WWEM III
maintenance costs, ease of use, auto-calibration, adjustable measurement frequency and proven chemistry methodology.
UV detection
UV monitors can measure the absorption of ultraviolet light at 254nm commonly known as UV254, which is directly related to the levels of organic matter in the water. The levels of dissolved organics in a body of water are calculated by measuring a pulse of light at two wavelengths. One wavelength that provides a reading from a turbidity photodetector, and another from a UV photodetector. Put simply, in addition to the absorption measurement at 254 nm, a second measurement at 400 nm enables the monitor to compensate automatically for fl uctuations in turbidity. The benefi ts of a straight-through system, without the need for expensive and maintenance-intensive sample fi lter systems, ensures long-term reliability, essential for on-line control.
Many manufacturers, including ABB, also offer UV monitors that can be confi gured to measure UV transmission, or %UVT. In contrast to UV absorption, which measures the properties of a sample according to the amount of UV light it absorbs, UV transmission measures the light that passes through a sample, enabling it to produce a %UVT value for levels of key parameters such as colour, turbidity, particulates, and organic and non-
Aztec 600
they do not absorb light in the visible spectrum. To overcome this restriction and enable the substances to be measured, chemical reagents are used to create a reaction and form a coloured complex that can be read and measured.
The Aztec 600 Colour analyser has been designed specifi cally for the measurement of colour through the drinking water treatment process for coagulation optimization. It does that by measuring the absorbance of a water sample at 400 nm. The result of that absorbance test is then expressed as a colour that corresponds to the Platinum-Cobalt Scale (Pt-Co) or Alpha-Hazen Scale. Devised by chemist Allen Hazen in 1892, the Hazen colour scale compares a water colour to known concentrations of platinum- cobalt, ranging from 0 at the light end of the scale to 500 at the darkest.
All the sample and chemical fl uid handling for measurement, mixing and disposal is precisely controlled by the Aztec’s patented fl uid handling system, which cleans the measuring cell every time it moves.
Capable of measuring up to 12 streams per hour, the Aztec 600 uses a patented fl uid handling system that precisely controls the handling, measurement, and disposal of samples, thus ensuring highly accurate and reliable analysis of the colour of surface and treated waters up to 500 Hazen units.
Among others, one typical application of this method is to measure the effectiveness of the coagulation process, i.e., ensure that water is suffi ciently dosed and treated to reduce dissolved organics concentrations to approved safe levels. Additionally, by monitoring raw water colour prior to the coagulation process, colour analysers can be used to provide predictive coagulant control, therefore ensuring that suffi cient coagulants are administered throughout the process, minimizing the potential for inadvertent breakthroughs. Installing colour analysers at the fi nal treated water storage stage will also help to verify that the treatment process is working properly and that established water quality standards have been met.
One important factor to consider when measuring colour is the impact of turbidity. Turbidity is the quality of being cloudy or opaque and can cause issues when differentiating between true and apparent colour because it is a key test of water quality. For analytical purposes ‘true colour’ is attributed to dissolved matter, whilst ‘apparent colour’ is what arises from the presence of suspended matter in a sample. The unwelcome impact of turbidity is that it can result in the ‘apparent colour’ having a much higher value than the ‘true colour’, which can affect colour determination and, therefore, accurate results. That is why, whenever turbidity is a factor, it is imperative to properly fi lter a water sample prior to introduction to the analyser to obtain a true colour intensity and, therefore, accurate result.
Moreover, Aztec 600 Colour users also benefi t from low
WATER, WASTEWATER & ENVIRONMENTAL MONITORING
maintenance demands on these applications are minimal. When the UV lamp is fl ashed every two seconds the measured value is updated and calculated from more than 200 readings that are taken during the brief fl ash duration, which delivers far greater accuracy than conventional colour testing technology.
The AV400 can detect dissolved organics faster and more effectively than traditional methods and can therefore help save costs and improve safety and treatment process performance because it substantially improves the active monitoring of a water supply.
Like colour analysers, UV analysers can be used to help reduce the formation of THMs by ensuring optimum performance during the coagulation treatment process. Designed for measuring dissolved organics concentrations of 0 to 100mg-1C, ABB’s high range AV400 UV dissolved organics analyser can be used as a surrogate colour monitor where humic and fulvic acids form the major colour constituents of raw water because these acids readily absorb ultraviolet light at 254nm, making them easy to detect and measure by the AV400. These acids can also be used at the activated carbon stage to capture any dissolved organic materials that may break through the coagulation process, or at the fi nal treatment stage to enable corrective action to be taken the moment any increases in dissolved organics levels are detected.
organic matter present in a water sample.
In potable treatment processes, measuring %UVT can be used for checking the quality of treated water and assessing the effi ciency of the coagulation, fl occulation, sedimentation, fi ltration and carbon adsorption stages. Checking water quality for %UVT can also help to detect any residual dissolved organics that could result in the formation of disinfection byproducts at the chlorination stage.
Online analysers can detect dissolved organics much faster and more effectively than traditional methods, in most cases eliminating the need for laboratory testing. This leads to savings to the water utility through effective treatment and enhanced active monitoring of the water supply. These advances in detection devices are helping to reduce the likelihood of contamination by dissolved organics, leading to even safer supplies of drinking water.
ABB’s low range AV400 monitors, for example, provide a resolution of 0.01 milligrams per liter of dissolved organics over a range of 0-20mg/l. The transmitter incorporates the latest technology to provide a highly reliable yet fl exible, feature-packed device that is designed to satisfy a diverse range of process monitoring and control applications. The AV400 series of monitors are designed for optimizing the performance of potable water treatment plants, providing signifi cant cost savings, and ensuring the quality of the fi nal treated water.
In particular, they can be used to monitor the quality of the outlet from sand and carbon fi lters to provide a THM precursor measurement. Moreover, long term fi eld trials have shown that
Summary
Controlling dissolved organics have historically been a problem for the water industry and the presence of NOM-based THMs in the public water supply remains a daily challenge for many water treatment operators. The mandate to maximize the removal of natural organic matter while ensuring adequate microbial control is an important health consideration. However, as technology improves and the health risks continue to be identifi ed, standards of drinking water are steadily improving with it. Technology is also progressing to a point that it has enabled water companies to invest in even more safety measures at a lower cost than ever before. The steady march of a new generation of water monitors is already making clear, timely and accurate testing easier, therefore considerably reducing the risks of drinking water containing improperly dissolved organics
Using almost instantaneous online analysers to measure dissolved organics levels throughout the extensive potable water treatment process can play a major role in mitigating any health or effi ciency issues presented by the presence of contaminants. By providing an understanding of dissolved organics levels in real or near-real time, colour and UV analyser technologies can each make a major contribution to ensuring that water quality continues to consistently meets the required standards, and that any issues are identifi ed, examined, and resolved well before they escalate to become a widespread public health problem.
For more information about ABB’s solutions for dissolved organics monitoring, visit
https://bit.ly/ABBCWA_DOC.
Author Contact Details • ABB, Howard Road, Saint Neots, PE18 8EU • Tel: +44 1480 475 321 • Email:
enquiries.mp.uk@
gb.abb.com • Web:
www.abb.com/measurement
WWEM.UK.COM
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 |
Page 89 |
Page 90 |
Page 91 |
Page 92
