Researchers have developed a mechanical energy-driven platform that converts waste polyester plastics into methane fuel using piezoelectric materials and microbial metabolism. The study, published in Engineering, demonstrates how hydraulic energy from flowing water can be harvested to drive biocatalytic reactions, offering a sustainable approach to plastic waste management.

The research team from Tsinghua University and collaborating institutions constructed a biohybrid system by combining Methanosarcina barkeri with barium titanate (BaTiO₃) nanoparticles. The piezoelectric BaTiO₃ generates polarons when subjected to mechanical stimulation from water flow. The piezoelectric holes oxidize polylactic acid (PLA) plastic hydrolysates into small organic molecules including ethanol, acetaldehyde, acetic acid, and pyruvate, while the piezoelectrons are accepted by the microorganisms as bioavailable reducing equivalents for CO₂ reduction and methane production.

Under a water flow of 1 m/s, the M. barkeri@BaTiO₃ hybrid achieved a methane yield of 637.25 ± 15.36 μmol/g_catalyst after six days of reaction, representing a 5.46-fold increase compared to single microbes. The system exhibited a reaction turnover frequency of 1.24×10⁵ s⁻¹·cell⁻¹ and maintained high methane selectivity exceeding 98% over five consecutive six-day cycles. Isotopic labeling experiments using NaH¹³CO₃ revealed that 19.2% of the produced methane originated from CO₂ reduction, while 80.8% was derived from PLA-derived lactate oxidation.

The platform demonstrated practical applicability by successfully converting real-world postconsumer PLA products including straws, cups, forks, and spoons into methane fuel. When pretreated with alkaline hydrolysis, these products yielded 351.6 to 555.3 μmol/g_catalyst methane with selectivity above 92%. The system also proved effective with other biodegradable polyesters such as polyglycolic acid and polycaprolactone.

Transcriptomic analysis indicated that genes related to energy metabolism, pyruvate metabolism, carbon fixation, and methane metabolism were significantly upregulated in the biohybrid system. The expression of genes encoding cytochrome c and hydrogenases, which function as electron transporters and acceptors, increased substantially due to favorable kinetic transfer of piezoelectric electrons.

Life cycle assessment revealed that the mechanical energy-driven biocatalytic platform has a carbon emission of −38.6 kg/kg CH₄ production, achieving carbon-negative operation through effective utilization of both waste plastic carbon and CO₂ as feedstocks. The total energy efficiency reached 85.4%, with the majority recovered from methane fuel and residual biomass.

The piezo-driven strategy showed extensibility to other microbial cell factories. Sporomusa ovata@BaTiO₃ demonstrated enhanced acetate production with a 1.08-fold increase compared to static controls, while Rhodopseudomonas palustris@BaTiO₃ showed 1.32% improvement in polyhydroxybutyrate production under mechanical energy driving force.

The researchers emphasize that this approach circumvents the intermittency limitations of sunlight-dependent systems and avoids physical separation of electrodes and complex circuitry required in electrochemical systems. The platform operates under mild conditions without competing side reactions, potentially reducing product separation costs compared to photo- or electro-catalytic approaches.

The paper “A Low-Carbon Platform for Upgrading Waste Polyesters into Methane Fuels via Piezo-Driven Biocatalysis,” is authored by Lu Chen, Xiaoqiang An, Yuan Wen, Shunan Zhao, Huijuan Liu, Jiuhui Qu. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.11.027. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.