What does a higher sludge age in an activated sludge process generally indicate?

A higher sludge age in an activated sludge process generally indicates better settling characteristics. This is because with an increased sludge age, the microorganisms in the system have more time to grow and mature. As they adapt to the environment, these microorganisms tend to form larger flocs, which settle more effectively in the sedimentation tank. Enhanced settling characteristics reduce the likelihood of solids being carried over into the effluent, leading to improved water quality.

While the remaining choices may have their own relevance to the activated sludge process, they do not accurately reflect the implications of a higher sludge age. For instance, lower bacterial activity typically occurs with a shorter sludge age, not a longer one; higher oxygen demand can arise due to various process factors unrelated to sludge age; and although more organic matter can be removed over time, the effectiveness of removal in terms of floc formation and settling is a primary consideration of sludge age.