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Title: Anaerobic Co-Digestion of Tannery and Dairy Industry Wastes for Bio Energy Production
Other Titles: An Approach to Convert Waste to Energy in Agro industrial Sector
???metadata.dc.contributor.*???: Dr. Seyoum Leta
Berhe, Shifare
Keywords: Anaerobic Co-Digestion;Dairy Waste Water;Tannery Solid Waste;Tannery Waste Water
Issue Date: Sep-2017
Publisher: Addis Ababa University
Abstract: The introduction of cleaner technologies through the reuse of wastes for energy recovery can improve the environmental performance of agro processing industries. However, existing waste treatment methods in Ethiopian agro processing industries do not innovatively add value to the wastes by recovering bio-energy to contribute to the ever increasing energy demands in the country and reduce greenhouse gas emissions. In this study anaerobic co-digestion of agro-industrial wastes: tannery waste water (TWW), tannery solid waste (TSW) and dairy waste water (DWW) was investigated using two phase anaerobic sequencing batch reactor (ASBR) for enhanced waste to energy conversion. Laboratory scale anaerobic digesters; one used for acidogensis and the other for methanogensis with 0.4L and 0.6L working volumes, respectively, were used in semi continuous mode operation under mesophilic range (38+20C) . Operational parameters such as mixing ratios of substrates, hydraulic retention time (HRT) and organic loading rate (OLR) were optimized for improved process performance and stability of both hydrolytic-acidogenic and methanogenic steps. The optimum operational conditions of hydrolytic- acidogenic step at four mixing ratios of substrates (100:0, 75:25, 50:50 and 25:75) and at HRT of 5, 3 and 1days were examined. Based on the results obtained the highest process performance in terms of TVFA concentration (3990mgCH3COOH/L) with an acidification degree of 55.5% was achieved when hydrolytic- acidogenic reactor was fed with 50:50(TWW:DWW) and operated at HRT of 3days (OLR of 2.63gCOD/ Similarly, the substrate mixing ratio of 50:50(TWW:TSW), HRT of 5days and OLR of 1.20gCOD/L/day were found to be best values for achieving maximum TVFA (2450mgCH3COOH/L), degree of acidification (36.55%) and degree of hydrolysis(54.8%). The methanogenic process step also showed that methanogenic reactor feed with 50:50(TWW:DWW) operated at HRT of 15 days exhibited improved process stability in terms of pH (6.70), VFA accumulation i.e VFA/Alkalinity (0.363), alkalinity (3350 mgCaCO3/L) and ammonia (231mg/L) in which all values were with in optimum operating range. iv The rector also exhibited best process performances in terms of daily biogas (647ml/day), methane production (461ml/day), methane content (71.2%) and COD removal efficiency (85.6%) when operated at HRT of 15 days and equivalent OLR (0.517gCOD/ The biogas production, methane content and COD removal efficiency during anaerobic co-digestion of TWW and DWW (50:50) were enhanced by 94.3%, 47.4% and 22.5%, respectively, as compared to mono digestion of TWW. The best overall process performance efficiency (acidogenesis and methanogensis) for TCOD reduction (88.8%) was achieved when methanogenic reactor (50% TWW and 50% DWW) operated at HRT of 18 days (3 days for acidogenesis + 15 days for methanogensis). Similarly, methanogenic reactor feed with substrate mixing ratio of 50%TWW and 50%TSW at HRT of 20 days (OLR = 0.280gCOD/ exhibited pH of 6.8, VFA/Alkalinity of 0.305, alkalinity of 3210mgCaCO3/L and ammonia of 246mg/L which were found within optimum operating range. In this methanogenic reactor (50:50 of TWW and TSW) best process performances in terms of daily biogas (415ml/day), methane production (251ml/day), methane content (60.5%) and COD removal efficiency (75%) were achieved when operated at HRT of 20 days and OLR of 0.280gCOD/ The highest overall TCOD reduction (77.3%) was obtained when 50% TWW and 50%TSW in the two phase anaerobic system operated at HRT of 25days (5days for acidogenesis + 20 days for methanogenensis). In general improved process stabilities as well as performances were achieved during anaerobic co-digestion of TWW with DWW and TSW as compared to mono digestion of TWW. Furthermore the results obtained from this study provide fundamental information for scaling up the high performance two phase anaerobic co-digestion system in these agro industries to recover bio energy which can be used as fuel in their different unit operations.
Description: A Thesis Submitted to The Center for Environmental Science in Partial Fulfillment of the Degree of Doctor of Philosophy in Environmental Science
Appears in Collections:Thesis - Environmental Science

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