Waterman Environmental Services has developed washing systems for National Express which cut water use by 85% and costs by 60%.

National Express UK Division washed about 100 buses a day through vehicle washes at their 19 depots generating large amounts of sludge made up of road dirt and hydrocarbons from the vehicles.

The nature and volume of the sludge and the foul odour it created meant each wash system was completely emptied and cleaned once a week, with the waste water having to be taken away by road tanker.

Typical water usage at each site was 416,000 litres per annum - a total of 7,904,000 litres across all 19 depots.

The aim of Waterman's project was to evaluate the effects on the wash systems after controlled dosing with BIOcare® RWT - a specialised blend of aerobic bacilli.

They found that the time interval between sludge removals was extended to at least 20 weeks, the foul odour was eliminated and the water was kept at a neutral pH, minimising corrosion of the vehicles' aluminium trimmings.

This led to a 60% reduction in operating cost for each wash system, and an 85% reduction in water usage, and produced wastewater which could be safely washed down the drain.

A secondary enhanced filtration system was later installed, which allowed recycled wash water to be maintained for between six and 12 months without removal.

The project allowed National Express to reduce water costs by £18,179, and save another £266,760 in tanker costs.

Waterman hopes that the scheme will be adopted widely across the transport industry, where it could be used on buses, coaches, trains and lorries where washes are employed.

The company said the potential cost and environmental savings across the whole transport industry could be enormous.

The trial was expected to last just a few weeks, but it was not until 20 weeks that the level of solids in the water reached an unacceptable level - exceeding Waterman's expectations.

During the trial period, water use at each site was reduced from 9,200 litres to 1,200 litres a week, saving about 416,000 litres a year at the sites tested.

Waterman believes this could save as much as 7,904,000 litres a year across the whole of National Express UK, increasing to as much as 12,350,000 litres a year is secondary treatment was introduced.

The scheme also reduces the potential for pollution from water being blown onto the surrounding area because much cleaner water is being used, containing far less hydrocarbons and other contaminants.

It also cleans the water so that it can be disposed of in the drainage system, instead of removing the sludge to landfill following treatment, which can cause pollution of water courses.

According to Waterman's calculations, the scheme can also save 112,320kg of carbon dioxide emissions per year as a result of reducing the road tanker haulage.

Waterman hopes that as water becomes an increasingly valuable resource, this scheme will allow operators to put less demand on the need for water with no harmful effects on their business.