Grit slurry from grit chambers contains organic solids. Grit classifiers separate some organic solids and water from the slurry, but the product still contains around 30% mineral grit, 20% organic dry solids and 50% water (by weight). It is odorous and attractive to pathogen vectors, and transport and disposal are expensive. By effective grit washing, the product would become virtually odorless and its mass would be reduced to around 30%. Clean grit with an organic content of below 3% does not need to be disposed of, but can be used as construction material, e.g. for road or pipe bedding.

These objectives are achievable by using the fluidized bed grit washer RoSF4 COANDA. Organics are effectively removed from grit particles due to the turbulent flow and high shear forces within the fluidized bed. Stratification of layers in a fluidized bed does not depend on the size and settling velocity of particles, but only on their specific density, as is well known from backwashing of multilayer sand filters. Mineral grit particles have a far higher density than organic solids. Even very small grit particles accumulate in the bottom layer of a fluidized bed, while organic particles are either washed out at the top or form another layer above the grit layer, which is periodically removed.

Well-washed grit contains less than 3% organics and less than 10% water. The capture rate of 0.2 mm diameter (approx. 75 mesh) grit particles is above 95%. Grit washers must have at least the same grit capture rate as grit traps. Fluidized bed grit washers reduce the mass of grit slurries from grit traps, and therewith, their transport and disposal costs by as much as 70 to 90% depending on organic content. Typical return of investment periods as compared to conventional grit classifiers are three to five years.

About Huber Technology
Huber Technology provides state-of-the-art equipment for municipal and industrial water and wastewater treatment. Its main focus is liquid/solid separation in general and headworks equipment in particular. Huber offers a comprehensive line of stainless steel equipment. For more information, visit www.huber-technology.com.