The Lynn flow enters the facility via a 72 inch gravity interceptor where it is received at the Lynn Influent Pumping Station and Screening Room. Once removed, these screenings are ground by comminution equipment at which time they are ejected to the Solids Building to be burned with the sludge. The screened Lynn wastewater is combined with the Nahant, Saugus and Swampscott flows just prior to the grit removal system. Grit is sand and small hard inorganic material that, much like sand paper will wear down expensive equipment if not removed in the begining of the plant.
Grit removal is the next process for which all four combined flows receive treatment.
There are four aerated grit chambers in which a mild aeration process freshens and keeps light organic solids suspended in the wastewater while allowing the heavier inorganic solids to settle to the bottom of the tank and be collected by the bucket elevator system which removes these inorganic solids. Once removed, these solids are washed, collected and ejected into covered containers. Grit is transported in these containers to an onsite landfill, where the grit is dumped and covered daily. The wastewater then flow on to the Primary Treatment process.