Abstract
Sludge is a serious problem due to the risks to environment. Therefore, an energy-efficient, economic-feasible and environmental sustainable measure for sludge management is urgently required, while hydrothermal carbonization (HTC) has been regarded as one promising method. In this study hydrothermal carbonization was utilized to convert organic sludge (OS) into solid carbonaceous product (hydrochar) under various reaction temperature (T = 180–240 °C) and residence time (t = 60–240 min), respectively. The reaction pressure ranged from 2.7 to 4.8MPa, depending on the reaction conditions. The obtained hydrochar was analyzed by elemental analysis, proximate analysis, SEM, FTIR, and BET, to investigate the effect of reaction parameters on the hydrochar properties, followed by discussions on potential applications of the obtained hydrochar. Obvious reduction of H/C and O/C ratio after HTC was observed, based on the Van Krevelen diagram and FTIR analysis, revealing that the dehydration and decarboxylation occurred during the HTC process. The reaction temperature was regarded as the dominant parameter affecting hydrochar characteristic, compared to residence time. The severity factor (log Ro) at the range from 4.13 to 5.90 showed good linear relationship with the ash content, volatile matter (VM), N content and H/C ratio of hydrochar, indicating that the severity factor could serve as a useful indicator for analyzing the hydrochar property. Although the surface area and porosity were improved by HTC, subsequent modification and activation should be needed to broaden the application field. Owing to the characteristic of high ash content, hydrochar derived from organic sludge might not be feasible for fuel use. Instead, the precursor of the activated carbon and low-cost adsorbent might be the potential applications, while further works should be needed to verify the feasibility.
Highlights
As the environmental concerns and concepts of sustainable development increase, sludge management has gradually become an important issue discussed worldwide currently
The main purpose of this work are: (1) to explore the physical and chemical properties of hydrochar derived from organic sludge; (2) to investigate the effect of reaction temperature and residence time on hydrochar properties; (3) to evaluate the potential applications of sludge-derived hydrochar based on the obtained results
In summary, compared to the residence time, the reaction temperature was regarded as the dominant parameter affecting sludge-derived hydrochar characteristic
Summary
As the environmental concerns and concepts of sustainable development increase, sludge management has gradually become an important issue discussed worldwide currently. High moisture content, poor dewaterability, fouling odor problems, and presence of pathogens, appropriate sludge management and utilization are needed to reduce cost and handling difficulty and to avoid harmful effect on the environment and human being. The processes for sludge management typically include preliminary treatment, stabilization, conditioning, dewatering, followed by final treatments such as storage, landfilling, and agriculture use (Zhang et al 2017). Landfilling, land application, and incineration are mainly used as a final treatment for sludge manage-. Thermal processes included pyrolysis, gasification, and combustion are regarded as alternative methods for sludge management recently due to the advantage of volume reduction and increasing dewaterability of treated sludge during the process. The pre-drying step is necessary for the processes mentioned above because of the restriction on feedstock moisture, which makes them become less energy efficient due to the intensive energy requirement of the pre-drying step
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