Novel Filter Cleans Up Australian Sewage
Ron Scherer, writer of The Christian Science Monitor, The Christian Science Monitor
A UNIQUE Australian-made technology will soon clean up sewage that the New South Wales beach town of Cronulla now dumps into the ocean with only primary treatment to screen out the solid waste.
Noting that the technology can be exported, Nick Greiner, the premier of New South Wales, says, "Australians would also have the satisfaction of knowing that Australian technology was helping to clean up the environment in other parts of the world."
The new system, which the Cronulla treatment plant will start using in August to process waste for a population of 70,000, filters almost all solids, oils, greases, bacteria, and viruses from the sewage. No chemicals are used in the process, which cuts the waste-processing time from hours to six or eight minutes.
The key to the system is a patented filtration system developed by Memtec Limited, a Windsor, New South Wales, company that specializes in filters and water systems. Memtec makes a thin, flexible polypropylene filter that resembles cappelletti - thin pasta. The pores in the filter are only 0.2 microns in diameter, or 500 times smaller than a human hair. Seventy percent of the volume of the filter is air.
Suspended solids cannot get through the small holes. Since viruses and bacteria attach themselves to the minute particles in sewage, they are excluded from the cleansed product as well. Dr. Gary Grohmann, a virologist at the Westmead Hospital Research Institute, says tests he conducted on 26 separate runs showed no viruses passed through the Memtec membranes. "It is probably the only method of physically restraining viruses that is quite effective. There are chemical methods and the use of ultraviolet rays, but then you are starting to add new parameters to the environment," he says.
The system cleans the filters by blowing compressed air back through the polypropylene filters. The cleaning process takes about one minute, barely disrupting the disposal process.
Normally, sewage treatment begins by screening out solids as large as diapers or as small as grit. Then the sewage flows to large settling pools, allowing a portion of the sediment to drop to the bottom of the pool. …