SBIR-STTR Award

A proposed integrated wetland-chemical treatment system has the potential to be an effective, economical, and environmentally acceptable technique for removing phosphorus from agricultural wastewaters. The proposed system consists of a submersed macrophyte pond (SMP) for suspended solids, dissolved organic carbon and P removal, as well as elevation of water column pH levels. Effluent from the SMP is provided with additional pH adjustments and fluoride amendments, if required, and then is fed into a subsurface flow limerock bed where P precipitation occurs. Another SMP comprises the third and final treatment step, providing further P removal from the saturated effluent leaving the limerock bed. The major emphasis of the proposed research is on determining the optimum conditions for P coprecipitation or precipitation on the limerock, and for establishing SMP design and operational criteria for producing an "optimum" wastewater feed to the limerock filter. The following experiments will be conducted to establish concept feasibility; (i) a screening study on the growth of four submersed macrophytes in sugarcane field runoff water, and the effects of the macrophytes on water column constituent levels (pH, P, DOC, TSS); (ii) laboratory shaker table studies on the use of limerock for removing P from "soiled" distilled water, sugarcane field runoff, and effluent from the submersed macrophyte tanks; and (iii) a laboratory microcosm evaluation of the complete integrated P removal system (SMP-limerock filter-SMP), in which some optimization of design (relative sizes of system components) and operational (hydraulic residence times) characteristics will be evaluated. Saturation indexes and kinetic parameters will be calculated to assist in identifying the controlling solid phase(s) (i.e. calcite, amorphous tricalcium phosphate, hydroxyapatite, fluorapatite).

Anticipated Results:
Currently, there exist no cost-effective techniques for removing P from runoff (agricultural or urban) streams. Based on theoretical and empirical considerations, the unique combination of wetlands and limerock beds proposed herein should provide a reliable, non-energy intensive technique for runoff P removal. The proposed technology will provide the basis for environmentally acceptable low-cost P removal from a spectrum of waste streams. The design, construction and operation of wetland limerock P removal systems is a promising commercial application technology.

We have developed an integrated wetland-chemical treatment system that has the potential to be an effective, economical, and environmentally-acceptable technique for removing phosphorous (p) from agricultural wastewaters and runoff. The integrated system consists of a submersed aquatic vegetation (sav) dominated wetland or pond, followed by a limerock filter. Our Phase I work with sugarcane agricultural drainage water (adw) demonstrated marked removal of p in the sav unit process. Plant uptake was not a prominent p sink, and water chemistry changes suggest that p was removed principally as a calcium precipitate. The effluent from the sav unit was further polished by passage through a filter bed containing 0.5" or 1.0" limerock. The limestone appears to act as a heterogeneous nucleation site for metastable calcium-p compounds. We believe, based on water chemistry characteristics in the limerock bed, that the calcium-p compounds that accumulate on the limerock surfaces gradually are transformed to more stable (apatite) forms. For Phase II, we intend to better define the capabilities of this p removal system by: 1) evaluating the longevity of the limerock bed as a functional substrate for p removal, using high p (dairy) and low p (sugarcane) waters; 2) model the thermodynamics and kinetics of solid phase calcium-p compound formation in the limerock bed; 3) define the environmental conditions, if any, under which the limerock bed will export p; 4) assess techniques for minimizing export of sediment-derived soluble p in sav wetlands; and 5) demonstrate the technology at a field-scale, where we will optimize essential design features to maximize p removal efficiency.Applications:Currently, there exist no cost-effective techniques for removing p from agricultural wastewater or runoff streams. Based on empirical findings and theoretical considerations, we believe our unique combination of sav wetlands and limerock beds represents a reliable, passive and long-term p removal technology. At present, the most attractive near-term commercial opportunity for this technology is in removing p from sugarcane runoff in s. Florida, at both local and regional scales. The proposed Phase II research is designed to largely define the opportunities and limitations of the technology for a range of applications, including: animal wastewater treatment, urban and agricultural runoff treatment, domestic wastewater polishing, and lake management and restoration.