LIME SOFTENING WATER TREATMENT PLANT PRETREATMENT & CRYPTOSPORIDIUM COMPLIANCE
Fargo, North Dakota
New Classification in the Sheyenne River
Recent sampling on the Sheyenne River discovered an increase in Cryptosporidium (Crypto) concentration, which reclassified the Fargo Lime Softening Water Treatment Plant (LSWTP) from Bin 1 to Bin 2 per the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). While the new Membrane Water Treatment Plant (MWTP) will not be affected by the new Bin 2 classification because the treatment technology achieves sufficient Crypto treatment, the LSWTP will be required to provide an additional 1.0 log of Crypto treatment or inactivation beyond what is currently provided by their conventional filtration process. To address the upcoming compliance issue at the LSWTP, the City of Fargo retained AE2S to undertake this planning and preliminary design process and develop a Crypto treatment recommendation for the LSWTP.
Project Details
Date: 2018 – Present
Client: City of Fargo
Key Project Elements
- Medium Pressure UV Reactors
- Equipment Pre-Selection
- Motor Control Center Replacement
- Process Equipment Rehabilitation
- Chemical Storage and Feed Systems
- DWSRF Program Administration
Treatment Recommendations
The LT2ESWTR provides a microbial toolbox that outlines treatment technologies that are allowed to be used to achieve the additional log treatment credits for Crypto. AE2S worked closely with water treatment plant staff and the North Dakota Department of Environmental Quality (NDDEQ) to evaluate the viable alternatives on the basis of capital costs, operation and maintenance (O&M) costs, reliability, and operational difficulty. Ultimately, it was determined that an ultraviolet (UV) system offered the easiest operation and similar reliability to the alternative costly option of converting the conventional filters to an ultrafiltration (UF) system. The UV system will consist of medium pressure reactors that will be retro-fitted into the LSWTP’s existing post-filtration transfer pump station.
Minimizing Facility Interruptions and Project Cost Savers
As the Crypto Compliance project was under design, the AE2S – B&V team was also working with the City to develop a plan to rehabilitate the existing pretreatment system at the LSWTP. While the two projects were independent of each other, it was recognized that both had overlapping construction timelines and required scheduled facility shutdowns to perform the work. In an effort to minimize the impact of facility interruptions, the two projects were combined into a single bid package, which also resulted in cost savings due to lowering the contractor’s mobilization and bonding costs. Additionally, key process equipment was pre-selected during the design to prevent vendor equipment packaging which was experienced by the City in previous projects at the WTP.