Water is the most critical resource for life even in today’s high-tech world, and its safe supply continues to present considerable challenges to both governments and the private sector across the world. Regulations governing the treatment of water have evolved as the water industry has evolved, with the increased use of UV treatment in place of other disinfection methods being just one aspect of this development. Future changes are likely to be more dramatic; as the world’s population continues to grow and exert even greater pressure on freshwater resources, regulations will need to cope with new sources of water to ensure they are fit for purpose.
Cometh the hour, cometh the technology…
UV treatment is a relative newcomer to the world of water treatment. Although it was pioneered in the 1920s, it didn’t really catch on as a viable alternative to chlorination until the 1980s. This was driven in part by the discovery in 1974 of chlorinated disinfection by-products which were harmful to human health. The United States Environmental Protection Agency (USEPA) began studies into UV water treatment in 1978 and produced their first design manual in 1986. Several countries in Europe (Austria, the Netherlands and Germany) were also developing UV treatment design guidelines at the same time, and their findings formed the basis for the standard W 293, published by Eco-UV partner DVGW (the German Gas and Water Association) in 1994.
These early standards accelerated the adoption of UV water treatment in these countries, but it was still difficult to compare systems from different manufacturers as there was no standardised validation test. This changed in 1996, when the Austrian Standards Institute published a preliminary standard, closely followed in 1997 by DVGW’s technical standard W 294. These contained the first descriptions of a bioassay test to demonstrate that a system could deliver an adequate UV dose over a range of operating conditions. The UV industry had come of age. The Austrian standard ÖNORM M 5873 for low-pressure systems was published in 2001 and extended to medium-pressure systems in 2003. DVGW updated W 294 in 2006 to include revised guidance for operators, engineers, vendors and test laboratories. The USEPA produced its UV Disinfection Guidance Manual (UVDGM) in 2006 and this has allowed the industry to boom in the States, with increasingly large installations demonstrating that UV treatment is not restricted to small-scale water supplies. In 2012, more than a quarter of all wastewater plants in the USA treated their water with ultraviolet light. To date, these are the only standards covering UV water treatment of drinking water, and they are widely used around the world to set the benchmark for acceptable system performance.
Chlorine-free, Dutch style
Although UV treatment has been gathering momentum in many countries, chlorination is still widely used to secure the disinfection of drinking water while it is transported from the treatment plant to the consumer. In the USA, regulations require that drinking water must contain residual chlorine right up to the moment when it comes out of the customer’s tap. In complete contrast, the Netherlands has elected to stop using chlorine altogether, with the last chlorination plant being decommissioned in 2005 – and replaced with a UV system.
Not surprisingly, new regulations have been developed to support this significant change in approach, which go over and above the minimum standards required by the European Drinking Water Directive. All sources of water are required to meet the same standards, regardless of the number of consumers they serve. Drinking water must be associated with an estimated risk of infection of below 1 per 10,000 persons per year for any relevant pathogen. Direct monitoring of the microbial safety of the source water at various locations is performed to determine the levels of reduction that are required for each pathogen to comply with this requirement. Strict guidelines and protocols have been written on installing measures like backflow prevention valves and the construction and maintenance of distribution systems. The aim is to reduce leakage, prevent pressure fluctuations and minimise stagnant zones, all of which can contribute to contamination of the water downstream from the treatment plant. Under this regulatory regime, the country’s drinking water system has now been operating successfully without chlorine for over ten years.
Alongside the Dutch initiative, other European countries have sought to reduce their use of chlorine in treating drinking water. For example, many drinking water supplies in Germany do not require any disinfection. Where treatment is required, such as for surface water reservoirs, the market share of UV disinfection has grown significantly from 6% in 1991 to 42% in 2009, mostly by displacing the use of chlorine.
Different strokes for different folks
As well as treating municipal supplies of drinking water, UV has been adopted by other industries, such as food and beverage, pharmaceuticals and leisure (for treating swimming pools and spa water). This trend has led to the development of a range of new standards and codes specific to these applications. In the USA, the NSF 50 standard for swimming pools and other recreational water facilities specifies performance requirements for inactivating different pathogens when tested according to either the USEPA, DVGW or ÖNORM procedures. Similar guidelines have been produced by other national bodies, such as the Pool Water Treatment Advisory Group (PWTAG) in the United Kingdom. In the food and beverage and pharmaceutical industries, companies using ultraviolet water treatment usually specify their own performance requirements. National standards such as the US Federal Drug Administration 21 CFR 170-199 and EU framework regulation 1935:2004 describe how the system’s components should be tested to check that they are sufficiently stable to use with the fluids being processed, and will not leach out any contaminants into the treated water.
The ever-growing population of the world, combined with natural variations in climate (potentially exacerbated by climate change due to global warming), means that the world’s supplies of freshwater are under increasing pressure. Many developing countries have never enjoyed the benefits of a safe and plentiful water supply, but now even developed countries are experiencing unprecedented shortages, such as the ongoing drought in California and the western United States. These events have focussed attention on exploiting new sources of water, such as desalination of coastal waters or bank filtration (where water is filtered through river beds into underground aquifers). Each of these sources will generate water with subtly different properties, which govern how they can best be treated to ensure they are safe for human consumption.
Furthermore, there is now recognition that we cannot go on using potable water for all applications before discarding it to waste, as has traditionally been the case. The idea of reusing water for applications not involving direct consumption has become a hot topic, and the range of applications for reused water has broadened from predominantly agricultural irrigation to include manufacturing, service industries (such as laundering), refilling recreational water bodies, and even recharging ground water aquifers (which usually have natural filters to help clean the water). All of these applications rely on effective treatment of the reused water first, in which UV has a central role to play. Many states and countries are now beginning to draw up regulations governing reused water, to ensure that it can be kept separate from potable water and cannot mistakenly be used for drinking.
Notwithstanding its maturity and the fundamental part it plays in society, it seems likely that the water industry will have to adapt to change well into the future, and that regulations and treatment technologies will themselves have to go on adapting in order to keep up.
Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced Surface Water Treatment Rule, United States Environmental Protection Agency Report EPA 815-R-06-007, November 2006.
DVGW Work Sheet W 294: UV Devices for Disinfection of the Water Supply, Wirtschafts- und Verlagsgesellschaft Gas und Wasser mbH, Bonn, June 2006:
Part 1: Requirements for Composition, Function and Operation.
Part 2: Testing of Composition, Function and Disinfection Effectiveness.
Part 3: Measuring Windows and Sensors for the Radiometric Monitoring of UV Disinfection Devices; Requirements, Test and Calibration.
Smeets, Medema and van Dijk, “The Dutch secret: How to provide safe drinking water without chlorine in the Netherlands”, Drinking Water Engineering and Science, 2, 2009, 1-14; http://www.drink-water-eng-sci.net/2/1/2009/dwes-2-1-2009.pdf (accessed November 2016).
Ultraviolet Disinfection: Guidelines for Drinking Water and Water Reuse, 3rd edition, National Water Research Institute, August 2012.