2,4,6-trichlorophenol (TCP) is a pervasive carcinogenic water contaminant found
in a wide variety of water and waste systems and is a pertinent model compound of broader
aromatic organics, specifically organo-halide pesticides. These compounds are persistent
in the environment and show resilience to regular water and waste treatment protocols
thus warranting the development and implementation of novel treatment materials for
improved contaminant removal.
Zero-valent iron (ZVI) has demonstrated the ability to remove or degrade a wide
variety of inorganic and organic water contaminants, including chlorophenols, and has
been widely applied for in-situ groundwater remediation where contamination is often
localised in a low-oxygen environment. ZVI’s broader applications in water treatment have
remained mainly limited due to corrosion, particle dispersion, and confinement issues in
deployment. This work, therefore, explored the development, functionality, and potential
application of new modified nZVI materials (nZVI-Osorb) and assessed their potential to
improve iron’s intrinsic functionality while also gauging the material’s viability for TCP
remediation in water and waste systems.
Materials produced in this thesis were prepared utilising three different
embedment procedures (1-pot, multiple additions, oxygen-free). All embedment methods
resulted in tightly bound composites featuring high surface areas (340.2-449.1 sq. m/g)
with net iron composition ranging from 10% to 29.78% by mass. Electron imaging
microscopy verified even dispersion of iron throughout the substrate. Composite materials
did not exhibit a delayed rate of atmospheric corrosion over nZVI controls evincing an 18%
nZVI0 loss per day until reaching a stabilised concentration (7%) after 48 hrs. nZVI-Osorb
composites did produce more favourable iron oxide species which remain conducive to
electron transfer from core Fe0 atom. After 50 days, a majority of nZVI in nZVI-Osorb had
oxidised to maghemite (30%) and magnetite (26%) compared to control nZVI producing
19% and 12% respectively. Unreactive hematite accounted for 47% of the control and just
36% of the composite. While 1-pot embedment allowed the most substantial control over
final iron composition, the oxygen-free method allowed the most reliable preservation of
initial nZVI0 concentrations through restricted oxidation. Materials generated through
oxygen-free embedment were utilised in the following water treatment trials with TCP.
Parameters related to sorption and degradation mechanisms of TCP by nZVI-Osorb
were tested in aerobic conditions, e.g. surface and potable water. nZVI-Osorb materials
demonstrated high extraction capacity for TCP from aqueous solutions (Qe=1286.4 ±13.5
mg TCP/g Osorb, Qe=1253±106.7 mg TCP/g nZVI-Osorb, pH 5.1, 120mg/L TCP) and
followed pseudo second order kinetics. In the broader class of chlorophenols, sorptive
affinity mirrored partitioning values with highly substituted chlorophenols displaying the
highest sorption capacities. Degradation of TCP by nZVI-Osorb or nZVI controls was not
observed due to corrosive hindrance and inadequate reductive capacity, suggesting that
materials may not be suitable for highly aerated surface and potable water treatment
systems.
Environmental conditions pertinent to sorption and degradation mechanisms were
evaluated to improve understanding and robustness of functionality in low-oxygen
applications, such as wastewater and anaerobic digesters, where nZVI-Osorb treatment is
anticipated to be advantageous to TCP sorption and methane production. pH was found
to influence sorption dramatically. Acidic solutions below 5 found sorption >90%. This
capacity was reduced to <30% when pH was raised above TCP pKa value (6.23) to 7 and
above. Further trials found a positive effect on TCP sorption (+7.55%) linked to net pH
reduction (5.1 to 3.3) with the addition of secondary acids (volatile fatty acids: acetic,
propionic, butyric, 3x 100mg/L) commonly found in anaerobic digester systems. Salinity
did not affect TCP sorption. The removal of dissolved and atmospheric oxygen increased
total sorption (40ppm-+1.94%, 100ppm- +7.93%, 200ppm- +0.89%, 400mg/L- +14.59%)
through reduced iron corrosion and the production of favorable iron oxides, but did not
facilitate contaminant degradation.
Biodegradation mechanisms for TCP have broadly been established, and new
research has supported the improved cometabolic degradation of recalcitrant
contaminants like TCP and PCP in nZVI-dosed anaerobic digesters. Model anaerobic
digester systems (3.9 g/L nZVI-Osorb, 25mg/L TCP, 240 mg/L acetic, 120mg/L propionic,
120mg/L butyric acid) containing bioreactor sludge (62.5%) were observed through
standard water quality diagnostics (pH, ORP, COD, head pressure) for 14 days and
suggested that nZVI-Osorb did not inhibit cellular processes. Increased electron activity
from iron corrosion and hydrogen gas production, increased overall pH and decreased total
ORP in these AD systems. TCP degradation by-products (DCP, CP) were detected in dilute
concentrations (<0.01 mg/L) with poor recovery by LC-MS/MS. Results suggest that nZVIOsorb
may be well-suited additive for AD systems.
This study contributes to knowledge of the properties, functionality, and treatment
mechanisms of metal-sorbent composites with a model chlorinated aromatic water
contaminant in aerobic and anaerobic environments. The work identifies favourable
environmental and process conditions to apply these materials in larger scale applications,
particularly, anaerobic digestion and provides support for the continued refinement and
improvement of nZVI based remediation systems