Williamsburg Reverse Osmosis Water Treatment Plant


  • Local Governments
  • Public Sector


  • Engineering
  • Potable Water
  • Water


  • Williamsburg, Iowa

Challenge: The City of Williamsburg historically struggled with its pressure filtration treatment process and distribution system operation due to excess ammonia in its groundwater wells. The ammonia concentration was sufficiently high that even after formation of a chloramine disinfection residual, excess ammonia remained in the finished treated water. This excess ammonia caused biological activity in the City’s distribution system that led to violations of EPA’s primary standards caused by nitrite formation from ammonia.  

In addition, the City experienced elevated levels of lead in its sampling locations. The City previously utilized a phosphate-based corrosion inhibitor but had made this system inactive due to the excess nutrients accelerating the negative biological impacts to the water quality in the distribution system. HR Green conducted a desktop study for a short-term solution to re-initiate a corrosion inhibitor until a new, permanent treatment system could be completed.

Solution: HR Green evaluated potential treatment options to address the naturally-occurring ammonia in Williamsburg’s systems: increasing chlorine dose to breakpoint chlorinate the ammonia, a packaged ammonia removal system, and a reverse osmosis (RO) system. The RO system was selected due to additional treatment benefits for providing softening and superior water quality.  

The Williamsburg Reverse Osmosis treatment system design included modifications to the City’s wells to increase capacity, a direct-RO treatment scheme with Antiscalant pre-treatment, post-RO aerator to boost pH and remove dissolved odorous gases, and post-RO chemicals including phosphate corrosion inhibitor, sodium hydroxide for pH control, sodium hypochlorite for disinfection, and fluoride to replace the fluoride removed through RO. Modifications were made to the existing high-service pumps and finished water storage tanks to facilitate the new treatment equipment and hydraulic flows.

Benefit: The Williamsburg water treatment plant improvements reduced nutrient levels and removed odorous gases while increasing capacity and improving water quality. Additionally, a brand-new overall SCADA system allows City operational staff to provide automated control and remote access to the treatment facilities for improved management.

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