Cambridge Wastewater Treatment Facility

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Giles Flowers
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1 Cambridge Wastewater Treatment Facility Emergency Situations If you have a water or sewer emergency that relates to the City s utility system call the Public Works office at on normal working days, 7:30 a.m. to 4:00 p.m. For water or sewer emergencies outside of normal office hours, call the Isanti County Sheriff s office at and they will dispatch city staff. W elcome to the Cambridge Wastewater Treatment Facility (WWTF) located at th Avenue Northeast. This facility and staff have been recipients of two major awards since the completion of the facility in The City of Cambridge was awarded the Grand Award from the Consulting Engineers Council of Minnesota for Engineering Excellence and staff has received First Place in Region 5 for the USEPA Operation and Maintenance (O& M) Excellence Award in the Medium Advanced Category for Cambridge was selected from the medium sized facilities (one million ten million gallons treated per day) in the states of Minnesota, Wisconsin, Illinois, Indiana, Ohio, and Michigan. Cambridge faced numerous constraints on improving the existing facility, which was overloaded hydraulically and organically. Stringent site restrictions were posed by the plant s location on the Rum River, designated on Outstanding Resource Value (ORV) river. The City of Cambridge designed a new facility to provide improved wastewater treatment and developed a system which works in conjunction with existing equipment to provide increased operator control, process flexibility, and resource conservation at a reasonable cost.

W elcome to the Cambridge Wastewater Treatment Facility (WWTF) located at 800 7 th Avenue Northeast.

2 Site Limitations Common wall construction methods enabled best usage of the limited space. Caisson construction was used to sink the Pretreatment Building in place, so that other structures were not undermined and the existing treeline was protected. Protecting the Rum River The ORV designation for the Rum River legislates effluent standards for nutrient removal and advanced treatment. Effluent filters enable the plant to comply with strict tertiary standards. Traveling bridge filters, selected for their low headloss characteristics, incorporate air scouring with the normal bridge backwashing. This process results in much cleaner media bed cells and longer run times between backwashing. Controlling Odors The existing plant s location in a populated area near the hospital caused many odor and traffic complaints. Covered tanks, attractive campus-like buildings and a naturally landscaped outfall now minimize the problems caused by the plant s location. Activated-carbon odor-control units have been added to the existing and new facilities.

Protecting the Rum River The ORV designation for the Rum River legislates effluent standards for nutrient removal and advanced treatment.

3 Future Expansion Cambridge is undergoing rapid residential and commercial growth through development and annexation. The new wastewater treatment facility serves the growing population cost effectively, and has been designed to allow easy expansion in the future. Wastewater Process 1. Wastewater Conveyance: Fifty miles of sanitary sewers throughout the City carry wastewater by gravity flow to ten lift stations. The treatment process begins when flow arrives at the Pretreatment Building. 2. Pretreatment Building: In this complex, the total flow passed through a 12 Parshall flume for metering. Variable speed pumps are used to move the flow through fine screening and grit removal. The screenings and grit are dewatered and the water is returned to the wet well. The flow splits to the existing plant and new plant, controlled by gates and weirs. 3. Mix box: Flow split to the existing facility rejoins the process at this point (along with the returned biological solids from step 5) for the biological process. The mix Box used finebubble diffusers to thoroughly mix the flow streams for a minute contact time before splitting the flow to either oxidation ditch.

Wastewater Conveyance: Fifty miles of sanitary sewers throughout the City carry wastewater by gravity flow to ten lift stations.

4 4. Oxidation ditches: Biological treatment of the wastewater occurs in the two oxidation ditches. Microorganisms mixed with the raw wastewater feed on available bacteria and organic material. During the aeration and detention time of about 24 hours, the microorganisms clump together to form what is called biological floc. Aeration and mixing is accomplished by centrifugal blowers providing air to a jet aeration system with four headers and one pump per header. 5. Final Clarifiers: Flow from the oxidation ditch enters the final clarifier at the center column and slowly moves to the outer clarifier weirs. The biological floc settles out and clean treated water flows over the weirs to the next process step. Adding polymers at this step can enhance the settling performance, too. The biological floc is returned to the mix box to support the biological treatment in the oxidation ditches. 6. Effluent filter: The two multi-celled effluent filters are composed of a filter media that is 2 inches of gravel, 14 inches of sand, and 10 inches of anthracite. The water flows by gravity through this filter bed, which traps and removes any solid particles that remain in the effluent. The system used liquid level sensors to monitor headloss, which indicates that the filter is becoming plugged. A traveling bridge assembly backwashes one cell at a time, and allows the other cells of the filter to stay in operation. 7. Disinfection: The filter effluent is monitored by a state-of-the-art oxidation reduction potential controller that predicts the chlorine demand. Chlorine gas is added and mixed for at least 15 minutes detention time. Sulfur dioxide is added to remove any chlorine residual. Finally, the effluent is aerated to strip any chemical residues and then cascades over a fish ladder to assure maximum dissolved oxygen levels when discharged to the Rum River. 8. Solids Handling: Some of the sludge produced by the biological process is pumped to the aerated, waste-activated solids (WAS) tank. This sludge is thickened through a gravity belt thickener and pumped to the primary digester for further treatment. A secondary digester

Aeration and mixing is accomplished by centrifugal blowers providing air to a jet aeration system with four headers and one pump per header. 5.

5 and storage tank provide a long-term storage of digested biosolids. biosolids are periodically spread on agricultural ground. The stabilized 9. Process Control: Process monitoring and control is provided by a Supervisory Control and Data Acquisition (SCADA) System. The major components of the SCADA system are programmable logic controllers, personal computers and monitoring equipment such as flow meters and dissolved oxygen analyzers. The SCADA system also monitors remote lift stations, wells and elevated water storage tanks using radio communications equipment. Historical data of the wastewater and water systems performance is compiled by the SCADA systems. The data is used to optimize system operation and forecast the City s future needs.

The major components of the SCADA system are programmable logic controllers, personal computers and monitoring equipment such as flow meters and dissolved oxygen analyzers.

6 10. Laboratory: Testing for such parameters as BOD (Biochemical Oxygen Demand), TSS (Total Suspended Solids), ammonia-nitrogen, fecal coliform and other process testing is conducted regularly to help optimize and track plant performance and to meet the discharge permit requirements. Design Summary Average Dry Weather Flow: 1.84 MGD Average Wet Weather Flow: 1.92 MGD Peak Instantaneous Wet Weather Flow: 4.23 MGD Average BOD5 Loading: 4,170 PPD Average Suspended Solids Loading: 3,710 PPD Average Ammonia Nitrogen Loading: 550 PPD Effluent BOD5 Standard: Varies (Mass Limit PPD) Effluent Suspended Solids Standard: Varies (Mass Limit PPD) Effluent Ammonia-Nitrogen: 14.0 mg/l (June September) Effluent Fecal Coliform Limit: 200 per 100 ml Design Population 10,000 Design Year 2014 MGD = million gallons per day BOD5 = 5 day biochemical oxygen demand PPD = pounds per day mg/l = milligrams per liter

92 MGD Peak Instantaneous Wet Weather Flow: 4.

7 Utilities Director Lead Operator/Lab Director Operators Assistant Todd Schwab Rob Bredeson John Bergloff Ted Knudson Randy Hatch Luke Fedor Matthew Rotz Betsy Potrament

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