The Village of Ohio City Wastewater Treatment Plant
BY DANIEL W. MILLER, P.E., DIRECTOR OF WASTEWATER; JOSEPH HOTZ, P.E., VICE PRESIDENT; PAUL FLETCHER, PROJECT ENGINEER; DOUG BROOKHART, OOPERATIONS SPECIALIST
The Village of Ohio City is located in Liberty Township in the southern part of Van Wert County. As of the census of 2000, there were 784 people residing in the village. The population has been stable over the last 10 years.
The original wastewater treatment plant, constructed in 1968, had an average daily flow of 120,000 gallons per day (gpd), a design capacity of 150,000 gpd and a peak flow of 350,000 gpd. Treatment consisted of a Spiragester for primary settlement and solids stabilization, one rock media trickling filter, one final clarifier and chlorination followed later by dechlorination. Thickened sludge from the Spiragester was transferred to drying beds. The treatment plant had overall removals for TSS, BOD and ammonia of 81%, 85% and 67% respectively. The plant discharges to Prairie Ditch, a tributary of Little Auglaize River.
A number of upgrades to the collection system were made between 1993 and 2001. However, although these upgrades being fairly recent, there were high flows during wet weather, and ongoing I/I issues.
By 2005, the average daily flow was 130,000 gpd and peak daily flow had increased to almost 620,000 gpd, which consisted of 350,000 gpd treated flow and 270,000 gpd through the plant bypass.
The WWTP has been missing its effluent limits on both BOD and ammonia as far back as 2003 and has also had some more recent failures on total suspended solids (TSS). 30 day limits were 2.3 mg/l ammonia (summer) and 6.0 mg/l ammonia (winter), 10 mg/l BOD and 20 mg/l TSS. In addition, with the equipment being almost 40 years old, it was becoming difficult to maintain. With one of each process unit, there was also no redundancy.
With the renewal of the NPDES Permit in 2007, the Village hired a local consultant (Mote & Associates) to address modifications required to the WWTP to allow it to consistently meet the permitted levels for BOD and ammonia.
In March 2007, Mote & Associates hired Jones & Henry Engineers to provide engineering services. Jones & Henry produced a preliminary WWTP Expansion report. The report proposed demolition of the pump station, clarifier, trickling filter and Spiragester tank and construction of a new WWTP on a 5 acre site the Village owned adjacent to the existing plant. The existing chlorination tank and outfall structure were to be left in place. Demolition would include removal of the equipment and demolishing the structures to below grade. The area would then be re-graded and seeded.
Funding for the new plant project involved three sources. The sources included a $500,000 CDBG grant, a $500,000 OPWC grant, a $1,000,000 OPWC loan and a $1,500,000 WPCLF loan.
Three extended aeration process configurations were considered. All configurations were costed as a complete installed system with pumping, screening, disinfection and sludge stabilization included in the construction and operational costs.
The first configuration was a packaged extended aeration system - with the carbonaceous and nitrifying stages in series - and final clarifiers.
The second configuration was a continuous sequential batch reactor (SBR). SBR is a fill and draw system with flow equalization, aeration and settlement all occurring in the same tank.
The third configuration considered was an oxidation ditch / clarifier combination. Oxidation ditches can typically handle peak: average flow ratios of up to 5:1. Aeration in the ditches is typically by surface aeration using brushes or rotors. Owing to the simple external mechanisms, oxidation ditches require low maintenance and minimal operator attention. Oxidation ditch technology can be simple for BOD and ammonia removal or become more complex should denitrification and biological phosphorous removal be required. For Ohio City, the system had two ditches operating in parallel followed by two clarifiers. A common sludge pumping system would be used.
Life cycle cost analysis done over a 20 year period using 5 percent interest found the three configurations to be extremely close in terms of Net Present Worth (NPW). The option with the lowest NPW was the oxidation ditch, which had the highest project installation costs but the lowest labor and maintenance / replacement costs. The oxidation ditch also was the most secure in terms of permit limits under storm flow conditions. This is the treatment option that was proposed to the Village.
Early on in the detailed design stage of the project, it was proposed that the two oxidation ditch system be modified to a single ‘Orbal’ type ditch (Siemens) with two rings, with which they would be able to use their SmartBNR system to cope with storm flows. SmartBNR has two modes of operation depending on influent flows. For high flows, the system would operate in Storm Flow Mode, which diverts return sludge flows to hold solids within the activated sludge system and prevent solids loss from the clarifiers.
The Orbal design was originally a simple two channel design which made no allowance for future permit modifications, in particular the addition of a denitrification requirement which would require an anoxic tank. The Orbal design was therefore modified, adding a simple stirred tank connected to the outer channel, which could be used for mixing incoming wastewater and return sludge at this stage and as an anoxic tank in future.
In addition to the oxidation ditches, the project also included replacement of the lift station that was removed, screening prior to treatment, UV disinfection and aerobic digestion for stabilization of waste sludges. The existing sludge drying beds were to remain.
Flows now gravitate to a new submersible pump station at the wastewater treatment plant, where they are pumped to treatment. Supernatant and drainage also flow through the new pump station.
A mechanical fine screen is located in a channel above the anoxic tank. The screen and washwater supply is insulated and trace heated. Raw sewage flow is pumped to this channel and screened sewage drops through a hole in the screen channel floor into the anoxic tank; the return sludge is pumped directly into the anoxic tank. From the anoxic tank, flows proceed into the Orbal for biological treatment. Selection of whether flows pass to the inner or outer channel of the Orbal is made by valving.
Flows are fed to the outer Orbal channel most of the time. Flows run around the outer channel and pass through a submerged orifice to the inner channel. Both channels have surface aeration which operates as required. From the inner channel, aerated wastewater passes through an adjustable sluice gate and over a weir and is piped to the clarifiers. The adjustable gate allows the depth of liquid in the Orbal to be altered, which in turn alters the depth of submergence if the aerators and the amount of oxygen transferred.
Clarifiers are concrete with bridge supported mechanisms to push the settling sludges to the center of the tank. Sludges are withdrawn to a common return and waste sludge pump station. A timed valving arrangement either returns sludge to the Orbal or wastes sludge to the aerobic digesters to be stabilized.
Clarified effluent passes forward for disinfection through a UV disinfection system. The chlorine contact tank was taken out of service and a new channel constructed for the UV lamps. The existing final effluent v-notch flow measurement weir was modified to be able to measure larger flows. The original outfall pipe remains.
Waste sludges are stabilized in new aerobic digesters. Two new tanks with new supernatant decant telescoping valves, blowers, piping and diffusers were installed as part of the project.
Once stable, sludges are pumped to either existing sludge drying beds – from where they can be transferred to new sludge storage – or direct to tanker for transport off-site for land application.
Drainage from the drying beds and sludge storage, as well as supernatant decanted from the aerobic digesters, are routed back to the raw wastewater pump station.
The final part of the contract was construction of a service building to accommodate laboratory and office space, a restroom, an electrical room for the controls and motor control center and a garage.
Jones & Henry Engineers also assisted the Village with start-up of the new treatment plant. The plant was started up on July 5, 2011. On that day, aeration channels and clarifiers were filled with final effluent from the Village’s existing trickling filter plant. On July 6th, a piping change was made at the inlet to the old treatment plant allowing raw sewage to begin flowing to the new raw sewage pumping station.
During the day, a local hauler brought in 20,000 gallons of return sludge from the Van Wert Wastewater Treatment Plant which is located ten miles north of Ohio City. Prior inspection of the Van Wert return sludge revealed a stable activated sludge with no filaments and a very good history of ammonia, and cBOD removal.
Within two days of the start-up, cBOD, TSS and ammonia removals were occurring and just over a week after start-up, laboratory results indicated effluent from the Orbal contained 5.2 mg/L cBOD, 2.8 mg/L TSS and 0.5 mg/L ammonia.
The build-up of mixed liquor suspended solids concentration in the outer and inner aeration channels took some time based upon daily flows of 110,000 gpm and raw sewage cBOD concentrations of 100 – 200 mg/l. Within three weeks MLSS values were over 2000 mg/l.
As months went by, the Village experienced increased flows during rain events. Figure 1 shows a graph of rainfall and daily flow for the month of October 2011.
Wastewater Treatment Plant, Sandusky, Ohio
BY DAIL HOLLOPETER, P.E.
In December 2010, the facilities constituting the most recent improvements to the Sandusky Wastewater Treatment Plant were started up. This marked the culmination of two phases of significant improvements which were originally planned as part of a 1997 General Plan, ordered to be prepared by a 1995 Consent Order.
The first wastewater treatment plant in Sandusky went into operation in December 1915. Reportedly this plant was operated for only a few months until it was decided that due to high flows received at the plant it would be permanently bypassed. For the next four and one half decades, the wastewater from the City of Sandusky was discharged untreated directly into Sandusky Bay. The water quality in Sandusky Bay gradually deteriorated and swimming was eventually banned in Sandusky Bay. Over the years, the City had several studies prepared on evaluating treatment of the wastewater to improve the water quality in Sandusky Bay. In 1940, the potable water problem was solved by constructing a new water treatment plant with a raw water intake extending beyond the confines of Sandusky Bay.
Due to increasing pressure from the State Board of Health, the City commissioned another wastewater study and recommendations were made in 1950 for construction of an interceptor system and primary treatment facility to be located at the present site on the banks of Sandusky Bay at the foot of Harrison Street. These facilities were sized to accommodate the needs of the City as well as neighboring portions of Erie County. In 1960, the new 12.0 mgd average daily flow primary treatment facilities with anaerobic sludge digestion and vacuum filter sludge dewatering along with an interceptor system were placed in operation. Total construction costs were $4.2 million.
Secondary treatment facilities consisting of an activated sludge system, with a design capacity of 12.5 mgd average daily flow, were started up in 1971. Additional anaerobic sludge digestion facilities were added in 1992.
The first phase of improvements mandated by the 1995 Consent Order and the resulting 1997 General Plan, were completed in 2005 and consisted primarily of three new headworks screens, one grit removal tank, a primary settling tank, a primary digester, and UV effluent disinfection. At the completion of the Phase I, the treatment plant had a rated average daily flow of 14.7 mgd and a peak hydraulic capacity of 24 mgd. The facilities installed in Phase I were sized to accommodate an eventual average daily flow of 15.7 mgd and a peak hydraulic capacity of 36.0 mgd.
Effluent Permit Limits
The monthly effluent concentration limits include TSS of 19 mg/L, CBOD of 14 mg/L, ammonia of 14 mg/L, total phosphorus of 1.0 mg/L, and E. coli of 126/100 ml. Effluent mass loading limits are based on wet weather flow of 22.0 mgd.
Phase II Improvements
At the start of Phase II, the scope of work as described in the 1997 General Plan consisted of a new aeration tank, new or rehabilitated final clarifier, new secondary digester, and rehabilitation or modifications of the Aeration Control Building, sludge heat exchangers, secondary digesters and site improvements. The project budget was $18.0 million.
The design work was authorized in early 2007. Ohio EPA called for a meeting in April 2007 to announce that a Preliminary Engineering Report was to be prepared and submitted to Ohio EPA for approval before a Permit to Install could be submitted. This Preliminary Engineering Report was to re-examine the flows generated within the collection system and review all feasible alternatives to minimize combined sewer overflows. This reexamination ultimately led to Ohio EPA’s requirement to modify all necessary facilities at the wastewater plant to allow 42.0 mgd to be processed through the plant. This required modifications to the existing grit tanks and an additional 16.0 mgd capacity UV system to be added at the plant effluent. These changes were in addition to the upsizing of the new final clarifiers, related piping, and effluent pumps. In addition, the final contract included modifications to the plant laboratory and locker rooms, a centrifuge for sludge dewatering and an off-site sludge cake storage pad. The existing rectangular and relatively shallow final settling tanks were demolished to make room for the second new final clarifier. About 7 to 8 feet of very hard dolomite limestone bedrock had to be excavated for the new deeper final clarifiers and lesser amounts of the rock had to be removed for the new aeration tank, secondary digester, and effluent pump station. Final construction cost, including all change orders, was $17.3 million.
The construction and engineering costs were shared between the City and Erie County on the basis of a negotiated level of participation. Each party secured a separate loan from the Ohio Water Development Authority to cover their portion of the project costs.
Wastewater Treatment Plant Description
All wastewater enters the treatment plant through a 66 inch interceptor. Three screens, each four feet wide provide screening prior to the raw wastewater pumps. Five raw pumps, ranging in capacity from 12.0 mgd to 22.0 mgd and two of which are engine-driven, discharge to three aerated grit tanks. Primary treatment is provided in three 100-feet diameter settling tanks. The activated sludge system consists of three two-pass aeration tanks, each pass 26 feet by 190 feet by 15 feet swd, with fine bubble diffused air. Two final clarifiers, 132 feet diameter 14 feet swd are peripheral feed peripheral overflow with single manifold return activated sludge removal. Effluent disinfection is provided by a 36.0 mgd rated and a 16.0 mgd rated high intensity medium pressure ultraviolet light systems. Four submersible propeller effluent pumps, each rated for 17 .3 mgd, are available as needed during high lake levels and/or during high wet weather flow rates through the treatment plant.
Six new return sludge pumps and two new waste sludge pumps were installed. The activated sludge system can be run in conventional mode, or in contact stabilization or step feed mode. Three new peristaltic pumps were added for ferrous chloride addition to the aeration tanks. The four existing blowers were sized sufficiently to supply all three aeration tanks due to the increased efficiency of the new membrane diffusers.
Primary sludge and gravity-thickened waste activated sludge are anaerobically digested in four primary digesters followed by two secondary digesters and an existing 50 feet diameter secondary digester which was converted to a storage tank, The storage tank is used to feed the new centrifuge rated to thicken or dewater digested sludge at a peak feed rate of 200 gpm for thickening and 120 gpm for dewatering. The new centrifuge provides the City with several options for biosolids disposal. They may continue to land apply liquid biosolids, land apply thickened (7-8%)liquid biosolids, or produce biosolids cake from the centrifuge. The City plans to review multiple disposal strategies with the new options available
The new secondary digester has a dual membrane cover for increased digester gas storage. The plant makes very good use of digester gas for heating the primary digesters, running the engine-driven raw wastewater pumps and running the engine-driven blowers for the aerated grit tanks.
One other interesting feature of the treatment plant is the outfall to Sandusky Bay. This 48 inch diameter outfall was constructed in 1957, is below the lake bottom over its full length of 1900 feet. The outfall profile includes a 37 foot dip in the middle of its length to pass under a shipping channel which is 300 feet wide. The presence of the shipping channel required the pipe to be placed at a depth that resulted in the removal of 15 to 20 feet of dolomite limestone bedrock. The end of the outfall is supported on timber piles and discharges into a pit excavated 11 feet deep into the lake bottom. At the shore where the outfall pipe starts, an overflow chamber was built with weirs at a height that allows the treated effluent to overflow during very high water levels and/or very high plant discharge flow rates.
Plant Control System
Plant processes and equipment are monitored and controlled via a PLC based plant-wide process control system. Distributed PLCs are connected via fiber optic cable. Wonderware software is loaded on numerous PCs for use by the plant staff to interact with the control system. A radio receiver is used for obtaining alarms and data from remote pump stations and CSOs.
The wastewater treatment plant is staffed at all times. Fourteen people are responsible for operations and maintenance. Three people are assigned to laboratory, regulatory reporting, and industrial pretreatment. The wastewater superintendent supervises all plant personnel.
The project was managed throughout the design and construction phases by a steering team consisting of the WWTP Superintendent, the City Engineer and the County Sanitary Engineer working with the engineering consultant, Jones & Henry Engineers, Ltd. This steering team selected the engineering consultant, met regularly with the engineering team during the design phase to review progress and budget status, attended meetings with Ohio EPA, and participated in monthly construction meetings. The project was a successful example of joint management and cooperation between two governmental entities on a significant capital improvement project.
Green Building Ramblings
BY JEFF HERSHA
So,…when is green, GREEN?
What is Green Building and how does it affect your community?
The Green movement has its’ proverbial roots in the cultural revolution of the 1960’s. Americans saw rivers ablaze, chemical waste leaching from the ground, and waterways turned to sewers. Smog was settling permanently into the LA Basin and agricultural run-off was creating a chemical dead zone in the Gulf of Mexico. Many cities and towns were discovering the byproducts of Civic and Corporate abuse and neglect of the environment.
As the impact of our growing industrial and consumer lifestyle became apparent the country moved to make amends. The formation of the United States Environmental Protection Agency,(USEPA), and the passing of the Clean Air and Clean Water Acts were center stage at the national level. State agencies such as our Indiana Department of Environmental Management,(IDEM), were formed to regulate at a state level, and grassroots organizations in our neighborhoods began picking up garbage and trash from our rivers and roadways. Recycling programs took off. We had made some terrible messes…and now we were cleaning them up.
As the awareness of our environment grew, we started thinking about the buildings in which we live and work. We looked at how the built environment impacted our natural environment. A new generation of architects, engineers, planners and builders began looking at better ways to build. We looked at the environmental impact of how and why we build, as well as the energy and environmental impacts of constructing, powering, and then ultimately razing our structures. We now look more critically at the life cycle impact of a building. The concept of “cradle to grave costs” entered the lexicon.
Leading the way today, is the U.S. Green Building Council, (USGBC) a “non-profit organization committed to expanding sustainable building practices.” The USGBC uses the Leadership in Energy and Environmental Design (LEED) Green Building Rating System to quantify and score a building’s “Greenness”. As the reigning organization of green building principals in residential, commercial, and municipal building projects, a USGBC LEED certification carries clout.
We have all seen the radio and TV commercials, as well as print advertising touting the latest in “Green”. My beautiful wife informed me one evening that our quick Thursday night dinner before soccer and Cub Scouts was “processed by an environmentally responsible food manufacturer”, and, “was produced in the world’s first LEED Certified frozen food manufacturing plant”. Wow! I had never felt better about stir-fry.
So what does this all mean to you? You are the leaders of your communities. As you look at your next fire station, wastewater plant, or administrative office building, what does this new “GREEN” mean? I can say, without reservation, “It Depends”.
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