Drinking Water 2015: Developments in Water Quality, Treatment and Distribution
18 November 2015
Mike Waite, FWR Water Supply Co-ordinator
There were many informative papers presented at this meeting, on a broad range of topics, and only a flavour can be given here.
Tim Latcham described Bournemouth Water’s use of a floating solar-powered ultrasound source with internal quality monitors to control algal blooms.The system was provided by a Dutch company and quality results were telemetered to them and they then advised on the sound requirements. The ultrasound is said to prevent algae from getting to the reservoir surface, thereby red ucing access to light, and will also cause some cell disruption. Results to date have been inconclusive but the company has been able to increase the proportion of River Stour water feeding the works.
Helen Pickett outlined an approach to automated coagulant control developed by Severn Trent. Coagulation destabilises the charge on particles and stops repulsion. Raw water quality can change very quickly and unpredictably and coagulation aims to minimise the zeta potential on particulates. Zeta potential is affected by pH and effective coagulation is difficult above pH 7. Severn Trent has developed the COMPASS in-line monitor which uses UV and visible spectrophotmetry to measure the organic content and advise operators on conditions to apply. Comparing the use of COMPASS with conventional practice showed 4.5% failed jar tests with COMPASS compared to 39%. COMPASS scans the raw water every two minutes and its adoption has meant a 5% cost saving on coagulation.
Quyen Bautista (University of Glasgow) talked about Biological Drinking Water Treatment Solutions, referring to the development of biofilms on GAC (Granular Activated Carbon) which can remove many compounds including nitrate and chlorate ions with the advantage of no reagent costs and no introduction of contaminants. The limitations of this technology are biostability, scalability, reliability and, above all, public acceptance. A US survey in 2008 showed that only 44% would accept biological treatment because of the possibility of ‘adding germs’.
John Fawell (Consultant Toxicologist) then bravely attempted to cover current and future developments in drinking water quality regulation and advice in 20 minutes! There is a WHO Guidelines addendum due in 2016, with a 5th edition expected in 2020. The Guidelines strongly influence EU regulation and there are proposals for a full revision of the EU Directive to start in 2016. The Annexes to the Directive have already been amended to include the concept of Water Safety Plans. WHO will lead on the revision of Annex 1 and a long list of regulated parameters is not anticipated, but it is recognised that as well as health considerations there will be political pressures. WHO is considering improved advice on operational monitoring with a new background document on turbidity, plus the implications of mixtures. Other parameters and substances being reassessed include nitrate/nitrite, chlorate, chromium VI, bromate, barium, nickel, manganese, perchlorate, alternative disinfectants, cyanotoxins, and also a new approach to pesticides. An update meeting on radioactivity was taking place in December 2015. Some parameters such as cyanide, which is only found in incidents, are likely to be removed. Rather than proposing standards for individual endocrine disrupting compounds, it is likely that screening for groups of these will be recommended.
Robert Pitchers (WRc plc) provided an update on microbial risks. These fall into two groups: faecal/oral pathogens and opportunistic pathogens. Many agents have been suggested as possible drinking water threats including MERS (Middle East Respiratory Syndrome), mycobacteria, antibiotic resistant bacteria, and pathogenic amoebae. While Toxoplasma can be found in source waters, treatment effective against Cryptosporidium would deal with any risk. Addressing the future approaches to standards and compliance, Robert said that although indicator bacteria such as coliforms and E. coli remain in general use for compliance, WHO is pushing towards targets for microbial safety assessments. While the USEPA rules are based on a 1 in 10,000 risk, WHO favours the use of disability-adjusted life years (DALYs) and this approach is becoming more widely accepted. It is not practicable to look for a single virus in 1mgd but it is possible to provide treatment which will reduce any viruses to this level. Regarding opportunistic pathogens, he reported that premise plumbing was seen as being at most risk and pointed out that Legionella is now being monitored in households in Germany. Techniques for pathogen detection are continually improving and he drew attention to changes in regulations facilitating the use of alternative disinfection techniques.
Tom Bond (Imperial College) provided a summary of research on disinfection by-products (DBPs) over the 40+ years since they were first recognised, before describing results of two research projects carried out by Imperial. A Defra/DWI sponsored project looked at various nitrogenous DBPs in 20 English drinking water supplies. These comprised 7 haloacetonitriles, 3 haloacetamides, 8 halonitromethanes and cyanogen chloride. Brominated species are reported to be more toxic than the related chlorine- containing compounds and it was significant that while median concentrations of haloacetonitriles and haloacetamides were lower in chloraminated water than chlorinated waters, bromine substitution was twice as high in chloraminated waters than in chlorinated waters. Cyanogen chloride only occurred in a few samples but when present it was in higher concentrations than other nitrogenous DBPs. The second project looked at DBP production when making various teas and coffees. Using water spiked with chlorine it was shown that only 5–19% of chlorine was lost during boiling. The project nevertheless concluded that THM (trihalomethane) concentrations in tea made using tap water were likely to be insignificant.
Geoff Keam (Atkins) covered distribution system management, stressing that systems were usually reticulated and sources of post-treatment quality problems were often hard to locate; however, computer-based hydraulic modelling systems could help. About 65% of water quality complaints were about discolouration. After focusing on smaller mains in previous AMP rounds, it was time to tackle trunk mains. One key to minimising discolouration is to avoid rapid or significant increases in flow rate. Where flow rates have to be increased significantly, doing this slowly and incrementally can minimise disturbance of deposits.
Jeanette Sheldon (South East Water) began her presentation concerning online water quality monitoring by pointing out that Ofwat’s Outcome Delivery Incentives (ODI) included a penalty of £700 for every quality-related customer contact above the ODI target maximum, with financial rewards for significantly fewer contacts than the target. South East Water has developed water quality monitors which are installed in the distribution system and examples of their use in managing distribution and solving water quality problems were given.
Finally, Stuart Trow (Independent Consultant) referred to recent EU publications on leakage management and the CIWEM Policy Position Statement and described the difficulties in leakage estimation. There is a top-down approach which deducts known usage from total system input, or a bottom-up approach based on district metering area inputs. While total elimination of leakage is not feasible there is a sustainable economic level of leakage (SELL) to be aimed for. Background leakage (ie that which can’t be seen) accounts for 50–70% of leakage in England and Wales and most of this is on the service connection. Overall leakage is increasing and half of all companies have shown no reduction over the past five years. Under Ofwat ODIs, companies have received rewards of £228 million but suffered penalties of £510 million. A Consumer Council for Water survey revealed that the major concerns of consumers were leakage and infrastructure maintenance. Stuart outlined recent improvements in leak detection technology, including use of satellite imagery, and described benefits ensuing from Southern Water's move to universal metering. Improvements in detection technology, the use of novel techniques for fixing leaks, and benefits from better pressure management concluded the afternoon session and the day’s informative conference.