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Long-term stability of water treatment residuals (WTR)- immobilized phosphorus PhD research proposal Submitted by Sampson Agyin-Birikorang Soil and Water.

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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:

1 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

2 Outline  Introduction  Objectives  Hypotheses  Research approach  Expected benefits

3 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

4 Using of WTRs to reduce P pollution  (“Waste” product from drinking water treatment plants)

5 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

6  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

7  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

8  In the intermediate term (~ 5.5 y) WTRs has been effective in P immobilization

9 But for how long? The long-term stability of sorbed P on the WTRs has not been thoroughly explained nor documented

10 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)

11 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

12 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.

13 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

14 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

15  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).

16 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).

17  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

18 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

19 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

20  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

21 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

22 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 ).

23  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.

24  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 ).

25 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

26 Thank You  Questions and suggestions???


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