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Biogas production from municipal waste mixed with different portions of orange peel
University of Borås, School of Engineering.
University of Borås, School of Engineering.
2009 (English)Independent thesis Advanced level (degree of Master (One Year))Student thesis
Abstract [en]

Orange cultivation is a huge industry which increasing for each year. By the year 2010 the orange production of the world is expected to reach 66.4 million tons per year. Most of the oranges are used for orange juice production. Consequently, a large amount of organic wastes, including seeds, segment membranes and peel, counting up to half of the weight of used oranges, are generated As alternatives to land filling and incineration, source separation and composting together with biogas production are being considered as suitable methods for treating this fraction of wastes, because it holds a high amount of organic materials in form of valuable carbohydrate polymers. However, the presence of peel oil, limonene, known to have antimicrobial effects, has showed to be a strong inhibitor for the biogas producing microorganisms. Therefore the orange peel waste (OP) was mixed with the organic fraction of municipal solid waste (MSW) in this study to keep the concentration of this inhibitory compound at low level. Based on the results from previous batch experiments, this study was performed in order to confirm and develop the possible use of orange peel waste in biogas production. Since the batch experiments showed that the methane production was not affected, when a mixture of 70% MSW and 30% OP (calculated on the basis of volatile solids (VS) content added) was used as substrate, a continuous anaerobic digestion experiment was performed using the same mixture of MSW and OP as a substrate in this study. Furthermore, a reactor utilizing only MSW was used as a control. Both reactors were operated during 35 days at thermophilic conditions (55ºC), with an organic loading rate of 3gVS/L/day and a hydraulic retention time of 21 days. The methane production was around 0,5 Nm3/kgVS/day in both reactors during the first period of operation. However, the production of methane started to decrease after 20 days followed by a sharp decrease during the last 5 days in the orange peel-containing reactor. Furthermore, a steadily increase (from 4,85g/L to 6,51g/L) in the total content of volatile fatty acids (VFA) could be observed here, while the total content of VFA in the control reactor remained at low levels (0,84g/L). A second experimental set up using a decreased amount of OP (20% OP and 80% MSW) in the substrate mixture and operating at the same conditions s the previous experiment was also performed and showed similar trends in the results. The failure of the process can be explained by inhibition in the system, which led to the accumulation of VFA’s resulting in a decreased and finally no methane production. This inhibition might be caused by the accumulation of the inhibitory compound, limonene, presented in the orange peel waste. Therefore some treatment of the OP is necessary prior to digestion to avoid this inhibition. Batch digestion of treated vs untreated OP showed that the methane production of treated OP could be increased to 0,628 Nm3/kgVS compared to that of 0,408 Nm3/kgVS from the untreated sample. Further investigations utilizing this treated OP fraction in continuous biogas process are necessary in the future.

Place, publisher, year, edition, pages
University of Borås/School of Engineering , 2009.
Series
Magisteruppsats
Keywords [en]
biogas, orange peel, municipal waste, batch experiment, semicontinious experiment, pre-treatment
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:hb:diva-19554Local ID: 2320/5402OAI: oai:DiVA.org:hb-19554DiVA, id: diva2:1311488
Available from: 2019-04-30 Created: 2019-04-30

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