Challenges in using natural peatlands for treatment of mining-influenced water in a cold climate. Considerations for arsenic, antimony, nickel,
nitrogen, and sulfate removal

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Linnanmaa, auditorium L5. Remote connection : https://oulu.zoom.us/j/63237829074

Topic of the dissertation

Challenges in using natural peatlands for treatment of mining-influenced water in a cold climate. Considerations for arsenic, antimony, nickel,
nitrogen, and sulfate removal

Doctoral candidate

Master of Science (Tech) Uzair Akbar Khan

Faculty and unit

University of Oulu Graduate School, Faculty of Technology, Water, Energy and Environmental Engineering Research Unit

Subject of study

Environmental Engineering

Opponent

Tohtori Adam Jarvis, Newcastle University

Custos

Docent Anna-Kaisa Ronkanen, Univeristy of Oulu

Add event to calendar

Challenges in using natural peatlands for treatment of mining-influenced water in a cold climate

Natural peatlands are commonly used in Finland as treatment wetlands to provide final treatment
to mining-influenced water. Their use is convenient as they are cost-effective, abundant in
Finland, and often located close to mining sites. This thesis explored contaminant removal
processes in treatment peatlands, and factors that affect these processes, through laboratory
experiments, analysis of monitoring data, pilot wetlands, and reactive transport modeling. The
results showed that, under the right conditions, treatment peatlands can provide efficient year-
round removal of arsenic (As), antimony (Sb), nickel (Ni), and nitrogen (N), even in a cold
climate. Sulfate (SO42-) removal in the studied peatlands was negligible, due to high SO42-
concentrations in inflow mining-influenced water and unfavorable conditions for SO42- removal.
Low hydraulic loading was found to be the most important parameter for efficient contaminant
removal. Inflow water composition affected removal efficiency and mobilization of contaminants.
Temperature had no major systematic effect in batch experiments, but studies on full-scale
peatlands indicated slightly better removal of Sb in summer than in winter. Removal of As and Sb
was higher at pH 6, while leaching was higher at pH 9. The opposite was true for Ni. Mean
residence times were shorter in frozen conditions, indicating loss of available peatland volume
during winter. The freezing-thawing pilot wetlands also provided evidence of presence of
preferential flow paths. Long-term use of treatment peatlands led to contaminant accumulation,
confirming high removal efficiency. However, the accumulated contaminants were mobilized
when inflow water concentrations decreased drastically. Pilot wetlands and reactive transport
modeling proved useful in understanding treatment peatland processes. Pilot wetlands adequately
replicated various peatland processes during the simulated freeze-thaw cycles. Unfrozen
conditions were better simulated than frozen conditions by the HYDRUS wetland module,
indicating a need for more accurate model parameters. Therefore, use of treatment peatlands is
challenged by varying environmental conditions and mine water composition, making it difficult
to control removal/retention processes. To address these challenges, there is a need for innovative
approaches of peatland use where the benefits to receiving water bodies exceed the risks
associated with their long-term use.
Last updated: 26.11.2020