Presented by Reem Satti
Post on 31-Dec-2015
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Increasing biogas production by thermal (70◦C) sludge pre-treatment 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
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