Wastewater Treatment Facility


Orange City Prepares for the Future

Addition of mechanical treatment facility meets capacity and compliance

Project Owner:
City of Orange City, IA

Key Features:

  • New flow-through sequencing batch reactor (SBR) wastewater treatment facility
  • Preliminary treatment includes spiral screening and grit removal
  • UV disinfection

The City of Orange City, IA, population approximately 6,000, received an Administrative Consent Order from the Iowa Department of Natural Resources for effluent ammonia violations of their National Pollution Discharge Elimination (NPDES) permit in 2015. The City was required to make improvements to their wastewater treatment plant to bring them into compliance with effluent limits. In turn, the City evaluated treatment options to not only meet existing permit limits, but also to comply with anticipated future limits including provisions for the Iowa Nutrient Reduction Strategy.

DGR Engineering (DGR) worked with the City to evaluate alternatives, which included constructing a sequencing batch reactor (SBR), mixed bed biofilm reactor (MBBR), retention and land application, activated sludge, or submerged attached growth reactor (SAGR).

The evaluation considered capital costs, long-term operation and maintenance costs, operational flexibility and expandability. After consideration and numerous site visits, the City ultimately determined a flow-through style SBR system to be the preferred choice based on the selection criteria and the ability to meet anticipated permit limits.


Preliminary treatment includes a spiral screen and vortex grit removal system. An ultraviolet (UV) disinfection system was also included to meet effluent disinfection requirements. A full-plant supervisory control and data acquisition (SCADA) system was incorporated in the project for remote monitoring.

The existing facility consisted of a six cell aerated lagoon system which included an industrial pretreatment cell with surface aerators, three aerated cells with diffused air, along with two quiescent cells.

The new system will utilize two of the existing lagoon cells’ flow equalization and sludge storage prior to land application. During peak flow events, the facility can split flow to utilize the dedicated lagoon for equalization and then send back influent wastewater through the plant when flows subside.

The facility was designed to treat a total flow of 2.45 million gallons per day (MGD) to accommodate projected 20-year domestic and industrial growth.

The new facility was designed for an increased population of 6,500. The improvements made the facility easily expandable for future needs and was designed with impending nutrient limits in mind.

Due to the complexity of the new facility, the required operator certification increased from a Grade II to a Grade IV certification. DGR Engineering worked closely with the City and IDNR to determine a pathway for expedited training and certification of existing staff.

Total project cost was $9.9 Million. The City used local bonds for the project costs.