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 (Qmax) 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.

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.

Measurements of Soil Carbon by Neutron-Gamma Analysis in Static and Scanning Modes.

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of gamma rays created when neutrons interact with soil elements. The main parts of the INS system are a pulsed neutron generator, NaI(Tl) gamma detectors, split electronics to separate gamma spectra due to INS and thermo-neutron capture (TNC) processes, and software for gamma spectra acquisition and data processing. This method has several advantages over other methods in that it is a non-destructive in situ method that measures the average carbon content in large soil volumes, is negligibly impacted by local sharp changes in soil carbon, and can be used in stationary or scanning modes. The result of the INS method is the carbon content from a site with a footprint of ~2.5 - 3 m2 in the stationary regime, or the average carbon content of the traversed area in the scanning regime. The measurement range of the current INS system is >1.5 carbon weight % (standard deviation ± 0.3 w%) in the upper 10 cm soil layer for a 1 hmeasurement.

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.