Quantitative Characterization of Aqueous Byproducts from

Research Article pubs.acs.org/journal/ascecg

Quantitative Characterization of Aqueous Byproducts from Hydrothermal Liquefaction of Municipal Wastes, Food Industry Wastes, and Biomass Grown on Waste Balakrishna Maddi,* Ellen Panisko, Thomas Wietsma, Teresa Lemmon, Marie Swita, Karl Albrecht, and Daniel Howe Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States Downloaded via NEW MEXICO STATE UNIV on July 1, 2018 at 13:28:44 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: Hydrothermal liquefaction (HTL) is a viable thermochemical process for converting wet solid wastes into biocrude that can be hydroprocessed to liquid transportation fuel blendstocks and specialty chemicals. The aqueous byproduct from HTL contains significant amounts (20− 50%) of the biogenic feed carbon, which must be valorized to enhance economic sustainability of the process on an industrial scale. In this study, aqueous fractions produced from HTL of food industry wastes, municipal wastes, and biomass cultivated on wastewater were characterized using a wide variety of analytical approaches. Organic species present in these aqueous fractions were identified using two-dimensional gas chromatography equipped with time-of-flight mass spectrometry. Identified compounds include organic acids, nitrogen compounds, alcohols, aldehydes, and ketones. Conventional gas chromatography coupled with flame ionization detection and liquid chromatography utilizing refractive index detection were employed to quantify the identified compounds. Inorganic species in the aqueous streams were also were quantified using ion chromatography and inductively coupled plasma optical emission spectroscopy. The concentrations of organic compounds and inorganic species are reported, and the significance of these results are discussed in detail. KEYWORDS: Municipal waste, Hydrothermal liquefaction, Food industry waste, Aqueous byproduct, Biorefinery, Biofuels, Biocrude

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INTRODUCTION Based on a recent survey of fossil energy resources, energy security and independence are challenges encountered by the United States as well as developing countries.1−3 Therefore, there is an incentive to explore renewable energy resources that have potential for use in producing liquid transportation fuels (especially jet fuel and diesel) and/or fuel additives. Conventional biomass, which includes lignocellulosic and aquatic feedstocks, has the potential to produce liquid transportation fuels via biochemical and thermochemical conversion processes.4 According to several techno-economic studies, lignocellulosic biomass can only satisfy 30% of today’s energy demand. For large-scale production of liquid transportation fuels, several scientific, technical, economical, and logistical challenges must be overcome before aquatic biomass is viable.5 Therefore, attention has shifted to the estimated 18 billion metric tons of carbon6 that is discarded across the globe annually for liquid fuel blendstocks production. Wet solid wastes generated at municipal wastewater treatment plants and by food processing industry have attracted significant interest for biofuel production.7 These wet solid wastes are generated continuously from existing infrastructures/industries and have the potential to produce liquid transportation fuels at the industrial scale via either biochemical or thermochemical pathways. © 2017 American Chemical Society

Wet solid waste generated from municipal wastewater plants consist of 80−97% moisture depending on dewatering techniques or sludge generation operations employed.8,9 At present, wet municipal sludge has been utilized to generate methane or hydrogen via anaerobic digestion.10,11 The remaining residue from this process has been employed as a nutrient source for cultivating agricultural crops and aquatic species such as algae, bacteria, fungi, and yeast.12−16 This sludge residue also can be applied as a landfill cover material.11,17 Similarly, wet solid waste generated from food processing industries also has been anaerobically digested to produce methane/hydrogen, and the residue produced has been used to fertilize agricultural crops or as a material cover to landfills.18−20 Municipal solid wastes contain heavy metals and toxic chemicals that might be harmful to the environment;12 therefore, their application as fertilizer and landfill cover material is regulated under environmental laws.11,12,21,22 As an alternative to the conventional anaerobic digestion approach, wet solid wastes from food industry and municipal wastewater treatment plants are also being thermally processed to produce electricity, process heat, or syngas.23−25 Received: September 30, 2016 Revised: December 21, 2016 Published: January 9, 2017 2205

DOI: 10.1021/acssuschemeng.6b02367 ACS Sustainable Chem. Eng. 2017, 5, 2205−2214

Research Article

ACS Sustainable Chemistry & Engineering

Table 1. Operating Parameters Used to Generate the Aqueous Fraction from HTL of Food Industry Waste, Municipal Wastewater Treatment Waste, and Biomass Grown on Wastes municipal waste water treatment plant (MWWTP)

food industry waste

ash-free solids in feed (wt %) reactor temp (°C) reactor pressure (Mpa) space velocity (L/L·h) feed rate (L/h) pH of aqueous fraction aqueous carbon yield (wt %) water content in aqueous byproduct (wt %) COD (g/L)

biomass grown on waste streams

FIW01

FIW02

FIW03

FIW04

primary sludge

secondary sludge

digested sludge

oleaginous yeast grown on corn stover lignin residue

mixed algae grown on MWWTP

10.6 349 20.0 2.1 1.5 7.5 42 91.8

14.9 339 20.3 2.1 1.5 7.5 29 94.3

14.1 338 20.1 2.1 1.5 4.7 55 94.7

12.8 331 20.1 8 4.0 6.2 26 99.3

11.0 339 20.2 2.1 1.5 6.4 22 98.9

8.1 332 20.0 2.1 1.5 8.0 42 98.3

11.5 350 20.0 1.2 1.5 8.0 26 96.8

14.9 345 20.0 1.2 1.5 4.1 21 97.7

14.4 329 20.0 2.1 1.5 7.9 32 96.1

98.0

84.7

110.4

55.9

40.8

73.0

48.2

59.0

68.1

aqueous stream generated from HTL of wet solid wastes, qualitative and quantitative data of constituent organic and inorganic species are required. Limited information is available in the literature about the chemical composition of the aqueous phase generated from the HTL of food industry waste, municipal wastewater treatment plant solids or aquatic biomass grown on wastewater streams.41 In this article, a wide variety of analytical techniques are employed to qualitatively and quantitatively characterize the organic and inorganic constituents present in these aqueous streams.

Hydrothermal liquefaction (HTL) is a thermochemical process that uses water naturally associated with wet feedstocks such as aquatic feedstocks, or with additional water in the case of lignocellulosic feedstocks, to produce an intermediate biocrude material as the first step in the production of liquid transportation fuels.25−29 Wet wastes have a natural advantage over lignocellulosics for HTL because they do not require drying, grinding, and rehydration to make a pumpable slurry, reducing the overall feedstock preprocessing and preparation steps. The products from HTL include an organic biocrude fraction, an aqueous stream, a solid residue, and a small fraction of gaseous product.27 The biocrude product is readily converted into liquid transportation fuels via a single temperature catalytic hydroprocessing step with subsequent fractionation/distillation.30,31 The HTL of biomass is an active area of research so there are no definitive process conditions. A recent study that collected data from over 30 previously published HTL experiments revealed that biocrude yields ranged from 0% to 85%, with the mean at 26% oil.32 Consequently, the organic yield to the aqueous phase also demonstrated a similar phenomenon. The minimum water-soluble organic was 2%, the maximum was 75%, and the mean was 28%. The statistical analysis performed revealed that the increase in concentration of organics to the aqueous phase correlated with long reaction times, fast heating rates, high concentrations of catalysts, high lipid and lignin feedstocks, and low carbon/hydrogen ratio feedstocks.32 Techno-economic analysis of liquid fuel production utilizing HTL with woody biomass determined that the waste disposal costs associated with the aqueous phase was second only to feedstock costs.30 Utilizing organic as well as inorganic species in the aqueous phase is one pathway to reduce operating costs of a biomass HTL to fuel facility. Since this aqueous stream from biomass HTL (lignocellulosic and algal feedstocks) contains biogenic carbon,33,34 nitrogen, phosphorus, and micronutrients, it can be used to cultivate algal/aquatic feedstocks.35,36 Aqueous byproducts from biomass HTL can also be utilized to produce 48.5−63.4 MJ/m3 fuel gas via anaerobic digestion or catalytic hydrothermal gasification or catalytic reforming.37,38 High-value specialty chemicals (such as ethanol, acetic acid, acetone, and N-methylsuccinimide) derived via liquid−liquid extraction followed by catalytic processes39,40 may also be viable. Alternatively, the aqueous fraction can be sent to water treatment plant for discharge into natural water bodies provided the constituents are within permitted ranges.41 For effective downstream conversion or conditioning of the

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MATERIALS AND METHODS

Feedstocks. Wastes used in this study were obtained from food processing and municipal wastewater treatment plants. Food industry wastes (FIW) 1 and 2 were Montepulciano grape pomace (collected from Sleeping Dog Wines, Benton City, WA) and Cabernet Sauvignon grape pomace (obtained from Columbia Crest Winery, Paterson, WA), respectively. FIW3 was sugar beet tailings (from an industrial collaborator, Fargo, ND), and FIW4 was the extracted grain procured from Ice Harbor Brewing Company (Kennewick, WA). Primary, secondary, and digested sludge were provided by Metro Vancouver (Canada). Two biomass feedstocks, oleaginous yeast (PNNL, Richland, WA) grown on corn stover lignin residue (NREL, Golden, CO) and a mixed algae culture grown on municipal wastewater (produced by the full-scale algae raceway wastewater treatment facility in Delhi, CA) were utilized. Hydrothermal Liquefaction of Municipal and Industrial Waste. HTL was performed on the wastes described above at 350 °C and 3000 psi using a continuous-flow, bench-scale system. A process flow diagram of HTL continuous-flow, bench-scale system is shown in the Supporting Information, Figure S1. Table 1 shows the processing conditions used to generate aqueous streams that were analyzed in this study. Ultimate analysis of the feedstocks processed using HTL is shown in Table S1. Calculation of the percentage feedstock carbon reporting to the aqueous phase is simply the measured concentration of C in the aqueous phase times the total volume generated divided by the total measured C in the feedstock. Detailed information on HTL experiments and calculations for percent carbon of feedstock present in aqueous phase and high heating value (HHV) of biocrude for municipal wastes is presented elsewhere.42,43 Similarly, HTL experiments on grape pomace are presented elsewhere.44 Total Carbon, Inorganic Carbon, Total Nitrogen, Cation, and Anion Analysis. Total carbon, total nitrogen, and inorganic carbon content of these HTL aqueous streams were determined using a Shimadzu (Columbia, MD) TOC-5000A TC analyzer equipped with a Shimadzu ASI-5000A autosampler and a nondispersive infrared detector. Cation analysis was performed on a PerkinElmer (Waltham, MA) Optima 7300DV inductively coupled plasma optical emission 2206


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Figure 1. 3D plot of aqueous byproducts generated from HTL of Cabernet Sauvignon grape pomace (FIW02). The units for the primary and secondary axes are seconds. Some chemical compounds are marked in the figure. For a full list of chemical compounds, refer to Table S3.

Figure 2. 3D plot of aqueous byproducts generated from HTL of sugar beet tailings (FIW03). The units of the primary and secondary axes are seconds. Some chemical compounds are marked in the figure. For a full list of chemical compounds, refer to Table S4. into the gas chromatograph. The GC injector temperature was maintained at 260 °C. A split ratio of 1:150 was used in this analysis. The temperature program for the GC primary column was as follows: constant temperature of 40 °C for 0.2 min followed by a temperature ramp to 250 °C at 5 °C min−1 and finally holding at a constant temperature of 260 °C for 5 min. An optimum modulation period of 6 s was used with 1.2 s of hot pulse and 1.8 s of cold pulse. The temperature of the modulator was maintained 5 °C higher than the secondary column while the temperature of the GC secondary column was maintained 5 °C higher than the primary column. The transfer line connecting the GC×GC and the TOF/MS was maintained at 260 °C. The MS ion source was maintained at 225 °C. An acquisition rate of 200 spectra s−1 was used for the MS detector. Data processing was performed using ChromaTOF version 4.50. Chemical compounds were identified using the NIST2008 mass spectral database.

spectrometer with a Meinhard nebulizer, glass cylonic spray chamber, and 2.0 mm alumina injector. Anion content was estimated using a Dionex-3000 (Sunnyvale, CA) Liquid Chromatography system equipped with a conductivity detector and a Dionex IonPac AS 11 hydrocracking column. Data acquisition methods used for estimating total carbon, total nitrogen, inorganic carbon, and the cation and anion contents of aqueous byproducts from HTL of waste feedstocks have been described previously in the literature.33,34 Chemical oxygen demand and ammonia content were determined using an HACH (Loveland, CO) reagent-kit and spectrophotometry. Qualitative Characterization Using Two-Dimensional Gas Chromatography with Time-of-Flight Mass Spectrometry (GC×GC-TOF-MS). All aqueous byproducts from HTL of wastes were characterized using a LECO (St. Joseph, MI) Pegasus 4D instrument. The data acquisition method has been described extensively in the literature.33,45 For each sample, 0.5 μL was injected 2207


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Figure 3. 3D plot of aqueous byproducts generated from HTL of municipal waste−secondary sludge. The units of the primary and secondary axes are seconds. Some chemical compounds are marked in the figure. For a full list of chemical compounds, refer to Table S7.

Figure 4. 3D plot of aqueous byproducts generated from HTL of biomass grown on municipal wastes. The units of the primary and secondary axes are seconds. Some chemical compounds are marked in the figure. For a full list of chemical compounds, refer to Table S9. Quantitative Gas Chromatography and Liquid Chromatography Analysis. Organic compounds in aqueous coproducts from HTL of municipal waste, food industry waste, and biomass feedstocks grown on wastes identified using GC×GC-TOF-MS were quantified using one-dimensional gas chromatography. An Agilent (Santa Clara, CA) 7890 GC equipped flame ionization detection (FID) and fused silica capillary column with a stationary phase of 5%-phenylmethylpolysiloxane (Agilent HP-5 column; 30 m × 0.25 mm × 0.25 μm) was used for quantification analysis. Prepared or purchased standards were used for quantitative characterization. A custom commercial calibration mixture was purchased from Restek Corporation containing acetone, 2-butanone, cyclopenatanone, 2-cyclopenten-1-one, 2-pyrrolidinone, and N-methylpyrrolidone at 1.0% (weight/weight) in water. Other standards contained ethanol, pyrazine, acetamide, N-methylsuccinimide, 3-pyrindol, phenol, and N-ethylsuccinimide, each at 1.0 wt % in water. Sample preparation, standard calibration ranges, and the GC data acquisition method were described previously in the literature.33,34 Each standard solution was diluted with water gravimetrically to produce eight-point calibration ranges from approximately 0.005−1.0% (weight/weight). Four

replicates of all HTL aqueous samples and each standard mixture at every calibration level were prepared for GC/MS, GC/flame ionization detection (FID), and liquid chromatography analysis and were analyzed in a blocked randomized experimental design to control for instrument performance. This procedure was recommended by NIST (Chapter 2, Section 2.3.6.2 Data Collection).46 Calibration and testing are coupled in one design to maintain statistical balance, avoid confounding of treatment effects estimates, improve the estimation of variance components, and simplify the statistical analysis. An Agilent (Santa Clara, CA) 1100 Liquid Chromatography system equipped with a refractive index (RI) detector was used to quantify the organic acids present in the aqueous samples. An Aminex HPX-87H (7.8 mm × 300 mm) ion exclusion column equipped with a guard column (4.6 mm × 30 mm) was used for this analysis. A custom commercial calibration mixture containing acetic acid, propanoic acid, and butanoic acid at 1.0% (weight/weight) in water was purchased from Restek Corporation. Sample preparation, standard calibration range, and liquid chromatography data acquisition method were described previously in the literature.33,34 The R2 value from the linear 2208


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ACS Sustainable Chemistry & Engineering regression of calibrations utilized to generate data reported in this publication was >0.98.

to examining process conditions to increase biocrude yield, strategies to utilize products partitioned into the aqueous phase will improve economics and carbon yields for HTL processes. Aqueous phases generated from HTL of FIW03, oleaginous yeast grown on corn stover lignin residue, and FIW04 are slightly acidic (4 to 6 pH). The acidic nature of these aqueous streams is likely the result of the presence of organic acids formed from degradation of either monomeric sugars or carbohydrates present in the feed during HTL. Aqueous byproducts generated from HTL of municipal waste, FIW01, FIW02, and algae grown on municipal waste are mildly basic (pH of 6 to 8). The alkaline nature of these aqueous streams likely result from the high concentration of nitrogenous compounds that are formed during degradation of constituent proteins in the waste feedstocks.49 As reported previously,33,34 the aqueous byproduct from HTL has a very high COD that will necessitate either onsite wastewater treatment facilities or further processing to valorize the carbon present. The COD of the streams shown in Table 1 range from 41 to 110 g/L, compared to 0.2−1.2 g/L50 for raw municipal wastewater. For different HTL feedstocks, this compares to ranges of 41−77 g/L for lignocellulosic feedstocks,34 and 44−85 for algal feedstocks.33 GC×GC-TOF-MS was used to identify compounds present in aqueous byproducts generated from HTL of municipal waste, food industry wastes, and biomass grown on municipal/ food waste. Three-dimensional (3D) plots of the total ion chromatogram obtained for the HTL aqueous byproducts of FIW02 and FIW03 are shown in Figures 1 and 2, respectively (3D plots of aqueous byproduct from HTL of Montepulciano grape pomace and extracted grain from beer brewing are shown in Supporting Information, Figure S2 and Figure S3.) Organic acids (acetic acid), oxygenates (ethanol, acetone, butanone, and alkyl derivatives of 2-cyclopenten-1-one), and anhydrous sugars (such as isosorbide) are observed in the aqueous fraction generated from HTL of food industry wastes, (shown in Tables S2, S3, S4, and S5). Organic acids, oxygenates, and anhydrous sugars could be formed from degradation of carbohydrates present in these waste materials during HTL. In addition to organic acids and oxygenates, aqueous streams generated from HTL of municipal wastes and algae grown on municipal wastes (shown in Figures 3, 4, S4, and S5) contain nitrogenous compounds (pyrazine, 2-pyrrolidinone, 2-piperdine, N-methyl succinimide, and 3-pyrindol). These nitrogenous compounds are likely produced from the degradation of proteins present in the feedstocks during HTL. These compounds i.e., organic acids, oxygenates and nitrogenous compounds were observed previously in the aqueous coproduct produced from HTL of algae cultures grown on municipal wastes.16 Dissolved carbon dioxide and/or carbon dioxide-ammonia salts such as ammonium carbamate also were observed in HTL aqueous streams from municipal waste and algae cultivated on municipal waste. These carbon dioxide-ammonia salts also were observed in the aqueous byproducts generated from HTL of algal feedstocks not grown on municipal wastewater.33 Organic compounds present in the aqueous streams generated from HTL of municipal wastes and algae grown on municipal waste were similar to those obtained from algal biomass.33 Therefore, wet municipal wastes and algal cultures may be co-fed to an HTL reactor for production of organic biocrude and aqueous byproducts. Because the maximum programmable temperature of GC×GC-TOF-MS was 250 °C, higher molecular weight

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RESULTS AND DISCUSSION Although the HTL process itself is not the main focus of this paper, differences in the processing conditions and results can

Figure 5. Total carbon content and inorganic content of the aqueous byproducts generated from HTL of food industry waste, municipal waste, and biomass grown on municipal/food wastes: BF1 biomass feedstock grown on corn stover lignin residue; BF2 biomass feedstock grown on municipal waste.

help elucidate the quantity and nature of the aqueous byproduct. The differences in the solids loading for the feeds reported in Table 1 were due to the necessity of producing a pumpable slurry that is not prone to dewatering effects. Hence the weight percent of solids in the slurry varies from 8.1 to 14.9%. The mass-basis yield of biogenic carbon which reports to the aqueous fractions generated from HTL of municipal waste, food industry wastes, and biomass grown on municipal/ food wastes is in the 20−55 wt % range. The broad interval of 20−55 wt % of feed carbon in the aqueous phase is a significant challenge for the overall sustainability of industrial processes if the entire stream is considered as waste.30 The disparity of the biogenic carbon in the aqueous stream could be due to either the operating conditions of the HTL process (such as solid loading, space velocity) or the type of waste/biomass feedstock. The two species of grape pomace provide a striking example, where one strain, FIW01, has a 1.5 fold greater aqueous carbon yield than the FIW02 strain (the aqueous carbon yield values shown in Table 1). While it has been determined for HTL of algae that increased solids loading assist in retaining carbon in the oil phase,27 there is also evidence that chemical compositions of grape pomace can differ by cultivation.47 Three varieties of red wine grapes with seedless pomaces have oil contents that range from 3 to 6%, monosaccharides from 21 to 31%, and tannins from 26 to 36%. Pomace containing grape seeds have been reported to have oil up to 14%.48 Higher lipid content in algal feedstocks resulted in increased biocrude yields in comparison to those strains that had high carbohydrate composition.27 Similarly, compositional analysis of wastewater sludge may indicate why the secondary sludge sample had the highest amount of carbon in the aqueous phase. The secondary sludge at 50% protein was more than twice that of the primary sludge (21%), and nearly twice the digested sample (28%). This feedstock was also the only sample that experienced issues in separating the biocrude from the aqueous phase. In addition 2209


2210

0.00829 ± 0.0003 0.02846 ± 0.001 0.03139 ± 0.002 0.021 ± 0.002

0.00798 ± 0.001

0.02089 ± 0.0025

0.016107 ± 0.002 0.01546 ± 0.004

Mean value ±2× standard deviation are shown.

0.0067 ± 0.0001

0.00561 ± 0.001

a

0.19 0.0171 0.0286 0.1114 0.0234

0.12 0.01497 ± 0.011 0.01725 ± 0.002 0.1170 ± 0.006 0.02098 ± 0.003 0.002 0.005 0.008 0.002

1.5 ± 0.12 0.0118 ± 0.001

2.0849 ± 0.2 0.0155 ± 0.0022

± ± ± ±

FIW02 0.6326 ± 0.019 0.0737 ± 0.009

FIW01

0.44 ± 0.007 0.05813 ± 0.006

chemical compounds

acetic acid propanoic acid butanoic acid ethanol pyrazine pyrazine, methyl ammonia (assay) phenol N-methylsuccinimide acetone 2-butanone 2-butanone, hydroxy cyclopentanone 2-cyclopenten-1-one 2(3H)-furanone, dihydro-5-methyl 2-pyrrolidinone, 1methyl 2-pyrrolidinone 2-piperidinone isosorbide acetamide N-methyl-acetamide 0.26936 ± 0.02

0.04363 ± 0.006

0.086 0.0127 ± 0.0006 0.0273 ± 0.002 0.0931 ± 0.005 0.0447 ± 0.007 0.07914 ± 0.03 0.0135 ± 0.001 0.0088 ± 0.0007 0.0149 ± 0.0008

0.4421 ± 0.06 0.009 ± 0.0005

1.0827 ± 0.02 0.07196 ± 0.01

FIW03

0.04123 ± 0.003 0.0147 ± 0.001

0.01085 ± 0.0007

0.00719 ± 0.0008

0.00326 ± 0.0003

0.05784 ± 0.001 0.00879 ± 0.001 0.01284 ± 0.001 0.069 0.01279 ± 0.0007 0.0169 ± 0.001 0.01547 ± 0.0008 0.0071 ± 0.0009

0.2119 ± 0.04 0.01525 ± 0.01

FIW04

0.1312 ± 0.002 0.09107 ± 0.0009

0.05317 ± 0.001 0.0255 ± 0.003

0.03728 ± 0.002

0.0311 ± 0.004 0.02792 ± 0.002 0.03962 ± 0.003 0.368 0.0127 ± 0.0005 0.03149 ± 0.004 0.10219 ± 0.005 0.03675 ± 0.0018 0.04471 ± 0.02 0.01329 ± 0.0003 0.00164 ± 0.00001 0.00695 ± 0.0001

0.32426 ± 0.029 0.08555 ± 0.02

primary sludge

± ± ± ± 0.001 0.004 0.004 0.002

± 0.006 ± 0.006 ± 0.0018

0.1001 ± 0.003 0.0964 ± 0.004

0.06353 ± 0.0026 0.0290 ± 0.0127

0.02714 ± 0.013

0.0008 ± 0.0002 0.0186 ± 0.002 0.00982 ± 0.006

0.05137 0.02142 0.02538 0.57 0.01340 0.04296 0.04996 0.02347

0.33025 ± 0.007 0.0965 ± 0.002

secondary sludge

0.1038 ± 0.003 0.098 ± 0.005

0.080 ± 0.002 0.033 ± 0.001

0.0428 ± 0.0002

0.00496 ± 0.0001 0.01289 ± 0.0005

0.04035 ± 0.0045 0.0117 ± 0.0005 0.01157 ± 0.0004 0.69 0.01519 ± 0.001 0.05367 ± 0.007 0.1325 ± 0.005 0.0377 ± 0.0014

0.3078 ± 0.005 0.04269 ± 0.0015

digested sludge

0.0434 ± 0.0005 0.02 ± 0.001

0.06 ± 0.03

0.0736 ± 0.004 0.0088 ± 0.001 0.0101 ± 0.002 0.025 0.0247 ± 0.001 0.0313 ± 0.001 0.141 ± 0.0008 0.0433 ± 0.0002 0.07026 ± 0.004 0.01235 ± 0.0001 0.01057 ± 0.0001 0.0085 ± 0.0001

0.993 ± 0.004 0.0723 ± 0.012

BF1

0.1809 ± 0.013 0.2185 ± 0.01

0.1216 ± 0.013 0.0583 ± 0.007

0.0557 ± 0.006

0.0845 ± 0.005 0.0166 ± 0.005 0.0434 ± 0.002 1.24 0.017 ± 0.001 0.1197 ± 0.01 0.124 ± 0.006 0.0482 ± 0.002 0.0369 ± 0.02 0.00482 ± 0.001 0.0533 ± 0.001 0.00522 ± 0.0005

0.5233 ± 0.008 0.0742 ± 0.008

BF2

Table 2. Concentration, in Weight Percent, of Major Organic Constituents Identified in the Aqueous Fraction Generated from HTL of Municipal Wastes, Food Industry Wastes, and Biomass Feedstock (BF) Grown on Wastesa

ACS Sustainable Chemistry & Engineering Research Article


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streams generated from HTL of sugar beet tailings (shown in Figure S7) but were not quantified in this study. The total carbon and inorganic carbon contents were determined prior to quantifying the organic compounds present in the aqueous byproducts obtained from HTL of municipal wastes, food industry wastes, and biomass feedstocks grown on wastes. The total carbon content determined for aqueous byproducts collected from HTL of municipal waste, food industry wastes, and biomass feedstocks grown on food/ municipal wastes are in the 1.0−3.0 wt % range (shown in Figure 5). The amounts of these identified compounds present in all of the aqueous byproduct generated from HTL of both food industry and municipal wastes are shown in Table 2. The total amounts of quantified organic carbon compared to the total organic carbon for each sample is shown in Figure 6. The quantified carbon (except for FIW04) is in the 40−70% range of the total organic carbon. The quantified carbon for the aqueous stream produced from HTL of extracted grains from beer brewing is 25% of the total organic carbon. This may be due to the presence of many low concentration compounds that are below the detection limit for gas and liquid chromatography. The high amount of ethanol present in the aqueous phase of the two grape pomace samples (1.5% and 2%) are by far the highest observed for any aqueous phase from HTL to date.33,34 It is probable a significant amount of ethanol is retained by the wet grape pomace following wine fermentation. The total nitrogen and ammonia contents in the aqueous byproducts examined in this paper were also determined. Trace amounts (

Quantitative Characterization of Aqueous Byproducts from

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