CODeq measurement based on Hybrid Ultrasonic Spectroscopy
23 March 2009, News release from Process Measurement & Analysis Ltd
The latest technology now available for full control of industrial waste streams
Waste streams at manufacturing facilities contain potentially unplanned leakages; off-spec products, surface water run off and cleaning liquids from the factory. In most cases the waste stream contains food and or toxins with respect to microbial organisms or algae. This is fed to a digester. Subsequently post digester output COD etc is removed via aerobic treatment. Although the bacteria needs a continuous stream of food, the waste flow also contains raw products that should ideally remain within the production process.
By continuously measuring the amount of contamination in the waste streams, it is possible to generate an alarm should an incident occur, ideally learn from this, and reduce the risks of process inhibition or environmental pollution. Ultimately reduce costs in the WWTP.
Figure 1 Influent WWTP Brewery
Sensors for COD
Early detection and identification of pollutants in the waste water is the goal for any diligent company. In addition to the classic conductivity, pH, DO sensors, the development of various analyzers in the last few years to determine COD has occurred as follows :
1.Extractive analyzers for TOC and COD according to laboratory methods provide high accuracy, but also high cost, lots of maintenance and analysis delay of about 8 minutes per measurement.
2.Optical UV 254 and UVVIS spectrometers, suffer from contamination in almost all industrial processes and generally offer very low correlation with laboratory COD. Especially for spectrometry, a high level technical service specialist is required on site to change software models, perform acid cleaning and calibration.
Optical measurement for CODeq are based on the absorption of light in the UV range. As most commonly used industrial dissolved solids, like sugars or oils, does not absorb light in this range, the correlation is based on the measurement of additives that combine/occur at unpredictable levels, and therefore lack accuracy and reliability.
Figure 2 - Influent MBR of Land fill
The contribution of real-time Hybrid Ultrasonic Spectroscopy
Real-time Hybrid Ultrasonic Spectroscopy (HUSS) solves all the mentioned problems of the former technologies and is therefore suitable for light or heavy industrial waste water contamination measurement.
The HUSS offer 6 embedded technologies:
- US temperature measurement, to compensate the measured concentrations for temperature dependency
- US spectroscopy measurement, accurate measurement of the transit time of the sound pulse on 60 specific wavelengths (between 0,7 and 12,5 MHz) through the medium, resulting in the calculation of the dissolved COD components
- US spectroscopy measurement, determination of the fingerprint of the liquid, resulting in identification of specific dissolved or undissolved components, eg Glycol.
- Attenuation measurement, determination of the absorption of the energy of the pulse by undissolved components in the liquid, resulting in the measurement of turbidity up to high solids concentrations >50 wt%
- Acoustic Impedance measurement, determination of the density of the liquid or slurry without the need for transition of the sound pulse through the medium
Each measurement (20 measurements per second) allows the analyser to collect data from the sensor defining the so called ultrasonic fingerprint of the water. Employing a "global calibration" a number of different parameters (e.g. FTUeq, CODf.eq, TSS.eq, TOCeq, brix.eq, acids, bases, oils, salts, sugars) are calculated using the data available in these fingerprints.
"Global calibrations" are standard algorithms available for typical applications (e.g. waste water, process liquids - like acids, bases, oils, salts) and allow the use of the Rhosonics monitoring system as a plug and play system. It is ready for use at once when installed on-site.
With a local calibration the respective parameters can be adapted to the actual concentrations if the global calibration proves not accurate enough for quantitative measurements. As the global calibration is derived as the average of a large number of measurements, it might not provide an entirely perfect for the local conditions at a specific site. Therefore, a local calibration can be performed with Rhosonics onboard software incorporated within the ana-lyzer. This can be done directly on site without demounting the Rhosonics monitoring system and does not require the use of standard solutions. The only thing required is the input of results from the laboratory analysis in the calibration software.
In case the local calibration is not accurate enough, a new global calibration should be selected from the internal database or requested from Rhosonics R&D department.
For specific measuring mediums not covered by Rhosonics global calibrations, the development of an individual calibration (parameter-X) can be offered by Rhosonics R&D.
The database for each global calibration are the results of conventional laboratory analysis on the one hand and the fingerprints measured with the ultrasonic probes on the other hand. Because the reference analysis are made in the laboratory and the measurement of the fingerprint takes place directly in the process (on-line and in-situ) the quality of the calibration will be influenced by the difference between the methods but also due to total sampling failure (difference in time of analysis, sample preservation methods, homogeneity of medium, biochemical reactions that occur in the space of time between sampling and analysis in the lab).
Figure 3 - Influent WWTP Paper Mill
How to install a Rhosonics CODeq analyzer in the Waste Water Stream
The simplest installation method for the Rhosonic sensor/ analyzer in any given waste stream is by means of the direct submersion "diver" probe. Alternative mounting options include utilisation of a "wafer" or "spool piece" between pipe flanges. In all cases,fouling is avoided this eliminates situations leading to drift in the dissolved COD or other parameter under analysis.
For further information please email Process Measurement & Analysis Ltd