Two processes influencing the functionality of a filter are ripening and regeneration.At the beginning of a new filter run, the filter efficiency increases simultaneously with the number of captured particles in the medium. This process is called filter ripening. During filter ripening the effluent might not meet quality criteria and must be reinjected at previous steps in the plant. Regeneration methods allow the reuse of the filter medium. Accumulated solids from the filter bed are removed. During backwashing, water (and air) is pumped backwards through the filter system. Backwash water may partially be reinjected in front of the filter process and generated sewage needs to be discarded. The backwashing time is determined by either the turbidity value behind the filter, which must not exceed a set threshold, or by the head loss across the filter medium, which must also not exceed a certain value.