Effects of ultrasound pretreatment and anaerobic digestion on the energy potential of sludge

Çelebi, Emrehan Berkay
The by-product of wastewater treatment, sludge, is generated in tons everyday all around the world. As environmental regulations in Turkey are becoming stricter during the European Union adaptation period, the previously wide-spread disposal method of landfilling the sludge will not be applicable. Instead, dried sludge is expected to be used in revenue generating methods like land application or combustion. Combustion can be thought of as more beneficial as it uses sludge as an energy source. However, it is not the only way to exploit the energy potential of sludge; anaerobic digestion also provides energy as biogas. While it is known that anaerobic digestion reduces the calorific value of the sludge, this effect is not yet fully investigated. Thus, the primary purpose of this study was to determine the effect of anaerobic digestion (with or without sonication pretreatment) on the calorific value of sludge. Additionally the study investigates the optimal sludge management strategy that maximizes the energy gain. After the inital experiments that determined the sonication duration as 10 minutes, anaerobic batch reactors with 2.5 L active volumes were used to track the changes in the fuel properties of sludge during digestion. Results showed that sonication provided a 340% increase in sCOD, a 15% increase in biogas production and a 32% increase in methane production. Using the data from the experiments, the energy analysis showed that the optimal method is the combination of thickening, dewatering, thermal drying and combustion. Adding digestion and ultrasound pretreatment to this scenario reduces the overall gain.


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Citation Formats
E. B. Çelebi, “Effects of ultrasound pretreatment and anaerobic digestion on the energy potential of sludge,” M.S. - Master of Science, Middle East Technical University, 2015.