Flagging-up improvements

Southern Water's capital investment plan begins to pay dividends

Southern spent £2M developing new technology

Southern spent £2M developing new technology

Traditional final settlement tanks may eventually be replaced by spiral seperators
Ford STW: regional sludge recycling centre
During the 1999 bathing season, bathing water quality at Newhaven failed to meet the mandatory standard. The town's bathing water is the responsibility of Southern Water, which reversed this trend in 2001, achieving a 99% pass rate. Of 74 beaches monitored in Southern's region, 73 have passed the mandatory standard. Just one failed, in north Kent, where there is an issue over discharge from a private cistern. In total, 54% of the beaches are also meeting guideline standards promoted by the Environment Agency. This is a huge improvement when you consider that in 1988, when Southern began its capital investment plan, only 40% of beaches were meeting the mandatory standard.

It was decided early in the design stage that Newhaven STW would utilise a compact gravity settlement system, the spiral separator (WWT September 2001), which requires just 3-4% of the area used by conventional treatment processes. Main contractor Miller Civil Engineering Services (now Morgan Est) and process contractor Purac had a relatively smooth ride when it came to construction, only an environmental survey of the site threw up problems. It was found that land between Newhaven and Lewes, where Edmund Nuttall would be laying pipeline, was inhabited by great crested newts, a protected species. Special netting was erected to prevent newts entering the site and construction work was put on hold until their breeding period was over.

Local residents' concern was alleviated when Southern held public exhibitions to detail its plans. To soften the visual impact the water company will also landscape the area around the Newhaven site. Construction work began in October 1999 and consent was met in December 2000. The project took eighteen months from commencement to completion. The £20M spent on the project included all transfer work on the 11km pipeline and pumping station at Lewes.

Newhaven can now deal with 28.5Ml/d of wastewater, achieving 75% COD and BOD removal across the plant and turbidity of 100ntu. The use of spiral separators has revolutionised the treatment process. Driven by hydraulic powerpacks, they are energy efficient, cheap to run and require low maintenance. They currently achieve 5% solids removal in contrast to conventional technology in which 1-2% can be expected. Southern Water is continuing testing in order to refine the process further. The company admits it worked hard to get such efficiency in the beginning - getting settings right, achieving the correct flow and coping with influent levels. But from the outset Southern Water recognised the spiral separator's potential, investing £2M to develop the technology.

Southern anticipates the Newhaven plant will have a 15-20 year working life. During this time the company sees no reason why the spiral technology should not become commonplace throughout the industry. It even predicts a spiral separator for final as well as primary settlement.

Nearly 40 miles along the coast, Ford aerodrome was chosen as the ideal site for another STW. Ford was built to meet the Urban Wastewater Treatment Directive, before its construction preliminary treatment only existed at headworks in Bognor and Littlehampton. One of Southern's largest plants, Ford STW provides treatment for a combined population equivalent of 150,000, for the separate catchments of Littlehampton and Bognor Regis.

The works consists of three primary settlement tanks, 30m in diameter, secondary phase aeration lanes and four 30m diameter final settlement tanks. Ford runs two process streams. Not only is Southern making a dramatic improvement to water, it is producing a commercially viable sludge product. Sludge drawn off at various stages in the treatment process then goes through anaerobic digestion. The digested sludge is then processed from a liquid into a cake using centrifuges. The final cake is 25% dry solids.

This material is sent through a further drying process to produce fertiliser pellets. Ford, a regional sludge recycling centre, also deals with sludge from satellite plants. It can handle 8,000 tonnes of dry solids a year, of that, approximately 4,000 tonnes is imported as either cake or liquid.

A number of sites were assessed before Ford was chosen. Existing works in Littlehampton and Bognor were obvious possibilities. In essence, this would have been Southern Water's cheapest solution. However, Ford stood out because it had potential as a green field site. It was an old aerodrome, so space was not a constraint. It was also an acceptable distance from the two head works. Once plans were announced Southern met with local opposition, similar to that raised in Newhaven. As well as running exhibitions, the company arranged a public meeting. Site visits to operational STWs were organised for a council committee, to help them understand how problem areas, such as odour, would be overcome. Local people were consulted during the construction phase through a liaison group initiated by the county council. Ultimately only three meetings took place because interest waned once people were reassured of Southern Water's intentions.

The project underwent two planning phases. Following the outline phase, the water company made dramatic changes to the scheme which involved a further planning phase and detailed application. This was largely due to a rearrangement of the site to provide for secondary treatment. A series of design reviews were necessary to comply with the Urban Wastewater Treatment Directive. Southern originally intended to use a chemically aided primary settlement (CAPS) process, which satisfied the directive, but met with local opposition because of a question mark over standards of treatment. The government initially approved CAPS treatment because effluent would be discharged into a high dispersion area, but after residents met with Mr Meacher, the government reversed its decision, taking away the natural dispersion provision, forcing Southern to provide secondary treatment.


The second phase of planning generated some 30 conditions. These included a 12m height restriction on all buildings, which meant the dryer building had to be part buried. There is a 10m restriction on any future development, less than the general provision of 15m. Extensive landscaping and tree planting has been carried out around the site, to further limit visual impact. Construction traffic could only use the A259, a lower coast road, and operational traffic is not permitted to use the route through nearby Arundel in case it worsens an existing bottleneck. There are stringent odour emission standards, hydrogen sulphide levels must not exceed 1.3ppb at, or beyond, the boundary of the plant. To achieve this the plant is fully enclosed, the sludge treatment system and primary settlement tanks are covered and air is ducted back to a two-stage chemical scrubbing system.

In addition, Southern Water was required to undertake an extensive archeological survey of the site, before construction work began. The company spent considerable time with the county archeologist and a specialised firm of archeologists. A study of the proposed STW site unearthed artifacts from roman, bronze and iron age periods, making it the second most important archeological site in the south of England. The old aerodrome also relinquished an unexploded bomb, which required a controlled explosion.

Work on the plant began in May 1999 and it was receiving flows for treatment in October 2000, two months ahead of schedule. Plant design includes provisions for future demand. Southern Water has consent to 2005, but a design horizon to 2015.


Tags



Topics


Click a keyword to see more stories on that topic, view related news, or find more related items.

Comments

You need to be logged in to make a comment. Don't have an account? Set one up right now in seconds!


© Faversham House Group Ltd 2001. edie news articles may be copied or forwarded for individual use only. No other reproduction or distribution is permitted without prior written consent.