Upcycling potential of hazardous tannery sludge to value-added products: Process modelling, simulation, and 3E analysis

The sustainability of the tannery sector largely depends on the eco-friendly management of its solid and liquid wastes. Unfortunately, the global tannery sector is strappingly suffering a significant challenge to meet environmental standards towards sustainability due to a lack of tannery sludge (TS) management facilities as well as lacking research on hazardous TS upcycling facilities to value-added products. Hence, TS from leather processing generally undergoes open dumping, responsible for environmental pollution, including water, soil, and air pollution. To ensure the sustainability of tannery sector, pioneeringly, this study attempts to conceptually design gasification based on four novel upcycling potentials of TS-to-value added products such as (i) TS to syngas with steam generation (TS-SS), (ii) TS to hydrogen with power generation (TS-HP), (iii) TS to power generation with carbon capture (TS-PCC), and (iv) TS to methanol production with power production (TS-MPP) using ASPEN Plus® simulator. Further, this research offers a comprehensive techno-economic analysis to evaluate the economic feasibility of the proposed four TS upcycling processes. The TS-PCC and TS-HP processes outperformed for their net energy efficiencies of 72.80 % and 50.22 %, correspondingly, compared to TS-HP (39.13 %) and TS-MPP (40.38 %). Regarding exergy efficiency, the TS upcycling processes coded TS-MPP and TS-HP demonstrated better net exergy efficiencies of 34.34 % and 27.20 %, respectively, compared to TS-SS and TS-PCC upcycling processes. These results confirm that TS-HP is much more efficient in terms of exergy. Furthermore, techno-economic analysis has confirmed that the developed processes, namely TS-SS and TS-PCC, are economically viable at a 70 % plant efficiency, whereas other processes, such as TS-HP and TS-MPP, are financially viable only if a subsidy of $33/ton subsidy is provided. The study findings have a significant impact on the development of circular economy-based industrial-scale TS management facilities in developing countries, which can ensure the sustainability of the leather sector.