A CHEAP alternative to conventional sewage treatment was investigated by Karen Willoughby, Siobhan Maher and Emma Lyons, from the Ursuline Convent, Thurles, Co Tipperary.
They built a 180 foot long reed bed in a horseshoe shape and planted it with reeds, bulrushes and yellow flag.
They then allowed waste water to filter slowly through the reeds, as an alternative to the conventional sludge settling tank system.
Their results may prove of interest to small municipal authorities throughout the State - under an EU directive on water quality, local authorities are required to provide secondary sewage treatment for towns with more than 2,000 inhabitants by early in the next century.
"The rooted plants mainly act as surfaces for microbial growth, while at the same time facilitating the absorption of nutrients from the effluent into the plants," the girls concluded.
The treatment removed up to 95 per cent of suspended solids from the waste after five days in the reed bed, "at approximately one tenth the cost of an activated sludge plant.
"It is a cheap and extremely effective system, requiring little in the way of infrastructure in construction, and near zero energy input.
"The materials needed are cheap and readily available, such as earth, clay, reeds, rushes ... they are natural water cleansers and this ecological function makes them eminently suitable for treating waste waters", the young scientists reported.