Wastewater Treatment Plant Upgrades
The City of Wood Dale needed to evaluate the best way to increase the capacity of their two WWTPs to process current flows and projected increased flows created by development along the Thorndale Avenue / Elgin – O’Hare corridor. The City retained HR Green to complete an evaluation of expanding capacity on-site at the two WWTP locations. In addition to the increased capacity, any proposed WWTP expansions would also have to meet more restrictive discharge limits to comply with the TMDL limits in Salt Creek, the receiving stream. The evaluation included estimating the existing and proposed projected flows to each WWTP, evaluating the current conditions and capacities of both WWTPs, evaluating the impacts of the more restrictive future effluent limits, and preparing conceptual designs for modifications to the WWTPs to meet the future flows and discharge limits.
The results of this evaluation concluded that the existing South WWTP needed only regular maintenance upgrades, and de-rated from 1.13 MGD to 0.96 MGD to accommodate the current and future estimated flows. The recommendations for the North WWTP included conceptual designs for a capacity expansion from 1.97 MGD to 3.47 MGD.
For the final design of the improvements at the North Plant, HR Green evaluated different blower alternatives for both the activated sludge aeration tanks and the aerobic digesters to come up with the most efficient system for the City. The aeration tanks at the plant include the four existing tanks, and one new tank that will be added this year. The City is installing a single HSI turbo blower this year that will supply air to the existing aeration tanks and existing digesters, and utilize their old multi-stage centrifugal blowers for the balance of the air needs. During our efficiency and performance evaluation for the future air needs, we looked at multi-stage centrifugal blowers, turbo blowers and rotary lobe blowers for the different air needs.
Our final design includes three turbo blowers for the aeration tanks, and three rotary lobe blowers for the aerobic digesters. Using multiple smaller blowers, the system will more closely match the actual air needed while still providing the amount of air required by the IEPA. The turbo blowers were determined to be the most efficient for the operating conditions in the aeration tanks, and the rotary lobe blowers achieved efficiencies almost as good as the turbo blowers while meeting the variable flow and head conditions present in the digesters. The turn down capabilities of the turbo blowers limited their ability to meet the variable conditions present in the digester operations. All of the blowers will have variable frequency drives (VFDs) that will be controlled based on the desired dissolved oxygen (DO) levels in the aeration tanks and digesters. Controlling the VFDs to attain the desired DO levels will improve overall efficiency and reduce the operating costs at the plant.
HR Green is currently under contract to provide construction services for the Wood Dale North Wastewater Treatment Plant Upgrades. The major components of this project consist of a new raw sewage pump station, preliminary treatment building, excess flow facility, aeration basin improvements, secondary clarifier, secondary treatment control building, site work, and other ancillary equipment necessary to complete the work. The project will be constructed in 2 phases and is scheduled to be completed in June 2015 at a cost of approximately $30 million dollars.