Step 1: Recall the definition of pyrolysis.
Pyrolysis is the thermal decomposition of organic materials in the absence (or near absence) of oxygen.
Step 2: Identify the correct process.
Since the waste is heated in an oxygen-free atmosphere,
\[
\boxed{\text{Pyrolysis}}
\]
is the correct answer.
Hence,
\[
\boxed{(A)}
\]
is the correct answer.