Right choice is (d) Noise
Explanation: Noise is not a waste that is generated in the waste treatment processes as it is a sound which affects the environment but physically doesn’t, so, it’s not a major concern. Whereas, sludge, ash, organic solvents are generated during various processes like incineration, wet scrubbers, distillation etc. These are generated in waste treatment processes and can be a serious threat to the environment if not disposed of properly.