Role of waste-based geopolymer spheres addition for pH control and efficiency enhancement of anaerobic digestion process


In anaerobic digestion processes, pH has a vital role due to the direct impacts on the microbial community. An eco-friendly approach has been applied to control pH in anaerobic bioreactors, using waste-containing fly ash geopolymer spheres (GS) instead of powdered chemical compounds, to promote continuous alkalis leaching. The influence of GS porosity and concentration on the behavior of anaerobic sequential batch reactor treating cheese whey was evaluated. Results showed that the use of GS with the highest concentration and porosity promoted an increase in methane yield up to 30%, compared to the assay with powdered chemical compounds addition. In addition, GS boosted butyric acid production to the detriment of propionic acid, which favored methane production by a factor up to 1.2. This innovative approach indicates that GS addition can regulate pH in anaerobic digesters treating challenging wastewaters and, simultaneously, improve not only its efficiency but also the sustainability of the entire process.

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Anaerobic digestion


Anaerobic sequential batch reactor


Chemical oxygen demand

CH4 :



Geopolymer spheres


High porosity geopolymers spheres


Low porosity geopolymers spheres


Volatile fatty acids


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R. M. Novais and J. Carvalheiras wish to thank Fundação para a Ciência e a Tecnologia (FCT) for supporting their work (Ref. CEECIND/00335/2017 and SFRH/BD/144562/2019). This work was developed within the scope of the project CESAM—Centre for Environmental and Marine Studies (UIDP/50017/2020 and UIDB/50017/2020), and CICECO—Aveiro Institute of Materials (UIDB/50011/2020 and UIDP/50011/2020), both financed by national funds through the FCT/MCTES.

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Gameiro, T., Novais, R.M., Correia, C.L. et al. Role of waste-based geopolymer spheres addition for pH control and efficiency enhancement of anaerobic digestion process. Bioprocess Biosyst Eng (2021).

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  • Anaerobic digestion
  • Biogas
  • pH control
  • Fly ash
  • Wastewater