Dealing with Fine Grit at WWTPs

Fine grit consists of inorganic abrasive solids. Failure to remove grit from the treatment process results in wear of mechanical equipment, grit deposits in settling basins, aeration systems, digesters, Membrane Biological Reactors, and sequencing batch reactors. Grit handling and disposal are increasingly difficult tasks because many grit removal systems yield a final product that is high in organic content and retains substantial amounts of moisture, making it highly susceptible to decomposition and odor generation. Desired degree of washing, space constraints, and available budget are some of the factors that determine which system will most closely serve the needs of a community. Fine grit removal challenges at each WWTP may be different depending on native grit characteristics and plant processes employed. Proper sampling prior to design will determine sizing requirements necessary to achieve a specified removal performance. Most grit enters the WWTP during peak flow events, scouring out the collection system, therefore testing of the grit load should be performed during these periods. This paper discusses multiple fine grit removal systems and present data from pilot studies carried out in Florida and Georgia.