EnviroMix delivers significant energy savings with BioCycle-D process

North Wastewater Treatment Plant in Adairsville, GA 

BioMix nozzle headers easily interlace with the coarse bubble aeration grid. 

With a population of approximately 5,000 residents, the City of Adairsville is located 60 miles northwest of Atlanta, GA — about halfway between Atlanta and Chattanooga, TN.

In 2017, the city began designing the upgraded North Wastewater Treatment Plant (WWTP). The purpose of the project was to increase plant capacity and meet lower effluent total phosphorus limits. Finished in 2021, the upgrade expanded capacity from 1 MGD to 2 MGD average flow with a peak capacity of 4 MGD and included major process equipment: headworks, oxidation ditch, effluent filters, UV disinfection, and aerobic digestion.

Challenge

Conventional aerobic digester designs utilize diffused aeration for both mixing and process oxygen demands. This design approach often results in over-aeration which leads to uncontrolled nitrification, depletion of alkalinity, and excessive energy consumption.  

Solution

EnviroMix’s BioCycle-D Optimized Aerobic Digestion Process provides ideal conditions for aerobic sludge digestion and reduction of organic matter through endogenous respiration, maximizing volatile solids destruction. The process is based on automatically alternating aerobic and anoxic cycles, and it minimizes energy consumption by decoupling aeration from mixing.

Compared to diffused aeration, BioCycle-D delivers significant energy savings by decoupling aeration from mixing — in other words, the function of mixing is no longer provided by the diffused aeration system, allowing for smaller blowers and significant turndown. In many cases, the volume of air required to mix the digester’s contents is far greater than the volume of air required to satisfy the oxygen demand. This condition is commonly referred to as “mixing limited.” 

The system’s blowers, compressor, and master control panel are located tankside. 

Results

The BioCycle-D process was selected because of the significant energy savings it provides and the reduction in nutrient recycle enabled by automated process control. The technology’s decoupled approach eliminates mixing limited conditions because the system is designed so that:

• Aeration is designed for VS destruction only, not to mix the tank. 
• Concurrent operation of aeration and mixing enables unmatched aeration turndown. 
• Tank contents are consistently mixed, maximizing denitrification, alkalinity recovery, and VS destruction. 
• Completely mixed, air-off time periods allow for further conditioning of the sludge for dewatering. 

By decoupling aeration from mixing, the Adairsville North WWTP’s BioCycle-D process provides more than 45% energy savings versus a conventional diffused air mixing system designed at the Ten State Standards.