Project Overview

Client City of Colusa
Project City of Colusa Wastewater Treatment Plant and Recycled Water Project
Location Colusa, California
NEXGEN’s Role Permitting, Planning, Financial Planning, Design, Bid Support, Construction Management, Inspection, Operations Support
Quick Fact $8 million in grant funding and $7 million in low interest loans through the CWSRF program
Outcome
  • The City has diversified its effluent disposal options by adding land reclamation and effectively reducing the impact of the effluent on the unnamed tributary to Powell Slough and downstream water bodies and reduced groundwater pumping and reliance on potable water.
  • The WWTP can now reliably meet its permit requirement of less than 10 mg/L nitrate in the effluent.
  • The second secondary clarifier added a level of redundancy the WWTP previously lacked.
  • Biosolids can now be reliably dewatered after improvements to the SSBs and the addition of a new, more robust liner.

There are three general areas of improvements included in this project.  They include:

  • Secondary process improvements
  • Storage basin improvements
  • Wastewater reclamation (recycled water)

NEXGEN, as the City’s wastewater consultant, provided all services from the initial permitting and planning, all the way through construction management and operations support for all of these improvements.

Secondary process improvements design included the addition of a Wave Oxidation (Biolac) control system to the City’s aeration basins, which is a form of simultaneous nitrification and denitrification and the addition of a second 55-foot diameter secondary clarifier and associated piping and RAS pumping improvements.

New, more robust liners were added to the equalization basin and sludge storage basins.

The City plans to use 400,000 gallons per day of recycled water to grow and sell alfalfa on 200 City-owned acres adjacent to the WWTP for about 6 months during the growing season.  This recycled water supply system will reduce the impact of the City’s wastewater effluent on the unnamed tributary to Powell Slough and downstream water bodies and reduce groundwater pumping and reliance on potable water.  The infrastructure for this project is partially complete and is anticipated to be ready by 2020.