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Efficient domestic wastewater management is essential for mitigating the impact of wastewater on human health and the environment. Wastewater management with conventional technologies generates sewage sludge. The present study considered a modelling approach to evaluate various processing pathways to produce energy from the sewage sludge. Anaerobic digestion, gasification, pyrolysis, and hydrothermal liquefaction are analysed in terms of their energy generation potentials with the Aspen Plus software. A techno-economic assessment is performed to assess the economic viability of each pathway. It reveals that gasification appears as the most promising method to produce electricity, with 0.76 kWh/kg drysludge , followed by anaerobic digestion (0.53 kWh/kg drysludge), pyrolysis (0.34 kWh/kg drysludge), and hydrothermal liquefaction (0.13 kWh/kg drysludge). In contrast, the techno-economic analysis underscores the viability of anaerobic digestion with levelized cost of electricity as 0.02 $/kWh followed by gasification (0.11 $/kWh), pyrolysis (0.14 $/kWh), and hydrothermal liquefaction (2.21 $/kWh). At the same time, if the products or electricity from the processing unit is sold, equivalent results prevail. The present study is a comprehensive assessment of sludge management for researchers and policymakers. The result of the study can also assist policymakers and industry stakeholders in deciding on alternative options for energy recovery and revenue generation from sewage sludge. [Display omitted] • Comparative analysis of four sewage sludge processing units. • Gasification produces 41% more electricity than anaerobic digestion. • Anaerobic digestion has 81% lower LCOE than gasification. • Pyrolysis has the highest energy content per kg. • Anaerobic digestion has the highest NPV through electricity or other products. [ABSTRACT FROM AUTHOR]

A variety of novel processes are being proposed in order to face global challenges such as degradation of the environment and the efficient utilization of energy. Modeling and simulation tools play a crucial role in the understanding and enhancing of the execution, design and construction of these processes. Although different computational tools are available to quantify the process at different levels, they are normally utilized independently and on a stand-alone basis. This decoupled approach may undermine the true potential of these tools. The present study highlights the advantages of interlinked process modeling at different levels. This study focuses on a promising gasification technology, namely the dual fluidized bed gasifier. A computational fluid dynamics (CFD) model was used to understand the flow patterns inside a fluidized bed. This elevated the understanding of the hydrodynamics of the gasifier freeboard, which is neglected by the conventional two-phase methodology. The CFD simulation was utilized to perform a residence time distribution (RTD) analysis of the reactor. Four tracer approaches namely the frozen velocity approach, the snapshot approach, the data sampling approach and the transient approach, were compared. The RTD analysis formed the basis of a steady-state compartment model that was developed in ASPEN Plus simulation software. The ASPEN Plus gasifier model decoupled the pyrolysis, gasification, and combustion sections of the gasifier to affect a better comprehension of the process and results. The model predicated satisfactory results upon validation. Additionally, the model could also be used to predict the output for different biomass feedstocks. [ABSTRACT FROM AUTHOR]