Archer Western and Stantec will lead Chattanooga, Tenn.'s effort to upgrade wastewater facilities at its Moccasin Bend Environmental Campus on the Tennessee River, including plans for the world’s largest membrane-aerated biofilm reactor. 

The team will design-build Phase 1 of a Class A Process Optimization for Wastewater Energy Recovery (POWER) project and wastewater treatment plant upgrades at the site, where the city has installed infrastructure to support energy, water and cost savings, including solar electricity generation. Archer Western Construction will be lead contractor for the project, with Stantec leading design and engineering. The facility is expected to be operational in December 2028. 

In an announcement, Stantec and Archer Western say the progressive design-build project is expected to incorporate a thermal hydrolysis process (THP) facility, anaerobic digestion upgrades and conversion of a high-purity oxygen facility to a membrane aerated biofilm reactor (MABR). 

Waste-to-energy systems convert the organic solids in wastewater into biogas, which is used on-site to power operations and to be further processed and sold as a natural gas substitute. 

Upon completion, according to the announcement, the facility will be the world’s largest MABR facility, described as an energy-efficient, intensified nutrient removal process that will allow Chattanooga to utilize existing tanks while meeting future nutrient limits in effluent discharged from the Moccasin Bend site.

It will produce Class A biosolids that can be used as a soil additive in nearby farms, and biogas that will be reused to generate steam, with excess generating power for the facility.

To meet the city's sustainability and operational goals, the biosolids portion will integrate the THP facility within the existing biosolids treatment process, improving anaerobic digestion and biogas production while reducing the volume of biosolids for disposal. 

The project was unveiled in September 2023 at a meeting of the city's Industrial Development Board, with Mark Heinzer, Chattanooga's wastewater administrator, telling the board that the project could cost $130 million to $150 million. 

He said the city currently hauls away up to 15 truckloads per day of Class B biosolids, which must be taken at least 50 miles away to be applied. 

According to minutes from that meeting, 49% of the project is being funded through a $186-million federal Water Infrastructure Finance and Innovation Act (WIFIA) loan approved in 2022 that’s being split among three other projects as well, carrying a Dec. 31, 2028 deadline. 

Heinzer told the board that the leftover gas can be put back into the grid for renewable energy credits or can power vehicles, expecting $4 million per year in the sale of renewable energy credits. In total, he said it represents a savings of up to $9 million for the city annually.

Chattanooga Mayor Tim Kelly said in a subsequent release that the facility upgrade will help the city decentralize its renewable energy generation efforts and double the wastewater system’s efficiency to better deal with continued growth in the region. 

Portions of the city’s wastewater infrastructure system are reaching the end of their useful lives, the city says, contributing to failures during heavy rains and sanitary sewer overflows.

The project is part of the city’s Clear Chattanooga effort, a community-wide plan to decrease the number of sewer overflows to meet an April 2013 consent decree agreement with the EPA, state of Tennessee and Tennessee Clean Water network following a lawsuit alleging the city had violated the Clean Water Act.

The consent decree agreement includes a commitment from Chattanooga to spend $784 million on a multi-year program including major upgrades, system revisions, pipe replacement and more.