A Review on Sewage Sludge Valorization via Hydrothermal Carbonization and Applications for Circular Economy

Author(s):  
Dilvin Çebi ◽  
Melih Soner Celiktas ◽  
Hasan Sarptaş

Abstract In pursuit of establishing a circular economy, waste-to-energy approach is gaining increasing attention. In this manner valorization of sewage sludge constitutes a critical importance due to generation in high quantities, difficulties in disposal and associating environmental impacts. Hydrothermal carbonization (HTC) is a relatively recent, however acclaimed method for sewage sludge management and valorization due to process compliance with sludge characteristics. In this review, research studies are evaluated under the categorization of application fields of sludge derived HTC products such as solid fuel production, gas production, soil remediation, nutrient recovery, water treatment and energy storage. Research findings are compiled and a network mapping is employed for the visualization of the current situation and correlation in respective fields. The potential of HTC for sewage sludge valorization and future projections concerning available techniques are assessed within the context of circular economy.

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2890 ◽  
Author(s):  
Fabio Merzari ◽  
Jillian Goldfarb ◽  
Gianni Andreottola ◽  
Tanja Mimmo ◽  
Maurizio Volpe ◽  
...  

Conventional activated sludge systems, still widely used to treat wastewater, produce large amounts of solid waste that is commonly landfilled or incinerated. This study addresses the potential use of Hydrothermal Carbonization (HTC) to valorize sewage sludge residues examining the properties of hydrochars depending on HTC process conditions and sewage sludge withdrawal point. With increasing HTC severity (process residence time and temperature), solid yield, total Chemical Oxygen Demand (COD) and solid pH decrease while ash content increases. Hydrochars produced from primary (thickened) and secondary (digested and dewatered) sludge show peculiar distinct properties. Hydrochars produced from thickened sludge show good fuel properties in terms of Higher Heating Value (HHV) and reduced ash content. However, relatively high volatile matter and O:C and H:C ratios result in thermal reactivity significantly higher than typical coals. Both series of carbonized secondary sludges show neutral pH, low COD, enhanced phosphorous content and low heavy metals concentration: as a whole, they show properties compatible with their use as soil amendments.


2021 ◽  
Author(s):  
Shuai Guo ◽  
DanDan Xu ◽  
Xin Guo ◽  
Xingcan Li ◽  
Chenchen Zhao

Abstract The harmful effects of improper sewage sludge (SS) treatment on the environment inspire the search for more benign sludge processing techniques such as hydrothermal carbonization (HTC); the abundant organic matter in SS is used for energy recovery. Herein, response surface methodology (RSM) was used to optimize the HTC-based preparation of SS hydrochar and its gasification performance. Specifically, the hydrochar yield, higher heating value (HHV), and gasification activity index were selected as optimization goals, while carbonization temperature (160–260°C), residence time (30–150 min), and acetic acid concentration (0–1.5 M) were selected as factors influencing the HTC process and CO2-assisted gasification performance. Carbonization temperature was the dominant parameter determining hydrochar yield, HHV, and gasification activity. The hydrochar yield (82.69%) and calorific value (7820.99 kJ kg−1) were maximized under comparatively mild conditions (160°C, 30 min, and 0.07 M acetic acid), whereas the gasification activity index (0.288 s−1) was maximized under harsher conditions (211.34°C, 88.16 min, and 1.58 M acetic acid). The obtained results help to guide the HTC of SS intended for gasification, thus promoting the development of this promising waste-to-energy technology, and may facilitate the design and further optimization of thermochemical SS conversion.


2020 ◽  
Vol 12 (9) ◽  
pp. 3686 ◽  
Author(s):  
Ksymena Rosiek

Landfilling was the main method of sewage sludge disposal in Poland for decades. After Poland’s accession to the European Union (EU), many investments have been made into providing better access to tap water as well as to collect and treat municipal sewage. However, sewage sludge treatment has not been treated as an integral part of the implementation of wastewater management obligations. Stricter European Union regulations regarding the management of municipal sewage sludge (MSS) pose new challenges for Poland. The aim of this study was to analyze changes in the direction of the final management of municipal sewage sludge in Poland based on the analysis of strategic documents, regulations, literature, and available statistical data. The aim of the analysis was to search for directions to modify how sewage sludge is managed, given the approach promoted by the circular economy concept. The results prove that investments in wastewater treatment plants according to the EU sewage directive are not applied to the development of infrastructure that would enable the disposal of sewage sludge, which, for many years, has been stored (landfilling) or used directly in agriculture and ground reclamation. The introduction of stricter regulations in the area of sewage sludge usage and better wastewater treatment have increased the level of difficulties concerning sewage sludge management. Poland faces the challenge of defining sewage sludge management directions. The circular economy concept offers an approach that can be the basis for the creation of a new sewage sludge management strategy for Poland. The concept allows the combined goals of sewage sludge disposal and of energy and nutrients recovery to be achieved.


2021 ◽  
Vol 12 (1) ◽  
pp. 9-25
Author(s):  
Vesna Mislej ◽  
Viktor Grilc ◽  
Barbara Novosel ◽  
Ana Mladenovič ◽  
Vesna Zalar Serjun

The treated sewage sludge under consideration is a hygienized biodegradable waste in the form of pellets. It can be used as a fertilizer, but only for spreading on non-agricultural land. Regarding “waste to energy” philosophy, the specification of pellets as an alternative solid fuel according to EN 15359 resulted in “NCV4; Cl1; Hg3-4” class. The major problem regarding the final pellets utilization is the lack of facilities for energy and material recovery from this type of waste in Slovenia. According to the newest legislation regarding the waste management, a product status for residues generated in combustion and pyrolysis of pellets on a laboratory and semi-pilot scale was not achieved. The holistic approach to final pellets utilization was studied and regarding the full-scale level of self-sufficient sewage sludge management in Slovenia, some legislative provisions become significant obstacles.


RSC Advances ◽  
2016 ◽  
Vol 6 (104) ◽  
pp. 101827-101834 ◽  
Author(s):  
Ana Spataru ◽  
Rohan Jain ◽  
Jae Wook Chung ◽  
Gabriel Gerner ◽  
Rolf Krebs ◽  
...  

Hydrochar, produced by hydrothermal carbonization of sewage sludge, adsorbs orthophosphate to improve effluent quality, recover & reutilize phosphorous and positively impact sewage sludge management.


2021 ◽  
Author(s):  
Małgorzata Jadwiga Kacprzak

Abstract Introduction of the circular economy package as a result of the necessity to protect natural resources has also forced a new approach for effective wastewater and biowaste treatment and management. Wastewater treatment plants (WWTPs) have become crucial elements of regional bioeconomy - mainly through energy (waste to energy) and matter (nutrients-energy-water) recovery as an element of sustainable development of a smart city. In Poland in 2019 operated 3278 municipal wastewater treatment plants. To achieve specific effluent goals for BOD, nitrogen and phosphorus, different adaptations and modifications have been made. Modernization of technological lines of wastewater treatment has led to a significant improvement in the quality of treated sewage, at the largest WWTPs in Warsaw, Cracow or Gdansk. Eleven WWTPs produce approx. 34% of the total volume of approx. 337 GWh of electricity from biogas in Poland. The potential of producing electricity from biogas in WWTPs in Poland can be estimated at approx. 700–850 GWh per year. According to the data of the Statistics Poland in 2019 in Poland approx. 25% of sewage sludge was used directly in agriculture and for land reclamation. Simultaneously more than 100 WWTPs produce compost at high quality. However only few produce organic/organic-mineral fertilizers, mainly with addition of calcium.


Author(s):  
Malgorzata J. Kacprzak ◽  
Iwona Kupich

AbstractWastewater treatment plants (WWTPs) have become crucial elements of the regional bioeconomy—mainly through energy (waste to energy) and matter (nutrients–energy–water) recovery as an element of sustainable development of a smart city. In Poland, a decentralized system functioned with 3278 municipal wastewater treatment plants, and less than 80% of the population were connected to public urban wastewater treatment systems. The paper presents the technology selection and implementation of circular economy at WWTPs and the practical approach to challenge of energy-positive and environmentally friendly wastewater and sewage sludge sector. The modernization of technological lines of wastewater treatment has led to a significant improvement in the quality of treated sewage, at the largest WWTPs in Warsaw, Cracow, or Gdansk. Eleven WWTPs produce 34% of the total volume of approximately 337 GWh of electricity from biogas in Poland. The potential of producing electricity from biogas in WWTPs in Poland can be estimated at approximately 700–850 GWh per year. According to the data of the Statistics Poland in Poland, approximately 25% of sewage sludge was used directly in agriculture and for land reclamation. Simultaneously, more than 100 WWTPs produce compost at a high quality. However, only few produce organic/organic-mineral fertilizers, mainly with addition of calcium. Decentralization leads to different technologies used in wastewater treatment plants, and environmental, economic, and social conditions determine the direction of changes and introduction of a circular economy paradigm in the Polish wastewater sector. Graphic abstract


Processes ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 618
Author(s):  
Vicky Shettigondahalli Ekanthalu ◽  
Satyanarayana Narra ◽  
Jan Sprafke ◽  
Michael Nelles

The high moisture content present in sewage sludge hinders the use of sewage sludge in incineration or energy application. This limitation of moisture present in sewage sludge can be obviated by using the hydrothermal carbonization (HTC) process. In sewage sludge management, the HTC process requires less energy compared to other conventional thermo–chemical management processes. The HTC process produces energy-rich hydrochar products and simultaneously enables phosphorus recovery. This study investigates the influence of organic acids, inorganic acid, and alkali as additives on phosphorus transformation, yield, proximate analysis and the heating value of subsequently produced hydrochar. The analysis includes various process temperatures (200 °C, 220 °C, and 240 °C) in the presence of deionized water, acids (0.1 M and 0.25 M; H2SO4, HCOOH, CH3COOH), and alkali (0.1 M and 0.25 M; NaOH) solutions as feed water. The results show that phosphorus leaching into the process-water, hydrochar yield, proximate analysis, and the heating value of produced hydrochar is pH- and temperature-dependent, and particularly significant in the presence of H2SO4. In contrast, utilization of H2SO4 and NaOH as an additive has a negative influence on the heating value of produced hydrochar.


2011 ◽  
Vol 6 (4) ◽  
Author(s):  
C. Peregrina ◽  
J. M. Audic ◽  
P. Dauthuille

Assimilate sludge to a fuel is not new. Sludge incineration and Combined Heat and Power (CHP) engines powered with sludge-derived anaerobic digestion gas (ADG) are operations widely used. However, they have a room of improvement to reach simultaneously a positive net power generation and a significant level of waste reduction and stabilization. Gasification has been used in other realms for the conversion of any negative-value carbon-based materials, that would otherwise be disposed as waste, to a gaseous product with a usable heating value for power generation . In fact, the produced gas, the so-called synthetic gas (or syngas), could be suitable for combined heat and power motors. Within this framework gasification could be seen as an optimum alternative for the sludge management that would allow the highest waste reduction yield (similar to incineration) with a high power generation. Although gasification remains a promising route for sewage sludge valorisation, campaigns of measurements show that is not a simple operation and there are still several technical issues to resolve before that gasification was considered to be fully applied in the sludge management. Fluidised bed was chosen by certain technology developers because it is an easy and well known process for solid combustion, and very suitable for non-conventional fuels. However, our tests showed a poor reliable process for gasification of sludge giving a low quality gas production with a significant amount of tars to be treated. The cleaning system that was proposed shows a very limited removal performance and difficulties to be operated. Within the sizes of more common WWTP, an alternative solution to the fluidised bed reactor would be the downdraft bed gasifier that was also audited. Most relevant data of this audit suggest that the technology is more adapted to the idea of sludge gasification presented in the beginning of this paper where a maximum waste reduction is achieved with a great electricity generation thanks to the use of a “good” quality syngas in a CHP engine. Audit show also that there is still some work to do in order to push sludge gasification to a more industrial stage. Regardless what solution would be preferred, the resulting gasification system would involve a more complex scenario compared to Anaerobic Digestion and Incineration, characterised by a thermal dryer and gasifier with a complete gas cleaning system. At the end, economics, reliability and mass and energy yields should be carefully analysed in order to set the place that gasification would play in the forthcoming processing of sewage sludge.


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