The quality of tap water has improved enormously in recent decades, but for largely technological reasons, until recently, knowledge of water quality between the treatment works and the tap has been an almost impossible dream for water treatment and distribution network managers. In this article, Jo Cooper, Product Specialist at Intellitect Water, will look at the ways in which the challenges have been overcome in order to turn that dream into reality.
Drinking water generally leaves treatment plants in excellent condition before entering a network of underground pipes, of varying age, that can extend for many miles. It has always been difficult to identify water quality problems until after the water has reached the consumer. An array of technological challenges had to be overcome before it would be possible to measure in-pipe water quality without incurring major capital or operational costs. However, following a substantial research and development programme, the Intellisonde monitors were launched in 2008 and have since found application worldwide in pipes and bypass flow cells for drinking water, rivers and wastewater installations. The remainder of this article will examine the most significant hurdles that were overcome in the development of this technology.
1. Water quality parameters
Most traditional water quality sensors would be unsuitable for use inside pressurised pipes, so it was necessary for Intellitect’s engineers to develop sensor technologies that would be small, low cost, low power, robust and require almost no service or calibration. As a result, the head of an Intellisonde (see picture on right) is a mere 3.6cm in diameter, but fully populated can deliver continuous water quality data for 12 parameters. Measurement options include Free Chlorine, Mono-chloramine, Dissolved Oxygen, Conductivity, pH, ORP/Redox, Flow, Pressure, Temperature, Turbidity and Colour. An ISE channel is also available for Fluoride or Ammonium. The measurements are flow independent because the unit features an automatic stirrer which starts when low flow is detected.
Intellisonde users are able to specify the required parameters such that monitors can be installed to meet customers’ specific needs.
2. Maintenance and consumables
Clearly, it would not be feasible to install a network of monitoring equipment in underground pipes that requires frequent recalibration, spares or maintenance. This was a major challenge because many traditional water quality monitoring technologies for parameters such as dissolved oxygen and chlorine require recalibration as often as fortnightly to address sensor drift. In addition to regular recalibration, these traditional membrane-covered amperometric sensors also necessitate occasional replacement of membranes and the sensors’ internal electrolyte solution.
Colorimetric water quality analysis techniques would also be unfeasible for an in-pipe monitoring application, because such techniques generate waste chemicals that could contaminate ground water if no waste water disposal facility is available and also necessitate a supply of reagents that would add to operational costs and create an unacceptable maintenance requirement.
The Intellisonde sensors are solid state and require no recalibration once they have settled following installation. Furthermore, no membranes or chemicals are required and no maintenance is necessary until the sensor head is quickly and easily serviced after typically 6 months.
3. Labour costs
As outlined above, traditional monitoring techniques can create a significant labour requirement for ongoing instrument service. However, there are two other issues that affect labour costs. Firstly, instrument installation and secondly, the labour costs incurred by water quality problem investigations.
Intellisonde requires just a standard inspection pit and 2” gate valve for installation. Other instrumentation may require a roadside cabinet, waste collection and mains power which increase the cost very significantly.
The Intellisonde has been designed to minimise labour costs. This has been achieved with miniature sensors and an extremely low power requirement; the probe can be fitted into large pressurised pipes (via a 3.8 or 5cm valve) as well as pipes only ten centimetres in diameter, for street level monitoring. An adjustable collar allows the sonde to be set to a pre-determined depth, ensuring maximum flexibility to adapt to local conditions. A variant of the sonde (Intellisonde SA – short application) enables continuous monitoring of a customer’s supply by insertion into a water metering box.
The cost of excavation is highly significant and represents a significant barrier to water quality problem investigations, particularly if excavation work is likely to become a nuisance to road users for example. This is an area in which Intellisondes offer enormous benefits because the provision of live in-pipe water quality data enables network managers to detect problems before they become serious and also to significantly improve the speed with which the location of a problem is identified, thereby avoiding unnecessary excavations.
4. Data collection
Intellisondes incorporate an internal datalogger that can be configured to measure and log data from the sensors at intervals from once per minute to once per hour. This data can be collected manually, but more commonly real-time data is transmitted through a variety of communication methods so that network managers have visibility of water quality.
Communications options include RS232 or RS485 serial outputs via MODBUS, Analogue Outputs and GPRS. As a result, Intellisondes can interface with almost any SCADA system or data collection platform. There are also two analogue inputs available for external sensors such as pressure transducers, and each of the 12 analogue voltage outputs can be connected to telemetry loggers for integration into an existing data collection system. GPRS transmission can occur after each sensor reading, enabling rapid response to any incidents.
5. Multiple applications
Whilst in-pipe monitoring of drinking water quality is the main application for Intellisondes, the monitors have also been employed very successfully in a number of other applications. These include river monitoring for intake protection and environmental purposes, final effluent monitoring at wastewater treatment works and in swimming pools.