4. Conclusion
Co-digestion of mixed waste sludge with 25% FVW showed enhanced process
stability and biomethanation compared to co-digestion with 50% FVW.
Increased acidification observed in thermophilic phase I of co-digestion
(1:1) led to process instability and consequently, 33% less methane
yield in subsequent phase II compared to co-digestion (3:1). Application
of hybrid (MW-H2O2) pre-treatment
significantly enhanced the methane production and quality in
co-digestion (3:1). It increased the initial sludge solubilisation by
33% and facilitated 2.91-fold higher methane production in thermophilic
phase-I compared to untreated digestion. Besides, the biogas quality was
also improved with an average of 1.55
CH4/CO2 ratio in the treated digester.
The process stability was enhanced in treated digester with an average
FOS/TAC of 0.26 in phase-II and helped achieve a 2.17-fold higher
overall methane yield compared to the untreated digester. The improved
process stability in the treated digester is mostly attributed to buffer
capacity exhibited by biopolymers released during the treatment. A study
on the oxidative status of the current anaerobic digestion revealed that
superoxide radicals negatively correlate with sludge bioactivity.
Further investigations on free radical production in anaerobic digestion
could establish the mechanisms of free radical generation and their
significance in anaerobic digestion. Overall these results reveal the
high potential of co-digestion of FVW with mixed activated sewage sludge
to enhance the performance of anaerobic digestion and overcome some of
its fundamental operational limitations.