Adding powdered activated carbon to a used GAC fluidized-bed reactor can help regenerate the exhausted GAC. By studying the behavior of p-nitrophenol in the system, researchers found that the desorption process was faster with the addition of powdered activated carbon. This means that the exhausted GAC can be partially regenerated by periodically adding powdered activated carbon to the reactor. The majority of the added powdered activated carbon stays in the reactor even at high flow rates, extending its usefulness.