This invention proposes the use of Thermal Hydrolysis (or Thermal Carbonization) at different temperatures and pressures in alternate waste streams to achieve an optimal mix of high digestion rates and pasteurization rates while still achieving large viscosity reduction. In the disclosed embodiments means of combining Thermal Hydrolysis (or Thermal Carbonization) and Pasteurization including but not limited to placing the waste streams in parallel, placing them in series, utilizing heat input in parallel and heat exchangers in series are explored to optimize hydrolysis rates, minimize the use of high pressure tanks, optimize energy used, and manage viscosity characteristics of the solids.