Techno-economic analysis of electricity generation from household sewage sludge in different regions of Nigeria

Modelling and techno-economic assessment of possible pathways from sewage sludge to green energy in India

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/kgdrysludge, followed by anaerobic digestion (0.53 kWh/kgdrysludge), pyrolysis (0.34 kWh/kgdrysludge), and hydrothermal liquefaction (0.13 kWh/kgdrysludge). 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.

Capacity of waste heat recovery-based polygeneration to achieve sustainable development goals

The objective of this study is twofold. First, it aims to bridge a significant gap in the existing literature by reviewing the integration of waste heat recovery (WHR) into polygeneration systems. Thus, it scrutinizes the methods and challenges of WHR-based polygeneration systems and explores their energy and economic potential based on data gathered from the literature and using key indicators. Second, it addresses the scarcity of existing studies assessing the environmental impact of these systems. Therefore, an environmental analysis is conducted to evaluate the potential mitigation of greenhouse gas emissions achievable through their implementation. The findings of the study reveal significant energy and exergy efficiencies, varying in the ranges of 20.8 %-96.9 % and 24.1 %-63.6 %, respectively, proving high performance of WHR-based polygeneration systems. Economically, these systems exhibit competitiveness, with short payback periods ranging from 1.4 to 6.7 years, along with average levelized costs of electricity, cooling, and heating of 0.17, 0.37 and 0.13 $/kWh, sequentially. Moreover, the environmental assessment confirmed substantial reductions in greenhouse gas emissions, reaching on average 2.45 kt of carbon dioxide per MW of installed capacity, annually. The study could contribute to raising awareness regarding the energy, economic, and environmental benefits of WHR-based polygeneration systems, thereby fostering the widespread adoption of these sustainable systems.