To reduce the cost for discharge of wastewater and disposal of fats, a Dutch slaughterhouse installed a finescreen before the existing grease trap. The finescreen removes the present suspended solids (TSS) and fats (FOG) and dewaters it to a solid product. The grease trap remained in operation for the removal of remaining fats that can be separated because of cooling of wastewater. The scum layer of grease trap is returned to the finescreen were it is dewatered with the first stage separated material.