Electrohydrolysis pretreatment of waste activated sludge to enhance anaerobic digestion
Minang, John-Kennedy Chenwi (2025)
Diplomityö
2025
School of Engineering Science, Kemiantekniikka
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2025082584464
https://urn.fi/URN:NBN:fi-fe2025082584464
Tiivistelmä
As energy demand rises and environmental concerns persist, there is a shift away from conventional energy sources, such as fossil fuels, to more sustainable alternatives. In this context, anaerobic digestion (AD) of waste-activated sludge (WAS) serves as an effective waste management technique that contributes to this shift by creating valuable products. However, WAS has a complex microbial floc structure composed of Extracellular polymeric substances(EPS) and microorganisms, which hinders the effective hydrolysis of organic matter into biomethane. Studies indicate that this challenge can be overcome by pretreating WAS with electrohydrolysis (EH), resulting in noticeable improvements in the sludge biodegradability index (BD), disintegration degree (DDCOD), and an increase in biochemical methane production (BMP).
This study investigates the pretreatment of WAS using the novel electrohydrolysis technology, which has shown promise in enhancing the hydrolytic phase of anaerobic digestion (AD). For this purpose, this work evaluates the effect of applied energy, cathode material and current intensity on the performance of the AD process. The assessment was based on the changes of soluble chemical oxygen demand (sCOD), total chemical oxygen demand (tCOD), total biochemical oxygen demand (tBOD), BD and DDCOD.
Preliminary analysis indicates that BOD tests have highlighted a substantial increase in the degradability of the pretreated WAS, and the optimum DDCOD for sludge treated with C1 was 4.10 % ± 0.01. The C1 cathode was found to provide a more sustained and linear improvement in BMP, peaking at a 79.27% increase at 5000 kJ/kgTS. In contrast, the C2 cathode achieved a better performance at lower energies, with a 68.61% increase at just 500 kJ/kgTS, after which its efficiency declined. A positive correlation was also found between increasing current intensity and EH performance, with a maximum BMP increase of 51.12% at 0.4 A. The BD post EH pretreatment at different conditions ranged from 0.07- 0.12, further highlights the improved biodegradability of EH treated WAS. The Gompertz model was effective in predicting the AD kinetics, with high R² values of 0.95 to 0.99, confirming its reliability. Overall, the study demonstrated that EH effectively enhances the AD of WAS by improving sludge solubilization and biodegradability, thereby significantly increasing methane yield.
This study investigates the pretreatment of WAS using the novel electrohydrolysis technology, which has shown promise in enhancing the hydrolytic phase of anaerobic digestion (AD). For this purpose, this work evaluates the effect of applied energy, cathode material and current intensity on the performance of the AD process. The assessment was based on the changes of soluble chemical oxygen demand (sCOD), total chemical oxygen demand (tCOD), total biochemical oxygen demand (tBOD), BD and DDCOD.
Preliminary analysis indicates that BOD tests have highlighted a substantial increase in the degradability of the pretreated WAS, and the optimum DDCOD for sludge treated with C1 was 4.10 % ± 0.01. The C1 cathode was found to provide a more sustained and linear improvement in BMP, peaking at a 79.27% increase at 5000 kJ/kgTS. In contrast, the C2 cathode achieved a better performance at lower energies, with a 68.61% increase at just 500 kJ/kgTS, after which its efficiency declined. A positive correlation was also found between increasing current intensity and EH performance, with a maximum BMP increase of 51.12% at 0.4 A. The BD post EH pretreatment at different conditions ranged from 0.07- 0.12, further highlights the improved biodegradability of EH treated WAS. The Gompertz model was effective in predicting the AD kinetics, with high R² values of 0.95 to 0.99, confirming its reliability. Overall, the study demonstrated that EH effectively enhances the AD of WAS by improving sludge solubilization and biodegradability, thereby significantly increasing methane yield.