Protecting Historic Charm
The Village of Dundee, Mich., listed on the National Register of Historic Places, is a growing community that has long recognized the importance of maintaining its historic charm. The village government had the foresight to ensure that the distinctive character of “The Triangle District” and Old Mill, both situated along the River Raisin, be protected. They have also worked toward ensuring that the quality of the river itself is protected.
In 2003, the village began work to upgrade their wastewater treatment plant (WWTP), in response to modifications to their NPDES permit that significantly lowered their discharge limits, primarily on biochemical oxygen demand and ammonia-nitrogen. The Michigan Department of Environmental Quality (MDEQ) lowered the plant discharge limits because water in the receiving stream did not meet federal water quality standards.
The existing village WWTP was also operating at near-full capacity, due to overall growth of the area, and needed to be expanded to support continued growth of the region.
The next challenge for the village was to select a treatment technology that could be integrated into their existing facility, could produce a high-quality effluent to meet the new NPDES limits, and would be easy to operate and maintain. ARCADIS-FPS, the design engineer, determined that membrane bioreactor (MBR) technology would be the best alternative. The village received competitive bids in July 2003 and selected Enviroquip, Inc. to supply an MBR technology package for the new plant.
The new MBR facility utilizes as much of the existing plant as possible, with the existing sequencing batch reactors utilized as the biological process basins for the new system. New basins for the membranes were constructed adjacent to the existing tanks. The membrane basins are outside and are equipped with aluminum covers to protect the membranes and piping from the elements.
The plant has been designed for a full build-out capacity of 2 mgd average daily flow and 4 mgd peak daily flow. Approximately 1.67 mgd (3.33 mgd peak) of membrane capacity has been installed initially and additional membrane units will be added as required. All other equipment has been installed for the full build-out flows.
Aerobic digestion system
The existing aerobic digestion system was also upgraded as part of the plant expansion, as the system lacked sufficient storage volume to permit retention of digested sludge throughout the winter. Enviroquip’s PAD-K process utilizing membrane thickening was installed to expand the sludge holding capabilities of the existing digester basins.
Waste sludge generated in the MBR process is sent to the upgraded digesters and then thickened in the membrane thickener. The membrane thickener is capable of concentrating the waste sludge up to 4% solids and greatly expands the solids retention capabilities of the digesters.
“The PAD-K system has taken the hassle out of the way our aerobic sludge is thickened,” said Dave Rigel, superintendent of the Dundee WWTP. “We no longer have to manually lower the telescoping valves to remove supernate, or have concerns with the settling characteristics of the sludge to achieve high quality supernate. Naturally, land application costs are greatly reduced due to the increased solids percentage of the sludge.”
The MBR began operation in June 2005, and the membrane thickener began operation in July 2005. The new Enviroquip MBR and PAD-K systems will provide the historic village with a reliable, high-performance solution to their wastewater treatment needs for many years to come.