Andrew N. Hennig
Using Biochar in a Permeable Reactive Barrier for Contaminated Groundwater Remediation
Permeable reactive barriers (PRB) are a developing technology that has been widely acknowledged as a cost effective option for the in situ remediation of contaminated groundwater. PRBs work on several different mechanisms, including immobilization, transformation, biotransformation, and precipitation. Biochar is a form of charcoal that is currently receiving much interest from the scientific community because of the noteworthy potential for the carbon sequestration. Biochar has been shown to be an effective material for the sequestration of carbon dioxide, as well as reducing the soil emissions of NOx and CH4, both powerful greenhouse gases. In addition to reducing greenhouse gases, soil that is rich in biochar has been shown to increase water quality and crop yield in even nutrient depleted soils, as well as reducing levels of contaminants in plants grown in contaminated soils. To this point, no work has been done to examine the potential that biochar may have as a material for use in PRBs.
The research undertaken during this dissertation will test the sorption capacity of biochar for three heavy metals, Nickel, Copper, and Zinc. Solutions of the three metals (both individually, and in each possible combination) are made, and different amounts (and sizes) of biochar added to samples of the solutions. One subset of samples is agitated in a shaker for 24 hours, while the other subset is left stationary for the same amount of time. It has been assumed that after 24 hours, maximum sorption has taken place. Once the biochar has been filtered out of the sample solutions, the samples can be analysed for in the ICP (Inductively Couples Plasma Mass Spectrometer) for their metal content, and the concentration of metal sorped by the biochar can then be determined.
Preliminary results show that particle size has a significant impact on sorption, with the smallest particle size effectively absorbing large amounts of metal, while the raw bio-char has struggled to achieve even low rates of sorption. Results have also shown that the three metals examined have vastly different affinities for biochar sorption. While the sorption capacity of Copper is encouraging, the sorption rates of Zinc and Nickel are very low, particularly for Nickel, where the sorption is almost non-existent. More interesting is the fact that Copper has shown a higher sorption capacity when it is in solution with the other metals, particularly when it is in solution with either Zinc or Nickel alone. Throughout all trials undertaken so far, the only trial where the Copper in the contaminated water solution was able to be fully sorped was when Copper and Zinc were in solution together, this was not the case when Copper, Nickel and Zinc were all in solution. The reason for this discrepancy is unclear, and further trials will be undertaken to try and ascertain the relationship between Copper and the other ions present to account for the increase in sorption.
These preliminary results are encouraging, and further experimental analysis and literature review will reveal possibilities for biochar as a remediation agent in the future.