Presentation on theme: "Long-term stability of water treatment residuals (WTR)- immobilized phosphorus PhD research proposal Submitted by Sampson Agyin-Birikorang Soil and Water."— Presentation transcript:
Long-term stability of water treatment residuals (WTR)- immobilized phosphorus PhD research proposal Submitted by Sampson Agyin-Birikorang Soil and Water Science Dept. University of Florida
Introduction Loss of P from agricultural croplands is one of the major factors responsible for accelerated eutrophication. There is therefore the need to increase P sorbing capacity of poorly sorbing soils to mitigate this problem
Using of WTRs to reduce P pollution (“Waste” product from drinking water treatment plants)
Using of WTRs to reduce P pollution High Low Al (Ca, Fe) oxide Content Soil Substitute Landfill cover Reclamation P Sorbent Reduce P solubility Runoff Potential Beneficial Uses of WTR
Cost-effective Abundant – over 1000 drinking water treatment plants in USA producing > 2 million tonnes of WTR daily Disposal problems therefore can be converted to beneficial use
In the short term, WTRs can dramatically reduce soluble P levels in soils and in runoff 3.33 mg/L 0.77 mg/L 77% reduction 0.32 mg/L 90%reduction Runoff P (mg/L) Real Life ResReal Life Res P sorption by WTRs- Runoff water study WTR application Runoff P (mg/L) WTR application Dayton et al, 2003 P sorption by WTRs: Runoff study Makris, 2004
In the intermediate term (~ 5.5 y) WTRs has been effective in P immobilization
But for how long? The long-term stability of sorbed P on the WTRs has not been thoroughly explained nor documented
Previous study Three approaches were used to simulate long-term effects (Makris, 2004) Spectroscopic analysis of the physical nature of the WTRs Thermal incubation of P-impacted WTRs (46, 70 o C) for 2 y Field monitoring of the longevity of WTR’s effect on soil P at two sites (Holland, MI)
Objectives Overall objective: To assess the long-term stability of WTR- immobilized P Specific objectives: Specific objectives: To evaluate the lability of WTR-immobilized P from field samples and artificially “aged” fresh samples using radioisotopes of P. To calculate the solubility of WTR-immobilized P from field samples and artificially “aged” fresh samples using chemical equilibrium models. To identify possible solid phase control of the solubilities of WTR-sorbed P
Hypotheses: Time will induce changes in the nature of WTR-P binding, which will prevent sorbed P from being released into solution. Sorbed P will remain unaffected indefinitely by reasonably anticipated changes in pH and ionic strength and by organic ligand attack.
Experiment 1 ASSESSING LONG TERM REACTIONS AND CHARACTERISTICS OF SORBED P WITH WTR Time constraints associated with conducting long-term (>20 y) field experiment Need to artificially “age” freshly amended samples
Materials and methods a. Incubation of WTRs Treatments:4 WTRs * 2 P rates = 8 tmts WTR types:High adsorption capacity (2) Low adsorption capacity (2) P rates:0 mg P/kg and mg P/kg Replications:3 Design:completely randomised design
b. Incubation of amended soil Treatments: 4 WTRs * 3 P rates = 12 treatments Soil: Unamended soil samples (Immokalee) Amendment: 2.5 % (by wt.) air-dried WTRs (mentioned above); + unamended (control) P rates:no P, “low rate” (43mg P/kg) and “high rate” (100 mg P/kg) added as TSP dissolved in 0.01M KCl These will be incubated by drying and rewetting cycles (~ 2 y).
Incubation Samples will be incubated at 30 o C in an incubator Kept for 7 d at ~ 80 % field capacity (covered) Air-dried to constant weight (uncovered).
Periodic sampling (~ 3 months) for the following analyses: X-Ray Diffraction analyses Surface Area measurement Oxalate and pyrophosphate extraction Water extractable P, Fe, Al and Ca Chemical equilibrium modelling Determination of P Lability
Experiment 2 CHEMICAL EQUILIBRIUM CALCULATIONS TO DETERMINE THE SOLUBILITY OF WTR-IMMOBILIZED P Solubility of P is usually controlled by the solid phases present in the medium MINTEQA2 (Allison et al., 1991) chemical equilibrium software will be used for the modeling
Materials and methods Two grams of WTR-amended samples (from the field and incubated samples) + 20 mL of deionized water. Shake on a reciprocal shaker for 1 d to obtain a steady state (Hetrick & Schwab, 1992). The suspensions will be centrifuged, filtered, and analyzed for: Phosphorus Cations (Ca, Mg and Al) Anions (SO 4 2-, Cl - and NO 3 - ) pH, Eh, EC
Ionic strength (Griffin and Jurinak, 1973) ionic strength = EC (dS m -1 ) x These analytical data will serve as input for MINTEQA2 to: calculate activities of ions and complexes predict the theoretical change in solution composition as a result of possible solid phase formation
Experiment 3 ISOTOPIC STUDIES TO EVALUATE THE LABILTY OF WTR-IMMOBILIZED P Isotopic dilution techniques can help to distinguish between labile (isotopically exchangeable) P and fixed (non- isotopically exchangeable) P pools following incorporation of remediation materials
Materials and methods Four grams of WTR-amended samples (from the field and incubated samples) + 40 mL of deionized water. Appropriate aliquots of diluted HCl or NaOH will be added to the samples to provide a series of 5 pH levels (range = 4-7) The soil suspensions will be equilibrated for 4 d ( Lombi et al., 2003 ) in an end-over-end shaker Samples will be spiked with 50μL of solution containing 32 P (~10-30 KBq) The samples will then be allowed to equilibrate for an additional 3 d ( Lombi et al ).
Determination of the specific activity (S.A.) of a sample will require two independent measurements: 1. Determination of the activity (dpm or dps) of the radioisotope by radio-assay techniques using appropriate detectors, i.e., liquid scintillation counting, 2. Determination of the total P content by any conventional chemical method, i.e. total P by spectrophotometric method.
The labile pools (E) of P will be determined as: E = (C sol /C* sol ) * R * (V/ W) (Hamon et al., 2002). where C sol is the concentration of total P in solution (μg mL -1 ), C* sol is the concentration of radioisotope remaining in solution after equilibration (Bq mL -1 ), R is the total amount of radioisotope that was added to each sample (Bq mL -1 ), and V/W is the ratio of solution to sample (10 ml g -1 ).
Expected Benefits The results from this work, together with the chemical analyses and spectroscopic studies (Makris, 2004) will help address the long-term stability of the WTR-immobilized P Regulators concerned with the ultimate fate of P added and/or immobilized by WTR additions will profit from the data to support needed regulations