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Evaluation of Flue Gas Desulfurization Gypsum as a Novel Precipitant for the Removal and Recovery of Phosphorus from Anaerobic Digestion Effluent

Khalaf, Adam
http://rave.ohiolink.edu/etdc/view?acc_num=osu1480334876351851

Abstract Details

2016, Master of Science, Ohio State University, Food, Agricultural and Biological Engineering.
Anaerobic digestion (AD) is a waste-to-energy technology in which microorganisms convert organic materials into two main products: a methane-rich biogas that can be used as a renewable energy source, and a nutrient-rich liquid effluent that is an effective organic fertilizer. The primary method for effluent disposal is land application to crops. However, AD effluent typically has a high phosphorus content and a lower than optimal N:P ratio for crops. Land application often supplies excess phosphorus, contributing to eutrophication and limiting application rates in areas with strict environmental regulations. The inability to dispose of AD effluent has emerged as a major barrier to the advancement of Ohio’s waste-to-energy industry. A potential solution is to remove and recover phosphorus from AD effluent prior to land application to improve disposability and protect water quality. Following solid-liquid separation, soluble phosphorus in the liquid stream (i.e. AD effluent filtrate) can be removed using calcium precipitation. The insoluble calcium phosphates that form during calcium treatment can be recovered and potentially reused in agriculture. Although this method is effective, calcium treatment is often prohibitively costly, in part because large quantities of precipitant are required for effective treatment. The objective of this study was to investigate the use of flue gas desulfurization (FGD) gypsum as a novel, low-cost calcium source for the removal and recovery of phosphorus from AD effluent filtrate. FGD gypsum is high purity CaSO4·2H2O that is produced in abundance as a waste product at coal power plants during the scrubbing of SO2 from coal combustion off-gases. FGD gypsum consistently contains very low heavy metal content and is widely used as a soil amendment in agriculture. In contrast to other low-cost materials that have been studied for phosphorus removal, FGD gypsum is widely available and has high potential for reuse after treatment. FGD gypsum (~95% CaSO4·2H2O) from an Ohio coal plant was used to recover phosphorus from synthetic wastewater and real AD effluent filtrate. Kinetic and equilibrium studies in synthetic solutions demonstrated that phosphorus removal likely occurred by both adsorption and precipitation. The presence of carbonate alkalinity significantly inhibited phosphorus removal. In AD effluent filtrate (102.8 mg P/L), FGD gypsum dosages of 20 mM Ca (3.44 g/L) and 40 mM Ca (6.89 mg/L) removed up to 97.1% of soluble phosphorus within 60-90 minutes. The final precipitates contained up to 5.2% P and consisted of undissolved gypsum, CaCO3, and amorphous calcium phosphates. Initial pH had a significant effect on phosphorus removal efficiency, with higher pH values favoring precipitation. Air stripping for CO2 removal increased pH from 8.57 to 9.21 within 3 hours, but did not significantly improve phosphorus removal efficiency. Combining FGD gypsum treatment with traditional chemical treatments using Ca(OH)2 or FeCl3 could achieve >99% phosphorus removal with reduced chemical costs. This study demonstrated that FGD gypsum is an effective calcium precipitant for phosphorus removal/recovery. These results can be used as a baseline for scale-up and development of a pilot scale, FGD gypsum-based phosphorus recovery system.
Yebo Li (Advisor)
Jay Martin (Committee Member)
Warren Dick (Committee Member)
127 p.
Agricultural Engineering; Alternative Energy; Environmental Engineering; Water Resource Management
Flue Gas Desulfurization Gypsum for the Removal, Flue Gas Desulfurization Gypsum as Recovery, Phosphorus from Anaerobic Digestion Effluent

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Citations

  • Khalaf, A. (2016). Evaluation of Flue Gas Desulfurization Gypsum as a Novel Precipitant for the Removal and Recovery of Phosphorus from Anaerobic Digestion Effluent [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480334876351851

    APA Style (7th edition)

  • Khalaf, Adam. Evaluation of Flue Gas Desulfurization Gypsum as a Novel Precipitant for the Removal and Recovery of Phosphorus from Anaerobic Digestion Effluent. 2016. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1480334876351851.

    MLA Style (8th edition)

  • Khalaf, Adam. "Evaluation of Flue Gas Desulfurization Gypsum as a Novel Precipitant for the Removal and Recovery of Phosphorus from Anaerobic Digestion Effluent." Master's thesis, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480334876351851

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.