First constructed in 1930, the Lima Wastewater Treatment Plant consisted of screening, grit removal, primary sedimentation, and anaerobic digestion. Throughout the years, secondary treatment, tertiary treatment and additional sludge digestion were added. In 1973, the plant was expanded to an average dry weather flow capacity of 18.5 million gallons per day (MGD), and a peak flow capacity of 53 MGD. The design concept called for secondary and advanced treatment processes of the plant to operate at a peak rate of 33 MGD, with any remaining flow receiving primary settling and chlorination. Since 1973 the plant has provided primary, secondary and tertiary treatment, as well as biosolids and digester gas recycling.
The most recent upgrade, in 2016 entailed rebuilding the headworks and primary treatment at the plant to increase the peak flow capacity to 70 MGD with four new bar screens (headworks) rated at 23.3 MGD each; four aerated grit tanks using two Hydrogritter systems; and four new primary settling tanks, bringing the total number of primary tanks to seven.
Facility staff maintain 32 sewage lift stations throughout the collection system, the interceptor sewer, 18 permitted CSO (combined sewer overflow) locations and the 13 million gallon combined sewer storage tank.