A technoeconomic assessment of an on-site biocrude production from sewage sludge in Qatar's wastewater treatment plants

The generation of sewage sludge in the State of Qatar is increasing with the rapid growth of its population. Around 300,000 m³ of wet sludge is generated every year. Although the sludge is being treated to meet the international standards, its final disposal into landfills raises concerns associated with the limited land areas in the country, as well as the possible contamination of soil and groundwater. On the other hand, the hydrothermal liquefaction (HTL) technology is attracting more and more attention at the expense of other thermochemical waste valorisation pathways including incineration, gasification and pyrolysis. Since it can tolerate the high-water content of wet feedstocks, while the HTL biocrude has a comparable heating value to that of crude petroleum and has the potential to be co-processed in existing oil refineries. Therefore, this study investigates the techno-economic aspects of an on-site biocrude production from sewage sludge at wastewater treatment plants in Qatar via hydrothermal liquefaction. The system is modelled using Aspen Plus, while an economic assessment is conducted with the aid of Aspen Process Economic Analyser (APEA). The results indicate a significant biocrude yield of up to 38.2 wt.% (on dry and ash-free basis). In addition, based on the economic feasibility evaluation, the produced biocrude achieved a competitive minimum selling price of 52.6 US$/bbl, which is below the past 5-year global average price of crude petroleum. As such, the incorporation of biocrude into the oil refining process can be a promising alternative for oil-refining countries, especially at times of petroleum prices hikes.