LAN provided design improvements and upgrades to the City’s Northwest Treatment Plant (NW WWTP), a 4.5-mgd package plant with the last significant upgrade occurring in 2003. The preliminary engineering report prepared by LAN identified four major deficiencies and developed a priority schedule for addressing the issues which included a phased approach to design and construction. Phase One of the project focused on energy efficiency, with new process and digester blowers and replacement of the diffused aeration system. The system design from 1983 utilized a coarse bubble system suspended from air bridges; however, it had previously been modified to a fine bubble system. As a result, tank mixing and oxygen transfer (pounds per day) had decreased to the point where during the summer months, the plant was not able to fully nitrify. LAN designed a system which included high-efficiency turbo blowers and utilized submersible aerator/mixers to increase mixing and transfer. Since its installation in the summer of 2016, electrical usage has decreased by 25% or approximately $5,000 per month.

The second phase of the project focused on operational enhancements, which included mitigating the impact of flood stage in the nearby stream, replacement of failed/problematic screens and sludge thickeners, and miscellaneous equipment replacements and enhancements. During flood stage, the discharge pipe to the nearby stream submerged and subsequently flooded the UV units installed in the 2003 improvements. To protect the units, gate valves were installed with an overflow to an existing, unutilized tank for pumping to a protected downstream manhole with an emergency pump.