Evaluating the Biomass Pellet Production Potential of Different Biomass Residues Using Integrated Environmental and Economic Life Cycle Assessment

Abstract

The generation of biomass residues and biowaste is both a challenge to the environment and to resource management worldwide but is also a significant renewable resource for energy and material recovery. Biomass residues are utilised along multiple pathways such as direct use for energy production, anaerobic digestion and biogas production, biofuel generation, composting, soil amendment, and conversion into value-added products at a global scale. On the other hand, many lignocellulosic and other biomass residues are characterized by low bulk density, heterogeneous characteristics, and seasonal availability, thus complicating collection, handling, storage, and transportation. Densification into solid fuel pellets is a viable solution for transforming these low-density residues into a compact, handleable, and transportable form with increased energy density. Although biomass residues have global potential, past pelletisation studies in Punjab, Pakistan, have generally considered only a few of two to three seasonal feedstocks that do not cover the uncertainty of potential feedstock availability in several seasons of the year, alongside the judgment of suitable biomass input. This study was, therefore, designed to explore nine agro-residues with different seasons in Punjab, e.g., tree residues, grass clippings, animal waste, crop residues, and herb biomass, for robust conversion into solid fuel pellets. Gate-to-gate Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) methods were used to evaluate the production system of the pellets from biomass residues. A functional unit of 1 tonne of biomass solid fuel pellets was defined, and the resulting environmental impacts were modelled using GaBi software and the ReCiPe 2016 methodology. Process performance and production hotspots were assessed by attributing the environmental impacts that occurred at individual pellet-production stages to the overall impacts, while LCC was used to evaluate economic costs, both internal and external, from pellet production. The results of hotspot analysis indicated that flash/pneumatic drying represented the most important contributor for all investigated impact categories, followed by the pellet-milling and packaging stages. The total estimated cost of the pellets was USD 72.6 t−1, with an internal cost of USD 51.7 t−1 and an environmental cost of USD 20.9 t−1. Two other energy scenarios provided evidence through which to understand the potential for reductions in GHG emissions linked to the production of pellets. These findings suggest that differing and seasonally accessible biomass residues in Punjab can be converted into solid biofuels to concurrently aid sustainable waste management, energy security, climate-change amelioration, and rural economic growth. This study is novel because it compares nine heterogeneous biomass residues in a seasonal common-pellet production framework, using an integrated environmental and economic approach to provide stakeholders with practical evidence they can use to select the biomass feedstock that is most environmentally and economically preferable. These results help achieve the Sustainable Development Goals 7, 11, 12, and 13.