The activated sludge treatment plant broke down for a period of several days. It has since started up again. My question is how this is going to affect the trickling filter and whether this will be noticeable right away or will it take time?
Stoppage in a trickling filter is not as bad as when it happens in the middle of the activated sludge process. If the ambient temperature is not too high (depending on what region of the world you are in) and the bed is not too dry, it won't take too long for the trickling filter to be up and running again. On the other hand, if you are in a colder area with low temperatures, this works to your advantage. The reduced bacterial activity is a plus, and in that case the trickling filter should be able to start up immediately.
Hope that gives you some insight.
Since you were not able to feed raw effluent into the system, were you able to maintain recirculation?