The Urban Waste Water Treatment (UWWT) directive aims to ensure that all significant discharges of sewage are treated before they are discharged either to inland surface watersgroundwatersestuaries or coastal waters.
In the UK alone this covers 11billion litres per day of wastewater being treated at roughly 9000 sewage treatment works.
Although the European water industry has already gone a significant way towards meeting UWWT requirementsthe regulations are continuing to drive major capital investment as another significant deadline looms at the end of the year.
For the purposes of the UWWT regulationssignificant discharges are those to fresh waters or to estuaries serving agglomerations (urban settlements) with population equivalents of more than 2000 peopleor those to coastal water serving agglomerations with population equivalents of more than 10000. Sewage must normally be subjected to secondary treatment using biological systemswhile discharges to ‘sensitive’ areas require more stringenttertiary measures.
Some sensitive areas are bodies of water that may become eutrophic. In these cases the water can be overly enriched by nutrientsespecially compounds of nitrogen and/or phosphorus. This causes the accelerated growth of algae and higher forms of plant life and disturbs the balance of organisms in the water. Other sensitive areas include surface fresh waters intended for drinking water abstraction.
These water sources can suffer from high nitrate levels without tertiary treatment. Bathing waters and those from which shellfish are harvested are also classed as sensitive. The deadline to provide appropriate treatment for those areas initially designated as sensitive under UWWT was 1998.
The biggest single deadline under the UWWT directive came at the end of 2000by which time the water companies had to have treatment schemes ready to serve almost all agglomerations with a population equivalent of more than 15000. Several agglomerations were given an extended deadline of 2005but the vast majority of schemes are now complete.
Furthermoreat the end of 2005the regulations also laid down a requirement for the provision of secondary treatment for every agglomeration with a population equivalent of between 2000 and 15000. In the UK alonethat bought well over 1000 extra agglomerations under UWWT. In additionin 2002 the government there announced it was adding a further 33 sensitive areas to its list and the deadline for tertiary treatment schemes for these most-recently designated sensitive areas is the end of 2008.
So the process is far from complete and the UWWT directive continues to provide a driver for water company investment. As moresmaller populations are brought under the regulationswater companies need reliable treatment plants that can be monitored remotely and that promise to reduce the amount of time engineers have to spend traipsing between sites. Only this can offer an economical approach to the increasingly distributed network of treatment works.
In the UKan ingenious pricing policy has been put into place that places water companies in fierce competition with one another to provide the most efficient service. Put simplythe most efficient companies are allowed to keep hold of a multiple of their savings for five years before passing them on to customers. Their less efficient counterparts will instead be penalised.
Advanced asset management
Advanced asset management is vital in this contextespecially for companies operating a growing network of treatment plants. Any control systems chosen should be able to integrate with the latest software.
Asset management extends the scope of traditional control systems to include all automation functions in a single environmentenabling plants to perform smarter and better with substantial cost savings. Modern asset management systems essentially integrate information to make it more visible to operators. This reduces the time needed to reach decisions and take action and thus optimises plant performance and availability.
When it comes to integrating distributed treatment operationsthe sort of control offered by a modern fieldbus solution also offers several benefitsincluding scope for increasing automation and remote working. Today’s established fieldbus systems are much more than communication paths – they fortify the communication backbone in automated systems.
Almost all instrumentation and control companies will support some form of fieldbusbut adaptability is the key to being able to get the system tailored to fit site- or company-specific requirements. ABBfor instanceoffers a full range of field devicesdrives and control products that are completely compatible with Foundation FieldbusPROFIBUS and HART protocols.
Built-in redundancy is another key feature of control and instrumentation designed to maximise plant availability and reduce the need for site visits. For exampleABB offers redundancy in its remote I/Ossystem controllerssystem serversfield devices and media/cables.
Field instrumentation forms the vital ‘eyes and ears’ of the control system. Although the technology varies with the specific measurements required at a particular sitethere are several generic rules of thumb that are worth bearing in mind when choosing instruments for remote operation.
Wherever possiblechoose technologies that deliver a rapid response and where the results are not prone to drift. In additionpicking instruments with self-diagnostic capabilities will make it easier to identify any problemswhile equipping them with an output to a central control room makes it more likely that data will be seen and acted upon appropriately. The new breed of electronic data recorders promise remote supervision and access to databut this will only benefit plant operators if the instrumentation out on the plant is providing the right information.
The implementation of the UWWT directive remains ongoing. Stiff competition for efficiency savings among the water companies means they must continue to invest in the right technologies to make their growing network of treatment plants as straightforward to manage and control as possible.
Jim Plumley is Analytical Product Manager for ABB Instrumentation. For more informationvisit www.abb.com"