential to produce

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liquid transportation fuels via biochemical and thermochemical conversion processes 4.

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According to several techno-economic studies, lignocellulosic biomass can only satisfy 30% of

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today’s energy demand. For large-scale production of liquid transportation fuels, several

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scientific, technical, economical and logistical challenges must be overcome before aquatic

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biomass is viable 5. Therefore, attention has shifted to the estimated 18 billion metric tons of

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carbon 6 that is discarded across the globe annually for liquid fuel blendstocks production. Wet

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solid wastes generated at municipal wastewater treatment plants and food processing industry

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have attracted significant interest for biofuel production 7. These wet solid wastes are generated

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continuously from existing infrastructures/industries and have the potential to produce liquid

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transportation fuels at the industrial scale via either biochemical or thermochemical pathways.

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Wet solid waste generated from municipal wastewater plants consist of 80 to 97 % moisture

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depending on dewatering techniques or sludge generation operations employed 8-9. At present,

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wet municipal sludge has been utilized to generate methane or hydrogen via anaerobic digestion

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10-11

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cultivating agricultural crops and aquatic species such as algae, bacteria, fungi, and yeast 12-16.

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This sludge residue also can be applied as a landfill cover material 11, 17. Similarly, wet solid

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waste generated from food processing industries also has been anaerobically digested to produce

. The remaining residue from this process has been employed as a nutrient source for


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methane/hydrogen, and the residue produced has been used to fertilize agricultural crops or as a

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material cover to landfills 18-20. Municipal solid wastes contain heavy metals and toxic chemicals

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that might be harmful to the environment 12; therefore, their application as fertilizer and landfill

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cover material is regulated under environmental laws 11-12, 21-22. As an alternative to the

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conventional anaerobic digestion approach, wet solid wastes from food industry and municipal

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wastewater treatment plants are also being thermally processed to produce electricity, process

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heat or syngas 23-25.

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Hydrothermal liquefaction (HTL) is a thermochemical process that uses water naturally

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associated with wet feedstocks such as aquatic feedstocks, or with additional water in the case of

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lignocellulosic feedstocks, to produce an intermediate biocrude material as the first step in the

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production of liquid transportation fuels 25-29.Wet wastes have a natural advantage over

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lignocellulosics for HTL because they do not require drying, grinding, and rehydration to make a

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pumpable slurry, reducing the overall feedstock preprocessing and preparation steps. The

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products from HTL include an organic biocrude fraction, an aqueous stream, a solid residue, and

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a small fraction of gaseous product 27. The bio-crude product is readily converted into liquid

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transportation fuels via a single temperature catalytic hydroprocessing step with subsequent

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fractionation/distillation 30-31.

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The HTL of biomass is an active area of research so there are no definitive process

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conditions. A recent study that collected data from over 30 previously published HTL

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experiments revealed that biocrude yields ranged from 0% to 85%, with the mean at 26% oil32.

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Consequently, the organic yield to the aqueous phase also demonstrated a similar phenomenon.

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The minimum water soluble organic was 2%, the maximum was 75% and the mean was 28%.

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The statistical analysis performed revealed that the increase in concentration of organics to the



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aqueous phase correlated with long reaction times, fast heating rates, high concentrations of

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catalysts, high lipid and lignin feedstocks, and low carbon/hydrogen ratio feedstocks32.

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Techno-economic analysis of liquid fuel production utilizing HTL with woody biomass

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determined that the waste disposal costs associated with the aqueous phase was second only to

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feedstock costs 30. Utilizing organic as well as inorganic species in the aqueous phase is one

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pathway to reduce operating costs of a biomass HTL to fuel facility. Since this aqueous stream

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from biomass HTL (lignocellulosic and algal feedstocks) contains biogenic carbon 33-34, nitrogen,

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phosphorous and micronutrients, it can be used to cultivate algal/aquatic feedstocks 35-36.

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Aqueous byproducts from biomass HTL can also be utilized to produce 48.5 – 63.4 MJ/m3 fuel

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gas via anaerobic digestion or catalytic hydrothermal gasification or catalytic reforming37-38.

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High-value specialty chemicals (such as ethanol, acetic acid, acetone and N-methylsuccinimide)

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derived via liquid-liquid extraction followed by catalytic processes 39-40 may also be viable.

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Alternatively, the aqueous fraction can be sent to water treatment plant for discharge into natural

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water bodies provided that the constituents are within permitted ranges41. For effective

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downstream conversion or conditioning of the aqueous stream generated from HTL of wet solid

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wastes, qualitative and quantitative data of constituent organic and inorganic species are

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required. Limited information is available in the literature about the chemical composition of the

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aqueous phase generated from the HTL of food industry waste, municipal wastewater treatment

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plant solids or aquatic biomass grown on wastewater streams41. In this article, a wide-variety of

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analytical techniques is employed to qualitatively and quantitatively characterize the organic and

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inorganic constituents present in these aqueous streams.

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2.

Materials and methods

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2.1

Feedstocks


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Wastes used in this study were obtained from food processing and municipal wastewater

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treatment plants. Food industry wastes (FIW) 1 and 2 were Montepulciano grape pomace

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(collected from Sleeping Dog Wines, Benton City, WA) and Cabernet Sauvignon grape pomace

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(obtained from Columbia Crest Winery, Paterson, WA), respectively. FIW3 was sugar beet

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tailings (from industrial collaborator, Fargo, ND), and FIW4 was the extracted grain procured

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from Ice Harbor Brewing Company (Kennewick, WA). Primary, secondary, and digested sludge

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were provided by Metro Vancouver (Canada). Two biomass feedstocks, oleaginous yeast

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(PNNL, Richland, WA) grown on corn stover lignin residue (NREL, Denver, CO) and a mixed

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algae culture grown on municipal wastewater (produced by the full-scale algae raceway

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wastewater treatment facility in Delhi, CA) were utilized.

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2.2

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Hydrothermal liquefaction of municipal and industrial waste HTL was performed on the wastes described above at 350°C and 3000 psi using a

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continuous-flow, bench-scale system. Process flow diagram of HTL continuous-flow, bench-

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scale system is shown in supplementary information, Figure S1. Table 1 shows the processing

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conditions used to generate aqueous streams that were analyzed in this study. Ultimate analysis

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of the feedstocks processed using HTL is shown in Table S1. Calculation of the percentage

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feedstock carbon reporting to the aqueous phase is simply the measured concentration of C in the

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aqueous phase times the total volume generated divided by the total measured C in the feedstock.

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Detailed information on HTL experiments and calculations for percent carbon of feedstock

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present in aqueous phase and high heating value (HHV) of bio-crude for municipal wastes is

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presented elsewhere 42-43. Similarly, HTL experiments on grape pomace are presented elsewhere

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44

.



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2.3

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Total carbon, inorganic carbon, total nitrogen, cation and anion analysis Total carbon, total nitrogen and inorganic carbon content of these HTL aqueous streams were

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determined using a Shimadzu (Columbia, MD) TOC-5000A TC analyzer equipped with a

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Shimadzu ASI-5000A auto-sampler and a non-dispersive infrared detector. Cation analysis was

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performed on a Perkin Elmer (Waltham, MA) Optima 7300DV inductively coupled plasma

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optical emission spectrometer with a Meinhard nebulizer, glass cylonic spray chamber and 2.0

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mm alumina injector. Anion content was estimated using a Dionex-3000 (Sunnyvale, CA) Liquid

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Chromatography system equipped with a conductivity detector and a Dionex IonPac AS 11

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hydrocracking column. Data acquisition methods used for estimating total carbon, total nitrogen,

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inorganic carbon, and the cation and anion contents of aqueous byproducts from HTL of waste

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feedstocks have been described previously in the literature 33-34. Chemical oxygen demand and

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ammonia content were determined using an HACH (Loveland, CO) reagent-kit and

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spectrophotometry.

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2.4

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of-flight mass spectrometry (GC × GC – TOF – MS )

Qualitative characterization using two-dimensional gas chromatography with time-

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All aqueous byproducts from HTL of wastes were characterized using a LECO (St. Joseph,

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MI) Pegasus 4DTM instrument. The data acquisition method has been described extensively in the

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literature 33, 45. For each sample, 0.5 µL was injected into the gas chromatograph. The GC

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injector temperature was maintained at 260°C. A split ratio of 1:150 was used in this analysis.

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The temperature program for the GC primary column was as follows: constant temperature of

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40°C for 0.2 min followed by a temperature ramp to 250°C at 5°C min-1 and finally holding at a

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constant temperature of 260°C for 5 min. An optimum modulation period of 6 s was used with

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1.2 s of hot pulse and 1.8 s of cold pulse. The temperature of the modulator was maintained 5°C


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higher than the secondary column while the temperature of the GC secondary column was

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maintained 5°C higher than the primary column. The transfer line connecting the GC × GC and

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the TOF/MS was maintained at 260°C. The MS ion source was maintained at 225°C. An

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acquisition rate of 200 spectra sec-1 was used for the MS detector. Data processing was

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performed using ChromaTOF version 4.50. Chemical compounds were identified using the

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NIST2008 mass spectral database.

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2.5

Quantitative gas chromatography and liquid chromatography analysis

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Organic compounds in aqueous co-products from HTL of municipal waste, food industry

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waste, and biomass feedstocks grown on wastes identified using GC × GC – TOF – MS were

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quantified using one-dimensional gas chromatography. An Agilent (Santa Clara, CA) 7890 GC

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equipped flame ionization detection (FID) and fused silica capillary column with a stationary

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phase of 5%-phenyl-methylpolysiloxane (Agilent HP-5 column; 30 m × 0.25 mm × 0.25 µm)

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was used for quantification analysis. Prepared or purchased standards were used for quantitative

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characterization. A custom commercial calibration mixture was purchased from Restek

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Corporation containing acetone, 2-butanone, cyclopenatanone, 2-cyclopenten-1-one, 2-

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pyrrolidinone, and N-methylpyrrolidone at 1.0% (weight/weight) in water. Other standards

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contained ethanol, pyrazine, acetamide, N-methylsuccinimide, 3-pyrindol, phenol, and N-

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ethylsuccinimide, each at 1.0 wt% in water. Sample preparation, standard calibration ranges, and

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the GC data acquisition method were described previously in the literature 33-34. Each standard

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solution was diluted with water gravimetrically to produce eight-point calibration ranges from

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approximately 0.005%–1.0% (weight/weight). Four replicates of all HTL aqueous samples and

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each standard mixture at every calibration level were prepared for GC/MS, GC/flame ionization

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detection (FID) and liquid chromatography analysis and were analyzed in a blocked randomized



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experimental design to control for instrument performance. This procedure was recommended by

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NIST (Chapter 2, Section 2.3.6.2 Data Collection)46. Calibration and testing are coupled in one

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design to maintain statistical balance, avoid confounding of treatment effects estimates, improve

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the estimation of variance components, and simplify the statistical analysis.

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An Agilent (Santa Clara, CA) 1100 Liquid Chromatography system equipped with a

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refractive index (RI) detector was used to quantify the organic acids present in the aqueous

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samples. An Aminex HPX-87H (7.8 × 300 mm2) ion exclusion column equipped with a guard

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column (4.6 × 30 mm2) was used for this analysis. A custom commercial calibration mixture

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containing acetic acid, propanoic acid, and butanoic acid at 1.0% (weight/weight) in water was

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purchased from Restek Corporation. Sample preparation, standards calibration range and liquid

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chromatography data acquisition method were described previously in the literature 33-34. The R2

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value from the linear regression of calibrations utilized to generate data reported in this

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publication was >0.98.

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3.

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Results and discussion Although the HTL process itself is not the main focus of this paper, differences in the

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processing conditions and results can help elucidate the quantity and nature of the aqueous

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byproduct. The differences in the solids loading for the feeds reported in Table 1 were due to the

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necessity of producing a pumpable slurry that is not prone to dewatering effects. Hence the wt%

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of solids in the slurry varies from 8.1 to 14.9%. The mass-basis yield of biogenic carbon which

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reports to the aqueous fractions generated from HTL of municipal waste, food industry wastes,

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and biomass grown on municipal/food wastes is in the 20 to 55 wt% range. The broad interval of

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20 to 55 wt% of feed carbon in the aqueous phase is a significant challenge for the overall


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sustainability of industrial processes if the entire stream is considered as waste30. The disparity of

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the biogenic carbon in the aqueous stream could be due to either the operating conditions of the

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HTL process (such as solid loading, space velocity) or the type of waste/biomass feedstock. The

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two species of grape pomace provide a striking example, where one strain, FIW01 has a 1.5 fold

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greater aqueous carbon yield than the FIW02 strain (the aqueous carbon yield values shown in

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Table 1). While it has been determined for HTL of algae that increased solids loading assist in

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retaining carbon in the oil phase27, there is also evidence that chemical compositions of grape

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pomace can differ by cultivation47. Three varieties of red wine grapes with seedless pomaces

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have oil contents that range from 3 to 6%, monosaccharides from 21 to 31% and tannins from 26

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to 36%. Pomace containing grape seeds have been reported to have oil up to 14%48. Higher lipid

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content in algal feedstocks resulted in increased bio-crude yields in comparison to those strains

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that had high carbohydrate composition 27. Similarly, compositional analysis of waste water

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sludge may indicate why the secondary sludge sample had the highest amount of carbon in the

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aqueous phase. The secondary sludge at 50% protein was more than twice that of the primary

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sludge (21%), and nearly twice the digested sample (28%). This feedstock was also the only

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sample that experienced issues in separating the bio-crude from the aqueous phase. In addition to

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examining process conditions to increase bio-crude yield, strategies to utilize products

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partitioned into the aqueous phase will improve economics and carbon yields for HTL processes.

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Aqueous phases generated from HTL of FIW03, oleaginous yeast grown on corn stover

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lignin residue, and FIW04 are slightly acidic (4 to 6 pH). The acidic nature of these aqueous

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streams is likely the result of the presence of organic acids formed from degradation of either

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monomeric sugars or carbohydrates present in the feed during HTL. Aqueous byproducts

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generated from HTL of municipal waste, FIW01, FIW02, and algae grown on municipal waste



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are mildly basic (pH of 6 to 8). The alkaline nature of these aqueous streams likely result from

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the high concentration of nitrogenous compounds that are formed during degradation of

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constituent proteins in the waste feedstocks 49.

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As reported previously33-34, the aqueous byproduct from HTL has a very high COD that

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will necessitate either onsite wastewater treatment facilities or further processing to valorize the

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carbon present. The COD of the streams shown in Table 1 range from 41 to 110 g/L, compared

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to 0.2 to 1.2 g/L50 for raw municipal wastewater. For different HTL feedstocks, this compares to

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ranges of 41 to77 g/L for lignocellulosic feedstocks34, and 44 to 85 for algal feedstocks33.

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GC × GC – TOF – MS was used to identify compounds present in aqueous byproducts

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generated from HTL of municipal waste, food industry wastes and biomass grown on

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municipal/food waste. Three-dimensional (3D) plots of the total ion chromatogram obtained for

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the HTL aqueous byproducts of FIW02 and FIW03 are shown in the Figure 1 and Figure 2,

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respectively (3D plots of aqueous byproduct from HTL of Montepulciano grape pomace and

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extracted grain from beer brewing are shown in supplementary data, Figure S2 and Figure S3.)

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Organic acids (acetic acid), oxygenates (ethanol, acetone, butanone, and alkyl derivatives of 2-

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cyclopenten-1-one) and anhydrous sugars (such as isosorbide) are observed in the aqueous

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fraction generated from HTL of food industry wastes, (shown in Table S2, S3, S4 and S5).

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Organic acids, oxygenates, and anhydrous sugars could be formed from degradation of

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carbohydrates present in these waste materials during HTL. In addition to organic acids and

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oxygenates, aqueous streams generated from HTL of municipal wastes and algae grown on

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municipal wastes (shown in Figure 3 and Figure 4 and Figure S4 and S5) contain nitrogenous

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compounds (pyrazine, 2-pyrrolidinone, 2-piperdine, N-methyl succinimide, and 3-pyrindol).

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These nitrogenous compounds are likely produced from the degradation of proteins present in


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the feedstocks during HTL. These compounds i.e. organic acids, oxygenates and nitrogenous

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compounds were observed previously in the aqueous co-product produced from HTL of algae

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cultures grown on municipal wastes 16. Dissolved carbon dioxide and/or carbon dioxide-

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ammonia salts such as ammonium carbamate also were observed in HTL aqueous streams from

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municipal waste and algae cultivated on municipal waste. These carbon dioxide-ammonia salts

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also were observed in the aqueous byproducts generated from HTL of algal feedstocks not grown

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on municipal wastewater 33. Organic compounds present in the aqueous streams generated from

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HTL of municipal wastes and algae grown on municipal waste were similar to those obtained

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from algal biomass 33. Therefore, wet municipal wastes and algal cultures may be co-fed to HTL

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reactor for production of organic bio-crude and aqueous byproducts.

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Because the maximum programmable temperature of GC × GC – TOF – MS was 250°C,

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higher molecular weight compounds cannot be identified using this method. Therefore, these

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aqueous samples were analyzed using conventional GC-MS with a maximum programmable

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temperature of 300°C. High molecular weight compounds were identified in aqueous streams

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generated from HTL of sugar beet tailings (shown in Figure S7) but were not quantified in this

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study.

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The total carbon and inorganic carbon contents were determined prior to quantifying the

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organic compounds present in the aqueous byproducts obtained from HTL of municipal wastes,

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food industry wastes, and biomass feedstocks grown on wastes,. The total carbon content

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determined for aqueous byproducts collected from HTL of municipal waste, food industry

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wastes, and biomass feedstocks grown on food/municipal wastes are in the 1.0 to 3.0 wt% range

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(shown in Figure 5). The amounts of these identified compounds present in all of the aqueous

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byproduct generated from HTL of both food industry and municipal wastes are shown in Table



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2. The total amounts of quantified organic carbon compared to the total organic carbon for each

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sample is shown in Figure 6. The quantified carbon (except for FIW04) is in the 40 to 70% range

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of the total organic carbon. The quantified carbon for the aqueous stream produced from HTL of

291

extracted grains from beer brewing is 25% of the total organic carbon. This may be due to the

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presence of many low concentration compounds that are below the detection limit for gas and

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liquid chromatography. The high amount of ethanol present in the aqueous phase of the two

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grape pomace samples (1.5% and 2%) are by far the highest observed for any aqueous phase

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from HTL to date33-34. It is probable a significant amount of ethanol is retained by the wet grape

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pomace following wine fermentation.

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Total nitrogen content and ammonia in the aqueous byproducts examined in this paper was

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also determined. Trace amounts (

Quantitative Characterization of Aqueous Byproducts from

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