In 2016, the Clairton Municipal Authority upgraded the city’s wastewater treatment plant, installing new headworks and increasing digestion capacity to facilitate Class B biosolids.
After numerous treatment solutions were evaluated, EnviroMix’s BioCycle-D Optimized Aerobic Digestion Process was selected as the best technology for the aerobic digesters because of the significant energy savings and improved sludge digestion.
Decoupled aeration from mixing facilitates independent control over mixing and oxygen delivery.
0.13
hp/1,000 FT3 mixing efficiency
50
% annual energy savings
Challenge
The conventional approach to aerobic digestion design utilizes the aeration system to provide the oxygen to the microorganisms as needed for the digestion process and the mixing energy needed to keep the basin contents mixed at all times. In most cases, and especially for treatment works that have extended aeration secondary processes, the air required to mix is greater than the air required to satisfy the oxygen demand, often resulting in over-aeration which can cause uncontrolled nitrification, depletion of alkalinity, and increased energy consumption.
To maximize efficiency and operational flexibility, the aeration system must be designed solely based on the oxygen requirements and the mixing system must be designed solely based on the mixing requirements.
EnviroMix control modules allow for adjustable mixing intensity to match system demands.
Solution
The BioCycle-D process is an energy-efficient aerobic sludge digestion process which decouples aeration from mixing and incorporates process feedback through instrumentation to control and maintain the optimum digestion environment.
As part of the Clairton upgrade project, the BioCycle-D process was installed in two (2) existing 35-foot diameter aerobic digesters with hopper bottoms. Additionally, BioCycle-D was installed in a new 120-foot diameter aerobic digester that was constructed to provide the volume required to achieve Class B biosolids.
BioCycle-D is designed by right-sizing the diffused aeration system to satisfy process oxygen demand and applying energy efficient mixing through the use of the BioMix™ Compressed Gas Mixing System.
BioMix nozzles in the cone bottom provide bottom-up mixing beneath the aeration grid eliminating dead zones.
BioCycle-D maximizes sludge destruction, minimizes energy consumption, maintains stable pH levels, and provides process control by decoupling aeration from mixing along with automated operation through instrumentation feedback.
Results
The Clairton plant experiences energy cost savings of more than $150,000 per year with BioCycle-D versus a conventional aerobic digester aeration system.