ABSTRACT
The incorporation of biochar into soils has been proposed as a means to sequester carbon from the atmosphere. An added environmental benefit is that biochar has been shown to increase soil retention of agrochemicals, and recent research has indicated that biochar may be effective in increasing soil retention of bacteria. In this study we investigate the transport behavior of O157:H7, serovar Typhimurium, and carboxylated polystyrene microspheres in water-saturated column experiments for two soils (fine sand and sandy loam) amended with 2% poultry litter or pine chip biochars pyrolyzed at 350 and 700°C. Adding poultry litter biochar pyrolyzed at 350°C did not improve soil retention of either bacteria in fine sand and even facilitated their transport in sandy loam. Addition of either biochar pyrolyzed at 700°C generally improved retention of bacteria in fine sand, with the pine chip biochars being more effective in limiting their transport. Results from the column studies and auxiliary batch studies suggest that changes in cell retention after biochar amendments were likely due to changes in bacterial attachment in the column and not to physical straining or changes in survivability. We also found that changes in bacterial hydrophobicity after biochar amendments were generally correlated with changes in bacterial retention. The influence of biochar amendment in increasing retention of both bacteria was generally more pronounced in fine sand and indicates that soil texture affects the transport behavior of bacteria through biochar-amended soils.
ABSTRACT
The effects of biochar feedstock, pyrolysis temperature, and application rate (1 and 2%) on the transport of two Escherichia coli isolates through a fine sand soil under water-saturated and partially saturated conditions were investigated in column experiments. Biochars from two feedstocks (poultry litter and pine chips) and pyrolyzed at two temperatures (350 and 700 °C) were evaluated. Both biochars pyrolyzed at 700 °C resulted in significant reductions in E. coli transport, with greater reductions observed with the pine chip biochars. For the low temperature biochars, increased transport was observed for the poultry litter biochar whereas reduced transport was observed for the pine chip biochar. In general, the effect of biochar application on E. coli transport was more pronounced in the unsaturated soils and for the 2% application rates. Large differences were also observed between the two isolates indicating that bacterial surface properties play a role in how biochar affects E. coli transport.
Subject(s)
Charcoal , Escherichia coli/physiology , Hot Temperature , Soil MicrobiologyABSTRACT
The incorporation of biochar into soils has been proposed as a means to sequester carbon from the atmosphere. An added environmental benefit is that biochar has also been shown to increase soil retention of nutrients, heavy metals, and pesticides. The goal of this study was to evaluate whether biochar amendments affect the transport of Escherichia coli through a water-saturated soil. We looked at the transport of three E. coli isolates through 10-cm columns packed with a fine sandy soil amended with 2 or 10% (w/w) poultry litter biochar pyrolyzed at 350 or 700°C. For all three isolates, mixing the high-temperature biochar at a rate of 2% into the soil had no impact on transport behavior. When added at a rate of 10%, a reduction of five orders of magnitude in the amount of E. coli transported through the soil was observed for two of the isolates, and a 60% reduction was observed for the third isolate. Mixing the low-temperature biochar into the soil resulted in enhanced transport through the soil for two of the isolates, whereas no significant differences in transport behavior were observed between the low-temperature and high-temperature biochar amendments for one isolate. Our results show that the addition of biochar can affect the retention and transport behavior of E. coli and that biochar application rate, biochar pyrolysis temperature, and bacterial surface characteristics were important factors determining the transport of E. coli through our test soil.
