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COLLECTION SYSTEM
 The water discharged from your homes and businesses enters a maze of underground pipes, which direct the flow to the Wastewater Treatment Plant. This is called the collection system. The City has about 13.7 miles of sewer lines. The collection system works primarily as a gravity system in which the water flows down hill through the lines. There are three lift stations, which have to pump the wastewater from low points in the city to a higher level so it will flow to the WWTP.
Maintenance of the collections system consists of inspecting the lines visually and with video equipment, cleaning the lines to prevent build up of grease or other debris which could block the lines, removal of roots growing through joints or cracks in the pipes, and repair or replacement of degraded lines, manholes, or lift stations and lift station equipment.
PRETREATMENT
Pretreatment is done prior to discharge to the collection system. It prevents hazardous or other harmful chemicals from being discharged to the collection system and Wastewater Treatment Plant. Pretreatment can include grease traps, used by restaurants and other businesses for the removal of fats, oils and grease (FOG).
WASTEWATER TREATMENT PLANT IN 2009
The City of La Center Wastewater Treatment Plant has been in the same location since 1967 when the first wastewater system was constructed. The plant has been upgraded about every 5 years during this time period to keep up with growth, technology and regulations. In August 2006, the City of La Center assumed operations of the wastewater treatment plant and collection system from Clark Public Utility District who had owned and operated it since 1992. The plant is classified as a Class II treatment plant and operates under regulations from the Department of Ecology (DOE) and the Environmental Protection Agency (EPA).
The National Pollutant Discharge Elimination System (N.P.D.E.S.) permits the city to discharge up to 0.56 Million Gallons per Day (MGD) with a maximum day flow of 1.0 MGD. The plant is designed to treat and annual average flow of 0.33 MGD. Current average daily flows in the summer are 0.22 MGD and winter flows average 0.28 MGD with a maximum day flow of 0.68 MGD. The treatment plant serves approximately 2,510 residents in La Center as well as the four cardrooms and other commercial businesses located in the city.
There are a number of steps to the treatment process. Treatment of the waste is done through both physical and biological means.
 
Preliminary — Preliminary treatment is the removal of large debris and inorganic matter like rags, sticks, coffee grounds, gravel etc. by physical means. The flow or influent enters the plant through a pipe to the Hycor Combi Unit where large material is collected on a screen. The screenings are conveyed out of the flow and dewatered and then discharged into a garbage can.
The heavier particles settle to the bottom of the chamber. The grit (coffee grounds, gravel, etc) is removed from the grit chamber by the second conveyor and discharged into a garbage can. The garbage cans are emptied daily into a dumpster. Waste Management Service empties the dumpster once a week and takes the grit to the Sanitary Transfer Station.
The water with the larger debris removed flows over a weir and into a parshall flume where the flow is measured. The water contains suspended and colloidal solids (small particles that will not dissolve and that remain dispersed in a liquid) and is pumped into one of the two processing units through the In Plant Pump Station.
 Secondary — The processing units are called Sequencing Batch Reactors (SBR). The treatment is done by timing 5 different cycles and alternating between two basins. The basin is filled with the waste water in the mix-fill cycle, aerated in the react cycle, allowed to separate in the settle cycle, clean water is removed in the decant cycle and solids are removed in the waste cycle. How this works is water containing the suspended and colloidal solids fill one tank and is mixed with a biomass containing bacteria and protozoa (mix fill). After a certain amount of time the blowers compress air and pump it into the tank giving the biomass oxygen creating an aerobic environment. This allows bacteria to break down the suspended and colloidal solids (organic matter). Protozoa (single and multi celled animals) feed on the bacteria which increases the biomass (mixed liquor) and creates a flock that is heavier than water.
  After oxidation the biomass is allowed to settle. After a set amount of time the decanter and discharge valve open allowing a clear layer of water to be removed from the SBR basin. The solids that remain in the basin contain a large concentration of bacteria and protozoa. We need to remove a portion to keep the organisms to the amount of solids entering the system in balance so we pump them to the solids storage basin for further processing. The remaining biomass is ready to receive waste in the next mix-fill cycle.
Disinfection and Discharge — The water that is decanted from the SBR is pumped to the Disk filter where fine particles are retained on a cloth media. After the water passes through the media it flows through an ultraviolet disinfection system.
The ultraviolet lights disrupt the DNA of any remaining bacteria and prevent them from growing, effectively disinfecting the effluent. The water is discharged through a diffuser into the East Fork of the Lewis River adjacent to the Treatment Plant.
SOLIDS PROCESSING
The solids and biomass that is removed from the SBR during the waste cycle flows into a solids storage basin where it is aerated with a mechanical mixer. The solids are digested further in this unit and then they are dewatered by injecting polymer and running them through a Rotary Fan Filter Press. The solids are about 1/2% solids before the press and 15% when they come off the press. The solids are then processed through a dryer where the final product is over 90% solids. The heat in the dryer kills the bacteria and allows the solids to be classified as a Class A exceptional biosolid.
 
The solids from the city are taken to the Lewis River Tree Farm where they are beneficially reused as fertilizer to grow trees for reforestation.
SAMPLING AND LABORATORY ANALYSIS
The city operates an accredited laboratory onsite. We run the analysis required by our permit as well as process control testing as necessary. Weekly approximately 124 tests are completed. Advanced testing is done twice yearly at an outside laboratory.
Sampling is the most critical part of water testing. If the sample does not represent the system being tested or if it is contaminated by outside sources the test is worthless. No matter how accurately the test is done, it will be meaningless if it does not represent the source from which it is taken.
WASTEWATER TREATMENT PLANT IN 2011
There are several drivers requiring the city to upgrade the existing facility including: capacity, reliability, increasing regulations, and growth. The City of LaCenter contracted with Kennedy/Jenks Consultants to design a Membrane Bioreactor Plant (MBR) on the existing site and utilizing as much of the existing facility as possible. The plan is to modify the existing basins and add additional basins for the new treatment processes. This is an artists rendering of what it may look like when completed.
The new facility is designed to be built in phases to be efficient and add capacity as needed. Phase 1 would add a new headworks facility, 4 new MBR basins, modification of 1 SBR basin into 2 MBR process basins, upgrades to the UV facilities, and other electrical and control modifications. Phase 1 would increase the flow capacity to 1.04 MGD average annual flow with a peak day flow of 3.0 MGD. Phase 2 would address the need for additional solids handling that would be required in 5 to 10 years. Phase 3 would double the capacity of the plant by duplicating the Phase 1 upgrades for the Membrane Bioreactors (MBR) and modifying the other SBR basin into MBR process basins and should have capacity to treat the 2028 population. Flow capacity would be 1.65 to 2.08 MGD average annual flow and a peak day flow of 4.2 to 6.0 MGD.
Construction is expected to start in June of 2009 with a scheduled completion date of November of 2010. The overall appearance of the plant will improve as the new buildings have been architecturally designed to fit in with the existing buildings and decorative handrails will be used around the basins. The hillside just north of the plant will be landscaped with shrubs and groundcover to improve the aesthetic appearance.
ENVIRONMENTALLY FRIENDLY DESIGN
The upgraded plant will result in significant energy and water use efficiency improvements over the existing facility. The high quality effluent released from the plant will allow innovative use of wastewater as well.
Energy Efficiency
The design of the upgraded wastewater treatment plant provides significant energy savings over typical treatment plant designs. The main sources of energy reduction include the following elements:
- Building an elevated headwork's facility to allow gravity flow through the plant.
- Eliminating the existing in-plant pump station substituting gravity flow.
- Selecting pump-assisted gravity MBR design, which eliminates permeate pumping energy demands for all but peak flow events.
- Simplifying the process design to minimize the number of mixers and recirculation pumps.
- Utilizing MBR basin scour air for oxygen demands, thereby reducing the number of blowers.
- Installing variable frequency drives on pumps and blowers to minimize energy consumption during low-flow periods.
- Requiring premium efficiency motors.
The table below presents the energy consumption of the plant based on a standard design and actual energy saving design. In the first year of plant operation, the average annual flow rate is anticipated to be 0.45 million gallons per day (mgd). Using a standard wastewater treatment plant design, the plant would have consumed 3,823,470 kilowatt hours. Using the energy-efficient design, the plant saves 1,181,090 kilowatt hours the first year of operation, and consumes only 2,642,380 kilowatt hours, which equates to a 30% reduction in energy consumption. This reduction in energy costs will provide economic benefit to the residents of La Center through lower sewer rates over the life of the plant.
| Average Annual Flow, 2010 |
0.45 mgd |
| Energy Consumption, Standard Design
| 3,823,470 kWh
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| Energy Consumption, Energy Efficient Design
| 2,642,380 kWh
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| Annual Energy Savings
| 1,181,090 kWh
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Water Efficiency
The existing plant does not reuse effluent for utility water within the plant. Potable water provided by Clark Public Utilities' water system must be used to cool the dryer, wash basins, clean units, and perform other tasks. Part of the project involves creating a water system using only effluent from the new MBR plant. The only use for potable water after completion of the project will be for the laboratory, which includes a bathroom and an eyewash station in the headworks building.
In 2007 and 2008, the average water use for the plant was 638,500 gallons a month or 7,600,000 gallons annually. Upon completion of this project the lab and eyewash station are expected to use about 8,100 gallons a month or 97,000 gallons annually, which represents a 98.7% reduction in water usage at the plant. This improvement will result in a significant cost savings for the city, in addition to providing environmental benefits by conserving groundwater supplies.
Environmental Innovations
The City of La Center Wastewater Treatment Plant is located on the north bank of the East Fork Lewis River next to the Lewis River wetlands (La Center Bottoms) and a seven-acre amphitheatre park-Sternwheeler City Park.
Completion of the upgrade project will produce Class A Reclaimed Water, as defined by Ecology. This high quality effluent could be used for parkland irrigation, river flow augmentation or for wetland enhancement. Using the reclaimed water will conserve groundwater to meet future potable water needs. Flow augmentation could improve stream flows in the East Fork and reduce high temperatures found in the river during the summer, supporting the goals of the East Fork Lewis River Watershed Management Plan. Wetland enhancements could improve wildlife habitat in La Center Bottoms and provide critical habitat for endangered salmonids migrating in the East Fork basin. All of these benefits would help improve water quality, enhance wildlife habitat and generally protect the environment.
DESIGN DRAWING LINKS
Click on the links below to view selected design drawings of the new La Center Wastewater Treatment Plant.
Surplus Equipment for the Wastewater Treatment Plant
The City of La Center is providing opportunities to bid on surplus used treatment plant equipment. Equipment will become available as it is removed from use. All equipment is sold in As-Is Condition and No Warranty will be provided.
WASTEWATER TREATMENT PLANT CONSTRUCTION UPDATE
Construction started 6/1/2009
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