Utility Week

Utility Week 11th October 2013

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Operations & Assets Market view Reuseful information Wastewater reuse can be a serious supply contender, but the right systems need to be in place to ensure safety, and users need to be brought on board. Vikki Williams provides a checklist. T he UK's use of recycled water is low. Historically, traditional sources of water have met the supply-demand balance. Increasingly, however, consumption, migration and changing weather patterns are placing pressure on those sources; especially in southeast England. Thames Water supplies 9 million people and predicts that this will rise to 10.4 million by 2040. According to South East Water, its region will face a shortfall of around 145 million litres by 2040. Although approaches to reuse can differ, depending on factors such as the end-uses, there are common steps that can help ensure the safety and acceptance of the programme. Understand the programme. Developing a full understanding from the outset of the applications for which the water will be reused is key to long-term success. The options include direct and indirect potable use, dual domestic use (greywater) and industrial use. Each of these requires different approaches in terms of treatment, supply network and system management. The successful outcome of the subsequent steps all stem from achieving clarity of purpose. Understand the source water. Different wastewater sources require different levels of treatment. The type of treatment required depends on how the treated water will be used. If the source is domestic wastewater it will be necessary to understand the type and nature of pharmaceutical contaminants, for instance. This is in addition to investigating pathogens and viruses. If the source wastewater has an industrial component, it is vital to know the types of industries discharging into the wastewater stream. This will help inform more detailed investigations into the nature of the wastewater. These are required because common metrics – such as chemical oxygen demand, solids and volume – provide insufficient information about the make-up of the wastewater stream to ensure safe reuse. It is important to understand if the sewerage system carrying the wastewater is dual usage, and therefore likely to carry run-off, because this can include hydrocarbons, for 22 | 11th - 17th October | UTILITY WEEK instance. Although traditional wastewater treatment practices and processes are good at removing solids, a multi-barrier approach may be required. Understand what treatment is required. The type of treatment will be governed by the standard the water needs to reach to ensure safe reuse. Some countries, including Australia and the US, grade treatment standards for different uses, but the UK does not have a standard for non-potable use. Given the sensitivities around reuse, consideration may also be given to additional treatment steps that go beyond the technical requirements. Such steps may help build the public health consensus vital to a successful reuse programme. When considering safety and suitability of treatment options it is essential to take into account the training and capabilities of the treatment plant's operators. Also significant is having the right policies and procedures to ensure the plant's safe operation in the long term. These procedures are vital in giving the public confidence. Operations staff need to have sufficient technical ability to recognise when there is a problem. They also need to be prepared and capable of solving it. Understand how to distribute the treated water. The application for which the water will be used has the greatest influence on distribution network requirements. Distribution needs to be viewed as an integral phase of reuse programme planning. If the reused water is for potable applications, connection to an existing network is possible. In this instance, compatibility with the existing supply needs to be addressed. This means considering things such as water hardness and residual disinfection within the network. If a non-chloraminated supply is mixing with other water, for example, the risk of trihalomethanes forming needs to be assessed and managed. When reused water is destined for nonpotable applications, a separate distribution network is necessary. The cost of this can make treating to non-potable standards unattractive even if the water is used for non- potable applications. To provide safe operation and maintenance it is important that a non-potable network is readily distinguishable from potable networks. Making the nonpotable network identifiable requires not just a physically distinguishable system but also good, easy-to-access records. To deliver longterm safety, the records need to be accompanied by policies and procedures that support network integrity. In essence, the non-potable system means a new asset class is being introduced into the asset base and, as a result, procedures need to be in place to ensure it is managed properly. Understand how the water will be used. This final step is in some ways close to the first, but also subtly different. Understanding the programme means knowing what application the reused water is for. Understanding how the water will be used refers to preparing in detail for what will happen to the water when it reaches the point of use. This is often the point at which the reuse supply ceases to be under the control of the utility. Where the supply has been treated to non-potable standards, safety dictates that taps and other end-user fittings are clearly labelled to indicate the water is not for consumption. As well as that, it needs to be clear the supply is unsuitable for food preparation and other uses which may lead to ingestion. For example, people often touch water features and fountains. Policies, procedures and documentation also need to be prepared to ensure a nonpotable system remains safe if the building in which it operates changes ownership. New owners, unfamiliar with a non-potable water supply, need to understand how to safely use the water and maintain the system. Water reuse has a viable role in an integrated water resource portfolio. The above steps represent a high-level, and not exhaustive, outline of some key considerations which will help ensure reused supplies are safe and, importantly, engender public confidence. Vikki Williams, asset management consultant, Black & Veatch

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