APPLICATION OF PHOTOSYNTHETIC MICROBIAL MAT TOWARD ATTENUATION OF MINING-IMPACTED WATERS

Mining-impacted waters and acid mine drainage remain important environmental concerns for areas of orphaned and ongoing mining activities. Solutions that incorporate nature-based treatment are promising for legacy sites where their comparatively passive operation can help achieve treatment goals with less labor and capital requirements. Here we investigate the capability of a unique type of engineered wetlands, macrophyte-free shallow open water wetlands, toward metal attenuation that has previously been applied for the sustainable treatment of nutrients, pharmaceuticals, and pesticides. Demonstration-scale systems exist at the Prado constructed wetlands complex in Corona, CA. Pronounced diel shifts that could enhance metal removal from the water column occur over pH ranges from circumneutral to in excess of 10 and dissolved oxygen (DO) concentrations from ~2-20 mg/L (night to day) caused by photosynthetic activities. Lab-scale flow-through reactors amended with biomat recreated analogous pH/DO diel cycles to the field and attenuated 51-86% of added metals under various concentrations. The removal of Zn was more pronounced at higher pH (daytime); whereas for Cu, the removal was more pronounced at lower pH (nighttime). Comparisons of dissolved and particulate metal concentrations indicated that sorptive contributions from inorganic and organic phases of the biomat play a role in metal removal. Furthermore, geochemical analyses of metal accumulation in the top surface layer (~1cm) and bottom layers of biomat associated with phylogenetic sequencing help us understand how metal removal mechanisms link to putative metabolic processes within the biomat and its long-term stability. Ongoing experiments aim to challenge both the batch and flow-through systems with acidic metal-impaired waters to assess the impacts of acidity and metal toxicity on biomat viability and metal removal processes. The combination of field data, laboratory geochemical data, and microbiology tools allow us to improve our understanding of temporal (diel) and spatial (surface versus deep) metal removal by open water wetlands under environmentally relevant conditions.