Sludge – A Semi-Solid Brew of Pathogens
by Jamie Manfuso & Scott Carroll
Every day people from Palmetto to Punta Gorda flush some 820,000 toilets, grind up waste in more than 200,000 garbage disposals and pour chemicals, cleaning products and blood down a million or more drains.
Messes from homes, hospitals and businesses travel into sewage treatment systems, where they mix into a chemical and bacterial stew that eventually ends up as fertilizer on fields in DeSoto, Charlotte, Manatee and Sarasota counties.
Though modern treatment can eliminate more than 95 percent of pathogens, enough remain in the concentrated goop that leaves treatment plants to pose a health risk. And while treatment kills most bacteria and viruses, those that survive are much stronger than an ordinary flu bug, said Maureen Reilly, a researcher with the University of Toronto, Canada.
"It's a great way to create a superbug," Reilly said. "It's a recipe for disaster, really."
In 1989, a federal Environmental Protection Agency study found 25 groups of pathogens in sludge, including bacteria such as e.coli and salmonella, viruses, including hepatitis A, intestinal worms, harmful protozoa and fungus.
Toilet flushings aren't all that ends up spread over pastures and cropland.
Sludge also includes traces of household chemicals poured down drains, detergents from washing machines, heavy metals from industry, synthetic hormones from birth control pills, pesticides and dioxins, a group of compounds that have been linked to cancer.
Scientists have found more than 60,000 toxic substances and chemical compounds in sludge, and are identifying another 700 to 1000 chemicals each year, according to The Waste Management Institute at Cornell University.
"There's an endless supply of chemicals that are in sludge," said Rob Hale, a researcher at Virginia Institute of Marine Sciences in Williamsburg, studying the effects of flame retardants used in furniture and clothing that are showing up in sludge.
Sludge is designed to be contaminated.
From the time waste water enters a treatment plant, the whole process is geared to create a disease-and-pollution free effluent: water that can be used safely on golf courses and in parks, or pumped underground. Sludge is what's left over. The better the treatment, the more concentrated the leftover gunk.
Irritant chemicals added during and after treatment also make sludge more harmful than your average manure.
These chemicals include ammonia, lime to reduce acidity and kill bacteria, and polymers that help remove water from sludge, turning it into black globs the texture of cottage cheese. When spread on land, those polymers break down into trimethyl amine, a irritant chemical.
"When sludge sits in the field, it will release up to 19 hazardous chemical compounds," said Sam Shepherd, a diplomat on the American Board of Forensic Engineering and Technology who has studied irritants in sludge.
People living near sludge dumps wind up breathing in the chemicals, which can be released as aerosols or blow off in dust when sludge dries.
"The chemicals in sludge can actually burn the throat and lungs," according to EPA microbiologist and sludge critic David Lewis.
In his research of 10 sludge spreading sites in the United States and Canada, Lewis found nearby residents were 25 times more likely to develop s.aureus infections, a form of staph, than hospital patients, a high-risk group. He presented his findings at a November conference at the Boston School of Public Health. The sludge industry, backed by the EPA maintains that its main problem is overcoming the public perception that sludge is just raw sewage – the stuff that gets flushed down toilets.
"It really isn't human waste or sewage any more," said Bob Bastian, a senior environmental scientist at the EPA's Office of Wastewater Management. He likened sludge to soil.
Shepherd, a sludge critic, points out at least one difference.
Sludge" basically is topsoil, but it contains 100,000 times the level of pathogens that topsoil contains."