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Journal ArticleDOI

A comparison of product yields and inorganic content in process streams following thermal hydrolysis and hydrothermal processing of microalgae, manure and digestate.

TL;DR: This study compares the behaviour of microalgae, digestate, swine and chicken manure by thermal hydrolysis and hydrothermal processing at increasing process severity to show promise for converting biomass into higher energy density fuels.
About: This article is published in Bioresource Technology.The article was published on 2016-01-01 and is currently open access. It has received 185 citations till now. The article focuses on the topics: Hydrothermal liquefaction & Chicken manure.

Summary (3 min read)

1. Introduction 24

  • There is a growing 3 interest in the recovery of nutrients from wet wastes such as manures and bio-solids and 4 hydrothermal processing has been proposed to facilitate the extraction of nitrogen, 5 phosphorus and potassium from these materials (Biller et al., 2012; Heilmann et al., 2014).
  • He e al., (2000) 23 performed HTL of swine manure at temperatures between 275 and 350 °C and observed that 24 the reaction conditions had little influence on the distribution of nitrogen, phosphorus and 25 potassium species (NPK) which was mainly found in the aqueous product (He et al., 2000).
  • The levels of phosphate recovery in the process water 5 were found to vary with feedstock (Lopez Barreiro et al., 2014) and once again are linked to 6 the inorganic content of the feedstock.

2.1 Materials 15

  • The four biomass feedstocks used in this study were obtained from different sources.
  • 16 Chlorella vulgaris was obtained as dry powder from a commercial source.
  • The poultry and swine manure were 18 collected from the University of Leeds farm.
  • 22 23 Ultimate analyses was performed using a CE Instruments Flash EA 1112 series elemental 24 analyser to determine the percentage composition of carbon, hydrogen, nitrogen, sulphur and 25 oxygen of the dry unprocessed biomass samples.
  • All measurements were performed in duplicate and the mean values 1 have been reported.

2.2 Hydrothermal processing 5

  • In each case the residence time was taken from the 11 point the reactor reached the desired temperature.
  • The heating rate was 10 °C min-1 and the 12 cooling rate was in a similar range.
  • The heating and cooling rates are the same for each 13 feedstock as the same reactor was used for all the experiments.

2.3 Product recovery and analysis 17

  • Following hydrothermal treatment, the reactor was allowed to cool to room temperature 18 before emptying.
  • The solid residues and the aqueous products were separated by filtration using a pre-20 weighed Whatman filter paper.
  • Significant quantities of bio-crude 24 were produced during the HTC and HTL process.
  • Metals such as potassium, calcium, magnesium, sodium, iron and 6 aluminium were analysed using atomic absorption spectroscopy (AAS) while nickel and 7 cobalt were analysed using inductively coupled plasma mass spectrometry (ICP-MS).
  • After complete digestion (as indicated by a greenish 15 colour) the samples were left to cool before the distillation step.

3.1 Characterisation of feedstock 4

  • The proximate and ultimate analyses of the four feedstock investigated are listed in Table 1. 5.
  • The microalgae and manure contained the higher carbon and hydrogen content at 47 13 wt.% and 6-7 wt.% respectively.
  • The digestate on the other hand contained significantly 16 lower levels of carbon (18 wt.%).
  • 21 22 Table 2 lists the nutrient and metal content of the four unprocessed biomass feedstocks.

3.2 Product yields during hydrothermal processing 5

  • The product yields (i.e, solid, liquid, gas and oil) following hydrothermal processing of each 6 feedstock are shown in Figure 1.
  • Thermal 15 hydrolysis at 170 °C typically produced the highest yields of solid residue for all the 16 feedstock.
  • The gas yield is more significant than in thermal hydrolysis and 1 ranges from 6-12%.

3.3 Characterization of the solid product 6

  • Table 3 lists the proximate and ultimate analysis of the residues produced from the different 7 hydrothermal processes together with their higher heating value (HHV).
  • The volatile matter is 10 significantly reduced with reaction severity producing a more carbonised product.
  • The carbon content of the hydrochar recovered 13 from the HTC of swine manure and chicken manure increases from 43-46 wt.% to 56 wt.% 14 and 60 wt.% respectively.
  • The level of 25 phosphorus in the residue increase with reaction severity.
  • High levels of 8 nickel have previously been observed in the process waters following SCWG and is a result 9 of nickel leaching from the reactor walls (Lopez Barreiro t al., 2014).

3.4 Characterization of the aqueous product (AP) 14

  • The aqueous products derived from each of the hydrothermal routes have been analysed 15 quantitatively for each feedstock to determine the concentrations of nitrogen (N), phosphorus 16 (P), total organic carbon (TOC) and other metals.
  • The pH of the aqueous products was also 17 monitored and the results are listed in Table 5. 18 19.

3.4.2 Total Organic Carbon (TOC) 29

  • The TOC level in SCWG water phase was the lowest compared to HTL, HTC or 31 thermal hydrolysis for all feedstock processed.
  • The presence of organic carbon in the SCWG 1 water phase implies that not all the organic content was converted to gas during the process.
  • The addition of catalysts during SCWG has been shown to reduce the TOC levels of the 3 aqueous product (Stucki et al., 2009).
  • The highest levels of TOC were in the 4 aqueous phase from hydrothermal processing of microalgae followed by the chicken manure, 5 swine manure and digestate.

3.4.3 Distribution of Nitrogen 8

  • Hydrothermal processing at different temperatures affects the distribution of nitrogen.
  • The 28 results show that 75% of the total nitrogen in the aqueous phase after thermal hydrolysis is 29 organic.
  • The reason for this is not obviously 1 apparent but will be investigated further later.

3.4.4 Distribution of Phosphorus 10

  • Figure 2 b shows the extraction of phosphorus into the aqueous phase for each of the 11 different conditions.
  • The aqueous phase from thermal hydrolysis has the highest 13 levels of total phosphorus (TP) which reduces significantly as the process severity increases.
  • At the lower temperatures, approximately 40% of the P was extracted from microalgae and 15 chicken manure although the levels are lower for digestate and swine manure.
  • This was confirmed with scanning electron microscopy and energy dispersive spectroscopy 4 which indicated the presence of Ca3(PO4)2 and Mg3(PO4)2.
  • After SCWG, the P is mainly associated 30 with the solid product with low levels of extraction into the aqueous phase.

3.4.5 Distribution of Potassium 5

  • The results in Figure 2c indicate that potassium is almost completely extracted under all 6 conditions.
  • At lower temperature processing, significant 22 levels of organic phosphorus and nitrogen are observed in the aqueous phase.
  • A summary and discussion of chemical mechanisms for process engineering, Biofuel Bioprod, also known as Hydrothermal carbonization of biomass.
  • Cultivation of microalgae with recovered nutrients after hydrothermal liquefaction.

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Citations
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Journal ArticleDOI
TL;DR: The research status in hydrothermal liquefaction of agricultural and forestry wastes is critically reviewed, particularly for the effects of liquefactions conditions on bio-oil yield and the decomposition mechanisms of main components in biomass.

199 citations

Journal ArticleDOI
01 Dec 2018-Fuel
TL;DR: In this article, the authors demonstrate the impact of processing conditions on the formation and composition of hydrochars and secondary char of municipal solid waste (OFMSW) and demonstrate that the secondary char is extractable with organic solvents and is comprised predominantly of organic acids, furfurals and phenols.

184 citations

Journal ArticleDOI
TL;DR: In this paper, the impact of HTL conditions and feedstock composition on the energy and elemental distribution of process outputs with specific emphasis on the hydrothermal liquefaction aqueous phase (HTL-AP) is discussed.

165 citations

Journal ArticleDOI
TL;DR: The results indicate that operating hydrothermal treatment in the presence of acidic additives has benefits in terms of improving the extraction of phosphorus and nitrogen.

155 citations


Cites background or result from "A comparison of product yields and ..."

  • ...(2016) indicated that higher temperature hydrothermal processing (HTL and SCWG) degraded organic-N significantly increasing the levels of NH4-N (Ekpo et al., 2016)....

    [...]

  • ...N (Ekpo et al., 2016)....

    [...]

  • ...Similarly in the study by Ekpo et al. (2016), NH4+-...

    [...]

  • ...In comparison, Ekpo et al. (2016) indicated that higher temperature hydrothermal processing (HTL and SCWG) degraded organic-N significantly increasing the levels of NH4+-...

    [...]

  • ...Generally speaking, phosphorus is concentrated in the hydrochar, however this is feedstock dependent and it is largely associated with the inorganic content of the feedstock (Ekpo et al., 2016; Dai et al., 2015)....

    [...]

Journal ArticleDOI
TL;DR: In this article, the potential of hydrothermal processing as a novel alternative to treat the digestate has been evaluated with respect to product yields, biomethane potential and solubilisation of organic carbon.

135 citations

References
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Journal ArticleDOI
TL;DR: The results show that the closed loop system using the recovered aqueous phase from the hydrothermal liquefaction of microalgae offers a promising route for sustainable oil production and nutrient management formicroalgae.
Abstract: Two major considerations of the emerging algae biofuel industry are the energy intensive dewatering of the algae slurry and nutrient management. The proposed closed loop process which involves nutrient recycling of the aqueous phase from the hydrothermal liquefaction of microalgae offers a solution to both aspects. Hydrothermal liquefaction has been shown to be a low energy process for bio-crude production from microalgae. For the purpose of this research, microalgae strains of Chlorella vulgaris , Scenedesmus dimorphus and the cyanobacteria Spirulina platensis and Chlorogloeopsis fritschii were processed in batch reactors at 300 °C and 350 °C. Following liquefaction the product phases were separated and the water phase recovered. The bio-crude yields ranged from 27 to 47 wt.%. The bio-crudes were of low O and N content and high heating value making them suitable for further processing. The water phase was analysed for all major nutrients, TOC and TN to determine the suitability of the recycled aqueous phase for algae cultivation. Growth trials were performed for each algae strain in a standard growth medium and compared to the growth rates in a series of dilutions of the recycled process water phase. Growth was determined by cell count and chlorophyll a absorbance. Growth occurred in heavy dilutions where the amount of growth inhibitors was not too high. The results show that the closed loop system using the recovered aqueous phase offers a promising route for sustainable oil production and nutrient management for microalgae.

446 citations


"A comparison of product yields and ..." refers background or result in this paper

  • ...%) after HTL and SCWG whereas for the swine and chicken manure, there are still significant even at 350 C and 500 C....

    [...]

  • ...Similar gas yields were observed by Biller et al. (2012) for HTL of microalgae....

    [...]

  • ...This study investigates the fate of NPK in the process streams following thermal hydrolysis, HTC, HTL and SCWG of swine and chicken manure and compares this to digestate and microalgae....

    [...]

  • ...A number of reports have shown that there are sufficient nutrients in the process waters following HTL and SCWG (Biller et al., 2012; Cherad et al., 2013; Lopez Barreiro et al., 2015; Tsukahara et al., 2001; Jena et al., 2011) and hydrothermal carbonisation of algae (Du et al., 2012) to cultivate…...

    [...]

  • ...There is a growing interest in the recovery of nutrients from wet wastes such as manures and bio-solids and hydrothermal processing has been proposed to facilitate the extraction of nitrogen, phosphorus and potassium from these materials (Biller et al., 2012; Heilmann et al., 2014)....

    [...]

Journal ArticleDOI
TL;DR: The hydrochars showed mainly amorphous macro-size features with a carbon content of 59-79% (ash-free, dry) and a higher heating value of 25-36 MJ kg⁻¹ and are potentially interesting for applications such as an alternative fuel or a soil conditioner.

343 citations


"A comparison of product yields and ..." refers background in this paper

  • ...At higher processing temperatures, there is an increased breakdown of nitrogen leading to the formation of ammonium and other alkaline products (Mumme et al., 2011; Cherad et al., 2013)....

    [...]

  • ...Hydrothermal carbonisation (HTC) is operated at 180–250 C and pressure between 2 and 10 MPa, and produces a carbon-rich bio-coal (Mumme et al., 2011)....

    [...]

Journal ArticleDOI
Guo Yu1, Yuanhui Zhang1, Lance Schideman1, Ted L. Funk1, Zhichao Wang1 
TL;DR: In this paper, a fast growing, low-lipid, high-protein microalga species, Chlorella pyrenoidosa, was converted via hydrothermal liquefaction (HTL) into four products: bio-crude oil, aqueous product, gaseous product and solid residue.
Abstract: Microalgae are considered to be a promising alternative feedstock for next generation biofuels because of their rapid photosynthetic growth rates and less impact on land-use for food production compared with grain and other lignocellulosic biomass. In this study, a fast-growing, low-lipid, high-protein microalga species, Chlorella pyrenoidosa, was converted via hydrothermal liquefaction (HTL) into four products: bio-crude oil, aqueous product, gaseous product, and solid residue. The effects of operating conditions (reaction temperature and retention time) on the distributions of carbon and nitrogen in HTL products were quantified. Carbon recovery (CR), nitrogen recovery (NR) and energy recovery in the bio-crude oil fraction generally increased with the increase of reaction temperature as well as the retention time. The highest energy recovery of bio-crude oil was 65.4%, obtained at 280 °C with 120 min retention time. Both carbon and nitrogen tended to preferentially accumulate in the HTL bio-crude oil products as temperature and retention time increased, but the opposite was true for the solid residual product. The NR values of HTL aqueous product also increased with reaction temperature and retention time. 65–70% of nitrogen and 35–40% of carbon in the original material were converted into water soluble compounds when reaction temperature was higher than 220 °C and retention time was longer than 10 min. The CR of gas was less than 10% and is primarily present in the form of carbon dioxide. This study also introduces a novel treatment process (Environment-Enhancing Energy) that integrates algal growth for wastewater treatment with HTL of algal biomass, which provides synergistic recycling of carbon dioxide from the HTL gaseous product and the nutrients from HTL aqueous product to support multiple stages of algae production.

307 citations


"A comparison of product yields and ..." refers background in this paper

  • ...Hydrothermal liquefaction of microalgae have indicated that a large proportion of the nitrogen and the phosphorus in the feedstock are found in the aqueous phase (Yu et al., 2011, 2014), and highlighted that the fate of P is closely linked to the metal composition of the feedstock....

    [...]

Journal ArticleDOI
TL;DR: The results indicate that the bio-crude yields from the liquefaction of microalgae were increased slightly with the use of heterogeneous catalysts but the higher heating value (HHV) and the level of de-oxygenation increased, by up to 10%.

266 citations

Journal ArticleDOI
TL;DR: The ACP stream from the TCL of Spirulina was characterized and evaluated its potential as a nutrient source for cultivation of microalgae and found to have high nitrogen, phosphorus, potassium, and secondary and micronutrients.

252 citations


"A comparison of product yields and ..." refers background in this paper

  • ...%) after HTL and SCWG whereas for the swine and chicken manure, there are still significant even at 350 C and 500 C....

    [...]

  • ...This study investigates the fate of NPK in the process streams following thermal hydrolysis, HTC, HTL and SCWG of swine and chicken manure and compares this to digestate and microalgae....

    [...]

  • ...…have shown that there are sufficient nutrients in the process waters following HTL and SCWG (Biller et al., 2012; Cherad et al., 2013; Lopez Barreiro et al., 2015; Tsukahara et al., 2001; Jena et al., 2011) and hydrothermal carbonisation of algae (Du et al., 2012) to cultivate fresh microalgae....

    [...]

  • ...Studies have shown that the bio-crude produced from HTL of microalgae have high heating values (Minowa et al., 1995; Biller and Ross, 2011; Jena et al., 2011)....

    [...]

  • ...After HTC at 250 C, it reduces to about 40–70% and reduced further under HTL and SCWG conditions....

    [...]

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