Operating Two Process Trains in Parallel to Achieve Nutrient Removal - A Tale of Two Plants at the Municipality of East St. Paul

The Municipality of East St. Paul is a thriving community located immediately north of the City of Winnipeg in Manitoba, Canada. The Municipality had successfully operated a Rotating Biological Contractor based sewage treatment plant (STP) since 1980 to meet the final effluent limits of 25 mg/L total-BOD5 and 30 mg/L total suspended solids. To address the significant growth in the community and new provincial regulations for nitrogen and phosphorus, a parallel Sequencing Batch Reactor (SBR) system was constructed to meet the immediate 10 year growth projection. This design approach will facilitate the addition of future SBR cells as the Municipality grows while allowing the Municipality to meet its daily maximum ammonia limits. The phosphorus limit of 1 mg/L in the final blended effluent was achieved by alum addition to both the RBC and the SBR systems. The existing gas chlorination system was replaced by a common low-pressure ultraviolet disinfection system. One of the key challenges of the project was to undertake the upgrades and connection to live services while maintaining continual operation of the existing STP processes. Despite numerous challenges, the upgraded and expanded facility was commissioned on schedule and on budget in the fall of 2009. Following an acclimation period, the STP has consistently met the effluent limits for cBOD5, TSS, total phosphorous and ammonia nitrogen. The SBR is designed such that any future requirement for total nitrogen (TN) can be met. The project showcases lessons learned on retrofitting a STP to meet both growth and stringent effluent limits in a small community with limited funding.