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Presented by Reem Satti

Increasing biogas production by thermal (70◦C) sludge pre-treatment prior to thermophilic anaerobic digestion. Presented by Reem Satti. Background. W astewater treatment process overview

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Presented by Reem Satti

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  1. Increasing biogas production by thermal (70◦C) sludge pre-treatment prior to thermophilic anaerobic digestion Presented by Reem Satti

  2. 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

  3. 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

  4. Objectives • Investigate the effect of a low temperature pre-treatment on the efficiency of digestion of primary and secondary waste sludge

  5. 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)

  6. 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

  7. 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)

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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?)

  15. 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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