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Sewage sludge-based activated carbon – Production and potential in wastewater and stormwater treatment

Betsholtz, Alexander LU ; Jacobsson, Stina; Haghighatafshar, Salar LU and Jönsson, Karin LU (2019)
Abstract
Summary
Sustainable sewage sludge management has been a heavily debated topic in Europe for more than a decade. Due to its content of pollutants such as heavy metals, pharmaceuticals and other organic micropollutants, the use of sewage sludge for farmland application is currently banned or restricted in most European countries. Therefore, alternative methods for sludge management are discussed. The production of sludge-based activated carbon (SBAC) from digested sewage sludge is an alternative that would make use of problematic waste—sewage sludge—to produce a potentially valuable adsorbent. In this study, SBAC has been reviewed based on its potential use as an adsorbent for pollutants in wastewater and stormwater. The study consists... (More)
Summary
Sustainable sewage sludge management has been a heavily debated topic in Europe for more than a decade. Due to its content of pollutants such as heavy metals, pharmaceuticals and other organic micropollutants, the use of sewage sludge for farmland application is currently banned or restricted in most European countries. Therefore, alternative methods for sludge management are discussed. The production of sludge-based activated carbon (SBAC) from digested sewage sludge is an alternative that would make use of problematic waste—sewage sludge—to produce a potentially valuable adsorbent. In this study, SBAC has been reviewed based on its potential use as an adsorbent for pollutants in wastewater and stormwater. The study consists of a literature review targeting (i) different methods for SBAC production, (ii) the influence of the production methods on the physical and chemical properties of the activated carbons and (iii) the importance of physical and chemical carbon properties on the adsorption of various types of pollutants in aquatic solutions. In connection to the literature study, SBAC was produced in the laboratory using a one-step steam activation method in order to study how various production parameters, such as pyrolysis temperature and steam oxidation, affect the porosity development of SBAC. The porosity of the carbon was assessed using N2adsorption and desorption isotherms at 77 K. Several combinations of the decisive parameters at various levels were tested and consequently the steam activated SBAC with highest volume of micropores (and highest specific surface area) was selected and tested for the adsorption of chemical oxygen demand (COD) and inorganic nutrients (NH4+, NO3-and PO43-) in wastewater from Källby WWTP in Lund, Sweden. As a reference, the SBAC was compared with a commercial activated carbon (CAC), Norit Sae Super (from Cabot), with a BET surface area of 975 m2/g. The results from existing literature show that SBAC, due to their high inorganic content, in general exhibit low micropore volumes compared to CAC, and therefore also tend to have a lower adsorption potential for small organic substances. However, the larger pores of the SBAC might be advantageous for adsorption of large organic pollutants such as dyes. In addition, the inorganic content of SBAC may contribute to the adsorption of charged and/or hydrophilic substances that are adsorbed through chemical interactions with surface functional groups of the carbon, rather than by physical adsorption to the core carbon structure. With respect to SBAC production, both feedstock type (e.g. biological sludge vs. chemical sludge) and production method (chemical vs. physical activation) have large influence on the properties of the carbon. In general, chemical activation using strong acids or based tend to generate SBAC with higher micropore volumes and abundance of surface functional groups compared to physical activation methods (such as steam activation), although its applicability can be questioned due to the large required input of chemicals. The result from the laboratory studies show that steam activated SBAC with BET surface areas of up to 162 m2/g could be generated using one-step steam activation at 800 °C for 30 minutes, although activation parameters were not optimized with respect to maximum surface area generation. The adsorption experiments showed that CAC was much better at adsorbing COD in effluent wastewater compared to the steam activated SBAC produced in lab, especially at low carbon concentrations. The experiments further showed that neither CAC nor SBAC was successful in adsorbing large quantities of inorganic nutrients (NH4+, NO3-and PO43-), probably due to lack of charged surface functional groups. Much work remains in order to demonstrate large scale production of SBAC in order to evaluate the economic feasibility of the process. In connection, more work is needed to understand how to maximize the potential of SBAC for the uptake of specific substances such as heavy metals or hydrophilic micropollutants.
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60 pages
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VA-teknik Södra
language
English
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yes
id
4232d2af-dd0f-4eda-a9c4-9b80d046cb28
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https://va-tekniksodra.se/wp-content/uploads/2019/02/Sewage-sludge-based-activated-carbon.-VA-teknik-S%C3%B6dra-rapport-12-2018-.pdf
date added to LUP
2019-04-16 14:13:14
date last changed
2019-04-24 02:18:16
@techreport{4232d2af-dd0f-4eda-a9c4-9b80d046cb28,
  abstract     = {Summary<br/>Sustainable sewage sludge management has been a heavily debated topic in Europe for more than a decade. Due to its content of pollutants such as heavy metals, pharmaceuticals and other organic micropollutants, the use of sewage sludge for farmland application is currently banned or restricted in most European countries. Therefore, alternative methods for sludge management are discussed. The production of sludge-based activated carbon (SBAC) from digested sewage sludge is an alternative that would make use of problematic waste—sewage sludge—to produce a potentially valuable adsorbent. In this study, SBAC has been reviewed based on its potential use as an adsorbent for pollutants in wastewater and stormwater. The study consists of a literature review targeting (i) different methods for SBAC production, (ii) the influence of the production methods on the physical and chemical properties of the activated carbons and (iii) the importance of physical and chemical carbon properties on the adsorption of various types of pollutants in aquatic solutions. In connection to the literature study, SBAC was produced in the laboratory using a one-step steam activation method in order to study how various production parameters, such as pyrolysis temperature and steam oxidation, affect the porosity development of SBAC. The porosity of the carbon was assessed using N2adsorption and desorption isotherms at 77 K. Several combinations of the decisive parameters at various levels were tested and consequently the steam activated SBAC with highest volume of micropores (and highest specific surface area) was selected and tested for the adsorption of chemical oxygen demand (COD) and inorganic nutrients (NH4+, NO3-and PO43-) in wastewater from Källby WWTP in Lund, Sweden. As a reference, the SBAC was compared with a commercial activated carbon (CAC), Norit Sae Super (from Cabot), with a BET surface area of 975 m2/g. The results from existing literature show that SBAC, due to their high inorganic content, in general exhibit low micropore volumes compared to CAC, and therefore also tend to have a lower adsorption potential for small organic substances. However, the larger pores of the SBAC might be advantageous for adsorption of large organic pollutants such as dyes. In addition, the inorganic content of SBAC may contribute to the adsorption of charged and/or hydrophilic substances that are adsorbed through chemical interactions with surface functional groups of the carbon, rather than by physical adsorption to the core carbon structure. With respect to SBAC production, both feedstock type (e.g. biological sludge vs. chemical sludge) and production method (chemical vs. physical activation) have large influence on the properties of the carbon. In general, chemical activation using strong acids or based tend to generate SBAC with higher micropore volumes and abundance of surface functional groups compared to physical activation methods (such as steam activation), although its applicability can be questioned due to the large required input of chemicals. The result from the laboratory studies show that steam activated SBAC with BET surface areas of up to 162 m2/g could be generated using one-step steam activation at 800 °C for 30 minutes, although activation parameters were not optimized with respect to maximum surface area generation. The adsorption experiments showed that CAC was much better at adsorbing COD in effluent wastewater compared to the steam activated SBAC produced in lab, especially at low carbon concentrations. The experiments further showed that neither CAC nor SBAC was successful in adsorbing large quantities of inorganic nutrients (NH4+, NO3-and PO43-), probably due to lack of charged surface functional groups. Much work remains in order to demonstrate large scale production of SBAC in order to evaluate the economic feasibility of the process. In connection, more work is needed to understand how to maximize the potential of SBAC for the uptake of specific substances such as heavy metals or hydrophilic micropollutants.<br/>},
  author       = {Betsholtz, Alexander and Jacobsson, Stina and Haghighatafshar, Salar and Jönsson, Karin},
  institution  = {VA-teknik Södra},
  language     = {eng},
  pages        = {60},
  title        = {Sewage sludge-based activated carbon – Production and potential in wastewater and stormwater treatment},
  year         = {2019},
}