Increasing biogas production by
thermal (70◦C) sludge pretreatment prior to thermophilic
anaerobic digestion
Presented by Reem Satti
Background
• Wastewater treatment process overview
• Facilities are designed in stages, each stage either
removes particles or changes dissolved material into
a form that can be removed.
• Modern wastewater treatment plant stages:
– Influent
– Primary treatment
– Secondary treatment
– Tertiary treatment
– Effluent discharge
Biogas Production
• The creation of biofuel through anaerobic
decomposition of organic materials
• Benefits
– Production of energy
– Transforms organic wastes into high quality
fertilizer
– Improves hygienic conditions
– Environmental advantages
Objectives
• Investigate the effect of a low temperature
pre-treatment on the efficiency of digestion of
primary and secondary waste sludge
Methods
• Sludge sampling and characterization
– Primary and secondary sludge was obtained from
a wastewater treatment plant (MWWTP) near
Barcelona.
– Samples were collected weekly and stored at 4
degrees Celsius until use
– Primary sludge (PS) and secondary waste
activated sludge (WAS) are thickened and mixed
– Mesophilic anaerobic digestion (38 ◦C)
Methods
• Low temperature pre-treatment
– Beakers with 0.5 L of sludge were submersed in a
thermostatic bath at 70 ◦C during 9, 24, 48, and 72
h.
– Samples of raw and pre-treated sludge were
analyzed for total solids , volatile solids, total
dissolved solids, volatile dissolved solids (VDS),
volatile fatty acids (VFA), and pH.
– Effect of pre-treatment assessed via increase in
VDS and VFA
Methods
• Anaerobic batch tests
– Used to determine biogas
production of raw and pretreated
sludge samples
– Conducted at 55 ◦C
– Inoculum: thermophilic sludge
from the effluent of a 5L
continuous stirred tank reactor
– Substrate: Pre-treated or raw
sludge
– Blank treatment with
inoculum only (determines
biogas production due to
endogenous respiration)
Methods
• Reactor constituents
– 100g of inoculum, 50 g substrate (blank
treatment: 150 g of inoculum)
– Purged with N2
• Bottles were incubated at 55 ◦C
• Biogas production
– Pressure increase in the headspace
Methods
• Analytical methods
– Solid content of sludge determined using different
procedures including centrifugation.
• Supernatant underwent filtration and suspended
particles were deduced
– VFA and biogas composition were determined by
gas chromatography
Results and Discussion
• Total dissolved solids and volatile dissolved solids increased after thermal
pre-treatment, as expected
– 1.5 g increase VDS in raw sludge compared to 11.9-13.9 g VDS after 9,
24, and 48 h pre-treatment. This means that the proportion of soluble
to total organic matter increased by almost 10 times, from 5% to
almost 50% after pre-treatment.
Results and Discussion
• VFA concentration
– Acetic and propionic acids were the main VFA generated
after 24h.
– Butyric and valeric acids were mostly detected after 48 h.
Results and Discussion
• At day 10, accumulated biogas production was nearly 300
mL for 9, 24, and 48 h pre-treated samples.
• The control was 200 mL , representing an almost 50%
volume increase
Results and Discussion
• Pre-treated sludge results show that the process was more efficient in
terms of biogas production and yield in all cases (30% higher).
• Methane content was always higher after sludge pre-treatment.
• Results suggest that a short period (9h) low temp. pre-treatment should
be enough to enhance methane production.
Limitations
• Effluent hygienisation was briefly discussed
– Reduced E. Coli, and Salmonella was absent
– Should have tested for other bacteria
• Duration for the control treatment and
experimental treatment were different (1 year
vs. 6 months)
• Statistical analysis
• Shorter periods should be tested (3h, 6h?)
References
• Directory of Industrial Supply and Agriculture. (2003). Biogas Production.
Retrieved from
http://www.habmigern2003.info/PDF/methane-digester.pdf
• Godfree, A., and Farrel, J. 200. Process for managing pathogens. J. Environ.
Qual. 34(1), pp. 105-113.
• Krishna, P. (2009) Strategies to enhance sludge processing through
anaerobic digestion. Retrieved from
http://www.tawwa.org/TW11Paper/803.pdf
• Green Power India Organization. Biogas benefits. Retrieved from
http://www.greenpowerindia.org/biogas_benefits.htm