Dean Hesterberg

Struvite precipitation in anaerobic swine lagoon liquid: effect of pH and Mg:P ratio and determination of rate constant

Because of increased concern about surface water eutrophication from nutrient-enriched agricultural runoff, many swine producers are encouraged to decrease application rates of waste-based P. Precipitation and subsequent removal of magnesium ammonium phosphate (MgNH(4)PO(4) x 6H(2)O), commonly known as struvite, is a promising mechanism for N and P removal from anaerobic swine lagoon effluent. The objectives of this research were to (i) quantify the effects of adjusting pH and Mg:P ratio on struvite precipitation and (ii) determine the rate constant pH effect for struvite precipitation in anaerobic swine lagoon liquid. Concentrations of PO(4)-P in liquid from two anaerobic swine lagoons were determined after 24 h of equilibration for a pH range of 7.5-9.5 and Mg:P ratios between 1:1 and 1.6:1. Struvite formation reduced the PO(4)-P concentration in the effluents to as low as 2 mgl(-1). Minimum concentrations of PO(4)-P occurred between pH 8.9 and 9.25 at all Mg:P ratios. Struvite precipitation decreased PO(4)-P concentrations by 85% within 20 min at pH 9.0 for an initial Mg:P ratio of 1.2:1. The rate of PO(4)-P decrease was described by a first-order kinetic model, with rate constants of 3.7, 7.9, and 12.3 h(-1) at pH 8.4, 8.7 and 9.0 respectively. Our results indicate that induced struvite formation is a technically feasible method to remove N and P from swine lagoon liquid and it may allow swine producers to recover nutrients for off-farm sale.

Biogeochemical cycles and processes leading to changes in mobility of chemicals in soils

Abstract There is a general lack of long-term field research showing the environmental fate of soil contaminants after agricultural land is converted to other uses. One concern is that long-term changes in soil properties induced by an alternative land use might cause a non-linear increase in the solubility and mobility of soil chemical contaminants. If a fairly rapid increase in contaminant mobility is delayed for years, then this event may be difficult to predict and to control. To help provide insights to long-term fate of soil contaminants, this paper gives an overview of some factors controlling their solubility and mobility. Because of their indefinite residence time in soils, heavy metals and other trace elements input to agricultural lands with soil amendments may pose the greatest (albeit undetermined) long-term threat. Certain macronutrients, especially N and P, and organic pesticides may have shorter-term detrimental effects on water quality and the environment. Important properties influencing soil contaminant solubility and mobility are the type of contaminant (e.g., heavy metal cation, oxyanion, pesticide), soil matrix composition (e.g., mineralogy and organic matter content), soil heterogeneity, pH, redox potential, and variations in dissolved organic matter concentration. By understanding the mechanisms of contaminant binding in the soil in relation to these properties, the long-term fate of contaminants is more predictable.

Spectroscopic Approaches for Phosphorus Speciation in Soils and other Environmental Systems

In the past decades, environmental scientists have become increasingly involved in developing novel approaches for applying emerging spectroscopic techniques to complex environmental matrices. The objective of this review is to convey the most common chemical species of phosphorus reported for soils, sediments, model systems, and waste materials based on analyses by four spectroscopic techniques: X-ray absorption near-edge structure, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and Raman spectroscopy. Unique information is provided by each technique at a level of specificity that depends in part on matrix complexity. The X-ray absorption near-edge structure and nuclear magnetic resonance techniques reveal inorganic and organic P species in intact environmental matrices or in chemical extracts, whereas the Fourier transform infrared and Raman techniques can provide more specific bonding information about mineral or adsorbed P species in model analogs of matrix components. The most common P species in soils and sediments as indicated by spectroscopy are hydroxyapatite and octacalcium phosphate minerals, phosphate adsorbed on Fe- and Al-oxides, pyrophosphates and polyphosphates, phosphate mono- and di-esters, and phosphonates. Continued advancements in spectroscopic methods should improve speciation-based models of P mobilization and transformations in the environment.

Phosphate bonding on noncrystalline Al/Fe-hydroxide coprecipitates.

Poorly crystalline minerals have high sorption capacities for environmentally important chemical species, but molecular-level mechanisms of sorption on complex mineral assemblages remain largely unknown. We determined the distribution of orthophosphate (PO(4)) bonding between Al and Fe in relation to structural properties of Al/Fe-hydroxide coprecipitates. Phosphate was sorbed at concentrations between 0.042 and 0.162 mol P mol(-1) Al+Fe on coprecipitates containing 0, 20, 50, 75, or 100 mol % of metal as Al. Phosphorus XANES analyses showed preferential bonding of PO(4) for Al on coprecipitates with 20 and 50 mol % Al, and no preference for either metal at 75 mol % Al, consistent with X-ray photoelectron spectroscopy (XPS) analyses of near-surface metal distributions. Structural ordering and the Fe-hydroxide domain size in coprecipitates decreased with increasing Al proportion, as shown by X-ray diffraction (XRD) and Fe EXAFS analyses. Structural interactions in coprecipitates imparted unique PO(4) sorption properties compared with isolated Al- or Fe-hydroxide.

Chapter 11 - Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus

Agricultural management strives to optimize phosphorus (P) nutrition of plants with minimal environmental impacts. Although most research on soil phosphorus has applied macroscale approaches, synchrotron X-ray absorption spectroscopy (XAS) is emerging as a nondestructive analytical technique for identifying phosphorus species in soils. The objective of this chapter is to convey the complementary nature of knowledge about soil phosphorus chemistry derived from various macroscale research approaches and XAS. A wealth of knowledge exists on phosphate sorption properties of soils and minerals. A limited number of XAS studies on soils have shown that multiple species of phosphate coexist, with Ca-phosphate minerals and phosphate sorbed to Fe- and Al-oxides commonly found in both acidic and calcareous soils. XAS analysis of phosphate associated with model soil matrix components provides more specific information on molecular bonding mechanisms. Such studies help to explain the behavior of P in soils and model systems, and they support mechanistic models for predicting long-term transformations, lability, and mobility of soil P.

X-ray microspectroscopy and chemical reactions in soil microsites.

Soils provide long-term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid-phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earths surface. In the context of historical developments in soil analytical techniques, we describe applications of bulk-sample and spatially resolved synchrotron X-ray absorption spectroscopy (XAS) for characterizing chemical species of contaminants in soils, and for determining the uniqueness of trace-element reactivity in different soil microsites. Spatially resolved X-ray techniques provide opportunities for following chemical changes within soil microsites that serve as highly localized chemical micro- (or nano-)reactors of unique composition. An example of this microreactor concept is shown for micro-X-ray absorption near edge structure analysis of metal sulfide oxidation in a contaminated soil. One research challenge is to use information and principles developed from microscale soil chemistry for predicting macroscale and field-scale behavior of soil contaminants.

Comparison of Trees and Grasses for Rhizoremediation of Petroleum Hydrocarbons

Rhizoremediation of petroleum contaminants is a phytoremediation process that depends on interactions among plants, microbes, and soils. Trees and grasses are commonly used for phytoremediation, with trees typically being chosen for remediation of BTEX while grasses are more commonly used for remediation of PAHs and total petroleum hydrocarbons. The objective of this review was to compare the effectiveness of trees and grasses for rhizoremediation of hydrocarbons and address the advantages of each vegetation type. Grasses were more heavily represented in the literature and therefore demonstrated a wider range of effectiveness. However, the greater biomass and depth of tree roots may have greater potential for promoting environmental conditions that can improve rhizoremediation, such as increased metabolizable organic carbon, oxygen, and water. Overall, we found little difference between grasses and trees with respect to average reduction of hydrocarbons for studies that compared planted treatments with a control. Additional detailed investigations into plant attributes that most influence hydrocarbon degradation rates should provide data needed to determine the potential for rhizoremediation with trees or grasses for a given site and identify which plant characteristics are most important.

Mixed Anion (Phosphate/Oxalate) Bonding to Iron(III) Materials

A novel phosphate/oxalate inorganic-organic hybrid material has been prepared to elucidate synthesis and bonding characteristics of iron(III) with both phosphate and organic matter (OM). Such mixed anion bonding of inorganic oxyanions and OM to iron(III) and aluminum(III) in environmental systems has been proposed but not proven, mainly because of the complexity of natural geochemical matrices. The compound reported here with the molecular formula of [C(3)H(12)N(2)](2)[Fe(5)(C(2)O(4))(2)(H(x)PO(4))(8)] (I) was hydrothermally synthesized and characterized by single crystal X-ray diffraction and X-ray absorption spectroscopy (XAS). In this new structure, Fe-O octahedra and P-O tetrahedra are connected by corner-sharing to form a 2-D network in the a-b plane. Oxalate anions cross-link these Fe-P layers constructing a 3-D anionic framework. A diprotonated structure-directing template, DAP (1,3-diaminopropane), resides in the oxalate layer of the structure and offsets the negative charge of the anionic framework. Iron K-edge XANES spectra confirmed that the iron in I is Fe(III). The crystal structure of I is used to successfully fit its Fe K-edge EXAFS spectrum, which exhibits spectral signatures that unambiguously identify iron-phosphate and iron-OM bonding. Such molecular spectroscopic features will be invaluable for the evaluation of complex environmental systems. Furthermore, syntheses demonstrated the critical role of the templating amine to mediate whether or not the iron(III) is reduced by the organic acid.

Comparison of phosphate adsorption on clay minerals for soilless root media

Abstract The greenhouse industry aims to decrease phosphate discharge to help reduce eutrophication of surface waters, to reduce fertilizer consumption, and to maintain a more constant level of plant‐available phosphate. Iron and aluminum oxides and some aluminosilicate minerals are efficient sorbents for phosphate. The phosphate adsorption characteristics of synthetic hematite (α‐Fe2O3), goethite (α‐FeOOH), and allophane (Si3Al4O12 nH2O), and a commercial alumina (A12O3) were evaluated to determine their potential for reducing phosphate leaching from soilless root media. The pH dependence of phosphate adsorption and maximum adsorption capacities were determined by reacting each mineral with various levels of phosphate between pH 4.0 and 9.0 in a 10 mM potassium chloride (KCl) background solution. Adsorbed phosphate was determined by loss from solution. Adsorption envelopes (adsorbed phosphate versus pH) showed a decrease in phosphate adsorption with increasing pH, particularly for alumina and allophane, ...

Phosphorus dynamics in Swedish agricultural soils as influenced by fertilization and mineralogical properties: Insights gained from batch experiments and XANES spectroscopy

The soil chemistry of phosphorus (P) is important for understanding the processes governing plant availability as well as the risk of environmental losses of P. The objective of this research was to investigate both the speciation and the pH-dependent solubility patterns of P in clayey agricultural soils in relation to soil mineralogy and fertilization history. The study focused on soil samples from six fields that were subjected to different P fertilization regimes for periods of 45 to 57years. Soil P speciation was analyzed by P K-edge XANES spectroscopy and chemical fractionation, sorption isotherms were constructed, and dissolved P was measured as a function of pH. The XANES fitting results showed that organic P and P adsorbed to Fe and Al (hydr)oxides were common P constituents in all soils. Calcium phosphates were identified in five of six soil samples. The XANES results also indicated an increase in P adsorbed to Al and to a lesser extent Fe (hydr)oxides as a result of fertilization. Moreover, the fluorescence intensity from the P K-edge XANES analysis was most strongly correlated with HCl-digestible P (r=0.81***). Consistent with the XANES analysis, laboratory sorption isotherm models showed that the Freundlich sorption coefficient (KF) was most closely related to oxalate-extractable Al. Greater proportions of Ca phosphate in two of the heavily fertilized soils in combination with enhanced PO4 solubilization upon sample acidification indicated neoformation of Ca-phosphate precipitates. The results for the unfertilized soil samples generally showed a minimum in dissolved PO4 between pH6.5 and 7.5, with increases particularly at lower pH. This behavior can be explained either by the dissolution of Al-hydroxide-type sorbents or Ca phosphates at lower pH. In fertilized soils, there was no consistent trend in pH-dependent solubilization of P, with a complex relationship to solid-phase speciation. To conclude, inorganic P species changed most dynamically in agricultural clay soils over a period of several decades, and the role of pH in the solubilization of P depended mainly on P fertilization history and the content of reactive Ca phosphates.