Sweet smell of success from sewage

Living downwind from a sewage treatment works could be more of a sweet-smelling existence following the work of Hydro Chemicals. The company, a winner for Environmental Achievement, has succeeded in limiting the stench of sewage.

All 10 of the big privatised water companies have opted to use Hydro's process in at least part of their network. Overpowering smells can can be classified as a statutory nuisance, but are difficult to eliminate.

Stephen Caldwell, national sales manager of Hydro Chemicals, says that a build-up of hydrogen sulphate gas - the common rotten egg smell beloved of school chemistry lessons - occurs when sewage is starved of oxygen.

"If waste water stays in a pipe for several hours, it will go septic", adds Mr Caldwell. "It will then smell when it pops out again under a manhole, in the sewage treatment works or in a pumping station."

Production of hydrogen sulphate is most common in long pipe runs, but can also happen if the water remains in the drains overnight before being flushed through by people's early-morning showers and baths.

Hydro's award is for the development of its "Hydrocare" system which allows a controlled dose of nitrate to be mixed with the waste. Nitrate is a naturally-occurring element of sewage, but increasing the volume allows it to replace oxygen as food for bacteria.

A sophisticated monitoring and measuring system has made the addition of nitrates an economic proposition and prompted Hydro, based in Immingham and part of the Norwegian-owned Norsk Hydro group, to more than double its turnover in the past two years.

Besides eliminating unpleasant smells, the system also cuts down the production of sulphuric acid, which is corrosive in concrete sewers. Levels of nitrates are closely monitored to make sure that they stay within tolerances set by water companies for the discharge of waste water. "We want to make maximum use of the dose of nitrates so that there is not an excess at the other end of the system."

Big savings of clean water have led to success for Hoover, which has also won an an award for environmental achievement for its three new ranges of washing machine. Besides using 31 per cent less water, the machines also consume 40 per cent less electricity and 36 per cent less detergent.

Manufactured at Hoover's plant at Merthyr Tydfil, South Wales, the machines are the first to be granted the Ecolabel by the European Union for meeting the criteria set out for water, energy and detergent consumption and for wash performance.

A second part of Hoover's award was for the environmental and energy savings during manufacture. Environmental audits at the factory brought about changes in production and the use of glass coupled polypropylene rather than the traditional vitreous enamel and stainless steel outer drum. Acting as an natural insulator, the drum's materials caused less noise and retained heat.

Packaging has also been altered to non-CFC materials with all waste packaging being returned to distribution depots for recycling and secondary use.