Effect of sludge biochar as an additive in thermophilic anaerobic digestion
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Infrastructure and environmental engineering (MPIEE), MSc
Publicerad
2024
Författare
Thakur , Aashutosh Kumar
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The production of sewage sludge, the main byproduct of municipal wastewater
treatment plants (WWTPs), is likely to increase due to growing urban populations and
stricter effluent disposal regulations. Anaerobic digestion (AD) is among the most
widely adopted methods in municipal WWTPs for the treatment and stabilisation of
sewage sludge. The AD process has been found to perform optimally in two
temperature regimes: mesophilic (35–40 °C) and thermophilic (55–60 °C), and it offers
the advantage of recovering clean energy in the form of methane-rich biogas which can
help offset the plant’s energy costs.
Given the increasing constraints on energy supply, exploring ways to enhance biogas
yield from AD becomes important. Sewage sludge pyrolysis is another technology that
has received growing attention as an alternative method of sludge management.
It involves heating the dewatered and dried sewage sludge at high temperatures
(300–800 °C) in the absence of oxygen, producing sludge biochar as a byproduct. With
properties that can favour microorganism growth and metabolism, sludge biochar could
potentially improve anaerobic digestion performance when used as an additive during
the digestion process.
This thesis investigates the impact of using sludge biochar as an additive in
thermophilic anaerobic digestion of easily biodegradable substrates, specifically
microcrystalline cellulose (MC) and sodium acetate (SA). A batch anaerobic digestion
experiment was conducted over 49 days in two consecutive phases: the first phase using
MC and the second phase using SA as substrates. Sludge biochar (SB) and synthetic
graphite (SG) were used as additives in two different reactor groups to assess their
impact on the cumulative biogas yield.
Results from Phase 1 showed that the overall biogas yield in the SB and SG dosed
reactors exceeded the control group by 1.5% and 2.1% respectively, indicating a
minimal impact of SB on thermophilic anaerobic digestion of MC. However, results
from Phase 2 using SA as the substrate showed that biogas yield in the SB and SG dosed
reactors exceeded the control by around 21% and 8.5% respectively, indicating a much
greater impact of the additive. This suggests that SB could have influenced the
methanogenesis reactions in the second phase, resulting in an increase in total biogas
yield. While SB shows potential as an additive for improving anaerobic digestion
performance, further investigations are needed to understand the enhancement
mechanism and its potential application with sewage sludge digestion.
Beskrivning
Ämne/nyckelord
wastewater treatment plant , sewage sludge , anaerobic digestion , sludge pyrolysis , biochar , sludge biochar , biogas , methanogenesis