CITY OF LIMA WATER POLLUTION CONTROL CENTER

The city of Lima is located in northwest Ohio on the Ottawa River, which was known as “Hog Creek” at the turn of the century. It acquired this name when a settler named McClure lost a herd of hogs that drown in the head waters of the Ottawa River in eastern Allen County. Because of the increasingly polluted conditions of the river in the early 1900’s, the name of Hog Creek was adopted by most in the community because of the odors of the stream.

History

In 1930, the waste water treatment facility was constructed. This provided primary treatment (2 tanks, 0.5 MG), aeration (3 tanks, 0.5 MG each), blowers (2), final tanks (2 tanks, 0.83MG each), thickener tank (0.25 MG) (this thickener tank was never commissioned), anaerobic digestion (2 digesters, 1 MG each), and drying beds for removal of the solids.

In 1955, the facility was expanded to a total of four primary tanks (.83 MG each), three final tanks (1.2 MG each) with the addition of chlorination for disinfection. A secondary digester was also installed at this time with a capacity of 1MG.

The plant remained the same until 1973, when a massive rebuild and upgrade to the WWTP was undertaken. The design capacity was increased to 53MGD peak flow with a normal dry weather flow of 18.5 MGD. During this construction phase the aeration was nearly doubled in capacity to 7 MG. The three final tanks were retrofitted, making them into 3 additional primary settling tanks and doubling the capacity of the primary treatment. Four new final tanks (1MG each) were constructed, along with the installation of two nitrification towers for tertiary treatment. The addition of a turbine generator provided

back up power in the case of an outage. The construction of the filter building with three two-meter rotary vacuum filters and the construction of a vehicle storage building were also part of this plant upgrade.

In 1993, the turbine was removed and twin Caterpillar generators (1360 KVA and.0.8 Kw each) were installed to provide back- up power to the facility. A new screen building was constructed with the removal of the two old rotary bar rake screens. The three replacement screens that were installed are Vulcan climbing screens with .5 inch opening, with each channel having the capacity of 17.5 MGD. Screening are compacted and hauled to the land fill for disposal.

In 1999, the filter building was retrofitted with the removal of three rotary vacuum filters and installation of three Ashbrook 2-meter roll presses along with the CemenTech unit for lime stabilization of the biosolids. The windrow building was also erected to provide storage of the EQS biosolids. These

presses typically operate 40 hours per week and produce a cake of 30+% solids. The filtrate is directed back to the headworks of the facility. The filter cake is conveyed to the CemenTech unit where waste products such as lime kiln dust and fly ash are mixed with it. This elevates the pH to >12.0 and increases the dryness to >50%. With the low metals concentration and high lime value, along with TKN, P205, and the other micronutrients of the waste solids, the finished product is very valuable to the agriculture world,

thus saving space in landfills. The city of Lima typically produces about 15,000 tons per year of product.

In 2010 a partial rebuild was contracted, when new draft tube clarifiers from Ovivo/Emico were installed in the four final tanks. There were also three primary and two thickener tank clarifiers retrofitted with new scrapers and skimmers, all from Ovivo/Emico. The most significant part of the rebuild was the electrical upgrades to the WPCC. The installation of the new Caterpillar switch gear, which is operated by a standalone programmable logic controller (PLC), monitors the supply power from the utility for a uniform signal from all three phases of the power supply. If the signal fails or fails to be uniform on all three phases, the PLC recognizes the failure and will start the generator and switch to backup power. The PLC also monitors the utility power supply for return back to utility from the backup power supply. The switch gear will do this automatically in closed transition with no loss of power to the facility.

Personnel

The operations at the city of Lima WPCC are accomplished with the team work of 18 full-time employees. Positions include: Superintendent Class IV, Assistant Superintendent Class III, Operations Specialist, 1 Lab Technician, 1 Chemist, 1 Industrial Monitoring Technician , 1 Industrial Monitor Chief/Lab Supervisor, 8 Operators (4 Class III, and 4 Class I), 4 Maintenance Mechanics (2 Class III , 1 Class I, and a Collection II).

Plant Profile

Lima’s Water Pollution Control Center is a combined system that receives flow from two sources; one is the Baxter pump station, and one from the Collett Sewer. The Baxter pump station has 3 screw pumps, with each pump being capable of pumping 30MGD and discharging to a 54” line. Collett sewer is a 36” gravity line that flows into a 54”. These twin 54” lines supply the WPCC and combine just prior to screening.

The wastewater then flows to the grit removal station, where ferrous chloride is added for phosphorus control and polymer is added to aid settling in the primary tanks. The detention time in the primary tanks is maintained from 1.5 to 2.5 hours depending on flows and number of primaries in service. The waste water then flows to the aeration basins (5 tanks @ 1.4 MG each) where biologically active sludge is continuously mixed with the wastewater in the presence of oxygen. Course bubble diffusers work to mix the primary effluent with the return, and fine bubble diffusers are used to provide oxygen and mixing for the microorganisms. Microorganisms break down the organic matter in the wastewater for food for growth and reproduction, and then convert the matter into settleable biomass. All detention times vary widely within the WPCC because of the wide variation in flow to the plant. Typically the operating range is 2500mg/L MLSS in the aeration with the return operating at 3500 mg/L.

Flow from the aeration tanks enters into a wet well and is divided among four 115 ft. diameter Ovivo/ Eimco final clarifiers. All clarifiers have a 14ft side wall depth. Each clarifier contains about 1 MG. The

clarifiers allow the heavier biomass to settle while the clear effluent flows over the weirs. The clarifiers are equipped with full width skimming mechanisms which continually skim floatable material from the surface of the clarifier and remove it to the scum pit. Scum from the clarifiers is then pumped to the thickener tanks and treated with the sludge. The skimmers are also equipped with a weir-cleaning brush system which keeps the solid baffle, v-notch weirs, and flume clear of algae, eliminating the manual cleaning of the weirs by the operators.

All four final tanks have the Stanford baffles installed to prevent short circuiting of the tanks. The solids are collected by double-arm collectors, with sludge collection piping and steel raking blades, which sweep the floor of the clarifier, directing sludge to the draft tube piping. Each rake mechanism has adjustable PVC draw-off pipes to remove settled solids. The sludge collection well is located next to the return pumps. RAS flow control is accomplished by the operation of the adjustable draw-off pipes and

the RAS pumps. The RAS pumps and the WAS pumps draw from the same wet well. RAS is withdrawn and returned to the distribution flume of the aeration. Lima is very unique in the sense that the return flow is 150% of the average dry weather flow. This is done to maintain the sludge blankets in the final tanks at a manageable level.

The waste flow is pumped (0.5% solids) to the thickener tanks and from there to the anaerobic digesters (1.5%solids). The primary and secondary anaerobic digesters have a detention time of about 30 days total. Solids are then moved to the holding tanks and then to the lime stabilization process. The methane gas is captured from the anaerobic digestion process and stored in the floating cover of the secondary digester. This gas is piped to a compressor system where moisture is removed; it is then passed through filters for removal of siloxane. The compressed gas is consumed by Capstone C65 micro-turbine which

produces electricity and hot water for heating the primary digesters. The C65 micro-turbine consumes 22 SCFM of the methane gas, with any additional gas produced is either consumed by boilers or flared to the atmosphere.

Effluent from the final clarifiers flows to the final lift building where it is pumped to the nitrification towers. The nitrification towers are a packed media trickling filter where the effluent is placed in contact with zooagleal mass growing on the media to convert the ammonia nitrogen in the effluent to nitrate nitrogen. This will also boost the DO of the effluent to nearly the point of saturation. Flow then enters the chlorine contact chambers where liquid (13%) sodium hypochlorite is added for disinfection. The chlorine level is closely monitored by the operator to ensure the disinfection levels are achieved and chemicals are not wasted. The effluent then flows

by gravity to the wet well where sodium metabisufite is added to remove any remaining chlorine residual. The effluent gravity flows to the next wet well for final sampling and monitoring. pH and DO samples are collected from this well and the effluent is finally discharged to the Ottawa River. The city of Lima has worked with the Ottawa River Coalition over many years to bring some awareness to the community of the vital resource that the rivers and streams provide to Lima and Allen County.

Eric L. Markley, Assistant Supervisor City of Lima Eric.markley@cityhall.lima.oh.us