Thames Water Utilites Ltd1
I. INTRODUCTION London, UK and other regions of the south and east of England are classified as water stressed areas (2). These areas are experiencing year on year increases in population and increasingly limited water resources. Thames Water Utilities Ltd, is predicting that there will be a shortfall of approximately 414 Ml/day by 2040 in the London region. To help reduce this shortfall Thames Water has implemented various water efficiency and demand management schemes, alongside improvements in leak detection and repair. However, Thames Water has identified through its Water Resources Management Plan (WRMP) that a new water resource may still be required. Consequently, Thames Water has undertaken an extensive programme of research into water reuse. Operating both large scale advanced treatment pilot facilities and community based non-potable schemes such as the Old Ford water recycling plant for the London Olympics 2012. This paper describes two water reuse case studies operated by Thames Water including the key challenges, operational experience and outcomes from each site II. COMMUNITY SCALE WATER REUSE FOR LONDON 2012 It is estimated that 160 litres per day per person is consumed within the Thames region, of this only 2% is drunk whilst 33% is used for toilet flushing. An approach to address this challenge is to create an alternative water product to be used only for toilet flushing and irrigation (non-potable reuse). Building on previous operational experience of small community scale water reuse scheme at the purpose built Beddington Zero Energy Development (3,4), Thames Water teamed up with the Olympic Delivery Authority (ODA) and commissioned the largest water recycling plant of its kind in the UK. The scheme's focus was to help meet sustainability targets of a 40% reduction in potable water usage at the London 2012 Olympic park. Such targets are significant drivers for water efficiencies and decreasing consumption within new building developments (1). Based at Old Ford, neighbouring the Olympic Park, the water recycling plant mines a major London sewer and through a combination of MBR and GAC technology is capable of supplying the Olympic park with 574m3/day non-potable water for toilet flushing and irrigation through a dedicated 3.65km network. Engaging customers and the public has been of great importance to ensure secure supply and usage, particularly in light of the building activities and the changing use and ownership of the park. In the UK there are no regulations for non-potable reuse; this has led to Thames Water working closely with regulators and customers to establish standards for fittings and pipework, alongside water quality targets. From the outset in 2011 the Queen Elisabeth Olympic Park was a hive of activity preparing for London 2012 and subsequent legacy transformation project. The greatest success has been to exceed the 90% plant availability target, whilst supplying a high quality product to customers. Due to a draught order and temporary use ban being in place in the build up to the London Olympics, the irrigation of parklands and open spaces would have been at risk without the Old Ford Plant to meet demand. The high flux in activity on the park has resulted in interesting challenges affecting the operation of the plant. Periods of high demand have challenged the capacity of the plant, whilst periods of low demand have raised issues regarding the maintenance of the biological process and the requirement for flushing the dedicated network. III. EXPLORING TREATMENT FOR INDIRECT POTABLE REUSE Much of London has already been built. The widespread retrofitting of dual pipework systems to accommodate non-potable water in every home and business is not viable. For large scale water reuse to take off in the UK, the most tenable and cost effect route is through the augmentation current surface water resources. Incorporating the water quality monitoring of candidate locations, potential receiving waters and the operation of a large scale, 600m3/day advanced treatment pilot plant facility between 2008 and 2012 at one of the candidate sites. The pilot plant treated conventional (activated sludge treatment) sewage effluent principally using microfiltration (MF) followed by reverse osmosis (RO) and advanced oxidation process (UV/H2O2 AOP) technology. Plant optimisation was carried out alongside various studies that challenged the treatment technologies, for example using elevated levels of micropollutants. Research activities have also included public perception and various collaborations with Universities. The pilot plant enabled the long term interrogation of the treatment performance of MF-RO-AOP, MF-AOP and included the substitution of RO for nanofiltration (NF). Whilst these trials have demonstrated that a high quality product can be produced, this is reliant on energy, cost and feed water quality. For example, the RO has shown the removal of a broad range of contaminants, but the product requires remineralisation and the process has a high energy cost. The NF demonstrated high organic compound removal with no need for remineralisation. However it is reliant on preceding treatment to provide removal of contaminants such as nitrate. AOP is highly dependent on good feed water quality to minimise energy and chemical consumption. During the research programme, Thames Water's water resources management plan underwent a public enquiry. The outcome of which was supportive of water reuse, but it did recognise the need to investigate lower forms of treatment and alternatives to the energy hungry RO and AOP options trialled. As a result of this enquiry the MBR-GAC process at Old Ford has provided a research platform as a treatment option for potential for IPR. The work from these additional trials has provided important evidence of significant and consistent removal of organic compounds such as 7α-ethinyl estradiol through the MBR. Recent research has also indicated the strong correlation between human pathogens such as norovirus and indicator species of bacteof bacteriophage and their significant removal through an MBR system. Although the MBR-GAC system performs well concerns still surround recalcitrant compounds such as Metaldehyde and the lack of multiple barriers to pathogens. IV. CONCLUSIONS The operation of a full scale non-potable water reuse plant in London has been met with great success and acceptance by both the customer and regulator. This scheme has helped meet challenging sustainability targets for the Olympic Games The research has created a good understanding of the human, environmental and aesthetic risks from source sewage through to final product. Ongoing research will hope to establish the performance of a combined approach of MBR-RO and MBR-AOP as an IPR treatment option. This valuable data and experience in various treatment technologies will inform future water management programmes within the UK. 1. Department for Communities and Local Goverment. (2010). Code for Sustainable Homes, 〈http://www.planningportal.gov.uk/uploads/code_for_sust_homes.pdf〉 (Aug. 12, 2010). 2. Environment Agency (2007). Areas of water stress: final classification. GEHO1207BNOC-E-E. Environment Agency, Bristol, UK 3. Verrecht, B., Maere, T., Benedetti, L., Nopens, I., and Judd, S. (2010). Model-based energy optimisation of a small-scale decentralised membrane bioreactor for urban reuse. Water Res., 44(14), 4047Â–4056. 4. Verrecht, B., James, C., Germain, E., Birks, R., Barugh, A., Pearce, P., Judd, S. (2012) Economical Evaluation and Operating Experiences of a Small-Scale MBR for Nonpotable Reuse. J. Environ. Eng. 138, 594-600.