Treating Peak Flows using Submerged MBR Technology – The Delphos, Oh MBR System

The City of Delphos, Ohio along with their engineers designed a new state-of-the-art wastewater treatment plant utilizing flat plate membrane technology coupled with a 2nd generation ATAD solids treatment system to address the current and future needs of the City as well as the Directors Final Findings and Orders (DFFOs) filed against the City by the Ohio Environmental Protection Agency (EPA). Start-up of the new facility occurred in October 2006. The City received funding for this project from the Ohio EPA's Division of Environmental and Financial Assistance (DEFA). The plant has a design average day flow of 3.83 MGD with a peak 48-hour flow of 12 MGD and an 8-hour peak flow of 18 MGD. The average dry weather flow is 1.5 MGD. The ATAD system is designed for a loading of 8,700 lbs/day. This paper will predominately focus on the logistics of the use of the flat plate membrane technology in dealing with the variable hydraulic fluctuations seen in the Delphos community.The project included: an addition to an existing equalization basin bringing the total storm equalization capacity of the system to 12 million gallons; a new pumping station with course screens at the existing plant with two 18 inch force mains to pump the flow to the new plant site; a headworks building with fine screening and grit and grease removal; a septage receiving station; a membrane bioreactor using flat plate technology; vertical ultraviolet (UV) disinfection system; ATAD (Class A or exceptional quality) solids handling system with gravity belt/ belt press units; SCADA control system; new administration building with offices, laboratory and vehicle storage and demolition of the existing facilities.The treatment plant is designed to deal with two unique situations present in Delphos. The City of Delphos has a seventy percent combined collection system; thus, there can be large fluctuations in flow during wet weather events. The average dry weather flow for the community is 1.5 MGD; however, with just ½ inch of rainfall, the flow at the plant can increase to 12 MGD quickly. The new plant is designed for an 8 hour peak sustained flow of 18 MGD and a 48 hour peak sustained flow of 12 MGD. In addition to the peak capacity of the plant, the City of Delphos has 12 million gallons of storm pond holding capacity connected to two interceptor sewers that collect water in excess of the capacity of the existing collection system.The second unique situation in Delphos is the design loading for the facility. The plant is designed for 12,000 lbs./day carbonaceous biological oxygen demand (CBOD5) and 9,000 lbs./day total suspended solids (TSS). The conventional loading to the facility is extremely high for a community of only 7,000 people. The population equivalent for the City of Delphos is in excess of 50,000 people. This is due to the high loading attributed to the food manufacturing flows coming from three industries located in Delphos. These facilities manufacturer such products as mashed potatoes, sour cream based dips and desserts, gelatin products and soybean meal and oil. Based on production of particular product lines and varying with holidays, the loading to the plant can be highly variable. The membrane bioreactor treatment system lends itself to dealing with this variability and the variation in hydraulic loadings much more easily than other types of conventional activated sludge facilities would have. In addition, the membranes provided for a smaller footprint allowing for future growth on the green site which was important to the City Administration in their quest for economic development of the City.