A continuous process for the biological solubilization of heavy metals from primary or other metal-laden sewage that utilizes indigenous sulphur oxidizing bacteria and elemental sulphur as the energy source, prevents nitrite formation and minimizes the residual sulphur remaining in the processed biosolids. The process includes the steps of: enriching indigenous sulphur oxidizing bacteria in sewage sludge in an aerobic biological reactor at or above ambient temperatures; the feeding of sludge and elemental sulphur to this reactor to achieve a steady-state characterized by a pH