The Stratford WPCF is an 11.5 million gallon per day (mgd) average annual daily flow treatment facility that is located in southwestern Connecticut and discharges into Long Island Sound (LIS) at the confluence of the Housatonic River. The treatment facility was upgraded in 2009 to include
low level nitrogen removal as part of the Total Maximum Daily Load (TMDL) for Long Island Sound. The biological nitrogen removal treatment process consists of two trains of a four stage suspended growth activated sludge process that include primary anoxic zones followed by aeration with
internal nitrate recycle, second anoxic zones with external carbon addition, and reaeration zones. The upgrade also added online nitrate analyzers to each second anoxic zone and the plant final effluent to provide continuous monitoring of nitrate removal efficiency. In 2009 Stratford completed
a 55 million dollar upgrade project for enhanced nitrogen removal down to 3 mg/l. This case study provides an overall appraisal and evaluation of the beneficial use of both online nitrate monitoring data and nitrogen removal improvement with supplemental carbon addition to the secondary anoxic
zone to efficiently lower total nitrogen discharged from the Stratford POTW.
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