This study numerically investigates the magnetohydrodynamic (MHD) flow of a chemically reacting non-Newtonian Casson ternary hybrid nanofluid (Cu-\(\hbox {Al}_2\) \(\hbox {O}_3\)-\(\hbox {TiO}_2\)/water) over a vertically oriented stretching Riga plate, offering critical theoretical insights for the optimization of industrial micro-cooling systems and advanced electromagnetic bio-reactors. The novelty of this work lies in coupling gyrotactic bioconvection, Arrhenius activation energy, and the non-classical Cattaneo-Christov heat flux to capture thermal relaxation in a ternary suspension. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations via similarity transformations and solved using the robust bvp4c collocation algorithm in MATLAB. Quantitative results reveal that increasing the modified Hartmann number (Riga plate parameter) from 0.5 to 2.0 substantially reduces the skin friction coefficient by 89.5%, owing to the wall-parallel Lorentz force suppressing boundary layer momentum. Furthermore, enhancing the ternary nanoparticle volume fraction to 10% elevates the local heat transfer rate (Nusselt number) by over 44%. The presence of motile microorganisms stabilizes the suspension, with higher Peclet numbers actively propelling microbes away from the wall. A Second Law thermodynamic analysis indicates that the electromagnetic actuator minimizes entropy generation at the fluid-solid interface. These fundamental findings demonstrate that integrating Riga plate actuators with ternary hybrid suspensions can effectively enhance convective heat transfer while minimizing thermodynamic irreversibility in practical engineering applications.
