Introduction
When used to measure the dissolved oxygen in an aeration tank, sensors tend to quickly become contaminated and need frequent cleaning. A cost-effective solution to this problem has finally been found with the development of the Yokogawa FLXA402 Dissolved Oxygen Converter system. With this system, the sensor is mounted in a float ball holder that protects it from contamination and enables continuous maintenance-free use for extended periods.
Expected Benefits
- Continuously and stably measures dissolved oxygen concentration
- Reduces operating costs
- Eliminates the need for manual cleaning
Process Overview
Sewage that flows into a treatment plant is sent to a primary sedimentation tank to remove the garbage and sludge. Thereafter, 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 oxygen and cause the organic substances in the sludge to proliferate and the generated solids to be precipitated.
A shortage of dissolved oxygen (DO) will kill the microorganisms, so the DO concentration in the aeration tank must be properly controlled. A DO analyzer is used to continuously measure the DO concentration.
Sewerage treatment procedure
The spherical float stays relatively clean because contaminants are washed off by the surface-level flow of water. The sensor diaphragm is kept relatively free of contamination as it is positioned at the same height as the top portion of the float.
Solution Details
Measurement System
- Detector: DO30G-NN-50-□□/PN
- Float holders:
Angled type: PB350G-PV-25-NN
Vertical type: PB360G-PV-□5-NN - Converter: FLXA402-A-B-□□-D1-NN-A2-WR
- Terminal box (as needed): WTB10-DO3-NN- □□/□
With the WTB10 terminal box, the sensors and the converter can be up to 50 meters apart.
Utilities
- Power supply:
100 V AC ±15 %, 50/60 Hz
115 VAC ± 15 %, 50/60 Hz
230 VAC ± 15 %, 50/60 Hz - Power consumption: max. 10 VA
Precautions
- The measuring point must be at a location where air bubbles are not a frequent occurrence.
- To prevent the sensor diaphragm from being damaged by solids in the sample liquid, the arm of an angled float holder should be pointed in the downstream direction.
Field Data
No effects of contamination after four months of continuous operation
We conducted a test with two DO30G sensors that were equipped with the PB350G Float Ball Holder. During the test, no maintenance was performed on one of the DO30G sensors, while the other DO30G sensor was cleaned every two weeks and calibrated monthly. Over the entire duration of the test, the DO30G sensor that did not receive cleaning showed minimal contamination. Furthermore, its measurements did not deviate appreciably from those of the sensor that was regularly maintained.
Industries
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Wastewater Treatment
Wastewater treatment plants involve many pieces of equipment such as motors, pumps and blowers, which makes it important to reduce their electricity consumption and save running costs. Yokogawa provides optimum control solutions with digital technologies to improve energy efficiency.
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Water & Wastewater
Water resources are finite, and therefore contributing to a sustainable water cycle is one of the Sustainable Development Goals (SDGs). Yokogawa has been providing advanced digital control solutions for the stable supply of clean and safe water, wastewater treatment for protecting the water environment, water loss management and optimization of plant operation for reducing CO2 emissions and running costs. With our leading-edge technologies, dependable products and extensive expertise and experience of diverse water projects around the world, we work with you to provide sustainable water solutions that boost your business and add value throughout the plant lifecycle.
Yokogawa supports a wide range of water control applications in both the municipal and industrial water markets.
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Water Treatment
Yokogawa provides optimum solutions to improve the reliable operation of water treatment plants. These solutions include sophisticated technologies, unsurpassed product quality, and extensive application know-how throughout the lifecycle.
Related Products & Solutions
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Measuring Sensor DO30G
The DO30G sensor for dissolved oxygen is designed for use in water treatment plants such as sewage treatment works, effluent activated sludge process, and potable water treatment. It is also effective in river monitoring, intake protection, fish farming, and other fields where water quality is important.
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Optical Dissolved Oxygen Sensors DO71/DO72
It is a fluorescent dissolved oxygen sensor that is easy to clean and stable for long term measurement. Sensor replacement is easy on site and reduces maintenance costs. It is possible to measure oxygen in a wide range including low concentration measurement.
Suitable for use in water treatment plants such as sewage treatment plants and wastewater treatment plants under severe measurement conditions.
Can be used in combination with FLXA402 liquid analyzer by digital communication. -
Dissolved Oxygen Sensors
Dissolved Oxygen (DO) electrodes and sensors are the sensing portions of a DO measurement. There are three common technologies for dissolved oxygen measurements: polographic, galvanic and optical. Various installation options including floating ball, retractable, flow thru, immersion, and direct insertion.
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Liquid Analyzers
Liquid analyzers are used for monitoring process chemistry including water quality, providing process optimization and control.