Abstract
Municipal wastewater treatment plants generate large amounts of sludge after a set of unit processes. The sewage sludge is an important resource for energy production because of its high level of biodegradability. Sewage sludges are generally made of non-toxic and biodegradable organic compounds mixed with a small fraction of non-toxic and toxic inorganic compounds having a very low biodegradability. The large fraction of biodegradable matter constitutes a pool for green/clean energy to be used for industrial and domestic applications. The generated energy can also be used in the wastewater treatment plant. Currently, fossil fuels are leading the energy world, however, they are being depleted and are considered to be among the main causes contributing to climate change and global warming. Domestic sewage sludge can be converted sustainably into bio-hydrogen and bio- methane. This conversion is achievable through anaerobic digestion, combustion, pyrolysis and gasification. With regard to the last three conversion processes, the organic and inorganic toxic compounds are eliminated. Production of biogas from sewage sludge is being undertaken worldwide on small, medium, and large scales. However, hydrogen production from sludge is still developing. There is an existence of substantial knowledge in this field, the production of hydrogen and biogas from sewage sludge is gaining interest. This study analyses various possibilities of sewage sludge conversion into clean energy. The analysis focuses on the technology strengths, weaknesses and gaps to be improved in future studies.
Highlights
INTRODUCTIONThe demand for energy is currently on the increasing trend due to the fact that energy is an important ingredient for a successful economic development
The demand for energy is currently on the increasing trend due to the fact that energy is an important ingredient for a successful economic development.On the other hand, the fossil fuel reserves are currently in a decreasing trend
Biogas and hydrogen are one of the options to be explored in order to reduce the gap between the supply and demand for renewable energy sources
Summary
The demand for energy is currently on the increasing trend due to the fact that energy is an important ingredient for a successful economic development. Considering the large amounts of sludge generated from wastewater treatment plants on a daily basis in many countries, it is a necessity to convert the biodegradable sewage sludge with the aim to produce cost effective and clean energy including hydrogen and biogas. Several studies have reported that there is a possibility to develop reliable, costs effective and sustainable processes in order to generate clean energy from biodegradable solid wastes with lower negative environmental impact. Pyrolysis and gasification are reported to be environmentally safe and costs effective options for sewage sludge treatment [8]. This study analyses various production options for conversion of sewage sludge to hydrogen and biogas, their strengths and weaknesses, the possibility for improvement for the existing processes.
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