Vivianite scaling in wastewater treatment plants: Occurrence, formation mechanisms and mitigation solutions.

The presence of soluble iron and phosphorus in wastewater sludge can lead to vivianite scaling. This problem is not often reported in literature, most likely due to the difficult identification and quantification of this mineral. It is usually present as a hard and blue deposit that can also be brown or black depending on its composition and location. From samples and information gathered in 14 wastewater treatment plants worldwide, it became clear that vivianite scaling is common and can cause operational issues. Vivianite scaling mainly occurred in 3 zones, for which formation hypotheses were discussed. Firstly, iron reduction seems to be the trigger for scaling in anaerobic zones like sludge pipes, mainly after sludge thickening. Secondly, pH increase was evaluated to be the major cause for the formation of a mixed scaling (a majority of oxidized vivianite with some iron hydroxides) around dewatering centrifuges of undigested sludge. Thirdly, the temperature dependence of vivianite solubility appears to be the driver for vivianite deposition in heat exchanger around mesophilic digesters (37 °C), while higher temperatures potentially aggravate the phenomenon, for instance in thermophilic digesters. Mitigation solutions like the use of buffer tanks or steam injections are discussed. Finally, best practices for safe mixing of sludges with each other are proposed, since poor admixing can contribute to scaling aggravation. The relevance of this study lays in the occurrence of ironphosphate scaling, while the use of iron coagulants will probably increase in the future to meet more stringent phosphorus discharge limits.

Full-scale increased iron dosage to stimulate the formation of vivianite and its recovery from digested sewage sludge.

The recovery of phosphorus from secondary sources like sewage sludge is essential in a world suffering from resources depletion. Recent studies have demonstrated that phosphorus can be magnetically recovered as vivianite (Fe(II)3(PO4)2∗8H2O) from the digested sludge (DS) of Waste Water Treatment Plants (WWTP) dosing iron. To study the production of vivianite in digested sludge, the quantity of Fe dosed at the WWTP of Nieuwveer (The Netherlands) was increased (from 0.83 to 1.53 kg Fe/kg P in the influent), and the possible benefits for the functioning of the WWTP were evaluated. Higher Fe dosing is not only relevant for P-recovery, but also for maximal recovery of organics from influent for e.g. biogas production. The share of phosphorus present as vivianite in the DS increased from 20% to 50% after the increase in Fe dosing, making more phosphorus available for future magnetic recovery. This increase was directly proportional to the increase of Fe in DS, suggesting that vivianite could be favored not only thermodynamically, but also kinetically. Interestingly, analyses suggest that several types of vivianite are formed in the WWTP, and could differ in their purity, oxidation state or crystallinity. These differences could have an impact on the subsequent magnetic separation. Following the Fe dosing increase, P in the effluent and H2S in the biogas both decreased: 1.28 to 0.42 ppm for P and 26 to 8 ppm for H2S. No negative impact on the nitrogen removal, biogas production, COD removal or dewaterability was observed. Since quantification of vivianite in DS is complicated, previous studies were reviewed and we proposed a more accurate Mössbauer spectroscopy analysis and fitting for sludge samples. This study is important from a P recovery point of view, but also because iron addition can play a crucial role in future resource recovery wastewater facilities.

Sulfide induced phosphate release from iron phosphates and its potential for phosphate recovery.

Sulfide is frequently suggested as a tool to release and recover phosphate from iron phosphate rich waste streams, such as sewage sludge, although systematic studies on mechanisms and efficiencies are missing. Batch experiments were conducted with different synthetic iron phosphates (purchased Fe(III)P, Fe(III)P synthesized in the lab and vivianite, Fe(II)3(PO4)2*8H2O), various sewage sludges (with different molar Fe:P ratios) and sewage sludge ash. When sulfide was added to synthetic iron phosphates (molar Fe:S = 1), phosphate release was completed within 1 h with a maximum release of 92% (vivianite), 60% (purchased Fe(III)P) and 76% (synthesized Fe(III)P). In the latter experiment, rebinding of phosphate to Fe(II) decreased net phosphate release to 56%. Prior to the re-precipitation, phosphate release was very efficient (P released/S input) because it was driven by Fe(III) reduction and not by, more sulfide demanding, FeSx formation. This was confirmed in low dose sulfide experiments without significant FeSx formation. Phosphate release from vivianite was very efficient because sulfide reacts directly (1:1) with Fe(II) to form FeSx, without Fe(III) reduction. At the same time vivianite-Fe(II) is as efficient as Fe(III) in binding phosphate. From digested sewage sludge, sulfide dissolved maximally 30% of all phosphate, from the sludge with the highest iron content which was not as high as suggested in earlier studies. Sludge dewaterability (capillary suction test, 0.13 ± 0.015 g2(s2m4)-1) dropped significantly after sulfide addition (0.06 ± 0.004 g2(s2m4)-1). Insignificant net phosphate release (1.5%) was observed from sewage sludge ash. Overall, sulfide can be a useful tool to release and recover phosphate bound to iron from sewage sludge. Drawbacks -deterioration of the dewaterability and a net phosphate release that is lower than expected-need to be investigated.

Vivianite as the main phosphate mineral in digested sewage sludge and its role for phosphate recovery.

Phosphate recovery from sewage sludge is essential in a circular economy. Currently, the main focus in centralized municipal wastewater treatment plants (MWTPs) lies on struvite recovery routes, land application of sludge or on technologies that rely on sludge incineration. These routes have several disadvantages. Our study shows that the mineral vivianite, Fe2(PO4)3 × 8H2O, is present in digested sludge and can be the major form of phosphate in the sludge. Thus, we suggest vivianite can be the nucleus for alternative phosphate recovery options. Excess and digested sewage sludge was sampled from full-scale MWTPs and analysed using x-ray diffraction (XRD), conventional scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), environmental SEM-EDX (eSEM-EDX) and Mössbauer spectroscopy. Vivianite was observed in all plants where iron was used for phosphate removal. In excess sludge before the anaerobic digestion, ferrous iron dominated the iron pool (≥50%) as shown by Mössbauer spectroscopy. XRD and Mössbauer spectroscopy showed no clear correlation between vivianite bound phosphate versus the iron content in excess sludge. In digested sludge, ferrous iron was the dominant iron form (>85%). Phosphate bound in vivianite increased with the iron content of the digested sludge but levelled off at high iron levels. 70-90% of all phosphate was bound in vivianite in the sludge with the highest iron content (molar Fe:P = 2.5). The quantification of vivianite was difficult and bears some uncertainty probably because of the presence of impure vivianite as indicated by SEM-EDX. eSEM-EDX indicates that the vivianite occurs as relatively small (20-100 µm) but free particles. We envisage very efficient phosphate recovery technologies that separate these particles based on their magnetic properties from the complex sludge matrix.

Vivianite as an important iron phosphate precipitate in sewage treatment plants.

Iron is an important element for modern sewage treatment, inter alia to remove phosphorus from sewage. However, phosphorus recovery from iron phosphorus containing sewage sludge, without incineration, is not yet economical. We believe, increasing the knowledge about iron-phosphorus speciation in sewage sludge can help to identify new routes for phosphorus recovery. Surplus and digested sludge of two sewage treatment plants was investigated. The plants relied either solely on iron based phosphorus removal or on biological phosphorus removal supported by iron dosing. Mössbauer spectroscopy showed that vivianite and pyrite were the dominating iron compounds in the surplus and anaerobically digested sludge solids in both plants. Mössbauer spectroscopy and XRD suggested that vivianite bound phosphorus made up between 10 and 30% (in the plant relying mainly on biological removal) and between 40 and 50% of total phosphorus (in the plant that relies on iron based phosphorus removal). Furthermore, Mössbauer spectroscopy indicated that none of the samples contained a significant amount of Fe(III), even though aerated treatment stages existed and although besides Fe(II) also Fe(III) was dosed. We hypothesize that chemical/microbial Fe(III) reduction in the treatment lines is relatively quick and triggers vivianite formation. Once formed, vivianite may endure oxygenated treatment zones due to slow oxidation kinetics and due to oxygen diffusion limitations into sludge flocs. These results indicate that vivianite is the major iron phosphorus compound in sewage treatment plants with moderate iron dosing. We hypothesize that vivianite is dominating in most plants where iron is dosed for phosphorus removal which could offer new routes for phosphorus recovery.

Influence of aromatic sulfonation on the geometry of [2.2]paracyclophane: crystal structures of one sulfonate, one disulfonic anhydride and five disulfonimides.

The crystal structures of potassium [2.2]paracyclophane-4-sulfonate (1), [2.2]paracyclophane-4,15-disulfonic anhydride (2), [2.2]paracyclophane-4,15-disulfonimide (3), N-n-propyl-[2.2]paracyclophane-4,15-disulfonimide (4), N-isopropyl-[2.2]paracyclophane-4,15-disulfonimide (5), N-cyclopropyl-[2.2]paracyclophane-4,15-disulfonimide (6) and N-phenyl-[2.2]paracyclophane-4,15-disulfonimide (7) were established by single-crystal X-ray diffraction. The structural changes caused by sulfonation are discussed with respect to the parent [2.2]paracyclophane (tricyclo[8.2.2.2(4,7)]hexadeca-4,6,10,12,13,15-hexaene). The main features are a change in the non-bonding distances between the para-phenylene rings and a rotation of these rings with respect to the molecular symmetry plane. The rings are rotated away from each other in the case of monosulfonation (1), but are rotated in the opposite way in the case of the disulfonic anhydride (2) or the disulfonimide compounds (3)-(7). The results are also discussed in terms of the parameters proposed by Keehn [(1983), Organic Chemistry, A Series of Monographs 45, edited by P. H. Keehn & S. M. Rosenfeld, Vol. 1, pp. 69-238. New York: Academic Press] showing that (bonded and non-bonded) angles involving the para-phenylene rings are mainly affected.

Structure determination of two metal-organic complexes from high-resolution synchrotron powder diffraction data.

The crystal structures of [1,2-bis(2,6-diisopropylphenylimino)acenaphthene-N,N']carbonylchlororhodium(I) (1) and [N,N'-ethylene-bis(3-methylsalicylideneiminato)-O,N,N',O'](tetrahydrofurfuryl)-cobalt(II) (2) have been determined from high-resolution synchrotron X-ray powder diffraction data. Compound 1 is the first neutral Rh complex, in contrast with findings in the literature, containing a bidentate nitrogen ligand, and compound 2 is the first three-dimensional structure of a (five-coordinated) tetrahydrofurfurylcobalt(III) complex. Grid-search and Rietveld refinement have been used to determine and refine the structures, respectively. Crystals of 1 are orthorhombic, space group Pbca, Z = 8, with cell parameters a = 21.729 (2), b = 27.376 (3), c = 11.580 (1) A. Crystals of 2 are monoclinic, space group P2(1)/n, Z = 4, a = 16.6701 (6), b = 9.4170 (4), c = 13.7088 (7) A and beta = 96.520 (3) degrees. Chemical diagrams for the two compounds are given. Soft restraints were applied during Rietveld refinement; for 1 converging to R(p) = 8.4%, R(w) = 11.0%, GoF = 2.3, and for 2 converging to R(p) = 8.5%, R(w) = 11.4%, GoF = 7.6.

Structure determination of the [Fe(teec)(6)](BF(4))(2) metal complex from laboratory and synchrotron X-ray powder diffraction data with grid-search techniques.

The structure of the coordination compound [Fe(teec)(6)](BF(4))(2), hexa[1-(2-chloroethyl)tetrazole]iron(II) di(borotetrafluoride), has been determined using the grid-search techniques of the program suite MRIA. A Guinier-camera data set was used to determine the unit cell, the space group and to position the initial model. A high-resolution synchrotron powder data set was used to position a more detailed model using torsion-angle variation and to refine the structure leading to Rp = 0.0689, Rw = 0.0805 and GoF = 1.38. The crystal structure at room temperature shows the existence of two symmetry-equivalent iron(II) ions in the high-spin state.

Intramolecular photochemical dioxenone-alkene [2 + 2] cycloadditions as an approach to the bicyclo[2.1.1]hexane moiety of solanoeclepin A.

A synthesis of the bicyclo[2.1.1]hexane substructure of solanoeclepin A (1), the most active natural hatching agent of potato cyst nematodes, was approached via an intramolecular [2 + 2] photocycloaddition. Aldehyde 12 containing the dioxenone chromophore served as a useful starting material, allowing the synthesis of a variety of photocycloaddition substrates via Grignard addition or via a Nozaki-Hiyama-Kishi reaction. Photolysis of the unsubstituted alkene 14 led to the expected crossed cycloadduct bicyclo[2.1.1]hexane 15 according to the so-called rule of five. However, several functionalized alkenes 18, 20, and 31 exhibited a complete reversal of cycloaddition regioselectivity, providing straight cycloadducts bicyclo[2.2.0]hexanes 21-26 and 4, respectively. Their structures were proved by a combination of extensive NMR measurements, X-ray analyses, and subsequent retro-aldol reactions. The latter de Mayo process allowed the formation of spiro-[3.5]nonane 35 and spiro[3.4]octane 36 as well as the cyclobutanes 37 and 38. Finally, the cyclization of the more rigid lactone precursor 28 occurred in high yield in the desired fashion with complete regio- and stereoselectivity to give 3 containing the core bicyclo[2.1.1]hexane skeleton of the natural product.

An X-ray study of the effect of the bite angle of chelating ligands on the geometry of palladium(allyl) complexes: implications for the regioselectivity in the allylic alkylation.

X-ray crystal structures of a series of cationic (P-P)palladium(1,1-(CH(3))(2)C(3)H(3)) complexes (P-P = dppe (1,2-bis(diphenylphosphino)ethane), dppf (1,1'-bis(diphenylphosphino)ferrocene), and DPEphos (2,2'-bis(diphenylphosphino)diphenyl ether)) and the (Xantphos)Pd(C(3)H(5))BF(4) (Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) complex have been determined. In the solid state structure, the phenyl rings of the ligand are oriented in the direction of the nonsymmetrically bound [1,1-(CH(3))(2)C(3)H(3)] moiety. An increase of the bite angle of the chelating ligand results in an increase of the cone angle. In complexes containing ligands having a large cone angle, the distances between the phenyl rings and the allyl moiety become small, resulting in a distortion of the symmetry of the palladium-allyl bond. In solution, two types of dynamic exchange have been observed, the pi-sigma rearrangement and the apparent rotation of the allyl moiety. At the same time, the folded structure of the ligand changes from an endo to an exo orientation or vice versa. The regioselectivity in the palladium-catalyzed allylic alkylation of 3-methyl-but-2-enyl acetate is determined by the cone angle of the bidentate phosphine ligand. Nucleophilic attack by a malonate anion takes place preferentially at the allylic carbon atom having the largest distance to palladium. Ligands with a larger cone angle direct the regioselectivity to the formation of the branched product, from 8% for dppe (1) to 61% found for Xantphos (6). The influence of the cone angle on the regioselectivity has been assigned to a sterically induced electronic effect.

Structure determination of two intercalated compounds VOPO4.(CH2)4O and VOPO4.OH-(CH2)2-O-(CH2)2-OH; synchrotron powder diffraction and molecular modelling.

The crystal structures of two intercalated compounds have been determined using a combination of synchrotron powder diffraction and molecular mechanics simulations: (1) vanadyl phosphate intercalated with tetrahydrofuran, VOPO(4).(CH(2))(4)O, and (2) vanadyl phosphate intercalated with diethylene glycol, VOPO(4).HO(CH(2))(2)O(CH(2))(2)OH. Both intercalates preserve the tetragonal space group P4/n, as found in the host structure VOPO(4).2H(2)O. (1): a = 6.208, c = 8.930 A, Z = 2, D(x) = 2.51 g cm(-3); (2): a = 6.223, c = 11.417 A, Z = 2, D(x) = 2.66 g cm(-3). Both intercalates exhibit the same type of orientational disorder in the arrangement of guest molecules, as observed in the same host compound intercalated with water. These two intercalates also exhibit, rather surprisingly, perfect ordering in layer stacking without the displacement disorder, characteristic of many intercalated layered structures. Thanks to this regularity in the arrangement of guests and layers, synchrotron powder diffraction could be used in the present structure determination. The present results also enabled the analysis of the effect of geometrical parameters characterizing the mutual host-guest complementarity and the effect of host-guest and guest-guest interaction on the crystal packing of intercalates.

Structure of CnCn+2Cn-type (n = even) beta'-triacylglycerols.

The crystal structures of the beta' phase of CLC (1, 3-didecanoyl-2-dodecanoylglycerol) and MPM (1, 3-ditetradecanoyl-2-hexadecanoylglycerol) have been determined from single-crystal X-ray diffraction and high-resolution X-ray powder diffraction data, respectively. Both these crystals are orthorhombic with space group Iba2 and Z = 8. The unit-cell parameters of beta'-CLC are a = 57.368 (6), b = 22.783 (2) and c = 5.6945 (6) A and the final R value is 0.175. The unit-cell parameters of beta'-MPM are a = 76.21 (4), b = 22.63 (1) and c = 5.673 (2) A and the final R(p) value is 0.057. Both the beta'-CLC and beta'-MPM molecules are crystallized in a chair conformation, having a bend at the glycerol moiety. The zigzag planes of the acyl chains are orthogonally packed, as is typical for a beta' phase. Furthermore, unit-cell parameters of some other members of the C(n)C(n+2)C(n)-type triacylglycerol series have been refined on their high-resolution X-ray powder diffraction pattern. Finally, the crystal structures are compared with the currently known structures and models of triacylglycerols.

New chiral phosphine-phosphite ligands in the enantioselective palladium-catalyzed allylic alkylation

A series of chiral phosphine-phosphite ligands 1-6 have been synthesized and used in the enantioselective palladium-catalyzed reaction of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. Ligands 1a, 2, 3, 5a, 6a, and 6b have been synthesized starting from racemic tert-butylphenylphosphinoborane. The use of dynamically resolved Li phosphide (-)-sparteine provided the optically pure ligands. Crystals of the allylpalladium (6a) complex were obtained, suitable for X-ray crystal structure determination. The X-ray crystal structure of the allylpalladium (6a) complex revealed a longer palladium-carbon bond distance trans to the phosphine moiety indicating that the attack of the nucleophile takes place at the carbon trans to the phosphine moiety. This was confirmed by the fact that the phosphine moiety did not affect the enantioselectivity directly. Under mild reaction conditions, enantioselectivities up to 83% were obtained (25 degrees C) with ligand 1e. Systematic variation of the ligand bridge and the phosphite moiety showed that the configuration of the product is controlled by the atropisomerism of the biphenyl substituent at the phosphite moiety. The conformation of the biphenyl group, in turn, is controlled by the substituent at the chiral carbon in the bridge. Ligands with large bite angles yielded higher enantioselectivities.

Characterization of the binding site of the histamine H3 receptor. 1. Various approaches to the synthesis of 2-(1H-imidazol-4-yl)cyclopropylamine and histaminergic activity of (1R,2R)- and (1S,2S)-2-(1H-imidazol-4-yl)-cyclopropylamine.

Various approaches to the synthesis of all four stereoisomers of 2-(1H-imidazol-4-yl)cyclopropylamine (cyclopropylhistamine) are described. The rapid and convenient synthesis and resolution of trans-cyclopropylhistamine is reported. The absolute configuration of its enantiomers was determined by single-crystal X-ray crystallographic analysis. The distinct trans-cyclopropylhistamine enantiomers were tested for their activity and affinity on the histamine H3 receptor. (1S,2S)-Cyclopropylhistamine (VUF 5297) acts as an agonist both on the rat cortex (pD2 = 7.1; alpha = 0.75) and on guinea pig jejunum (pD2 = 6.6; alpha = 0.75). Its enantiomer, (1R, 2R)-cyclopropylhistamine (VUF 5296), is about 1 order of magnitude less active. Both enantiomers show weak activity on H1 and H2 receptors. All synthetic attempts to cis-cyclopropylhistamine were unsuccessful. Nevertheless, the results of this study provide an ideal template for molecular modeling studies of histamine H3 receptor ligands.

Conformational analysis of 20-keto steroids. Single-crystal X-ray structure analysis of 16 alpha,17-epoxy-4-pregnene-3,20-dione.

The structure of 16 alpha,17-epoxy-4-pregnene-3,20-dione was determined. The 20-carbonyl group eclipses the C(13)-C(17) bond. No direct correlation between the observed structure and its progestational activity could be inferred from our investigation.