T.A. DeBusk, J.E. Peterson, K.R. Jensen 2
This report compares two bioremediation techniques for removing phosphorus (P) from agricultural wastewater and runoff. The first is nursery culture of the wetland macrophyte, Pontederia cordata, from seedlings to 3 month old plants. Agricultural wastewater is provided in the nursery as a nutrient source to support plant growth. The second technique is periphyton filter technology. Periphyton filters utilize intensively cultivated and harvested attached algae, microalgae and microorganisms grown in a raceway. The two systems were operated under different conditions. P. cordata cultures received a dairy wastewater (> 1.7 mgP/L) and the periphyton filters received sugar cane runoff that contained <0.1 mgP/L. P. cordata did not grow well during the winter and thus did not accumulate much P from water during this period. Periphyton filters operated well during cooler weather. P. cordata phosphorus uptake rates varied from 0.2 to 66.8 mg P / m2-day. Values were lowest for young (less than one month old) seedlings during winter. Periphyton phosphorus uptake was substantially higher, averaging 101 mgP/ m2-day during a December through May study. Periphyton filters are thus superior to P. cordata both in terms of amount of P removed and achievement of low levels of P in the treated water. Periphyton filters and P. cordata cultures both provide substantially higher P removal rates than passive (non-harvested) treatment wetlands. P. cordata presently has value as an aquascape plant, which provides additional economic incentive to use these macrophytes for bioremediation. High mass removal and effectiveness at removing P from low aqueous concentrations make periphyton filters useful bioremediation technologies, even though economic value of periphyton biomass remains to be developed.
