North Liberty, IA

Membrane Bioreactor Wastewater Treatment Plant: Phase II

  • Client City of North Liberty
  • Type Wastewater
  • Services Treatment
  • Construction Cost Estimated $16 Million
  • Project Manager Steve Troyer, P.E., BCEE
  • Project Engineer Jenny Ruddy, P.E.


Continued rapid growth (100% since 2007) required implementation of the Phase II plant expansion. FOX completed design and bidding of the expansion in 2015. This project, currently under construction, is truly a team effort with plant staff having a great deal of input on design; it will increase the treatment capacity to accommodate a population of approximately 28,000.

The expansion includes the addition of a fourth MBR train and incorporates biological nutrient removal (nitrogen and phosphorous). The design effort included using BioWin modeling software (a wastewater treatment process simulator) to select the best configuration and most economical sizing for the biological nutrient removal process. The modeling software was used to evaluate several different configurations. Based on this effort, the Modified University of Cape Town (MUCT) process was selected for biological nutrient removal.

Dewatering Building

Dewatering Building


The Phase II improvements include the addition of a biosolids dewatering system and dewatered biosolids storage facility which will increase operational flexibility and reduce the cost of biosolids hauling. Dewatering technologies evaluated during design were belt filter press, screw press, centrifuge, and rotary fan press. FOX worked closely with the plant staff to evaluate four dewatering technologies based on economic and non-economic factors. North Liberty decided that either the fan press or screw press equipment would be the best fit.

 Aeration Basin piping installation

Aeration Basin piping installation

Pilot testing of the fan press and screw press equipment was completed summer of 2014. Based on pilot testing performance, present-worth comparison with alternative technologies, and operator preference for equipment operation and maintenance, the rotary fan press was selected.


Construction of these Phase II improvements is expected to be substantially complete by June 2017.