Water quality improvement and plant root function in an ecological system treating dairy wastewater

Ecological treatment systems (ETS) are promising, sustainable alternatives to conventional wastewater treatment. These systems consist of anaerobic reactors, aerobic reactors, clarifiers and wetlands. Microbes and plants perform the majority of treatment through the utilization of carbon, nitrogen and phosphorus present in the wastewater. Through the reliance on renewable resources, ETS have successfully treated municipal and industrial effluents with reduced costs compared to conventional methods. However, their capacity to treat livestock wastewater is unknown. Additional gaps in ETS knowledge include the ability of the systems to remove coliforms from wastewater, and the role of plant roots in wastewater treatment.

The impact of three strengths of dairy wastewater on effluent water quality was assessed. Influent and effluent water samples were analyzed for PO₄, TP, TN, NH₄, NO₃, total suspended solids (TSS), and carbonaceous biochemical oxygen demand (CBOD₅). Influent volumetric loading rates were much greater than those of a similar system treating municipal wastewater. Regardless of wastewater strength, concentrations of all measured variables were significantly reduced between the influent and effluent of the ETS.

This dissertation also assessed the ability of an ETS to reduce concentrations of total coliforms and Escherichia coli from dairy wastewater. Regardless of wastewater strength, average total coliform and E. coli concentrations were consistently reduced by at least 99% from influent to effluent, with the majority of the removal (76%) occurring in the first two reactors. Relationships between internal concentrations of solids and coliforms indicated that increased removal of solids may further reduce coliform concentrations. The substantial reductions achieved indicate that ETS have the potential to successfully reduce coliforms in wastewater to meet discharge limits.

Finally, this research identified plant species that promote greater nitrogen removal, and whose use could lead to increased efficiency of ETS. Significantly more NO₃^-(mg l^-1hr^-1) was produced by bacteria associated with C. papyrus roots than in microcosms containing: only wastewater, or H. moscheutus, (P < 0.001). Potential denitrification rates were significantly greater in H. moscheutos and S. nigra root microcosms than in C. esculentus and C. papyrus root microcosms on dry weight, wet weight and root area bases (P < 0.001).