North Liberty Wastewater Treatment Plant Phase II Project Update

Continued rapid growth (100% since 2007) required implementation of the Phase II plant expansion at the North Liberty Wastewater Treatment Plant Facility. FOX completed design and bidding of the expansion in the spring of 2015. Construction began in June 2015 and is just over half complete.

Modifications of the Existing Aeration Basin for conversion to BNR

Modifications of the Existing Aeration Basin for conversion to BNR

The Phase II project is truly a team effort with plant staff having a great deal of input on design; it will increase the treatment capacity to accommodate a population of approximately 28,000.

The expansion includes improvements to preliminary treatment, secondary treatment, and solids handing facilities. Secondary treatment improvements include the addition of third and fourth fine screens, incorporation of biological nutrient removal (nitrogen and phosphorus), and the addition of a fourth membrane bioreactor (MBR) train. Solids handling improvements include improvements to the existing aerobic digesters, addition of a new biosolids dewatering facility and dewatered biosolids storage facility. Phase II Improvements will increase the average wet weather flow capacity of the facility to 4.43 MGD and a peak secondary treatment capacity of 7.0 MGD.

Current Construction Progress

The most progress has been made on the secondary treatment building, aeration basins, MBR tanks, and biosolids dewatering facility. Additional aeration capacity has been added, and the existing aeration basins are being modified with the addition of baffle walls to create anaerobic and anoxic zones for biological nutrient removal. The plant is designed to produce an effluent with 1 mg/L P and 10 mg/L N. Work in the Secondary Treatment Building has also begun, making room for two additional rotary drum fine screen units. Work on the fine screen expansion will continue over the next year.

Installation of the piping, valves, pumps, chemical feed equipment, and other required equipment has been underway in preparation for the addition of a fourth membrane bioreactor train. The new MBR train will be General Electric’s LEAPmbr System. Installation and startup of the new MBR train is scheduled for fall of 2016.

3. Biosolids dewatering fan press

Biosolids dewatering fan press

The new biosolids dewatering facility is nearing completion and will be ready for startup in the next few months once controls integration work is completed to tie the new facility into the SCADA system. The new dewatering facility includes a 6-channel fan press, polymer feed system, loadout conveyor, and other support equipment and controls for the biosolids dewatering process. The fan press is sized for dewatering 106,750 gallons of aerobically digested biosolids per week from 2% to approximately 14% solids.

The Biosolids Dewatering Building was sized for installation of a second 6-channel fan press and a dewatered solids loadout truck bay. A dewatered biosolids storage building is also being constructed to house dewatered biosolids.

4. Dewatered Biosolids Loadout Conveyor & Truck Bay

Dewatered Biosolids Loadout Conveyor & Truck Bay

Improvements to Come

While several improvements have been completed for the Phase II Improvements project, there are several that will take place between now and the completion date of August 2017. Over the next year, work in the existing aeration basins and three existing MBR tanks will continue. Improvements will also be completed in preliminary treatment, which will include replacement of the existing cylindrical screen with a climber screen and wash press. Raw wastewater pumps will be replaced to increase firm raw pumping capacity to 7 MGD, and a carbon adsorber odor control unit will be installed to help mitigate odors around the plant. This is of particular concern since an elementary school is located just north of the wastewater facility.

The existing administrative building will also see improvements; they include the addition of locker rooms, offices, and a conference room.

FOX Engineering is an environmental engineering firm based in Ames, Iowa. We specialize in water and wastewater solutions for our diverse municipal and industrial clients. Our work varies in size and scope and can be found throughout the Midwest and beyond.