Abstract
Proper treatment and careful management of sewage sludge are essential because its disposal can lead to adverse environmental impacts such as public health hazards, as well as air, soil, and water pollution. Several efforts are being made currently not only to safely dispose of sewage sludge but also to utilize it as an energy source. Therefore, in this study, initiatives were taken to valorize sewage sludge cake by reducing the moisture content and increasing the calorific value by applying a hydrothermal treatment technique for efficient energy recovery. The sludge cake treated at 200 °C for 1 h was found to be the optimum condition for hydrothermal carbonization, as, in this condition, the caloric value of the treated sludge increased by 10% and the moisture content removed was 20 wt.%. To recover energy from the hydrothermally treated sludge, a gasification technology was applied at 900 °C. The results showed that the product gas from hydrothermally treated sludge cake had a higher lower heating value (0.98 MJ/Nm3) and higher cold gas efficiency (5.8%). Furthermore, compared with raw sludge cake, less tar was generated during the gasification of hydrothermally treated sludge cake. The removal efficiency was 28.2%. Overall results depict that hydrothermally treated sewage sludge cake could be a good source of energy recovery via the gasification process.
Highlights
Due to the rapid growth in population and the industrialization of society, the demand of water supply is increasing all over the world
Compared to other investigations on the thermal treatments of sludge, the carbon and volatile components and the heating value were high, which is good as a fuel for gasification [39,41]
Dehydration is generally explained by the removal of hard siloxanes, and decarboxylation is the thermal cracking of long-chain carboxylic acids to carbonize the biomass by lowering the H/C and O/C ratios
Summary
Due to the rapid growth in population and the industrialization of society, the demand of water supply is increasing all over the world. To meet this demand, several water supply lines and sewerage lines are being constructed every year [1]. As the percentage of the sewered population is increasing rapidly, the sewage sludge production rate is increasing in a similar way. According to organization for economic cooperation and development (OECD) statistics, an increase was recorded in Korea and globally [2,3,4]. As of 2017, an average of 11,432 tons of sewage sludge is processed per day in 4072 sewage sludge treatment facilities nationwide [6]
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