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7 th International Conference on Sustainable Solid Waste Management, Heraklion, June 28 th , 2019 Characterization of char produced by pyrolysis and activation of wastewater sludge Giulia Ravenni, Zsuzsa Srossy, Jesper Ahrenfeldt, Ulrik B.

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Characterization of char produced by pyrolysis and activation of wastewater sludge

Giulia Ravenni, Zsuzsa Sárossy, Jesper Ahrenfeldt, Ulrik B. Henriksen

7th International Conference on Sustainable Solid Waste Management, Heraklion, June 28th, 2019

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Adsorbents: a possible valorisation route?

Traditional disposal routes

  • Spreading on agricultural land
  • Incineration
  • Landfjll, discharge into water

bodies

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(Hadi P . et al. 2015)

Alternative valorisation routes are to be found! Sludge-derived adsorbents for wastewater contaminants:

  • Dyes: Methylene blue, Reactive Red, Acid Yellow
  • Metals: Copper, Iron, Lead
  • Phenolics: Methylphenol, Bisphenol-A, Bromophenol
  • Phosphorus and Phosphates

 recent review papers on the topic (Hadi P . at al., 2015 and Devi P ., 2017)

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Drying and pyrolysis of wastewater sludge

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https://aquagreen.dk/ Drying stage Pyrolysis Carbonized sludge  System currently operating at Odense wastewater treatment plan , VandcenterSyd (https://www.vandcenter.dk/viden/spildevand)

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Char composition

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Char thermogravimetric analysis

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N2 atmosphere: loss of carbon fraction (≈ 16 wt%) visible after about 45

  • minutes. Afterwards the mass reduction progressed, leaving a residual mass of

80.5 wt%. Air atmosphere: oxidation at 900˚C left a residual mass 75.5 wt%, meaning that part of the inorganics left the sample in the gas phase.

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Steam activation of sludge char

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Steam activation (60 minutes)

  • ≈ 10 g of char activated in thermo-gravimetric reactor
  • ≈ 1 kg/h steam fmow
  • Activation temperatures: 650 – 700 – 750 – 800 – 900˚C
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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Surface characterization – N2 adsorption 77 K

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Surface characterization – N2 adsorption 77 K

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

ICP-OES analysis of inorganic fraction

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  • Sludge-derived char had a relatively low content of heavy metals (Cr, Ni,

Cu, Cd, Zn, Pb)

  • Cd and Cu concentrations resulted above the thresholds indicated in the

Danish legislation relative to waste materials for agricultural purposes (Fødevareministeriet, 2018).

  • The concentration of Cd and other elements (S, Zn, Pb, Al) decreased with

increasing activation temperature

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Conclusions

  • The analyzed sewage sludge char is rich in ashes and contains only about 16%
  • f carbon
  • Physical activation with steam is only partially efgective in increasing the

surface area and porosity of the char

  • Activation temperatures above 750˚C result in signifjcant degradation of the

surface

  • With increasing activation temperature, some inorganic species (Zn, Pb, Al, Cd

and S) are vaporized and leave the solid sample

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… and future work

  • Adsorption experiments using dyes and…?
  • Use of chemical activation (e.g KOH addition) for further improvement of

surface area and porosity

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Thank you!

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The authors would like to acknowledge Danish Environmental T echnology Development and Demonstration Program (MUDP) for the fjnancial support

  • f the project “Circular resource utilization of residual sludge: Development
  • f unit to produce Activated Carbon from Biochar.”

Acknowledgements

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

References

  • Hadi, P

. et al. 2015. “A Critical Review on Preparation, Characterization and Utilization of Sludge-Derived Activated Carbons for Wastewater T reatment.” Chemical Engineering Journal 260: 895–906.

  • Devi, P

., Saroha A.K. 2017. “Utilization of Sludge Based Adsorbents for the Removal of Various Pollutants: A Review.” Science of the T

  • tal Environment

578: 16–33.

  • Fødevareministeriet 2018, Bekendtgørelse om anvendelse af afgald til

jordbrugsformål. https://www.retsinformation.dk/Forms/R0710.aspx? id=202047#id82759b62-4821-4e9a-93e9-935c1c076536 (accessed May 2, 2019).

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

Vand Center Syd WWTP - Odense

https:// www.vandcenter.dk/viden/spildevand

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28 June 2019 DTU Chemical Engineering, Technical University of Denmark

ICP-OES analysis of inorganic fraction

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