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Expanding Acceptance and Use of Anaerobically Digested Biosolids by Promoting Microbial Safety

Long, Sharon
University of Wisconsin - Madison
Start date
End date
The objective of this research is to identify surrogates for viruses and helminth ova in biosolids anaerobic digestion processes in order to allow for more frequent monitoring and more rapid results. This would allow for more robust datasets of organism inactivation in biosolids to bolster public confidence in their beneficial reuse. Expanded use of biosolids would help to improve soil fertility and reduce localized soil losses.

Key research tasks include: Comparison of enteric virus inactivation to that of coliphages and enterococci; Comparison of helminth ova inactivation to that of bacterial and fungal spores; Analysis of the effects of pH, ammonia concentration, and temperature on organism inactivation; and Public outreach on the benefits of biosolids use.

More information
Non-Technical Summary:
With the human population fast approaching 7 billion and increases in soil loss and degradation of soil fertility, the challenges to maintaining food crop production are ever present. It is estimated that 10 million hectare of cropland is lost worldwide per year as a result of soil erosion, and this problem is also documented to be significant in the upper Midwest. The use of modified agricultural practices is one means of slowing soil erosion. Land application of organic and nutrient rich materials can improve the moisture holding capacity, structure, and fertility of soils. One such product is biosolids. However, issues of public perception, product safety and ecosystem maintenance impedes widespread acceptance of biosolids use. Anaerobic digestion is the most widely used biosolids treatment process in the Midwest, with over 200 facilities within the Central States (Illinois, Minnesota, and Wisconsin) alone. This research will focus on continuously mixed mesophilic and thermophilic anaerobic digestion processes that would require extensive pathogen monitoring to meet Class A biosolids standards. Facilities employing these processes stand to benefit the most from surrogate analysis, which can provide more rapid monitoring of the biosolids digestion process and the quality of the final biosolids produced. These facilities are also the ones that are most likely to experience public opposition to the application of their biosolids to land. The low concentrations of helminth ova and viruses in the influent sewage to most publicly owned treatment works (POTWs) make monitoring the inactivation of these pathogens difficult. The U.S. EPA approved methods for enumerating helminth ova and viruses are time-consuming and labor-intensive. Assays for surrogates could allow for more rapid results and less expenditure of personnel time for each sample. This would enable facilities to perform more frequent monitoring. In cases where the influent pathogens are too few to demonstrate a desired level of inactivation, surrogate analyses can provide assurance that treatment processes are operating properly. Therefore, it is the goal of this project to fully evaluate at the batch, bench, and full-scale, the efficacy of surrogates for demonstrating pathogen destruction during biosolids processing. If this project is successful, it is anticipated that demonstration of the absence of associated public health risks through robust monitoring databases will be enabled. It is hoped that this would increase the acceptance of land application of biosolids with would in turn increase crop production and reduce localized soil losses.

A four component approach has been designed for this project. This approach includes: Batch microcosm studies; Bench scale semi-batch digester studies; Full scale process monitoring; and Extension and education activities. Biosolids samples in microcosm, bench-scale reactor, or full-scale tests will be enumerated for a number of reference and surrogate measures. Those measures may be physical, chemical, and biological. Each measure will use standardized methods. These methods are as follows: fecal coliforms and E. coli by Standard Method 9223; (Salmonella by spread-plating methods; helminth ova by floatation and microscopy; viruses by ASTM D 4994-89 enterococci by Standard Method 9230 aerobic spores by Standard Method 9218; coliphage by modified EPA Method 1602; fungal spores by plating and microscopy; Clostridium perfringens by membrane filtration -chemistry including pH, ammonia, and solids

2012/01 TO 2012/12
OUTPUTS: In the intervening three months, a doctoral student and an hourly student have been recruited to work on the project. These students have received proper safety training and are now certified to work with wastewater and biosolids. The doctoral student has also been able to evaluate options for methods of (1) quantifying free ammonia and ammonium in samples, (2) quantifying Closttridium sp. and Clostridium perfringens spores in samples, and (3) enumerating fungal spores and populations in samples. The doctoral student is currently working on completing "Standard Operating Procedure" documents for selected methods to be applied in the experimental phase of work.
PARTICIPANTS: Sharon C. Long, Principal Investigator, Professor of Soil Science, University of Wisconsin Madison; Zachary S. Carroll, Graduate Research Assistant, Doctoral Student of Environmental Engineering, University of Wisconsin Madison; Peter Balogun, Student Hourly Research Assistant, Undergraduate Student, University of Wisconsin Madison.
TARGET AUDIENCES: Nothing significant to report during this reporting period.
PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

IMPACT: There are no significant impacts or outcomes to report as yet. We are pleased to report that the project has recruited talented students and experimental work will proceed when the students return for Spring Semester.

Funding Source
Nat'l. Inst. of Food and Agriculture
Project source
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Bacterial Pathogens
Natural Toxins
Microbial Genetics
Food Safety Modernization Act