Grimes, IA

Treatment Plant Improvements

  • Client City of Grimes
  • Type Wastewater
  • Services Feasibility Plan, WW Treatment Updates
  • Construction Cost $12.3 Million
  • Project Manager Steve Troyer, P.E., BCEE

CHALLENGE

A rapidly growing suburb of Des Moines, (population 8,246) the aging wastewater treatment plant was being severely overloaded by 1997 when FOX began working on the city’s wastewater facility plan (we were also simultaneously working on a facility plan for the water system).  With such growth, the facility plan recommended that the treatment plant be upgraded in three phases over the next 20 years.

Grit teacups

Grit teacups

SOLUTION

The first phase was rapidly implemented to bring the treatment plant into compliance. The facility originally had a small activated sludge plant followed by polishing lagoons which also received the plant’s waste-activated sludge for long term storage. During the facility study, it was determined that the sludge being stored in the polishing lagoons was denitrifying and returning ammonia to the treated wastewater, therefore raising the effluent concentration of ammonia above their permit limits. So, Phase I rerouted treated wastewater from the activated sludge plant directly to the creek for discharge and converted the polishing lagoons to stormwater equalization basins. The aeration equipment in the activated sludge tank was also upgraded, reducing the typical blower use from four 50-HP blowers to one.

Phase II was constructed in 2000-2001 and greatly expanded the plant to bring it into compliance with current design standards and provide necessary capacity until at least 2010. This project included a new primary lift station, mechanical bar screen, fine grit removal using Eutek Teacups, new membrane fine-bubble aeration tanks, RAS/WAS pump facility, aerobic digestion, and reed beds for sludge stabilization and storage. The reed beds store and stabilize the sludge for up to 10 years, substantially reducing the quantity of biosolids to be land-applied, more so than conventional dewatering.

 Influent Pumps

Influent Pumps

OUTCOME

In 2010 and 2011, an update to the 1997 facility plan was done to review the current flows and organic loadings, incorporate a review of any new effluent permit rules expected, and provide recommendation on when and which part of Phase III from 1997 should be implemented. This study determined that the existing facilities should be adequate several more years for organic treatment capacity. It was determined that additional raw wastewater pumping and flow equalization should be implemented. Implementation of the new facilities is just beginning, with the design of a new 42-inch interceptor sewer to the treatment plant to handle the expected maximum flow under complete development of the served drainage basins.

Currently, the city and FOX are working on improvements that include screw pumps, flow equalization basins, and screenings washing press. Completion is slated for early 2017.

RECOGNITION

FOX and the city received an Iowa ACEC Recognition Award for Engineering Excellence for the 2003 work.

Waste activated sludge pumps

Waste activated sludge pumps