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Mount Pleasant Wastewater Treatment Facility Plan

Challenge

The southeastern Iowa community of Mount Pleasant has a long history of keeping its city infrastructure up to date, which helps attract new businesses and encourages existing businesses to grow their operations.
 
To accommodate future growth, the City of Mount Pleasant knew it needed to upgrade the wastewater treatment and collection systems to meet upcoming Iowa Department of Natural Resources (IDNR) regulatory requirements, including new Total Phosphorous (TP) and Total Nitrogen (TN) discharge limits as well as disinfection.
 
The City was operating and maintaining two separate treatment facilities: the lagoon and the sequencing batch reactor (SBR) plant. In 2013, Mount Pleasant received new NPDES permits for both facilities, which required Facility Plans and other studies to identify the path to meeting the new limits. 
 
The City of Mount Pleasant wanted to weigh the different options for plant improvements, and asked Shive-Hattery to find cost-effective alternatives for wastewater nutrient removal and mandated disinfection while preparing the Facility Plan and other NPDES required documents.

Solution

Shive-Hattery evaluated several alternatives while preparing the IDNR-mandated Facility Plan, Anti-Degradation Analysis, and Nutrient Reduction Strategy Feasibility Report (NRSFR) documents. The most cost effective and beneficial alternative for Mount Pleasant recommended elimination of the lagoon and conveying all wastewater flow to the SBR plant for treatment. Not only will this reduce operation and maintenance expenses associated with the lagoon, but it negated needed capital improvements and will simplify the future permitting process. A variety of other cost reduction and O&M improvements were also recommended in the plan, including biological nutrient removal piloting. 

Shive-Hattery’s evaluation focused on three key criteria for the viability of the selected alternative.  First, it was determined the SBR plant was in good condition and had the capacity to handle current and projected future flows, including existing flows from the lagoon.  Second, evaluation showed that UV disinfection was cost effective in meeting new seasonal discharge limits.  And thirdly, our analysis indicated the plant could be optimized for TP and TN removal in line with Iowa’s recently adopted Nutrient Reduction Strategy. 
 
To build on the analysis of the Facility Plan, full-scale BNR Piloting occurred over 18 months to collect necessary data for the NRSFR and to evaluate the many alternative modes of operation for the SBR. This evaluation helped determine optimal conditions for nutrient removal. Eight months of pre-optimization were followed by five separate optimization periods, each testing different nutrient removal conditions.
 
During the optimization periods, TN levels were consistently driven below the 10 mg/L concentration goal set forth by the Iowa Nutrient Reduction Strategy. At the peak of optimization, the average TP effluent concentration came within 10% of the 1 mg/L goal of the state’s nutrient strategy, which was a significant improvement over the 2.71 mg/L pre-optimization average.
 
Upon completion of the BNR Piloting study, Shive-Hattery determined that simple operational changes would allow the WWTP to easily meet the anticipated TN discharge limits, but the addition of a chemical phosphorous removal would be the prudent path forward for this facility. The design data collected during the study allowed the size and cost of this system to be reduced while still being able to comply with the anticipated future TP discharge regulations.

Impact

The new wastewater treatment and collection system upgrades in Mount Pleasant will strengthen the opportunity to grow more in the next decade and beyond. The recommended upgrades will allow the City to meet the new IDNR requirements, while minimizing capital improvements at the plant and may save residents more than $2.5 million by no longer operating the lagoon.
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