Cleaning up the smart way
As legislation forces water companies to provide more comprehensive wastewater treatment to more of the country, the industry will need the best control and instrumentation technologies to manage it all, writes Jim Plumley.
Every day in the UK, about 347,000km of sewers collect more than 11B litres of wastewater. This is treated at roughly 9,000 WwTWs before discharge to inland waters, estuaries and the sea.
The Urban Waste Water Treatment (UWWT) Directive aims to ensure that all significant discharges of sewage are treated before they flow into inland surface waters, groundwaters, estuaries or coastal waters. And since about 96% of the UK population is connected to sewers leading to WwTWs, it is the effluent emerging from these treatment works that provides the main focus of the regulations.
Although the water industry has already gone a significant way towards meeting UWWT requirements, the regulations are continuing to drive major capital investment as another significant deadline looms at the end of the year.
In the five-year period to the end of 2005, it is estimated that the UK industry spent £1.2B to bring water treatment schemes into line with the directive.
For the purposes of the UWWT regulations, significant discharges are those to fresh waters or to estuaries serving agglomerations (urban settlements) with population equivalents of more than 2,000 people, or those to coastal water serving agglomerations with population equivalents of more than 10,000.
Sewage must normally be subjected to secondary treatment using biological systems, while discharges to sensitive areas require more stringent, tertiary measures.
Some sensitive areas are bodies of water that may become eutrophic. In these cases, the water can be overly enriched by nutrients, especially compounds of nitrogen 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 2000, by which time the water companies had to have treatment schemes ready to serve almost all agglomerations with a population equivalent of more than 15,000.
Furthermore, at the end of 2005, the regulations also required secondary treatment for every agglomeration in the UK with a population equivalent of between 2,000 and 15,000.
According to Defra figures, that brought considerably more than 1,000 extra agglomerations under UWWT. In addition, in 2002, the government 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 more, smaller populations are brought under the regulations, water 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.
In the UK, Ofwat has devised an ingenious pricing policy that places water companies in fierce competition with each another to provide the most efficient service. Put simply, the 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 is vital in this context, especially 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 environment, enabling 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 operations, the sort of control offered by a modern fieldbus solution also offers several benefits, including 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 fieldbus, but adaptability is the key to being able to get the system tailored to fit site- or company-specific requirements.
ABB, for instance, offers a full range of field devices, drives and control products that are completely compatible with Foundation Fieldbus, Profibus 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.
Eyes and ears
Field instrumentation forms the eyes and ears of the control system. There are several generic rules of thumb that are worth bearing in mind when choosing instruments for remote operation.
Wherever possible, choose technologies that deliver a rapid response and where the results are not prone to drift. In addition, picking instruments with self-diagnostic capabilities will make it easier to identify any problems, while 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 data, but 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 ABB’s analytical products expert. T: 01925 741517.
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