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 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 http://www.tawwa.org/TW11Paper/803.pdf Green Power India Organization. Biogas benefits. Retrieved from http://www.greenpowerindia.org/biogas_benefits.htm http://www.greenpowerindia.org/biogas_benefits.htm