Water works

Thanks to dramatic improvements in the quality of the UK‘s drinking water over the past 15 years or so we now enjoy some of the best water in the world.

Privatisation of the industry in 1989 and pressure from the EU’s Drinking Water Directive have played a major part in this success, but technically the improvement has been achieved by investment in a combination of wastewater management technologies and improvement of the UK‘s often ancient water distribution network.

Independent water/wastewater consultant Chris Binnie said: ‘Until about 15 years ago the UK standard was only wholesome, as defined by the World Health Organisation.’ Wholesome seems to equate to passable — perhaps explaining the boom in bottled water sales between the 1980s and 1990s.

‘Pre-privatisation, the water boards spent approximately £1bn a year on treatment and management, but since the sell-off, the investment by the utility companies has risen to about £3bn,’ he said. Naturally, to pay for these improvements water bills have increased.

Regional problems such as low rainfall, flooding, the threat from aggressive parasites like cryptosporidium, and the notorious leaky Victorian cast iron pipework (particularly in the heavily populated Thames water region where half of all mains pipes are at least a century old), mean there is plenty of work for specialised engineers.

Technologies such as granular activated carbon filtration are increasingly being used, and there is also growing take-up of ozonation compared with other remedial chemical techniques.

With many of the mains pipes still leaking, there is a substantial and ongoing programme of relining and refurbishment. But over the past 10 years the number of leaking pipes nationwide has been reduced by about a third.

Relining and replacing mains piping has been a major advance, particularly because it has enabled the distribution pressure to be reduced which has further cut losses and damage. Cast iron mains pipes also tend to develop health-threatening rust nodules on their inner surface.

The ways in which water and wastewater management processes have been improved are innumerable. Below are three examples.

Sludge recovery

Warrington-based United Utilities has developed a novel technique, High Rate Enzymic Hydrolysis, for making power and fertiliser from sewage works waste product. The process converts the ‘sludge’ created by treating wastewater into useful by-products and has been installed by the company at its treatment works in Macclesfield and Bromborough, with Blackburn and Crewe due for upgrades.

Shanthi Rasaratnam, UU’s programme manager, said: ‘Sludge is the unavoidable by-product we have left after cleaning wastewater, and an awful lot of it is produced every day.’

The innovation, developed in partnership with Monsal, converts the sludge into a rich, benign soil nutrient that meets the highest EU specifications so it can be used more extensively to improve agricultural land. The process also generates valuable biogas which can be used as fuel to generate electricity. Sufficient gas is produced at the Blackburn works to supply 1.5MW of power to the National Grid, while also cutting carbon emissions.

The process can be retrofitted to existing sludge treatment facilities, helping avoid unnecessary cost and disruption. Rasaratnam said: ‘Traditional sludge treatment is known as digestion, and works like an artificial stomach, breaking down organic material with enzymes and bacteria. Our new technology works like a mouth, breaking down the food before it even gets to the stomach. This makes the process much more efficient.’

Efficiency improvement

Following the replacement of just three of ABB’s 37kW AC drives on its water process pumps Severn Trent achieved a 65 per cent energy saving and a payback time of only seven months. Consequently, the utility established an energy saving project group to look at replacing other drives across its network of sewage treatment plants. The initiative is part of ST’s ongoing cost efficiency programme aimed at combating rising electricity prices, in line with OFWAT and Environment Agency requirements.

The catalyst for the drives overhaul has been a new service scheme introduced by the ABB Drives Alliance. Called DrivesAdvantage, the scheme offers several bespoke programmes aimed at upgrading or replacing drives. Brian Dick of the Alliance said: ‘Many of ST’s drives were installed 15 years ago. Since then, drives have become smaller, more efficient and reliable and less costly to purchase, install and run.’

ST’s Dan Hulse said: ‘After experimenting with ABB’s demo drive we knew it was time for us to change.’

Following training, the Alliance was invited to ST’s Wanlip Works in Leicestershire to log the power consumption on various applications including aerators, tertiary pumps and process water pumps.

The Alliance undertook an energy audit to determine typical levels of energy saving. ‘We estimated a return on investment of about 20 months and an energy reduction of about 30 per cent,’ said Dick. ‘This was based on a total investment in the drives below £7,000 and an energy saving of nearly £10,000 a year, as the old drives were consuming some 18kWh of energy compared to the equivalent ABB drive which consumes some 6kWh, representing a saving of over £46,000 over the five-year warranty period of the drives.’

Reverse osmosis

Most industrial and process companies use distilled water for injection (WFI) purposes. However, the use of the membrane processes in the production of WFI quality highly purified water (HPW), such as for the pharmaceutical industry, allows cost reductions by a factor of up to 7.5 compared to distillation, claims ultrapure water specialist firm Christ, a member of the Christ Water Technology Group, based in Mondsee, Austria.

The use of reverse osmosis combined with electro-deionisation and a subsequent reverse osmosis or ultrafiltration step is said to offer a clear financial benefit in controlling costs. The chemical and physical characteristics of water produced in this way comply with the specific requirements for WFI. In Europe, this method may be used to generate HPW.

With Osmotron Inject, Christ has introduced a technique for the production of HPW by means of two reverse osmosis stages and electro-deionisation. The compact unit is entirely hot water-sanitisable and constitutes a safe, closed system. For applications calling for an integrity test, a plant configuration replacing the second reverse osmosis stage with an ultrafiltration stage may be employed.

In both configurations, having passed the security filter, softened water reaches the reverse osmosis at the same [high] pressure as the first process step. Most of the water passes through the membrane with a residual salt content of approximately two per cent, leaving much of the dissolved and any suspended matter behind.

In the next step, the permeate passes to the temperature-stable Christ electro-deionisation module, Septrosan, where it is fully demineralised. This treatment also reduces pyrogens and microbial contamination to a great extent due to the very high pH gradients of pH2 to pH12. The last step is reverse osmosis, or ultrafiltration. When an integrity test is required an ultrafiltration (UF) stage is used. The hollow fibre UF module is also sanitisable and can be completely drained.

To integrity test the UF modules the concentrate (reject water) chambers are emptied and pressurised air is applied. A deficient module is identified when air bubbles are seen moving upwards on the filtrate side. The ultrafiltration process also allows a yield of 100 per cent.