(582b) A New Way to Convert Waste to Hydrogen

The growing global demand for clean energy, coupled with escalating concerns over environmental pollution, has accelerated the search for sustainable technologies capable of converting diverse waste streams into value-added products. Among these, Alkaline Thermal Treatment (ATT) has emerged as a highly promising approach for hydrogen production, offering a low-temperature, carbon-neutral pathway applicable to both organic and synthetic waste feedstocks. In this study, we present a comprehensive investigation of the ATT process for the simultaneous valorization of food waste sludge and mixed plastic waste—two of the most problematic yet abundant waste types in modern urban society.

For food waste sludge, ATT enabled the generation of high-purity hydrogen (44.02 mmol H₂/daf-g) under atmospheric pressure and without CO₂ emissions in the gas phase. The use of sodium hydroxide (NaOH) as both a catalyst and in-situ CO₂ sorbent allowed for the stabilization of carbon species as solid carbonates, thereby achieving integrated carbon capture during the hydrogen production process. This is a significant departure from traditional thermal processes, such as gasification or pyrolysis, which are typically energy-intensive and emit mixed syngas containing CO and CO₂.

Extending the applicability of ATT, we investigated its performance on mixed plastic waste, including polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP)—polymers that present significant recycling challenges due to the need for pre-sorting. Our study demonstrates that NaOH-assisted ATT effectively decomposes all three types of plastics into hydrogen at relatively low temperatures, with hydrogen yields reaching 42.45, 53.86, and 30.69 mmol/g for PET, PE, and PP, respectively. Notably, oxidative pretreatment of polyolefins (PE and PP) dramatically enhanced their reactivity, enabling the efficient cleavage of robust C–C and C–H bonds that are typically resistant to conventional thermochemical degradation.

Importantly, ATT proved effective even when applied to unsorted, mixed plastic waste, eliminating the need for costly and labor-intensive pre-sorting steps. This feature, combined with its dual capacity for waste treatment and clean hydrogen generation, highlights ATT’s viability for scalable, decentralized deployment in both municipal and industrial contexts. It also aligns with the principles of the circular economy, transforming waste liabilities into energy assets while reducing environmental burdens.

In conclusion, our research establishes Alkaline Thermal Treatment as a versatile, energy-efficient, and environmentally responsible method for hydrogen production from heterogeneous waste streams. By uniting waste management with clean energy generation, ATT opens a compelling avenue toward integrated resource recovery systems, where food residues and plastic pollutants are upcycled into zero-carbon hydrogen fuel, contributing directly to global decarbonization and sustainability efforts.