LOTT is recognized as an industry leader in progressive treatment approaches that meet some of the most stringent discharge limits in the United States. In 1994, they implemented a biological nutrient removal (BNR) process to remove nutrients, particularly nitrogen, from discharge into Budd Inlet and the greater Puget Sound. This project optimized the biological treatment process, replaced aging equipment, enhanced operational control and flexibility, and increased process reliability.

To optimize the current process, this project reconfigured existing basins into a five-cell, five-train BNR basin using new anoxic, swing, and aerated control cells to increase treatment efficacy and efficiency. The plant control system is one of the most capable and advanced in the country, employing the most current technology available. The improvements give LOTT the flexibility to operate multiple cells in swing modes of aerobic or anoxic to fine-tune nitrification and denitrification within the BNR basin, optimizing both nutrient removal and energy efficiency.

Parametrix and LOTT worked as an integrated team, engaging LOTT’s highly trained and knowledgeable staff throughout the design process. This ensured full consideration of operational and maintenance issues and minimized rework from one design phase to the next. This was the first project in the state of Washington to apply for and use an alternative contractor procurement process, which allowed LOTT to select three contractors based on qualifications to submit their best and final proposals.

The biological process improvements were completed on time and budget and have had impressive results. The plant has achieved near theoretical results for nitrogen removal of 0.6 milligrams per liter (mg/L) total inorganic nitrogen (TIN) and reduced power usage by 22% annually.