A Study of Energy Recovery Potential from Domestic Sewage Sludge

Domestic sewage sludge can be defined as a soft mud and a slimy precipitate product
produced from sewage. The objectives for this project are to determine the energy
recovery potential of domestic sewage sludge and to calculate the amount of energy that
can be recovered from daily sludge disposal. This project focuses on the characterization
of secondary sewage sludge and the amount of energy recovery based on Feed-in-Tariff
(FiT). Secondary sludge was chosen as it contains lesser moisture content compared
with primary sludge. The problem with sewage sludge is mainly cost. The cost for
disposal is too expensive. It also causes the cost of running sewage treatment plant to
increase. There is also very limited landfill for sludge disposal. In this work, the sewage
sludge was characterized by Thermal Gravimetric Analysis (TGA) for proximate
analysis to determine the moisture content, volatile matter, fixed carbon and ash content,
and CHNS analyzer for ultimate analysis to determine the C, H, Nand S composition in
the secondary sewage sludge. While the heating value of the sewage sludge was
determined by using Bomb Calorimeter. A few experiments for energy profiling and
energy content with time dependency were carried out. The heating value obtained from
the experiment was 15.54 ± 0.2 kJ/ g. It was found that, the heating value of secondary
sewage sludge is time dependent: the energy content was reduced more than 1 kJ/g after
7 days. Based on this finding, secondary sewage sludge is not recommended to be used
for energy recovery after 7 days. Based on the proximate analysis by using Thermal
Gravimetric Analyzer (TGA), moisture content in the secondary sludge was 10%,
volatile matter 49.5%, Ash content 28.6% and Fixed Carbon 21.9%. The ultimate
analysis using CHNS analyzer gave the result of Carbon 34.06%, Hydrogen 4.45%,
Nitrogen 6.28% and Sulfur 1.1 %. Based from this study, it was found that the amount of
sludge to be disposed in landfill can be reduced by using the sludge to generate
electricity; consequently health problem can be prevented. The power generated from
this energy recovery study can be used in reducing the cost of running sewage treatment
plant as well.