interest and the analyser measures the reaction products or the disappearance of the reagent, often electrochemically or using a photometer. Apart from phosphate, analysers offer the ability to detect contaminants, such as metals and arsenic, which cannot easily be measured in-line with other technologies. The disadvantage of analysers is the maintenance required, which includes the replenishment of reagents, tubing and pumps on a regular basis. This requires skilled personnel and easy site access, confining the applicability of analysers to centrally located monitoring stations with well-trained staff.


method, and allows optimisation of an instrument for a specific fraction of the oil (BTX, PAH, etc.) by selection of the excitation/emission wavelengths. However, these instruments suffer from the problem that oil does not dissolve well in water and may therefore be missed or incorrectly quantified, even during a significant contamination event. Widely used instruments include those from e.g. Turner Designs, YSI, Hach and Trios.


Many components of oil float on water. In such a case they can be detected by measuring the reflectivity of the water surface. Solutions for oil-on-water monitoring are available from e.g. GE, Trios, MultiSensor Systems and Partech. However, even with a combination of an oil-on-water and oil-in-water sensor, it remains impossible to guarantee detection of all oil contaminations due to their inhomogeneous character.


Ecological Status Monitoring Figure 2: Cabinet analysers at a monitoring station in China. Organic Parameters


The measurement of organic load, especially useful as an indicator of municipal and industrial wastewater discharges, has traditionally been dominated by analyser-type instruments; a typical TOC/COD analyser uses a reagent to oxidise the organic material in a sample


and measures the reaction products, e.g. CO2. These analysers, however, suffer from the same restrictions as those for phosphate, metals, etc. A low-maintenance, more robust alternative has recently appeared in the form of UV spectrometer instruments. UV absorption, most notably at 254nm, has long been used as an indicator of the concentration of organic materials in water. Such optical instruments, devoid of moving and replaceable parts, are highly robust and easy to use. With the increasing penetration of multi-wavelength and full-spectral instruments, performance has increased to a level at which they can be used for reliable measurement of TOC/DOC/COD/BOD as well as nitrate, nitrite and suspended solids, all in a single multiparameter instrument. Spectrometer instruments for in-situ measurement are available from manufacturers such as s::can, WTW, Trios and SAtlantic.


An interesting development in water quality assessment in Asia is the focus on the evaluation of its ecological as well as chemical status. Whereas ecological status was a latecomer in Western countries, the involvement of institutions such as the World Bank and European Union in the development of monitoring strategies in Asia means ecological status has been a key element from the start. The assessment of ecological status of water requires an inventory of the living organisms found there. Most small organisms are analysed and classified using a microscope. One exception is planktonic (free floating) algae, which can be measured using spectrofluorometry. The basic parameter measured in fluorometry is the total concentration of chlorophyll- a, which indicates total algal biomass, but does not provide any information on the various algal classes and their abundance. More advanced instruments measure a fluorescence fingerprint used to calculate concentrations of individual algal classes, such as green algae and cyanobacteria. Instruments for chlorophyll-a measurement are available from major instrument suppliers as well as many smaller producers. Instruments allowing algal classification are available from e.g. YSI, Turner Designs, Chelsea, WetLabs (green algae and/or cyanobacteria) and bbe Moldaenke (up to 5 algal classes simultaneously).


Toxicity Measurement


The quality of water is not linearly dependant on the sum of all the substances dissolved in it. When substances are present in a mixture, their (toxic) effect can be amplified or diminished. Currently, the only method of evaluating the effect of such a mixture on living organisms is by exposing those organisms to the water sample. Toximeters, also called online biomonitors, make use of this approach; an online biomonitor is an instrument that continuously records an organism’s behavioural and/or physiological response, and evaluates changes that could indicate pollution in the environment. Although these systems do not identify what triggers the response, the direct measurement of the toxic effects provides complementary information to that obtained from chemical monitoring. Known sites at which biomonitors have detected occurrences of a pollutant not detected by conventional, analytical systems have demonstrated the usefulness of these biomonitors in river water monitoring.3


China and South Korea are


heavily investing in the use of biomonitors, especially in rivers affected by industrial activities. The leading manufacturers of these


References:


1) World Bank, Environment and Social Development Department (2006): China Water Quality Management.


2) D. Liu, W. Yi, U.S. Commercial Service(2008): China: Water Monitoring Technologies and Instruments.


Figure 3: Submersible probes, including ISEs and a UV/Vis spectrometer, on a movable platform.


Since mineral oils are also mixtures of organic substances, their analysis is a different challenge. Although part of the mineral oil absorbs light, and is therefore visible to a UV spectrometer, it is fluorescence that is most frequently used for oil-in-water measurement. Fluorescence measurement is a highly sensitive


3) C.J. de Hoogh, A.J. Wagenvoort, F. Jonker, J.A. van Leerdam, A.C. Hogenboom (2006). HPLC-DAD and Q-TOF-MS Techniques Identify Cause of Daphnia Biomonitor Alarms in the River Meuse in Environ. Sci. Technol. Vol. 40, pp. 2678-2685.


Water/Wastewater 11 types of instruments are bbe Moldaenke, microLAN and Seiko.


Since biomonitors contain living organisms, their operation is often more critical than that of simple physico-chemical sensors; climate control, culturing and replacement of the organisms, maintenance of pumps, feeding systems, etc are all necessary. As with the cabinet analysers, this restricts their use to locations which have the necessary infrastructure and skilled personnel.


Discussion


A great number of technologies and systems are available for water quality monitoring. Increasingly, instruments can be deployed in-situ and can measure continuously and in real-time. Although most systems have reached a stage of maturity allowing deployment in the field, some have limited applicability due to their complex nature and the need for an advanced infrastructure. The less complex systems, however, allow autonomous operation for extended periods. Solar powered instruments with automatic cleaning systems and wireless communications interfaces for remote access and real-time data collection are becoming commonplace and enable deployment at remote, unmanned stations and in buoys. As more and more data is collected, handling and interpreting this information for management procedures is becoming the next challenge in water quality monitoring.


Figure 5: Example of a stand-alone solar powered monitoring station with wireless data transmission to a web-based data collection system as deployed in Singapore.


Figure 4: Daphnia Toximeter. Photos courtesy of s::can Messtechnik (Figures 1, 2, 3 and 5) and bbe Moldaenke (Figure 4).


www.envirotech-online.com AET Annual Buyers’ Guide 2013


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88