Comparative life cycle environmental and cost assessments of renewable natural gas production pathways

Abstract

Renewable natural gas (RNG) is one of the most prominent fuels that help reduce upstream emissions from conventional natural gas networks without significant infrastructure changes. While the current resources for RNG are insufficient, there is a substantial interest in establishing the viability of integrating RNG into the gaseous-fuel industry portfolio. However, holistic studies that support the assessment and selection of the fuel production paths are limited. Therefore, the current study attempts to close that gap by introducing a systematic approach to assess the project viability of RNG investments. Twelve waste-to-RNG configurations were evaluated based on three types of waste feedstock and four biogas upgrade technologies in three selected population centres. Life cycle environmental and life cycle cost assessment tools were employed to determine the ecological footprint and economic performance of RNG production routes. Multi-criteria decision-making was applied using the TOPSIS method under varying stakeholder perspectives to derive suitability indices for RNG investments. Finally, recommendations were provided based on the results obtained for successfully implementing waste-to-RNG supply chain paths. According to study findings, not all RNG production methods guarantee positive returns. The least environmental impacts were assured by the anaerobic digestion of animal manure. However, the lowest returns were obtained via the same route. From a pro-economic and neutral decision perspective, landfill gas-based RNG production achieved higher suitability scores. The proposed framework is flexible and can be customized to suit varying decision priorities. The findings are geared towards supporting utility providers, community developers, and potential investors to foresee the success of planned RNG projects to ensure sustainable gaseous fuel networks.