Wastewater contaminant transport and treatment in a nutrient limited ribbed fen

Abstract:

To minimize the discharge of wastewater contaminants from remote northern communities and mining operations, fen peatlands in sub-arctic regions are used for tertiary wastewater treatment to detain, transform, and remove these contaminants. However, there is a limited understanding of contaminant transport and treatment in fen peatlands, particularly in sub-arctic Canada. To better characterize wastewater contaminant transport and treatment in these systems, approximately 44 m³ day^-1 of simulated wastewater, concentrated custom-blend fertilizer (NO₃^-, PO₃^3-, and SO₄^2-) and Cl^- diluted with water, was pumped into a small 0.5 ha sub-arctic ribbed fen continuously for 47 days (July 15^th –August 31^st 2014). Contaminant concentration of 3 similar ribbed fens varied between 0.0-3.0 mg L^-1 over the study period (May – September 2014). An exponential increase in transmissivity (2.4 to 16.8 m² day^-1) as the water table rose (~0.16 m) increased the average linear groundwater velocity (0.5 to 3.4 m day^-1) and resulted in rapid SO₄^2- (0.8 m day^-1) and Cl^- (1.9 m day^-1) transport. Notwithstanding the rapid transport of Cl^-, diffusion into inactive pores still retarded Cl^- transport by a factor of 1.8. Contrary to the rapid transport of SO₄^2- and Cl^-, the other contaminants were rapidly removed from the pore water (likely through biological uptake or adsorption) and minimal transport was observed (0.29 and 0.04 m day^-1 for PO₃^3- and NO₃^-, respectively). Northern ribbed fens have a large capacity to detain certain wastewater contaminants (e.g., NO₃^- and PO₃^3-), yet allow rapid transport of others (e.g., SO₄^2- and Cl^-). Thus, these peatlands have the potential to significantly decrease wastewater contamination in northern aquatic environment by both biogeochemical and physical processes but careful management of the hydrology is required to prevent the release of mobile contaminants.