Abstract
Hydrothermal liquefaction (HTL) is a promising technology for the production of bio-crude. However, some unresolved issues still exist within HTL, which need to be resolved before its promotion on a commercial scale. The management of the aqueous phase is one of the leading challenges related to HTL. In this study, the sewage sludge has been liquefied at 350 °C with and without catalyst (K2CO3). Subsequently, aqueous phase recycling was applied to investigate the effect of recycling on bio-crude properties. Obtained results showed that the energy recovery in the form of bio-crude increased by 50% via aqueous phase recirculation, whereas nitrogen content in the bio-crude was approximately doubled after eight rounds of recycling. GCMS characterization of the aqueous phase indicated acetic acid as a major water-soluble compound, which employed as a catalyst (0.56 M), and resulted in a negligible increase in bio-crude yield. ICP-AES highlighted that the majority of the inorganics were transferred to the solid phase, while the higher accumulation of potassium and sodium was found in the aqueous phase via successive rounds of recycling.
Highlights
Increasing world population intensifies the global energy demand
1.4% that can be ignored under the experimental protocols
The slightly lower bio-crude yield with small error bars at 400-None might be due to the conversion of bio-crude fractions to aqueous or gas phase via cracking reactions above the critical point (374 â—¦ C)
Summary
Increasing world population intensifies the global energy demand. The imbalance in supply and demand emerges a need for the exploration of new pathways for the production of energy [1]. It has been established that renewable sources of energy have great importance for sustainable development. The increasing consciousness about environmental threats such as global warming has directed the world towards the usage of renewable sources [2]. Biomass is a renewable energy source that is abundantly available as a wide range of materials, which includes agricultural waste, organic wastes such as food, sewage sludge, etc. Sewage sludge (SS) is a heterogeneous material originated from the wastewater treatment. Due to massive urbanization and rapid growth in population, the production of SS has become a crucial issue that obstacles urban development and creates environmental pollution [5]
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