The grit settling unit or detritor is a continuous flow tank in which the grit settles due to gravity and the water overflows through the outlet weir on the opposite side. The settled grit is scrapped by means of a scraper mechanism towards the opening on the classifier sidewall at the bottom. Two or more scrapper arms are provided for pushing the grit into the bottom side wall opening to the cleaning chamber.

The collected grit is thoroughly washed and is delivered from the top of the classifier through a chute for disposal. Washed organic liquor, lying in the classifier, is returned to the detritor collection chamber via the organic return pump/mixer.