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Feng ZT, Xiong JB, Wang GF, Li L, Zhou CF, Zhou CH, Huang HJ. Treatment of swine manure by hydrothermal carbonization: The influential effect and preliminary mechanism of surfactants. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 946:174233. [PMID: 38936726 DOI: 10.1016/j.scitotenv.2024.174233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2024] [Revised: 06/19/2024] [Accepted: 06/21/2024] [Indexed: 06/29/2024]
Abstract
Treatment of swine manure by hydrothermal carbonization (HTC) with the aid of different surfactants was first explored in this study. PEG 400 (polyethylene glycol 400) and Tween 80 facilitated the formation of bio-oil. SLS (sodium lignosulfonate) and SDS (sodium dodecyl sulfate) promoted the formation of water-soluble matters/gases. Span 80 enhanced the formation of hydrochar, which resulted in a 50.19 % mass yield, 92.39 % energy yield, and a caloric value of 28.68 MJ/kg. The hydrochar obtained with Span 80 presented a similar combustion performance to raw swine manure and the best pyrolysis performance. The use of Span 80 promoted the transfer of degradation products to hydrochar, especially hydrophobic ester and ketone compounds. Notedly, Span 80 suppressed the synthesis of PAHs during the HTC process, which was reduced to 0.92 mg/kg. Furthermore, the hydrochar produced with Span 80 contained lower contents of heavy metals. On the whole, Span 80 has shown great potential in enhancing the HTC of swine manure. The acting mechanisms of surfactants in the HTC of swine manure included adsorption, dispersion, and electrostatics repulsion.
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Affiliation(s)
- Zhen-Tian Feng
- School of Land Resources and Environment, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Jiang-Bo Xiong
- School of Land Resources and Environment, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Guo-Feng Wang
- Jiangxi Academy of Ecological and Environmental Sciences, Jiangxi Key Laboratory of Environmental Pollution Control, Nanchang 330006, PR China
| | - Lin Li
- School of Land Resources and Environment, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Chun-Fei Zhou
- School of Land Resources and Environment, Jiangxi Agricultural University, Nanchang 330045, PR China; School of Forestry, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Chun-Huo Zhou
- School of Land Resources and Environment, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Hua-Jun Huang
- School of Land Resources and Environment, Jiangxi Agricultural University, Nanchang 330045, PR China.
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2
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Zhang R, Zhang Y, Goei R, Oh WD, Zhang Z, He C. Sustainable utilization of Sedum plumbizincicola as superior hydrochar for efficient nutrients recovery. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2023; 344:118441. [PMID: 37379626 DOI: 10.1016/j.jenvman.2023.118441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2023] [Revised: 05/29/2023] [Accepted: 06/15/2023] [Indexed: 06/30/2023]
Abstract
To realize sound disposal of hyperaccumulator harvested from phytoremediation, hydrothermal carbonization (HTC) has been employed to obtain superior hydrochar adsorbents for removal of phosphate and ammonium from water body. A series of hydrochars have been prepared under tuned HTC conditions to tailor hydrochar with desired properties. Generally, increased temperature and prolonged reaction time facilitated acidic oxygen functional groups on hydrochars, thereby improving adsorption capacity of hydrochar. In single solute system, a superior hydrochar, derived from HTC under 260 °C for 2 h, achieved a maximum phosphate and ammonium adsorption capacity of 52.46 mg/g and 27.56 mg/g at 45 °C, respectively. In binary system, synergistic adsorption was observed only in lower solute concentration, whereas competitive adsorption occurred under higher solute concentration. Characterization and adsorption kinetics suggested chemisorption may dominate the adsorption process, thus the adsorption capacity could be improved by tuning pHpzc of hydrochar. This study firstly demonstrates the sustainable utilization of hyperaccumulators into nutrients-enriched hydrochar as fertilizer for in-situ phytoremediation of contaminated sites with minimized environmental risks towards circular economy.
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Affiliation(s)
- Ruichi Zhang
- Faculty of Engineering and Natural Sciences, Tampere University, Korkeakoulunkatu 8, 33720, Tampere, Finland
| | - Yizhong Zhang
- Seawater Hydrogen Energy and Water Treatment Laboratory, Department of Environmental Technology, The Institute of Seawater Desalination and Multipurpose Utilization, Ministry of Natural Resources (MNR), Tianjin, 300192, China
| | - Ronn Goei
- School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Wen-Da Oh
- School of Chemical Sciences, Universiti Sains Malaysia, 11800, Penang, Malaysia
| | - Zhao Zhang
- Administration Committee of Yancheng Economic and Technological Development Zone, Yancheng, 224000, China
| | - Chao He
- Faculty of Engineering and Natural Sciences, Tampere University, Korkeakoulunkatu 8, 33720, Tampere, Finland.
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Ipiales RP, Mohedano AF, Diaz-Portuondo E, Diaz E, de la Rubia MA. Co-hydrothermal carbonization of swine manure and lignocellulosic waste: A new strategy for the integral valorization of biomass wastes. WASTE MANAGEMENT (NEW YORK, N.Y.) 2023; 169:267-275. [PMID: 37481937 DOI: 10.1016/j.wasman.2023.07.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Revised: 07/11/2023] [Accepted: 07/12/2023] [Indexed: 07/25/2023]
Abstract
Co-hydrothermal carbonization (co-HTC) is a promising strategy to improve hydrothermal carbonization (HTC) of low-quality wastes. HTC of swine manure (SM), with high N (2.9 wt%), S (0.7 wt%) and ash (22.6 wt%) contents, as well as low C (35.6 wt%) and higher heating value (HHV; 14.3 MJ kg-1), resulted in a hydrochar with unsuitable characteristics as a solid fuel. Co-HTC of SM and garden and park waste (GPW) improved hydrochar properties (C content (43 - 48 wt%) and HHV (18 - 20 MJ kg-1), and decreased N (∼2 wt%), S (<0.3 wt%) and ash (<15 wt%) content. A high GPW ratio (>50 wt%) during co-HTC resulted in a hydrochar similar to that obtained from GPW. The co-HTC increased nutrient migration to the process water, which allowed the precipitation of salt with high P (7.8 wt%) and negligible heavy metal content. Anaerobic digestion of co-HTC process water allowed high organic matter removal (up to 65%), and methane production (315 - 325 mL CH4 g-1CODadded). Gross energy recovery by HTC and anaerobic digestion was 5 - 6-fold higher than anaerobic treatment of feedstocks. Therefore, co-HTC of SM and GPW with a ratio > 50% GPW proved to be a suitable approach to valorize and manage SM and obtain value-added products (hydrochar, mineral fertilizer and methane).
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Affiliation(s)
- R P Ipiales
- Chemical Engineering Department, Universidad Autónoma de Madrid, 28049 Madrid, Spain; Arquimea-Agrotech, 28400 Collado Villalba, Madrid, Spain
| | - A F Mohedano
- Chemical Engineering Department, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
| | | | - E Diaz
- Chemical Engineering Department, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - M A de la Rubia
- Chemical Engineering Department, Universidad Autónoma de Madrid, 28049 Madrid, Spain
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Luo X, Zhao B, Peng M, Shen R, Mao L, Zhang W. Effects of Inorganic Passivators on Gas Production and Heavy Metal Passivation Performance during Anaerobic Digestion of Pig Manure and Corn Straw. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:14094. [PMID: 36360969 PMCID: PMC9654526 DOI: 10.3390/ijerph192114094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 10/25/2022] [Accepted: 10/26/2022] [Indexed: 06/16/2023]
Abstract
The treatment of livestock manure caused by the expansion of the breeding industry in China has attracted wide attention. Heavy metals in pig manure can pollute soil and water and even transfer to crops, posing harm to humans through the food chain. In this study, corn straw was selected as the additive and introduced into the anaerobic digestion. Sepiolite (SE), ferric oxide (Fe2O3), attapulgite (AT) and ferric sulfate (FeSO4) were used as passivators to compare the effects of these inorganic passivators on gas production and passivation of heavy metals during the process of the anaerobic digestion. When the dry mass ratio of pig manure to straw is 8:2, the gas production efficiency is optimal. SE, AT and ferric sulfate have a much stronger ability to improve gas production performance than Fe2O3. The total gas production increased by 10.34%, 6.62% and 4.56%, and the average methane production concentration increased by 0.7%, 0.3% and 0.4%, respectively. The influence of SE, AT and ferric sulfate on the passivation of heavy metals is much better than Fe2O3, and the fractions in biological effective forms of Cu and Zn reduced by 41.87 and 19.32%, respectively. The anaerobic digestion of mixed materials is conducive to the gas production and the passivation of heavy metals. Therefore, SE, AT and ferric sulfate are selected as composite passivators, and the optimal ratio of inorganic composite passivators i: AT 7.5 g/L, ferric sulfate 5 g/L and SE 7.5 g/L, according to the results of orthogonal experiments. This study can provide a theoretical basis for the safe application of biogas fertilizers.
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Karatas O, Khataee A, Kalderis D. Recent progress on the phytotoxic effects of hydrochars and toxicity reduction approaches. CHEMOSPHERE 2022; 298:134357. [PMID: 35313162 DOI: 10.1016/j.chemosphere.2022.134357] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Revised: 03/15/2022] [Accepted: 03/16/2022] [Indexed: 06/14/2023]
Abstract
Hydrothermal carbonization of wet biomasses has been known to produce added-value materials for a wide range of applications. From catalyst substrates, to biofuels and soil amendments, hydrochars have distinct advantages to offer compared to conventional materials. With respect to the agricultural application of hydrochars, both positive and negative results have been reported. The presence of N, P and K in certain hydrochars is appealing and may contribute to the reduction of chemical fertilizer application. However, regardless of biomass, hydrothermal carbonization results in the production of phytotoxic organic compounds. Additionally, hydrochars from sewage sludge often contain heavy metal concentrations which exceed the regulatory limits set for agricultural use. This review critically discusses the phytotoxic aspects of hydrochar and provides an account of the substances commonly responsible for these. Furthermore, phytotoxicity reduction approaches are proposed and compared with each other, in view of field-scale applications.
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Affiliation(s)
- Okan Karatas
- Department of Environmental Engineering, Gebze Technical University, Gebze, 41400, Turkey; Department of Environmental Engineering, Bursa Technical University, Bursa, 16310, Turkey
| | - Alireza Khataee
- Department of Environmental Engineering, Gebze Technical University, Gebze, 41400, Turkey; Research Laboratory of Advanced Water and Wastewater Treatment Processes, Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, 51666-16471, Iran
| | - Dimitrios Kalderis
- Department of Electronics Engineering, Hellenic Mediterranean University, Chania, Crete, 73100, Greece.
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Wang YJ, Yu Y, Huang HJ, Yu CL, Fang HS, Zhou CH, Yin X, Chen WH, Guo XC. Efficient conversion of sewage sludge into hydrochar by microwave-assisted hydrothermal carbonization. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 803:149874. [PMID: 34492491 DOI: 10.1016/j.scitotenv.2021.149874] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 08/12/2021] [Accepted: 08/20/2021] [Indexed: 06/13/2023]
Abstract
The treatment of sewage sludge (SS) is an environmental problem worldwide. In recent years, hydrothermal carbonization (HTC) of SS for hydrochar (HC) has attracted extensive attention. This study preliminarily explored the microwave-assisted HTC of SS for the first time. Increasing the reaction temperature (150-250 °C) and reaction time (0-120 min) resulted in a decrease in the HC yield, and it gradually increased with the rising solid-liquid ratio (0.03-0.25 g/mL). Compared with raw SS, the HC products possessed higher aromaticity, carbonization degree, porosity, and polarity, and lower content of soluble nutrients (N/P/K) and leachable heavy metals (Cu, Zn, Pb, Cd, Cr, and Ni), indicating a lower risk of nutrient and heavy metal loss. Attention should be paid to the total contents of Zn and Cd in HC exceeded the permitted value for use in cultivated land with edible crops. The use of CaO as a catalyst improved the yield of HC, made the HC and process water (PW) weakly alkaline, and further passivated the heavy metals in the HC. In the case of H3PO4, although the conversion of SS was enhanced (lower content of volatile organic matter in HC), the contents of soluble nutrients (N/P/K) in HC/PW increased, and the migration of Zn and Cd into process water was enhanced. The HCs obtained in this study had poor combustion properties, but higher ignition temperatures than raw SS. PW must be properly treated or recycled because it still contained high contents of organic matter and nutrients. This fundamental study provides basic insights into the microwave-assisted HTC of SS.
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Affiliation(s)
- Yu-Jie Wang
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Yi Yu
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Hua-Jun Huang
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China.
| | - Cheng-Long Yu
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Han-Sun Fang
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Chun-Huo Zhou
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Xin Yin
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Wei-Hua Chen
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China
| | - Xin-Chun Guo
- School of Land Resources and Environment, Key Laboratory of Agricultural Resource and Ecology in the Poyang Lake Basin of Jiangxi Province, Jiangxi Agricultural University, Nanchang 330045, PR China.
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Speciation of Main Nutrients (N/P/K) in Hydrochars Produced from the Hydrothermal Carbonization of Swine Manure under Different Reaction Temperatures. MATERIALS 2021; 14:ma14154114. [PMID: 34361308 PMCID: PMC8347720 DOI: 10.3390/ma14154114] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/24/2021] [Revised: 07/18/2021] [Accepted: 07/20/2021] [Indexed: 11/17/2022]
Abstract
Hydrothermal carbonization (HTC) has been proved to be a promising technology for swine manure (SM) treatment. Currently, there is a lack of systematic understanding of the transformation characteristics of nutrient speciation in the HTC of SM. In this study, the speciation of the main nutrients (N/P/K) in SM-derived hydrochar produced at different reaction temperatures (200-280 °C) was investigated. The recovery of P (61.0-67.1%) in hydrochars was significantly higher than that of N (23.0-39.8%) and K (25.5-30.0%), and the increase in reaction temperature promoted the recovery of P and reduced the recovery of N. After the HTC treatment, the percentage of soluble/available P was reduced from 61.6% in raw SM to 4.0-23.9% in hydrochars, while that of moderately labile/slow-release P was improved from 29.2% in raw SM feedstock to 65.5-82.7%. An obvious reduction was also found in the amounts of available N (from 51.3% in raw SM feedstock to 33.0-40.5% in hydrochars). The percentages of slow-release N and residual N in hydrochars produced at 240 °C reached the maximum and minimum values (46.4% and 18.9%), respectively. A total of 49.5-58.3% of K retained in hydrochars was residual (invalid) potassium. From the perspective of the mobility and availability of N, P and K only, it was suggested that the HTC of SM should be carried out at 220-240 °C. Compared with the original SM, it is safer and more effective to use the SM-derived hydrochar as an organic fertilizer.
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Khoshnevisan B, Duan N, Tsapekos P, Awasthi MK, Liu Z, Mohammadi A, Angelidaki I, Tsang DCW, Zhang Z, Pan J, Ma L, Aghbashlo M, Tabatabaei M, Liu H. A critical review on livestock manure biorefinery technologies: Sustainability, challenges, and future perspectives. RENEWABLE AND SUSTAINABLE ENERGY REVIEWS 2021; 135:110033. [DOI: 10.1016/j.rser.2020.110033] [Citation(s) in RCA: 76] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/20/2023]
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Tian X, Chai G, Wang J, Zhao X. Spatial Distribution of As and Cd in Co-contaminated Soils Within the Rice Root Microzone. BULLETIN OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 2021; 106:115-120. [PMID: 33392692 DOI: 10.1007/s00128-020-03066-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2020] [Accepted: 11/24/2020] [Indexed: 06/12/2023]
Abstract
Soil samples were collected from the As and Cd co-contaminated demonstration area to analyze the spatial distributions of As and Cd in soils within the rice root microzone using the treatment of soil cubes (50 mm × 50 mm × 50 mm). The results indicated that there was no significant difference in the spatial distributions of total As or Cd in the microzone with the percentage of root weight, horizontal distances (HD), and vertical depths (VD). Interestingly, available As or Cd increased with the increasing HD, and both of them showed a significant difference (p < 0.05) between < 75 mm and ≥ 120 mm. The availability of As or Cd increased from the center to the edge of the rice root microzone. Moreover, the risk assessment code (RAC) showed that the site with a high potential risk of As or Cd was located on the edge of the rice root microzone. This phenomenon implied that cultivating paddy rice in the low potential risk microzone might have a low accumulative risk.
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Affiliation(s)
- Xiaosong Tian
- College of Resources and Environment, Southwest University, Chongqing, 400715, China.
- Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing, 400716, China.
| | - Guanqun Chai
- Institute of Soil and Fertilizer, Guizhou Academy of Agricultural Sciences, Guiyang, 550006, China
| | | | - Xiulan Zhao
- College of Resources and Environment, Southwest University, Chongqing, 400715, China
- Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing, 400716, China
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Wang JX, Chen SW, Lai FY, Liu SY, Xiong JB, Zhou CF, Yi-Yu, Huang HJ. Microwave-assisted hydrothermal carbonization of pig feces for the production of hydrochar. J Supercrit Fluids 2020. [DOI: 10.1016/j.supflu.2020.104858] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Zhou J, Chen LH, Peng L, Luo S, Zeng QR. Phytoremediation of heavy metals under an oil crop rotation and treatment of biochar from contaminated biomass for safe use. CHEMOSPHERE 2020; 247:125856. [PMID: 31951954 DOI: 10.1016/j.chemosphere.2020.125856] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 12/26/2019] [Accepted: 01/04/2020] [Indexed: 06/10/2023]
Abstract
The disposal of contaminated plants limits the use of phytoremediation. Therefore, the disposal of contaminated sunflower was investigated after determining the phytoremediation of heavy metals under an oil crop rotation of sunflower (Helianthus annuus L)-sesame (Sesamum indicum L.). In the field experiment, the extraction efficiency of sunflower-sesame rotation was 0.07% for lead (Pb); 1.37% for zinc (Zn); 1.10% for copper (Cu); and 6.12% for cadmium (Cd). Contaminated sunflower stems were pyrolyzed at different temperature. The biochar produced at 300 °C was extracted in a two-step process (acid-extraction from biochar and metals precipitation in alkaline condition). At pH = 1, 65.67% of the Cd and much potassium (K) were extracted. After acid-extraction, adjust the pH of filtrate to 10, metals were precipitated and then separated from the K-enriched solution. Therefore, pyrolysis can process contaminated residues, and the biochar extracts can be reutilized as fertilizer to off-site crop production. Thus, an oil crop-rotation system, in addition to creating economic benefits, can be used by local farmers in contaminated soils.
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Affiliation(s)
- J Zhou
- College of Resources and Environment, Hunan Agricultural University, Changsha, 410128, Hunan, China
| | - L H Chen
- College of Resources and Environment, Hunan Agricultural University, Changsha, 410128, Hunan, China
| | - L Peng
- College of Resources and Environment, Hunan Agricultural University, Changsha, 410128, Hunan, China
| | - S Luo
- College of Resources and Environment, Hunan Agricultural University, Changsha, 410128, Hunan, China
| | - Q R Zeng
- College of Resources and Environment, Hunan Agricultural University, Changsha, 410128, Hunan, China.
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Abstract
There is a significant interest in valorizing swine manure that is produced in enormous quantities. Therefore, considering the high moisture content in swine manure, the objective of this research was to convert manure slurry into hydrochars via hydrothermal carbonization and analyze the yields, pH, energy contents, and thermal and oxidation kinetic parameters. Experiments were performed in triplicate in 250 mL kettle reactors lined with polypropylene at 180 °C, 200 °C, 240 °C, 220 °C, and 260 °C for 24 h. Analyses of the results indicated that the process temperature affected the hydrochar yields, with yield generally decreasing with increasing temperature, but it had little effect on the composition of the hydrochar. The hydrochars were found to have higher volatile contents and H/C and O/C ratios and about 85% of the energy compared to coal. However, the presence of high fraction (35–38%) of ash in hydrochars is a serious concern and needs to be addressed before the complete utilization of hydrochars as fuels. The surface characterization of hydrochars coupled with wet chemistry experiments indicated that hydrochars were equipped with nitrogen functional groups with points of zero charges between 6.76 and 7.85, making them suitable as adsorbents and soil remediation agents and energy storage devices.
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