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Biosolids

Introduction

Biosolids are nutrient-rich organic materials produced during the biological treatment of wastewater.  The Oregon Wastewater Treatment Plant uses the same biological and physical processes by which water is cleaned in nature.

Microorganisms (primarily bacteria) biologically break down the sewage in the facility’s aeration tanks.  These microorganisms, called activated sludge, utilize the organic material in sewage as a food source.  Air is pumped into aeration tanks to provide oxygen and mixing.

The sewage provides a constant food supply, which causes the bacteria to continually reproduce.  To maintain the proper balance of Food to Microorganisms in the aeration tanks, a portion of the activated sludge is removed and sent to the aerobic digestion tanks.

Once in the aerobic digesters, the activated sludge is dewatered to increase the solids content, and stabilized to reduce pathogens and odors. Only after it has been through this treatment process can it be called biosolids.

 biosolids pic801                                                                                                          Biosolids are created by the treatment of activated sludge in the aerboic digesters.

Biosolids Recycling

The Oregon Wastewater Treatment Plant recycles 100% of the biosolids it produces.    The biosolids are applied, primarily to agricultural land, as fertilizer to improve and maintain productive soils and to stimulate plant growth.

Biosolids contain significant amounts of nitrogen (N), phosphorous (P), and a trace of potassium (K).  The majority of the nitrogen is organic nitrogen, which is released slowly throughout the growing season and becomes available as the crop grows and takes it up. Biosolids also contain micronutrients that are essential for crop growth.  These include boron, calcium, copper, iron, magnesium, molybdenum, sulfur and zinc, among others.

Biosolids contain more than 50% organic matter.  Organic material conditions the soil by improving the soil structure, porosity and increasing nutrient and water retention.  Organic material improves the soil’s cation exchange capacity (CEC) and helps maintain healthy levels of soil bacteria.

biosolids pic952                                                                                                             Biosolids are removed from the aerobic digesters and loaded into a field applicator.

biosolids pic573                                                                                                                  The field applicator injects the biosolids beneath the soil surface.

Biosolids Benefits

  • Returns resources back to nature’s cycle
  • Adds nutrients to the soil that may not be added by commercial fertilizers
  • Improves soil structure and soil fertility

Regulations

Oregon only applies biosolids to sites approved and inspected by the Ohio Environmental Protection Agency.

Oregon applies its biosolids at or below the agronomic rate of the nitrogen requirements of the crop being grown.

Biosolids application is closely monitored and regulated to ensure that it presents no increased risk to people, animals or the environment.

Metals concentrations in Oregon’s Biosolids are well below regulatory levels: 

 

Metal

USEPA Monthly Limit mg/kg

Oregon 2008 Average mg/kg

Oregon 2007 Average mg/kg

Arsenic

41

8

10

Cadmium

39

2

2

Copper

1,500

340

350

Lead

300

44

42

Mercury

17

1.8

1.2

Nickel

420

24

24

Selenium

100

7

7

Zinc

2,800

730

750

Pathogen levels in Oregon’s Biosolids are consistently below the Class B 2,000,000 fecal coliform bacteria per dry gram of sludge limit.  In 2008, the average fecal coliform level was 12,000 fecal coliform bacteria per dry gram of sludge.  The highest 2008 fecal coliform bacteria level was 35,000.

To further reduce the risk of pathogens, farmers must wait before harvesting crops on land that has received biosolids.  This allows time for the pathogens to die in the soil.

Resources

City of Oregon Wastewater Treatment
Questions Concerning Biosolids?

Contact Todd Smith
Telephone: 419-698-7133

Ohio Environmental Protection Agency
Northwest District Office
347 North Dunbridge Road
Bowling Green, Ohio 43402-9398
Telephone: 419-352-8461

OEPA Biosolids Web Site:
www.epa.state.oh.us/dsw/sludge/biosolid.html

National Biosolids Partnership
601 Wythe Street
Alexandria, Virginia 22314-1994
Telephone:  703-684-2400

NBP Web Site:
www.biosolids.org

U.S. Environmental Protection Agency Region 5
77 West Jackson Boulevard
Chicago, IL 60604
Telephone:  312-886-6106

USEPA Biosolids Web Site:
www.epa.gov/OWM/mtb/biosolids/index.htm

 

 
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