| A piping trench is located between each pair of covered membrane tanks. Operators access the piping in the trench for "clean in-place" operations. |
From 2000 to 2005 Dundee's population had increased by 18% and growth in the commercial and industrial base in the village was even greater. The old plant was barely able to keep up with the increased flows and the sludge facilities did not have enough storage to comply with the state's detention requirements. Also, in 2003, the state of Michigan determined that a downstream portion of the receiving stream, the River Raisin, was not in compliance with its established warm water habitat designation. Therefore, Dundee's WWTP had to be upgraded to achieve effluent limits of Advanced Wastewater Treatment (AWT) technology. Summertime effluent limits for BOD and NH3 were set at 4 mg/l and 0.5 mg/l; respectively. The village was faced with the necessity of doubling the treatment capacity, producing a higher quality effluent, doubling the sludge storage detention time, fitting the treatment processes into an already confined site and providing for another future expansion on the same site.
Membrane Bio-Reactor
Dundee's former WWTP used a sequential batch reactor (SBR) treatment process. To meet the required effluent limits required by Advance Wastewater Treatment technology, a tertiary filtration process would have to be added to the expanded SBR process. However, the wastewater treatment plant site was too small to add such facilities. The initial plan of doubling the capacity of the plant with a larger SBR process would have maxed out the site and there would have been no future capacity at that location. The site is circumscribed by the river and other municipal buildings to the south, the railroad tracks to the east and private property to the north and west. Engineering evaluations were conducted to determine the type of wastewater treatment processes that would meet the regulatory limits but not require expansion of the treatment plant site. The Village selected a membrane bio-reactor (MBR) process for the new WWTP.
The new WWTP uses a system of flat plate membranes immersed within the biological treatment tanks. It was the first municipal use of this type of membrane in the state of Michigan. The biological treatment process operates with activated sludge concentrations several times greater than conventional activated sludge processes. The high density of the biomass allows for greatly reduced volumetric requirements to treat the wastewater. The nominal flux rate is about 10 gpd/ft2 at average flow. During the past five years of operation, the WWTP has produced an effluent that complied with the fecal coliform limits without the use of disinfection.
"Under most flow conditions, the WWTP operates well and the effluent is outstanding. We're actually improving the River Raisin with our effluent," said Dave Rigel, who was Dundee's WWTP Superintendent.
