Shape of the future - instrumental changes
Steve Russell of WRc looks at the impact of current technology and the direction of some areas of research.
One product, Siemens Clearcense, monitors water colour in distribution mains with an insertion device made possible by a blue LED. Recent developments in DO (dissolved oxygen) sensors use blue LEDs to sense changes in a chromophore responding to the presence of oxygen.
Blue and near-UV also stimulate fluorescence in many pollutants and this is being exploited in emerging environmental monitoring equipment. The excellent collimation of laser light has enabled instruments to go non-contact in difficult situations such as sewers and sewage treatment inlets. This approach was used in the recent EC project Loadmon co-ordinated by WRc. Loadmon sensors aim to track wastewater quality at a range of up to 2 metres to overcome the difficulties of direct contact with sewage.
Optical sensor advances
At the infrared end of the spectrum, availability of lasers and LEDs is improving steadily and the cost of optics is falling. This has brought advances in gas monitoring using optical sensors, and more recently in aqueous samples, where evanescent wave techniques are used to overcome the effects of water absorbance. Fourier Transform Infrared (FT-IR) spectrometry is now being used by researchers to identify and measure concentrations of specific compounds such as fatty acids in sludge digesters. Overall optical systems are steadily opening up the measurement of both broad classes of compounds such as dissolved organic materials at the UV end of the spectrum, and specific compounds in the mid-infrared range.
Electronics has created new possibilities, particularly in enabling precision at low cost and high volume. The Siemens Censar combined chlorine, DO, pH, Redox and temperature sensor can now be inserted into a 1.5” tapping, thanks to semiconductor manufacturing techniques.
Research at CSEM Neuchatel has demonstrated greatly improved performance for amperometric sensors using the ‘Au-Sensys’ microelectrode array, using semi-conductor techniques. Miniaturisation has been exploited in the Danfoss ‘Evita’ range of floating analysers. While using conventional chemistries, reagent consumption and the waste produced are minimised by very small-scale engineering.
The revolution in communications has been an important enabler. Instrument suppliers now post outputs on the web, while loggers can send data to a secure website via cellphone links. Less exciting, but highly significant, is the use of low-power unlicensed radio links. These are now replacing cabling across sites because they are much cheaper, quicker to implement and easy to move around. A recent WRc collaborative project found that low power radio can change some monitoring applications from having marginal return to being very cost effective.
Telemetry to remote sites can now use either radio links, the cellphone network, low earth orbit satellite communication or the ‘meteor burst’ system, making communications possible in the most remote and hostile areas - thus increasing numbers of river basin monitoring schemes worldwide can pass warnings of natural changes and pollution to utilities and regulators.
It is now routine for surface water treatment plants to look upstream and monitor both intake and river conditions. Real time monitoring of the delivery network’s water quality is moving us nearer to a Systems view where all parts will interact and may have an impact on the end user.
Similarly with wastewater, the catchment, sewer network, treatment plant and receiving water can be monitored and controls applied to minimise the impact of discharges. The sensors and communications technology are close to the stage where this becomes reality. This is timely, as the EU Water Framework Directive is expecting all those involved in the water sector to recognise the interactive nature of their activities on the environment.
Data - a plus or minus?
Handling and utilising data from a large composite system is a very different operation from running a treatment plant as a stand-alone operation. Computer models of the processes can be used effectively here in interpreting the data and predicting the outcome of possible actions. There is also considerable scope for the use of signal recognition and automated trend analysis to assist operators in dealing with the large volumes of data now available. For example, Cusum methods have been used to good effect at WRc to extract long term data trends obscured by short-term variations.
The process model used to be in the operator’s head, so it was necessarily a fairly simple model and varied between operators. Fast, cheap computers can readily run more realistic process models to provide both real time control, and decision support tools for plant operators.
Water in taps remains a very low cost product and it has been frustrating for suppliers and utilities to recognise that they cannot justify high cost analysers. Many of the developments of the last decade have been about lower cost alternatives to the unaffordable wet chemical analyser. However there are still many measurements, such as nitrogen, phosphorous and most metals, for which the alternatives are limited. Improved performance of N and P removal in wastewater treatment plants is in part limited by the high cost of measuring these.
A lower cost method of measuring this group of parameters remains a priority. Researchers are developing miniature plastic disposable sensors, with the data extracted by optical or electrical means such as conductivity. Key features will be small size, low maintenance, de-skilled operation and low environmental impact.
Water Industry instrumentation suppliers have been quite creative in transferring technology to meet the market need for low cost reliable equipment. Water is firmly on national and international agendas, and this will drive much greater changes over the coming decade. Oversized systems with minimal controls are no longer appropriate and will be replaced by reliable instruments and effective control systems.