Demonstration of combined zero-valent iron and electrical resistance heating for in situ trichloroethene remediation.

The effectiveness of in situ treatment using zero-valent iron (ZVI) for nonaqueous phase or significant sediment-associated contaminant mass can be limited by relatively low rates of mass transfer to bring contaminants in contact with the reactive media. For a field test in a trichloroethene (TCE) source area, combining moderate-temperature subsurface electrical resistance heating with in situ ZVI treatment was shown to accelerate TCE treatment by a factor of about 4 based on organic daughter products and a factor about 8 based on chloride concentrations. A mass-discharge-based analysis was used to evaluate reaction, dissolution, and volatilization processes at ambient groundwater temperature (~10 °C) and as temperature was increased up to about 50 °C. Increased reaction and contaminant dissolution were observed with increased temperature, but vapor- or aqueous-phase migration of TCE out of the treatment zone was minimal during the test because reactions maintained low aqueous-phase TCE concentrations.

Identification of a Brevibacterium marker gene specific to poultry litter and development of a quantitative PCR assay.

AIM: To identify a DNA sequence specific to a bacterium found in poultry litter that was indicative of faecal contamination by poultry sources. METHODS AND RESULTS: Faecally contaminated poultry litter and soils were used as source material for the development of a quantitative polymerase chain reaction (qPCR) method targeting the 16S rRNA gene of a Brevibacterium sp. The identified sequence had 98% nucleotide identity to the 16S rRNA gene of Brevibacterium avium. The qPCR method was tested on 17 soiled litter samples; 40 chicken faecal samples; and 116 nontarget faecal samples from cattle, swine, ducks, geese, and human sewage collected across the United States. The 571-bp product was detected in 76% of poultry-associated samples, but not in 93% of faecal samples from other sources. Marker concentrations were 10(7) -10(9) gene copies per gram in soiled litter, up to 10(5) gene copies per gram in spread-site soils, and 10(7) gene copies per litre in field run-off water. Results were corroborated by a blinded study conducted by a second laboratory. CONCLUSION: The poultry-specific PCR product is a useful marker gene for assessing the impact of faecal contamination as a result of land-applied poultry litter. SIGNIFICANCE AND IMPACT OF THE STUDY: This study describes the first quantitative, sensitive and specific microbial source tracking method for the detection of poultry litter contamination.