The wood industry produces enormous quantities of lignocellulosic by-products, such as sawdust, and their incineration for energy recovery results in substantial carbon emissions and the loss of valuable raw materials. Here, we introduce struvite as a fully recyclable inorganic binder for the consolidation of sawdust into high-performance hybrid materials. The mineral binder is produced in situ by an enzymatically induced solution-mediated phase transformation driven by ureolytic protein bodies extracted from watermelon seeds. The resulting material exhibits excellent fire resistance with a long time to ignition (51 ± 1 s), low peak heat release (118 ± 2 kW m⁻²), and fast flame self-extinction due to efficient char-layer formation. Moreover, it displays high compressive strength (4.71 ± 0.37 MPa). Crucially for sustainability, the struvite binder can be recovered under mild aqueous conditions without loss of performance, offering a valid path toward a circular materials economy.