Dissolved Oxygen Measurement in Continuous Aeration Sewage Treatment

Manage dissolved oxygen in wastewater treatment reliably with Yokogawa’s Dissolved Oxygen System.

Application

In wastewater treatment systems, dissolved oxygen (DO) levels must be managed to achieve ideal states of operation and remain within compliance standards. Sewage that flows into a treatment plant is sent to a primary sedimentation tank to remove the garbage and sludge. From there, it is routed to an aeration tank where activated sludge (sludge containing bacteria, protozoa, and other microorganisms) is added, and air is blown into the mixture to agitate it. The microorganisms in the activated sludge thrive on the added oxygen and cause the organic substances in the sludge to proliferate and the generated solids to be deposited from the solution. A DO analyzer is used to continuously measure the DO concentration.

Sewage Treatment Facility

Challenge

Operators are tasked with managing dissolved oxygen levels in the wastewater treatment system. Insufficient oxygen levels will allow necessary microbes to die and floc to break up. On the other end of the spectrum, too much oxygen increases power consumption past necessary levels. Aeration is one of the highest contributors to a treatment facility’s overall electricity use. With an online DO analyzer equipped to automated controls, the EPA reports that energy costs can be reduced by as much as 50%.

Water Treatment Filtration Process at Work

Another challenge encountered when used to measure the dissolved oxygen in an aeration tank is that sensors tend to quickly become contaminated and need frequent cleaning. This can result in unplanned outages, increasing operating cost. 

Solution

A cost-effective solution to these challenges is the Yokogawa FLXA402 Dissolved Oxygen Converter system. In combination with the DO71 and DO72 optical dissolved oxygen sensors, this system measures oxygen dissolved in water continuously and reliably, allowing operators to keep DO levels within ideal parameters. 
With this system, the sensor is mounted in a PB305G float ball holder that protects it from contamination as it is frequently washed by the surface-level flow of water, eliminating the need for manual cleaning. This enables continuous maintenance-free use for extended periods, reducing operating costs. Real-time diagnostics indicate sensor wellness, and ensures stable, continuous dissolved oxygen measurement. 

Figure 1: Dissolved Oxygen Measurement in Sewage Treatment Process

Overall, Dissolved Oxygen Sensors are part Yokogawa’s Liquid Analyzers portfolio that perform liquid process measurement for determining the amount of oxygen dissolved or carried in the process liquid. Our dissolved oxygen liquid analyzers provide high precision measurement and are built to withstand the harshest applications, requiring minimum maintenance and helping you achieve increased efficiency and reduced operating costs, for industries such as Water & Wastewater, Water Treatment and more.

Key Benefits

• Ensure stable, continuous dissolved oxygen measurement
• Reduce energy consumption with optimal DO level monitoring 
• Reduce maintenance time and associated cleaning costs with float-ball technology