Impact of flue gas desulfurization gypsum application on water quality in a coastal plain soil

Positive and negative impacts of flue gas desulfurization (FGD) gypsum on water quality

Flue gas desulfurization (FGD) gypsum, a by-product of carbon-based energy sources, has typically been incorporated as a component of concrete mixes and wallboard and beneficially used as an agricultural amendment to enhance terrestrial crop production and improve the quality of runoff. These various uses for the by-product aid in reducing the amount that is ultimately landfilled. Limited studies have investigated its benefits when used directly in aquatic settings, such as ponds and lakes, to increase hardness and potentially mitigate eutrophication. A 36-day field mesocosm experiment tested a larger range of FGD gypsum concentrations (500-2000 mg/L) than those previously tested in the literature to investigate its desired and potentially undesired impacts on water quality, including the algal community. High FGD gypsum concentrations, 1000 and 2000 mg/L, were found to have more undesired impacts than the 500 mg/L treatment, including an initial spike in cyanobacteria, a decrease in total zooplankton abundance, and an increase in certain trace metals in the highest treatment. Ultimately, the 500 mg/L FGD gypsum treatment was found to have fewer undesired impacts while still resulting in significant desired effects, including those on hardness and pH, as well as moderate reductions in algal abundance. This experiment provides a better understanding of the effects of FGD gypsum when directly used in an aquatic setting, determines an optimal dose for future field experiments, and helps provide the groundwork for developing an upper threshold on FGD gypsum so as to not have the negative effects outweigh the positive.

Enhancing dissolved inorganic phosphorous capture by gypsum-incorporated biochar: Synergic performance and mechanisms

Excess nutrients, such as phosphorus (P), in watersheds jeopardize water quality and trigger harmful algal blooms. Using phosphorus sorption material (PSM) to capture P from wastewater and agricultural runoff can help recover nutrients and prevent their water pollution. In this study, a novel designer biochar was generated by pyrolyzing woody biomass pretreated with a flue gas desulfurization gypsum. The removal of dissolved inorganic phosphorus (DIP) by the gypsum-incorporated designer biochar was more efficient than the gypsum, suggesting the pretreatment of biomass with the gypsum results in a synergic effect on enhancing DIP capture. The maximum P adsorption capacity of the designer biochar was more than 200 mg g-1 , which is one order of magnitude greater than that of the gypsum. This result clearly showed that the designer biochar is a better PSM to capture DIP from nutrient-contaminated water compared to the gypsum. Post-sorption characterization indicated that the sorption of DIP by the gypsum-incorporated biochar involves multiple mechanisms. The precipitation reactions of calcium (Ca) cations and P anions to form CaHPO4 and Ca3 (PO4 )2 precipitates on the highly alkaline surface of the designer biochar were identified as a main mechanism. By contrast, CaHPO4 ·2H2 O is the only precipitated product for DIP sorption by the gypsum. In addition, the initial solution pH and the coexisting bicarbonate had less effects on the DIP removal by the designer biochar in comparison with the gypsum, which further confirms that the former is an excellent PSM to capture DIP from a variety of aquatic media.

Effectiveness of flue gas desulfurization gypsum in reducing phosphorus solubility in poultry litter when applied as an in-house amendment

Phosphorus (P) runoff from agricultural lands receiving poultry litter (PL) poses a major environmental challenge. Application of flue-gas-desulfurization (FGD)-gypsum produced from coal power plants in agricultural lands has shown promise to reduce P losses. However, no information is available about the effectiveness of FGD-gypsum addition in reducing P solubility when applied as an in-house amendment. Hence, the objectives of this study were to understand a) effectiveness of FGD-gypsum as a litter amendment in reducing P loss risk; and b) how FGD-gypsum amendment in PL alters the distribution of P forms. Broiler chickens were raised for five flocks in seven individual litter treatments replicated four times in a randomized complete block design. Based on the FGD-gypsum addition, the PL treatments were broadly classified as FGD-gypsum treated and untreated. Toxic metal concentrations were analyzed in FGD-gypsum as well as the treatments. Sequential water extractions were performed to understand P solubility. Litter P fractionation was performed to identify bioavailable P (Water-P), labile P (NaHCO3-P), aluminum/iron chemisorbed P (NaOH-P), and mineral occluded P (HCl-P). Results indicated significantly higher soluble P in all untreated than in all FGD-gypsum treated litters in the initial water extraction. The FGD-gypsum treated litters reduced soluble P by 58 to 67% in the 1st water extraction compared to untreated litters. Fractionation study revealed lower proportion of Water-P and higher proportion of NaHCO3-P and HCl-P in all FGD-gypsum treated than in untreated litters. This study suggests reuse of FGD-gypsum in broiler houses can help reduce P mobility without any toxic metals concerns.

Sorptive removal of phosphorus by flue gas desulfurization gypsum in batch and column systems

Phosphorus (P) over-loading is often a central topic due to its linkage to harmful algal blooms (HABs) and its importance in wastewater treatment that has fueled immediate remediation attempts to reduce P loading from point (e.g., wastewater) and nonpoint sources (e.g., fertilizers). Conventional remediation techniques (e.g., filtration) are often expensive, ineffective, and difficult to implement at large scales. The flue gas desulfurization (FGD) gypsum produced as an energy plant waste byproduct has recently been advocated as a physiochemical remediation strategy for P through sorptive removal. However, limited research is available on the practical applications of FGD gypsum for P removal from water. Herein, batch sorption experiments were performed to investigate the sorptive removal efficiency of P by FGD gypsum under environmentally relevant P concentrations (0.01-0.25 mM). In parallel, fixed-bed column experiments packed with FGD gypsum were performed using elevated P concentrations (0.1-1.0 mM) to understand the scalability of FGD gypsum for large-scale practical applications. During batch experiments, P sorption equilibrium was reached within 24 h that includes an initially fast step (via boundary layer diffusion), followed by a slow rate-determining step (via intraparticle diffusion). P sorption kinetics followed the pseudo second-order kinetics, indicating chemisorption. P sorption at equilibrium can be simulated by both the Freundlich and Langmuir sorption isotherms. The Langmuir sorption isotherm yielded a maximum sorption capacity (Q_max) of 36.1 mM kg^-1. The fixed-bed column experimental results showed that sorption rate depends on the applied flow rate, irrespective of the tested P concentrations. Our findings can be extrapolated to evaluate the feasibility and scalability of FGD gypsum in removing P to counteract P runoff and mitigate HABs and P-loaded wastewater.

Enhanced adsorption of phosphorus in soil by lanthanum-modified biochar: improving phosphorus retention and storage capacity

Use of soil adsorbent is an effective method for the promotion of phosphorus adsorption capacity of soil, though most of the soil adsorbents have weak phosphorus retention ability. Herein, we compared the traditional gypsum (GP) and zeolite (ZP) adsorbents to explore the phosphorus retention ability of lanthanum modified walnut shell biochar (La-BC) in soil. The results showed that with the increase of exogenous phosphorus concentration, the adsorption amount of phosphorus by adsorbents in soil increased at first and then tended to be stable. The maximum adsorption capacity of soil to phosphorus is gypsum, lanthanum-modified biochar > zeolite, and the addition of lanthanum-modified biochar can improve the adsorption capacity of soil to phosphorus, enhance the binding strength of soil and phosphorus, improve the ability of soil to store phosphorus, reducing phosphorus adsorption saturation, and is beneficial to control the leaching of soil phosphorus. FTIR and XRD analysis showed that the adsorption of phosphorus by each adsorbent in soil was mainly chemical precipitation. The response surface analysis showed that the adsorption performance of La-BC+S was the best when the concentration of exogenous phosphorus was 50.0 mg/L, pH was 6.47, and the reaction time was 436.98 min. This study provides a reference for soil adsorbents to hold phosphorus and reduce the risk of phosphorus leaching to avoid groundwater pollution.

Influence of Flue Gas Desulfurization Gypsum on Phosphorus Loss from a Horticultural Growth Medium

In response to agriculture’s contribution to surface water quality, considerable effort is being made to develop best management practices to reduce nutrient loss. To evaluate the efficacy of gypsum as a horticultural media amendment for controlling phosphorus (P) leaching, flue gas desulfurization (FGD) gypsum was added to a standard horticultural growth medium at 0, 2.5, 5, 10 or 15% (v/v). FGD gypsum was either mixed with the growing medium or placed at the bottom of the containers. A fast-release or a control-release fertilizer was top-dressed to containers. The greatest P leaching occurred with the fertilizer-only treatments (no gypsum). Dissolved reactive P (DRP) losses were highest on the initial day of measurement for the fast-release fertilizer and then decreased rapidly. There was a delayed release of DRP from the controlled-release fertilizer. Increasing rates of FGD gypsum addition resulted in decreasing DRP leaching concentration loss and load. The FGD gypsum decreased leachate DRP concentration loss by a maximum of 75%, with an average decrease of 46%. Mixing the FGD gypsum with the medium (an easier/less expensive means of incorporation) was most effective with the fast-release fertilizer. These preliminary results indicate that less gypsum may be needed to reduce P loss from fast-released fertilizer as opposed to control-release fertilizer. FGD gypsum remained effective in reducing DRP loss throughout the experiment.

Recent advances in flue gas desulfurization gypsum processes and applications - A review

Flue gas desulfurization gypsum (FGDG) is an industrial by-product generated during the flue gas desulfurization process in coal-fired power plants. Due to its abundance, chemical and physical properties, FGDG has been used in several beneficial applications. However, during the past decade, the rate of beneficially used FGDG has gradually decreased, while its production has drastically increased. The presence of hazardous elements such as arsenic, mercury, cadmium, lead, and selenium in FGDG has reduced its beneficial value. Nevertheless, due to the recent developments in flue gas desulfurization processes, the "modern" FGDG contains lesser amounts of these elements, thus increasing its beneficial value and appeal to be included in other products. Hence, there are novel and traditional FGDG applications in different reuse scenarios investigated recently that have been deemed to pose minimal environmental concern - these need to be better understood. This review summarizes beneficial FGDG applications that have been deemed to pose minimal environmental concern, emphasizing their principles, research gaps, and potential developments, with the aim of increasing the reuse rate of FGDG.

Inhibiting effects of flue gas desulfurization gypsum on soil phosphorus loss in Chongming Dongtan, southeastern China

To explore the possibility of using flue gas desulfurization gypsum (FGDG) for inhibiting phosphorus (P) loss due to agricultural runoff, a 3-year study was performed in the farmlands of Chongming Dongtan between 2012 and 2015. Five different quantities of FGDG were used to treat the soil, and the effects of different treatments on the characteristics of soil P and crop growth were investigated. The results showed that 2 years after application of FGDG, the soil density at a depth of 0-10 cm decreased by 4.35-7.97%, the porosity increased by 1.77-11.0%, and the topsoil permeability increased by 0.87-3.81 times. Although the use of FGDG did not change the total P concentration in the soil, it decreased the concentration of sodium bicarbonate extractable P in the soil. Compared to the control, the average extractable P concentration at depths of 0-10 cm, 10-20 cm, and 20-30 cm decreased by 22.0-46.1%, 26.9-40.5%, and 22.8-34.8%, respectively. The inorganic P in the soil increased as the amount of FGDG increased, and the increase was mainly as Ca-P in the forms Ca₂-P and Ca₁₀-P. The decrease in bicarbonate extractable P and increase in inorganic P in the soil did not affect the growth of the crops, and the biomass and output of the crops increased compared to the control. Therefore, FGDG can enhance soil P immobilization, thus reducing soluble P runoff from farm fields, and improving water quality in receiving lakes and rivers while maintaining P nutrition to the crops.

Reducing Water-Soluble Phosphorus in Soil through Flue Gas Desulfurization Gypsum Application: Year of Application Effects at Multiple Sites in Wisconsin

Phosphorus runoff from agricultural land to surface water bodies, such as the Great Lakes, is an important environmental concern. Soil amendments, such as gypsum, may alter the chemistry of the soil solution to reduce the amount of water-soluble P (WSP) available for loss to runoff, and as such, the NRCS now recommends gypsum application as a Conservation Practice Standard (Code 333) for improving water quality. Interest in gypsum use has also increased as availability has increased from production of flue gas desulfurization (FGD) gypsum at many coal-burning power plants throughout the United States. This study tested three rates of unincorporated, surface-broadcast FGD gypsum application at 23 field sites in Wisconsin. The optimal rate for reducing WSP concentration and the relationship between selected soil properties and the beneficial effect of FGD gypsum application were evaluated. The FGD gypsum reduced WSP ( < 0.0001), with a significant effect compared with the control at the lowest tested rate of 1120 kg ha at 5 of the 23 sites. Few other sites saw a significant benefit. Correlation indicated that sites showing a beneficial reduction of WSP from FGD gypsum application were those with greater soil test P ( = 0.0002) and lower cation exchange capacity ( = 0.0087) values.

Meta-Analysis of Gypsum Effects on Crop Yields and Chemistry of Soils, Plant Tissues, and Vadose Water at Various Research Sites in the USA

Gypsum has a long history as a soil amendment. Information on how flue gas desulfurization (FGD) gypsum affects soil, water, and plant properties across a range of climates and soils is lacking. We conducted a meta-analysis using data from 10 field sites in the United States (Alabama, Arkansas, Indiana, New Mexico, North Dakota, Ohio, and Wisconsin). Each site used three rates each of mined and FGD gypsums plus an untreated control treatment. Gypsum rates included a presumed optimal agronomic rate plus one rate lower and one rate higher than the optimal. Gypsum was applied once at the beginning of each study, and then data were collected for 2 to 3 yr. The meta-analyses used response ratios () calculated by dividing the treatment value by the control value for crop yield or for each measured element in plant, soil, and vadose water. These values were tested for their significance with values. Most values varied only slightly from 1.00. Gypsum significantly changed more values from 1.00 for vadose water than for soil or crop tissue in terms of numbers of elements affected (11 for water, 7 for soil, and 8 for crop tissue). The highest value for soil was 1.57 (Ca) which was similar for both mined and FGD gypsum, for crop tissue was 1.46 (Sr) for mined gypsum, and for vadose water was 4.22 (S) for FGD gypsum. The large increase in Ca and S is often a desired response to gypsum application. Lowest values occurred in crop tissue for Mg (0.89) with FGD gypsum and for Ni (0.92 or 0.93) with both gypsums. Although some sites showed crop yield responses to gypsum, the overall mean values for mined gypsum (0.987) and for FGD gypsum (1.00) were not significantly different from 1.00 in this short-term study.

Impact of Flue Gas Desulfurization Gypsum and Manure Application on Transfer of Potentially Toxic Elements to Plants, Soil, and Runoff

There are concerns regarding the fate of nutrients from surface application of animal manure. One approach to reduce losses of P is to treat manure with industrial byproducts such as flue gas desulfurization (FGD) gypsum. However, concerns regarding potentially toxic elements contributed to the environment have arisen based on previous element-rich forms of FGD gypsum that included fly ash, whereas "new" FGD gypsum without fly ash is much lower in contaminants. This study examined the impact of FGD gypsum application on soil, plants, and runoff when applied alone or with poultry litter (PL) to soil. The study consisted of a plant response study (four rates of FGD gypsum of 0, 2.2, 4.4, and 8.9 Mg ha and four rates of PL of 0, 4.4, 8.9, and 13.4 Mg ha) and a rainfall simulation study (3.4 Mg PL ha with four rates of FGD gypsum of 0, 2.2, 4.4, and 8.9 Mg ha and controls). Plant, soil, and runoff samples were analyzed for As, Ba, Be, Ca, Cd, Ba, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Sb, Se, Tl, V, and Zn. Results indicated that FGD gypsum application would not result in increased potentially toxic elements in plants, soil, or runoff. In addition, the application of FGD gypsum significantly reduced P, As, and Fe concentrations in runoff, indicating that FGD gypsum can reduce the negative impact of manure surface application on surface water degradation.

Metals in Soil and Runoff from a Piedmont Hay Field Amended with Broiler Litter and Flue Gas Desulfurization Gypsum

Flue gas desulfurization gypsum (FGDG) from coal-fired power plants is readily available for agricultural use in many US regions. Broiler litter (BL) provides plant available N, P, and K but can be a source of unwanted As, Cu, and Zn. As a source of Ca and S, FGDG can reduce losses of P and other elements in runoff from BL-amended areas. Rainfall simulation plots (2.0 m) were established on a Piedmont Cecil soil growing 'Coastal' bermudagrass ( L.) for hay. Accumulation and transport of As, Cu, Cd, Cr, Hg, Pb, and Zn were evaluated after annual BL applications (13.5 Mg ha) with four FGDG rates (0, 2.2, 4.5, 9.0 Mg ha) and two FGDG treatments (0 and 9 Mg ha) without BL. Runoff As concentrations were sixfold greater with BL than without ( ≤ 0.01) and were similar to BL with FGDG at 2.2, 4.5 or 9.0 Mg ha ( ≤ 0.10). Runoff concentrations of target elements did not increase where FGDG was applied alone. After three annual applications of FGDG and BL, soil concentrations of As, Cr, Pb, Hg, and Cu were well below levels of environmental concern. Our findings indicate that runoff losses of As from BL application are not reduced with FGDG but support other research indicating no identifiable environmental risks from FGDG beneficial use in agricultural systems.

Potential Adherence of Flue Gas Desulfurization Gypsum to Forage as a Consideration for Excessive Ingestion by Ruminants

Gypsum (calcium sulfate dihydrate, CaSO⋅2HO) has long been used to improve soils and crop production, and its use has recently been encouraged by the USDA-NRCS for soil conservation through a new Conservation Practice Standard: Code 333. However, there is concern regarding the adverse effects of excessive direct ingestion of sulfate in gypsum by ruminants. The standard requires ruminants to be removed from grazing after application until after a rainfall, but there has been no research documenting gypsum adherence to forage or the potential for rainfall to reduce gypsum adherence. A study was established to examine the adherence and persistence of gypsum on different forage species. Two forages (bermudagrass [ L.] and tall fescue [ Schreb.]) were examined after gypsum applications at rates of 0, 1, and 5 Mg ha. The forage was sampled immediately after application, 1 wk after application, after a 1.5-cm rain, and after a 3.3-cm rain. Immediately after gypsum application, more gypsum adhered to the tall fescue (27.9 g gypsum kg) compared with bermudagrass (8.6 g gypsum kg), likely due to differences in the leaf structure. This represents S concentrations of 0.16 and 0.52% for any grazing ruminants feeding exclusively on the bermudagrass and tall fescue pastures. On succeeding sampling dates, substantial amounts of gypsum persisted only on the wider-leaved tall fescue. With tall fescue, a difference in gypsum adherence could be observed after a 1.5-cm rain, but no significant difference was observed between the gypsum application and the control after an additional 3.3-cm rain. Results indicate that care should be observed with grazing after gypsum application, especially on wide-leaved forages. However, using application rates within normal agronomic beneficial use guidelines (NRCS standard 333), negative results from direct ingestion of gypsum are not likely if grazing is discontinued several weeks and until a rainfall event occurs.

Decreasing Phosphorus Loss in Tile-Drained Landscapes Using Flue Gas Desulfurization Gypsum

Elevated phosphorus (P) loading from agricultural nonpoint-source pollution continues to impair inland waterbodies throughout the world. The application of flue gas desulfurization (FGD) gypsum to agricultural fields has been suggested to decrease P loading because of its high calcium content and P sorbing potential. A before-after control-impact paired field experiment was used to examine the water quality effects of successive FGD gypsum applications (2.24 Mg ha; 1 ton acre each) to an Ohio field with high soil test P levels (>480 ppm Mehlich-3 P). Analysis of covariance was used to compare event discharge, dissolved reactive P (DRP), and total P (TP) concentrations and loadings in surface runoff and tile discharge between the baseline period (86 precipitation events) and Treatment Period 1 (42 precipitation events) and Treatment Period 2 (84 precipitation events). Results showed that, after the first application of FGD gypsum, event mean DRP and TP concentrations in treatment field tile water were significantly reduced by 21 and 10%, respectively, and DRP concentrations in surface runoff were significantly reduced by 14%; however, no significant reductions were noted in DRP or TP loading. After the second application, DRP and TP loads were significantly reduced in surface runoff (DRP, 41%; TP 40%), tile discharge (DRP, 35%; TP, 15%), and combined (surface + tile) discharge (DRP, 36%; TP, 38%). These findings indicate that surface application of FGD gypsum can be used as a tool to address elevated P concentrations and loadings in drainage waters.

Influence of Flue Gas Desulfurization Gypsum on Reducing Soluble Phosphorus in Successive Runoff Events from a Coastal Plain Bermudagrass Pasture

Controlling the threat that pastures intensively managed with poultry litter (PL) pose to accelerating eutrophication is a major issue in the southeastern United States. Gypsum (CaSO) has been identified as a promising management tool for ameliorating litter P losses to runoff. Thus, research was conducted to elucidate gypsum's residual effects on P losses from a bermudagrass ( L.) pasture. Runoff events (60 min) were created using rainfall simulations. Treatments consisted of applying four flue gas desulfurization (FGD) gypsum rates (0, 2.2, 4.4, and 8.9 Mg ha) to bermudagrass fertilized with 13.4 Mg ha PL plus a nonfertilized check (no litter or gypsum) and 8.9 Mg ha FGD gypsum only as controls. Rainfall simulations (∼ 85 mm h) were conducted immediately, 5 wk, and 6 mo (i.e., at the end of growing season) after PL application to determine gypsum's effectiveness at controlling P loss over successive runoff events. The greatest dissolved P (DP) in runoff occurred immediately after PL application. Gypsum effectively reduced cumulative DP concentration losses (54%) compared with PL alone in initial runoff events. Gypsum reduced DP concentrations in succeeding runoff events also regardless of timing, suggesting that its effect is persistent and will not diminish over a growing season. Generally, maximum DP reductions were achieved with 8.9 Mg ha. However, it was surmised from this study that optimal P reduction in a bermudagrass pasture can be achieved with 4.4 Mg ha. Information ascertained from this study may be useful in aiding land managers making prescriptions for management practices that reduce DP losses from agricultural fields.

Composting and gypsum amendment of broiler litter to reduce nutrient leaching loss

The effect of composted litter relative to fresh litter on leaching losses of nutrients has not been well documented. Fresh and composted broiler litter was surface-applied to bermudagrass (hay) [ (L.) Pers.] established in undisturbed soil columns based on N need of the grass in the presence or absence of flue gas desulfurization (FGD) gypsum to evaluate an approach to reduce broiler litter nutrient leaching potential. Columns were periodically leached and biomass was harvested during the 60-d experiment. Total N applied to bermudagrass from broiler litter was 320 kg ha. Gypsum was mixed with fresh and composted litter at the rate based on 20% of litter weight. For composted broiler litter, NO-N, P, K, Cu, and Zn contents in the leachate obtained from the first leaching event were 58, 50, 40, 32, and 38% less than fresh broiler litter, respectively. Significant decreases in NO-N (13%), P (53%), Cu (17%), and Zn (28%) in leachate were obtained when gypsum was mixed with fresh broiler litter. Fresh broiler litter and composted broiler litter applications increased bermudagrass growth compared with the control and gypsum significantly increased yields when mixed with broiler litter. Composted broiler litter application significantly increased N and organic C in the soil compared with fresh litter. Results demonstrate that coapplication of composted broiler litter with FGD gypsum provide the most effective management option for minimizing leaching losses of nutrients while sustaining crop productivity.

Sustainable Uses of FGD Gypsum in Agricultural Systems: Introduction

Interest in using gypsum as a management tool to improve crop yields and soil and water quality has recently increased. Abundant supply and availability of flue gas desulfurization (FGD) gypsum, a by-product of scrubbing sulfur from combustion gases at coal-fired power plants, in major agricultural producing regions within the last two decades has attributed to this interest. Currently, published data on the long-term sustainability of FGD gypsum use in agricultural systems is limited. This has led to organization of the American Society of Agronomy's Community "By-product Gypsum Uses in Agriculture" and a special collection of nine technical research articles on various issues related to FGD gypsum uses in agricultural systems. A brief review of FGD gypsum, rationale for the special collection, overviews of articles, knowledge gaps, and future research directions are presented in this introductory paper. The nine articles are focused in three general areas: (i) mercury and other trace element impacts, (ii) water quality impacts, and (iii) agronomic responses and soil physical changes. While this is not an exhaustive review of the topic, results indicate that FGD gypsum use in sustainable agricultural production systems is promising. The environmental impacts of FGD gypsum are mostly positive, with only a few negative results observed, even when applied at rates representing cumulative 80-year applications. Thus, FGD gypsum, if properly managed, seems to represent an important potential input into agricultural systems.