MWWA 2020 Conference & Tradeshow

Expectations for grit system performance can often be limited. Operator dissatisfaction with grit removal systems is all too common. Conventional guidelines target removal of relatively coarse grit larger than 212 micron. In fact, many wastewater treatment plants find over 50% of their influent grit is smaller than 212 micron. In addition to targeting coarse particles, many designs do not account for slow settling grit which are impacted by irregular shape and lower specific gravity. This can lead to capture efficiencies far less than 50%. Wastewater grit is comprised of silica sand as well as various other materials that do not have a specific gravity of 2.65. Further, grit particles are not all perfect spheres and finally, grit is exposed to fats, oils, greases, and soaps in the collection system which coats the grit and changes its settling velocity. Grit systems can achieve removal efficiencies over 90% when designed with an accurate understanding of the nature and characteristics of the grit arriving at the treatment plant and how this grit actually behaves in wastewater. Advancements in grit management technology now allow 95% capture of grit ≥ 75 micron while producing a clean, dry output product.