A 3D-printed algal-bacterial microreactor for photobiological hydrogen production coupled with actual wastewater treatment.

Microalgae-driven photosynthetic hydrogen production has emerged as a promising approach to tackle the global energy crisis and reduce carbon emissions. Simultaneously, microalgae can remove phosphorus and nitrogen from wastewater while sequestering CO2 during hydrogen production. However, challenges such as the intrinsic oxygen sensitivity of hydrogenases and the relatively low hydrogen productivity remain major hurdles that constrain the process viability of microalgae for combined wastewater treatment and hydrogen production. A 3D-bioprinted algal-bacterial microreactor (ABMR) with a core-shell structure was constructed for simultaneous actual wastewater treatment and photobiological hydrogen production. 3D bioprinting was employed to achieve precise spatial segregation of Chlamydomonas reinhardtii in the core and Shewanella sp. in the shell, thereby promoting hydrogen production. The ABMR achieved effective pollutant removal (COD 98.3 %, TN 95.7 %, TP 94.0 %) and a cumulative hydrogen yield of 1681.5 μmol H2/mg Chl. Metabolomics revealed that algal-bacterial symbiosis promoted [Fe-Fe]-hydrogenase (HydA) maturation, strengthened photosynthetic carbon fixation, and activated pyruvate metabolism to supply additional electrons. Interspecies AI‑2 signalling and the stringent response regulator ppGpp were upregulated, enhancing metabolic coordination. The ABMR fixed CO2 at 53.8 g/(L·d) and achieved a net carbon emission of only -0.21 kg CO2/m3, substantially lower than conventional processes such as A/A/O and oxidation ditch. This study demonstrated that the 3D‑printed algal‑bacterial microreactor is a promising green platform integrating wastewater treatment, renewable hydrogen generation, and carbon reduction.