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 Examination of Microbial Characteristics of the Wastewater-Induced Soil Biozone
Jill M.B. Tomaras
Item Number: NRL2006AC-1
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Price: $20.00
In the U.S. today, nearly 25% of the population relies on onsite wastewater systems where wastewater is primarily treated then discharged to the soil. Biozone formation involves the buildup of pore-filling agents at and immediately below the infiltrative surface. It is at the infiltrative surface where treatment/removal of organisms occurs in these systems, thus a more complete understanding of its composition is imperative. While microbes are believed to be involved, there has been little research focused on identifying the organisms present or the mechanism by which clogging occurs. This work examined the microbial aspects of the biozone as part of a controlled field experiment. Biozone samples were taken from pilot scale subsurface wastewater disposal units in Golden, Colorado, having received septic tank effluent for 30 months. Three samples were aseptically taken from the top 1.5 cm of infiltrative surface (depth intervals of 0.5, 1.0, and 1.5 cm), and additional core samples were taken to a depth of 10 cm. Samples were analyzed for plate counts (heterotrophic plate count bacteria [HPC], fecal coliforms, and E. coli), for biomass determination (phospholipid extraction), and for molecular analysis (isolation of community DNA, amplification of a conserved region of the 16S rRNA gene via PCR, cloning into E. coli, and sequencing DNA). HPC, fecal coliform, as well as E. coli counts indicate a decrease in culturable organisms with depth, with one order of magnitude more counts in the top 0.5 cm compared to the 10 cm depth. Reinforcing the plate count results, total biomass data indicate a decrease in biomass with depth, with the top 0.5 cm of the biozone having nearly double the biomass of the next lower 0.5 cm interval. Molecular characterization indicates there is a higher diversity of bacteria in the biozone than samples taken from the septic tank. No dominant bacterial species have been identified. Understanding the composition of the biozone may aid in future design of onsite wastewater systems.