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A Case for the Safety and Sustainability of Class B Biosolids Land Application – Results of Microconstituent and Pathogen Research in Gainesville, FL

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Gainesville Regional Utilities (GRU) generates Class B biosolids at two municipal water reclamation facilities, Kanapaha Water Reclamation Facility (KWRF) and Main Street Water Reclamation Facility (MSWRF). For over 27 years, these Class B biosolids have been land applied at a 1,100-acre farming operation known as Whistling Pines Ranch (WPR). The biosolids supplement inorganic fertilizer was used to grow a variety of forage and row crops.

Changes in local land development regulations prompted a detailed scientific study documenting the potential exposure of WPR neighbors to microconstituents and pathogens resulting from the land application process. These studies were developed and conducted in conjunction with the Alachua County Environmental Protection Department (ACEPD) and the Florida Department of Health (FDOH)/Alachua County. A two-phase study plan was adopted to sequentially evaluate microconstituents and pathogens.

Phase 1 – Microconstituents. The microconstituents selected for study included estrogenic hormones and their metabolites (17-a-ethynylestradiol, 17-a-estradiol, 17-β-estradiol, Estriol, and Estrone), pharmaceutical-related compounds (Fluoxetine and Iopromide), industrial/home products that can potentially be estrogenic (Bisphenol A), and detergent/surfactant compounds and their metabolites (4-tert-Octylphenol, Nonylphenol, Nonylphenol monoethoxylate, and Nonylphenol diethoxylate). This list evaluates a range of representative compounds of interest for potential land application impacts.

Samples for these microconstituents were taken from groundwater supply wells and soil on the WPR site, and from the biosolids liquid phase. None of the microconstituents were detected in the four groundwater samples or the four composite soil leachate samples. Only 1 of the 12 microconstituents tested (Fluoxetine - i.e., Prozac) was detected in the biosolids liquid phase sample. The concentration of Fluoxetine detected was 110 nanograms per liter (ng/L); 5,000 pounds of dry biosolids would need to be consumed to equal one therapeutic dose of 20 milligrams (mg) per day. The results of this phase of testing indicate that the biosolids applied to the WPR site are not a significant source of microconstituents.

Phase 2 – Pathogens. Samples were taken from biosolids, biosolids-amended soils on the WPR site, and air samples during the land application and incorporation process (via disking). Typically, the biosolids are surface applied using a "GEA Houle" spreader system pulled behind a tractor and allowed to dry 1 day before disking into the soil profile. The pathogens and indicator organism analyses included enteric viruses, fecal coliforms, E. coli, Clostridium perfringens, Salmonella, and heterotrophic plate counts (HPC).

The pathogens and indicator bacteria present in the biosolids samples were significantly reduced by the aerobic digestion process performed at GRU's two water reclamation facilities. With the exception of Clostridium, the inactivation was >90 percent. Clostridium perfringens are ubiquitous in the environment and a very poor indicator of fecal pollution and the treatment process.

Biosolids-amended soils were sampled and analyzed for the indicators and pathogens, 1 hour and 3 months following land application. Results showed that the numbers of recovered pathogens and indicators in biosolids-amended soils were further substantially reduced. All biosolids-amended soil samples, regardless of 1-hour or 3-month, met the microbial criteria for Class A biosolids of less than 1 virus/4 dry grams. Additionally, after prolonged (3 months) incubation following land application, the pathogens and indicators are reduced to below detectable levels.

Aerosol sampling was conducted during the disking process at downwind distances of 100 feet, 65 feet, and 42 feet to simulate worst case exposure. At the closest downwind distance, the air sampling equipment was engulfed in a dust cloud as the disking tractor passed by. The air samples did not recover any of the pathogens or indicator bacteria present at low levels in the biosolids prior to land application. The only organism groups detected in both the background air samples and airborne bioaerosol samples were the HPC and Clostridium perfringens. Both these microorganisms are ubiquitous or indigenous bacteria that are present on most environmental surfaces. The absence of these species would be indicative of a sterile environment or a failure of the sample collection and analysis procedures.

The data indicate that pathogen and indicator organism levels in GRU biosolids are relatively low and that they pose minimal risk through direct exposure. Furthermore, upon the application of the biosolids to the soil at the sites tested during the observed operations, the risk to adjacent properties is extremely low.

Other Testing. In addition to the pathogen study in Phase 2, additional investigations were undertaken to address questions raised by area residents including:

Biosolids-amended soil samples were tested for metals and results showed all below residential Soil Cleanup Target Levels (SCTLs).

Biosolids tested for radionuclides and site exposures were found to be orders of magnitude below usual natural and manmade exposures.

University of Florida entomologist inspection found that the flies and vectors were typical of farm and local area land uses.

Offsite groundwater was tested by the Florida Department of Health (FDOH) and results showed no pathogen or indicator organisms, and nitrate levels typical of groundwater on farms in North Florida.

The future of land application of Class B biosolids on the WPR is under review by local governmental bodies and regulatory agencies. The scientific evidence collected during this study indicates that the WPR land application process with Class B site restrictions is as safe as that of Class A processes from the standpoint of microconstituents and pathogens.

Keywords: Bioaerosol; Class B biosolids; endocrine disruptors; land application; microconstituents; pathogens

Document Type: Research Article


Publication date: 2010-01-01

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