Wastewater Department Collection System
The Archbold sanitary sewer system is a separated system with a service area of approximately 2800 acres. The system consists of approximately 40 miles of sewer pipe ranging in size between 8 inches and 27 inches in diameter. Seven (7) wastewater pump stations are located in the Village’s collection system.
The Archbold Wastewater Treatment Plant is a 2.5 MGD (million gallons per day) design flow, 5.0 MGD peak flow, activated sludge process. Any influent over a flow rate of 5.0 MGD is diverted to an overflow retention basin. This flow is then slowly brought back to the plant when the flow rate subsides. Anaerobic digesters are used for sludge stabilization. Raw wastewater enters the plant and passes through an automatically cleaned bar screen, which removes rags and other debris which may cause plugging problems within the plant, and flows into the raw wet well. Four centrifugal pumps operate automatically to pump the wastewater into the aerated grit chamber. Lime is added to the grit tank effluent for phosphorus and solids removal in the primary settling tanks.
The grit tank effluent then flows by gravity to the four primary settling tanks. These tanks provide necessary solids settling to the bottom of the tank, thus allowing the cleaner wastewater to flow to the next phase of treatment. The combination surface scum collection and tank bottom scraping flights continuously operate to collect the solids for removal. Solids are periodically pumped to the digesters for further treatment.
Secondary treatment is provided in seven aeration tanks and two secondary settling tanks. Air is introduced into the aeration tanks to provide mixing and an optimum oxygen level for bacteria growth. The bacteria consume most of the dissolved organic matter and ammonia in the wastewater. The aeration tanks are operated in the contact stabilization mode. The aeration tank effluent then flows to the secondary settling tanks to separate the biomass (solids) from the water.
Most of the biomass is recycled back to the aeration tanks to provide proper bacteria levels in the aeration tanks. Secondary settling tank effluent flows into the chlorine contact tank followed by the post aeration tank where it is disinfected with chlorine to kill pathogenic organisms. Any remaining chlorine is removed using sodium bisulfite. The effluent from the post aeration tank flows through a parshall flume for flow measurement and then discharges to Brush Creek.
The solids removed during the treatment process are pumped to two anaerobic digesters which are heated to approximately 96 degrees F. The methane gas produced during the digestion process is used to heat the biosolids. The digested biosolids are then pumped from the digesters to the biosolids storage lagoons to allow for liquid and solids separation and to await land application. The biosolids are eventually land applied to fields as a source of nitrogen and phosphorus.
Treatment Plant and Collection System
The work of the personnel at the wastewater department is varied. They are responsible for the operation and maintenance of the equipment, buildings, lift stations, and grounds plus laboratory testing and EPA reporting. The plant is staffed seven days a week. The main responsibility is to protect the environment by ensuring that the wastewater from the Village entering into Brush Creek is as clean as the plant equipment and technology allows.
The U.S. and Ohio Environmental Protection Agencies mandates the degree of treatment that the wastewater plant must achieve. The Village is issued a National Pollutant Discharge Elimination System (NPDES) permit which sets effluent (discharge) limitations, monitoring requirements and additional requirements for influent (raw wastewater), upstream, downstream, and biosolids. The Village is required by the Clean Water Act to meet treatment standards or face court action to come into compliance with these requirements. If compliance is not met or treatment is inadequate, there can be fines of up to tens of thousands of dollars per day or per violation levied against the Village.
The Ohio EPA requires the treatment plant must be under the supervision of a Class III State certified operator. All six staff members currently hold various levels of certification. (5 Class III, 1 Class I) Information and training gained from this schooling helps the personnel maintain the equipment at the wastewater treatment plant. This includes approximately 20 pumps and controls, mechanical bar screen, grit collector, numerous gear reducers, air blowers, collector mechanisms, generator, chlorinators, boiler, many smaller items, building maintenance, and grounds keeping.
The wastewater treatment tanks must also be drained, cleaned, inspected, and repaired on a regular basis. Sanitary sewer taps from new buildings are inspected for conformance with the sewer use ordinance. The department also regularly cleans sewer lines to remove potential blockages and maintain flow. Personnel inspect existing sewers and manholes for structural conditions and monitor and maintain the seven lift stations. In 2010 the average CBOD received at the treatment plant was 10,589 lbs/day (63,407 population equivalent). The average suspended solids received was 8,374 lbs/day (41,870 population equivalent). The treatment plant treated an average daily flow of 1.641 MGD, removed 96.8% of the suspended solids, 99.1% of the CBOD, 92.4% of the ammonia, and 90.5% of the phosphorus entering the plant.