Presentation on theme: "Automatic Monitoring of Heavy Metals in Waters Øyvind Mikkelsen and Knut Schrøder SensAqua AS and Norwegian University of Science and Technology (NTNU)"— Presentation transcript:
Automatic Monitoring of Heavy Metals in Waters Øyvind Mikkelsen and Knut Schrøder SensAqua AS and Norwegian University of Science and Technology (NTNU) Department of Chemistry Trondheim, Norway
Weather data - are collected by automatic weather stations and the results are transferred automatically to a central unit, frequently also available immediately to the public via Internet. But pollution data - are normally collected manually by field visits and the samples are then brought to laboratories for analysis. Several resources are spent annually for sample collection and laboratory analyses of heavy metals OUR METHODS OPEN FOR DOING MUCH OF THIS AUTOMATICALLY like what has been done for years in meteorology
Analyses can in general be performed in three different ways: Samples are brought to laboratories to be analyzed with advanced instruments. A huge number of methods are available Direct field single analyses. Paper strips methods are very convenient in addition to the use of simple instruments like pH-meters, photometers etc. Continuous and on-line remote monitoring in the field. (dealt with in the present presentation)
Advantages by using automatic methods Possibilities to act immediately if the results exceed given threshold values A great number of data will be available for processing, this also enables studies of day or seasonal changes Low costs, then several sources can be monitored If it is wanted, the data can be immediately available for the general public on the Internet For quality assurance, conventional sampling and analyses in a laboratory are performed from time to time for comparison.
What can unattended be measured in waters? Temperature pH COD, TOC and other major components Conductivity Turbidity and color Flow rate and water level Some bacteria etc. But heavy metals are not on this list
Requirements for remote monitoring Long-time stability of the measuring system i.e. sufficiently long periods between required manual maintenance Acceptable sensitivity No use of toxic materials in the measuring system like liquid mercury and other materials Not too expensive installation costs, this to allow installation of several units, and also considering that the remote installations might be stolen or destroyed Presence of electricity (solar cells and batteries can be used if frost is not present) Availability of Internet or another telecommunication system Why are the heavy metals absent from this list? Simply because no acceptable analytical method has been available. The presumptions above are rarely fulfilled for heavy metals
The main problem in remote monitoring is when the concentrations are at trace levels - and very sophisticated instruments are required to exceed the detection limit. The very great difference between having a method which works fine in a lab and doing the same unattended and remotely in the field has to be emphasized. Too much published work is done in the laboratory only and assumed to be adaptable to be used the field. Different methods for remote monitoring….
Which analytical methods can be applied for monitoring of heavy metals in trace levels? In a laboratory spectroscopy is mainly used, like atomic absorption, and ICP-MS. However, for automatic monitoring we frequently have the mentioned problems with stability, sensitivity, toxicity or costs. An alternative is electroanalytical methods - potentiometry with ion selective electrodes voltammetry The use of potentiometry/ion selective electrodes might be an ideal solution, but frequently this is useless due to low sensitivity. Voltammetry is also a good method, if the use of toxic material like liquid mercury or mercury salts can be avoided. However, this has been required.
In voltammetry we measure the electrical current due to one or more redox reactions on the surface of an electrode. Here, the electrodes are essential as they “sense” the compounds (heavy metals) to be measured by giving that current. By calibration this current is used to find the actual concentrations.
Sufficient high overvoltage (for the redox process) to allow the measurements without interferences from hydrogen gas formation Sufficient long term stability without need of maintenance Sufficient sensitivity to allow monitoring of the pollutants (the heavy metals) That non-toxic material is used (very important for off-laboratory methods) Not too expensive material needed Totally there are five requirements for making such automatic voltammetric analyses useful:
The essential is to obtain long time stability, combined with sufficient overvoltage during the measurements to avoid the formation of hydrogen gas on the electrodes, without using any toxic material. The flow of current due to a formation of hydrogen gas will destroy the measuring signal. How to solve that…..?
SOLUTION: By alloying a metal with high hydrogen gas overvoltage with a metal with low such overvoltage. A significant increase in the hydrogen gas overvoltage is observed for the alloyed metal, even for small additions (2-4%).
The use of solid alloy electrodes cannot be new in voltammetry? Very astonishing this was never studied before we did our first experiments in One possible explanation is that it was believed that an electrode only worked properly being a one-component metal. Consequently nobody had bother to try. Later, and after our patenting, several publications appeared.
The new system has interesting advantages: Easy to implement online Non toxic Stable over a long time without attendance It can be used for detecting a range of different heavy metals
How to find suitable electrodes which give sufficient overvoltage?
Alloy electrodes! Liquid mercury or deposit of mercury film Solid and environmental friendly alloy sensors How to find suitable electrodes which give sufficient overvoltage?
Any needs for monitoring, what is there already…? Norway; 139 rivers, 20 incineration plants, 2500 water purification plants. Europe …… USA; 5000 already existing stations where heavy metal monitoring may be implemented, mines, 4000 industrial plants, water purification plants China; 111 already existing stations where heavy metal monitoring may be implemented, 3000 industrial plants Japan;135 rivers, 55 lakes, 1,400 incineration plants, 3,000 sewerage treatment plants, 1,500 water purification plants. India; 72 already existing stations where heavy metal monitoring may be implemented
Cadmium Electrode system: Working E DAM Counter E Pt Reference E Ag/AgCl/KCl NH 4 Ac (0,05M) Some examples For more examples, click here….
ATMS500 ATMS600 ATMS500 and the new ATMS600
The chemical principles and the electrode system are the same for the old and for the new version. The previous version used a PC to control the process. Now all the electronics is on a microprocessor board. A PC is only used for initiating and data presentation. This also simplifies service and maintenance in the field as the microprocessor board and the electrodes can be replaces. For that reason it is no need to dismount the unit for servicing in a workshop, as it was for the ATMS500. ATMS500 vs. ATMS600
Conclusions and further plans This method opens for new possibilities for automatic environmental surveillance. It has low costs and enables one to carry out monitoring in a great number of water systems. The pollution data can immediately be available to the general public e.g. via Internet. Practical and legal action can be taken immediately if irregularities appear in order to obtain better water quality and less polluted sewage systems. Our intentions here are to introduce the new possibilities.
Contacts Knut Schrøder, Professor, General Manager Øyvind Mikkelsen, Professor, Chairman of the Board Norwegian University of Science and Technology and SensAqua AS Click here to see Groups of customers Click here for Documentation Click here for more about voltammetry
Thank you for your attention Further information: Tel