Chester Engineers

Biological nutrient removal case study

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Courtesy of Chester Engineers

The Challenge

Chester Engineers was contracted by the Mountaintop Area Joint Sanitary Authority to design an upgrade to the existing treatment plant to address new Chesapeake Bay nutrient requirements and to eliminate the use of chlorine for ammonia nitrogen removal and disinfection to address trihalomethane permit violations.  Chester was also required to complete the design to permit submission level requirements within three months in order to allow the Authority to apply for possible grant funding from PENNVEST. 

The Interdisciplinary Approach

With the knowledge that nitrogen and phosphorous limits were going to be required of the Authority within 4 years, for approximately 6 months before the start of the design, Chester had been working with the plant personnel to obtain influent and effluent data on a number of different parameters in order to evaluate options.  Therefore, when the state announced a grant program for projects addressing the Chesapeake Bay initiative, significant information had already been collected.  Chester and the Authority quickly negotiated a design fee for an option that would maximize the use of existing facilities and address both short and long term permit issues.  Chester’s long-term knowledge of the existing facility through our 30 year relationship with the Authority provided the background information required to quickly finalize the process adjustments, receive Authority approval, and complete the design on time to submit for PENNVEST funding.

The Sustainable Result

Based upon the design, the Authority received a $2.7 million grant on the $7.5 million project and the project was completed three years prior to the new nitrogen and phosphorous limits becoming effective.  This additional lead time provided the Authority with time to understand the new process and to optimize system operation and performance.  Additionally, as part of the project, UV disinfection replaced chlorine for disinfection which eliminated trihalomethane violations at the facility that had been occurring for several years as the state reduced permitted discharges for trihalomethanes.  The use of UV disinfection was possible since the new biological nitrogen removal process replaced the breakpoint chlorination process for ammonia nitrogen removal allowing for other disinfection options.  Finally, the new process only required the construction of one new final clarifier and one new aerobic digester.  All other existing process tanks and facilities were utilized as part of the new process minimizing project costs.

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