Fate of Fecal Coliforms and Salmonella in Class B Biosolids-Amended Farmlands.
Lakhwinder S. Hundal, Albert Cox, Richard Gore, Geeta Rijal, James Zmuda, and Thomas Granato. Metropolitan Water Reclamation District of Greater Chicago, 6001 W Pershing Road, R&D Department, Section 123, Cicero, IL 60804-4112
The Metropolitan Water Reclamation District of Greater Chicago (District) treats about 1.5 billion gallons of wastewater per day, which generates about 190,000 dry tons of biosolids annually. The District operates a diverse biosolids management program to beneficially utilize both Class A (aged, air-dried biosolids) and Class B (centrifuge cake) biosolids. Up to 45 percent of the biosolids generated by the District are managed through farmland application of Class B biosolids centrifuge cake. Farmland application is cost-effective to the District and the nutrients in biosolids provide tremendous savings in fertilizer costs to farmers. However, environmentalists continue to raise issues with the safety of the practice of farmland application of Class B biosolids. Most of the concerns originate from misinformation about the fate of pathogens and other constituents in the farmlands fertilized with Class B biosolids. To ensure the viability of its Class B biosolids application to farmland program, the District initiated a field-scale research project to evaluate the fate of fecal coliforms and salmonella in the agricultural fields treated with Class B biosolids. The investigation was conducted on two farm fields representing two soil types; a silty clay loam (fine, mixed, mesic Typic Haplaquolls) and a fine sand (mixed, mesic Alfic Udipsamments). Class B centrifuge cake biosolids (approx. 25 percent solids content) were applied by using a manure spreader at 180 wet ton ha-1 yr-1 to a 1.3-ha plot at the silty clay loam site and at 135 wet ton ha-1 yr-1 to a 0.73-ha plot at the fine sand site. The biosolids were incorporated in soil by chisel plowing. The densities of fecal coliforms and salmonella were monitored over time by analyzing soil samples collected from the biosolids-amended plots at various intervals after biosolids application. The data collected during Year 1 of the investigation show that the density of fecal coliform from both plots decreased rapidly after the application and incorporation of Class B biosolids. Within 6 to 8 weeks of biosolids application, the density of fecal coliforms in the biosolids treated plots decreased to the levels found in the unamended soil. The density of salmonella in the amended soils did not exceed the levels found in the unamended soils. There were no indications of regrowth of fecal coliforms or salmonella in the amended soils. These observations indicate that application of Class B biosolids to farmland does not result in persistence or regrowth of fecal coliforms or salmonella in soil.