Center for Biofilm Engineering

Thesis Abstract:  

"Selecting plant species to optimize wastewater treatment"

Determining whether plants species have an effect on wastewater treatment, if those effects are species-specific, and understanding the mechanisms behind plant influences could increase the efficacy of wastewater treatment.  Additionally, if relationships exist between plant traits and species’ effects on wastewater, plants could be selected to optimize treatment.  My research investigated seasonal plant effects on wastewater treatment by monitoring water chemistry in model subsurface wetlands planted with monocultures of 19 plant species and unplanted controls.  COD removal in the unplanted control declined during colder temperatures, likely caused by a decrease in microbial activity.  In contrast, wetlands with select plant species had constant COD removal across seasons.  Redox potential and sulfate concentrations were measured as indirect measurements of the oxygenation state of the wastewater.  Wetlands that had a decline in COD removal in winter had constant low redox potential and sulfate concentrations throughout the seasons.  Wetlands with high COD removal across seasons had elevated redox potentials and sulfate concentrations during the winter, indicating elevated oxygen availability which may possibly offset the negative temperature effect on microbial processes.  Root oxygen loss is a possible explanation for the elevated sulfate concentrations and redox potential and constant COD removal.  I measured root oxygen loss in the summer and the winter to determine whether oxygen release was sufficient to influence wastewater treatment and cause seasonal and species-specific effects on water chemistry.  COD removal and ROL were positively correlated at 4˚C but not at 24˚C, however the amount of root oxygen release only accounted for a portion of the required oxygen to facilitate plant’s influence on COD removal.  Root oxygen loss is one possible mechanism for species-specific influences on treatment but further research is needed to investigate other mechanisms.  In addition to determining associations between COD removal and root oxygen loss, other plant traits including the plant’s botanical grouping, Wetland Indicator Status, and flooding tolerance were compared to plants’ influences on wastewater treatment.  All the sedges and rushes, obligate wetlands species, and 8 of 9 flood-tolerant plants had greater COD removal than the control at 4˚C, the coldest temperature incubation.  Results suggest that plant selection can optimize wastewater treatment, especially in cold climates. 

Selecting plant species to optimize wastewater treatment, thesis defense by Carrie Taylor M.S. candidate in Land Rehabilitation, Land Resources and Environmental Sciences, Montana State University, May 2008.