Dangers
In 2011, the EPA commissioned a study at the United States National Research Council (NRC) to determine the health risks of sludge>. In this document the NRC pointed out that many of the dangers of sludge are simply unknown and unassessed. Additionally "Regulations that limit contact with biosolids do not prevent environmental processes in the conceptual model such as aerosolization or erosion and the death or multiplication of pathogens."
Recent STEC research has stated that "Fecal material may contaminate meat during slaughter, may be washed or blown into lakes or drinking water sources, or may be deposited on fruits and vegetables by use of manure for fertilization or sewage-contaminated water for irrigation. Some animals, such as insects, birds, and rodents, may transport these bacteria from feces to drinking water or foods"
"Addition of fresh biosolids to soil caused E. coli levels to rise to significantly greater values due to unknown mechanisms involving the existing microflora of natural soils. However, when sterile biosolids were added to soil there was also an increase in pathogen numbers indicating that the addition of organic nutrients alone may result in multiplication of pathogens (Unc et al. 2006). "
"Following applications in different seasons, repeated assessments of bacterial concentrations in biosolid clumps, using most-probable-number (MPN) techniques, found sustained high levels of these bacteria. Bacterial concentrations were often well above soil background levels at 6 months, and in some cases 11-12 months, after land application. Survival in surface-applied biosolids was similar to that for biosolids incorporated into the soil, and between application rates of 10 or 30 dry t/ha"
"Sudden and substantial increases in fecal coliform and E.coli have been measured by a number of researchers and utilities after dewatering of digested sludges. Research has seemed to indicate that the increase is not due to floc dispersion or due to centrifuge contamination, although the results are not definitive. The results appear to support the conclusion that bacteria are underestimated after digestion because they become non-culturable, and after dewatering the bacteria are reactivated, making them culturable again."
Read more about this topic: Sludge
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