Abstract
Safe disposal of sewage sludge is one of the most pressing issues in the wastewater treatment cycle: at the European Union level, sludge production is expected to reach 13 Mt by year 2020. Sludge disposal costs may constitute up to, and sometimes above, 50% of the total cost of operation of a WWTP, and contribute to over 40% of its GHGs emissions. The most common disposal options at the moment are landfilling, disposal in agriculture (about 40% EU-wide), incineration or co-incineration, and use in the industrial production of bricks, asphalts and concrete. Sewage sludge, however, still contains beneficial resources such as nutrients, that can be recovered through specific processes (e.g. precipitation as struvite) and energy, recoverable through a variety of approaches. Microwave-assisted pyrolysis of urban waste sludge was applied for the production of oil, (Syn)gas, and biochar that were afterwards characterized and compared to mainstream alternative fuels (biodiesels) and other material recovery options. Sustainability issues related to the production of biodiesel/biochars from urban wastewater treatment sludge are also discussed. The paper shows that waste urban sludge can indeed be a full component of the urban circular economy by allowing, if properly processed, recovery of energy resources at multiple levels: bio-oils (biodiesel), syngas and bio-char, all having definite advantages for final residues use and disposal. Biodiesel, in particular, allowing energy recovery as liquid fuel, offers a much more flexible and efficient utilization.
Highlights
Residual urban sludge disposal costs may constitute up to, and sometimes above, 50% of the total cost of operation of Wastewater Treatment Plants (WWTPs) and contribute more than 40% of the total greenhouse gas (GHG) emissions associated with their operation (Liu et al, 2013)
lower calorific value (LCV) will vary according to process conditions: at higher process temperatures, the LCV of obtained biooil will tend to be lower for the same feedstock
It has been shown that waste urban sludge can be a full component of the urban circular economy by allowing, if properly processed, recovery of energy resources at multiple levels: bio-oils, syngas and bio-char
Summary
Residual urban sludge disposal costs may constitute up to, and sometimes above, 50% of the total cost of operation of Wastewater Treatment Plants (WWTPs) and contribute more than 40% of the total greenhouse gas (GHG) emissions associated with their operation (Liu et al, 2013). The safe disposal of such sludge is literally a “big” issue in urban wastewater treatment: at the European Union level, the 2020 sludge production is expected to reach close to 13 Mt by year 2020, an increase of more than 30% from today’s levels. According to Machado (2001), urban waste sludge production in Brazil is much lower (about 150 Kt per year) since about 80 million people in Brazil do not have their wastewater collected by centralized systems, but disposed of through separate unitary (septic tanks) systems, in which there is no centralized control over the final destination of excess organic solids. In 2008, the United Nations Human Settlement Programme more than doubled the previous estimate by Machado for the country, updating it to 370 kt per year (Mateo-Sagasta et al, 2015)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Ambiente e Agua - An Interdisciplinary Journal of Applied Science
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
