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PubMed2001

Assesing the potential for struvite recovery at sewage treatment works.

Struvite in wastewater treatment plants was identified as early as 1939. Problems with struvite formation date back to the 1960s when it was noticed at the Hyperion treatment plant, Los Angeles. Operators at the plant noticed crystalline deposits on the underside of post digestion screens. The digested sludge stream was diluted and it was thought the problem was solved, until five years later when the normal gravity flow of digested sludge had decreased to such a stage that pumping was required. This paper reports the findings of a series of experiments undertaken to identify the potential of recovering struvite from sludge liquors. Seven sludge treatment works (STW) have been investigated including one detail. A number of the works has the potential to form over 100 mg l(-1) of struvite.

Hemostatics↗
PubMed2001

Application of integrated chemical-physical processes modelling to aeration treatment of anaerobic digester liquors.

A three phase (aqueous/solid/gas) mixed weak acid/base kinetic model developed by Musvoto et al. is applied to simulate the physical and chemical processes that occur on aeration of anaerobic digester liquors. Included in the model are the kinetic reactions for (i) weak acid/base dissocations (water, carbonate, ammonium, phosphate, and short-chain fatty acids), (ii) precipitation of struvite, newberyite, amorphous calcium phosphate, calcium and magnesium carbonate, (iii) ion pair formation and (iv) stripping of CO2 and NH3 gases. To generate data for model application, batch aeration tests were conducted on two anaerobic digester liquors from (i) a spent wine upflow anaerobic sludge bed (UASB) digester and (a) a sewage sludge anaerobic digester. In the batch tests pH, Ca, Mg, PO4-P, free and saline ammonia (FSA)H2CO3* alkalinity (from which inorganic carbon is calculated) were measured. After establishing from the lIterature values for (i) weak acid/base equilbrium constants (pKa), (ii) weak add/base kinetic rate constants (K(ra)), and (iii) ion pair stability constants (pK(ST)), and trial and error determination of (iv) mineral solubility products (pK(SP)) (within the range reported in the literature), (v) ion pair kinetic rate constants (K(rIP)), (vi) mineral precipitation rate constants (Kppt) and (vii) gas stripping rates (K(rG)), a good correlation between predicted and measured data was obtained for all the parameters for both liquors. The solubility product values for the minerals that precipitated were the same for both liquors and fall in the range of values quoted in the literature, but the specific precipitation rate constants of the minerals differed for the two liquors.

Bacteria, Anaerobic↗
PubMed2001

Recovery of ammonia as struvite from anaerobic digester effluents.

The effects of environmental conditions on ammonia removal as struvite (Magnesium ammonium phosphate, MAP) were studied in a laboratory scale batch reactor. MAP precipitation was carried out by adding phosphoric acid and magnesium source either as MgCl, or MgO. The effect of temperature, pH, MgN:P ratios were studied. Temperature did not significantly affect ammonia removal between 25-40 degrees C and over 90% removal was obtained. The effect of pH, however,was significant and highest removal was reached at pH 8.5-9.0. The various stoichiometric ratios of ammonium to Mg and P have been tested and slight excess of Mg and P found to be beneficial for higher recovery of ammonia as struvite. However further increase in Mg and P ratios did not result in further ammonia removal which is also costly for the practical application of the process. When MgO was used as M source,the ammonia recovery was 60-70% whereas the useMgCl2 has increased this figure up to 95%. In addition a two step purification process was developed to recover MAP crystals from impurities of the anaerobic digester. Firstly, precipitates were dissolved in acid and impurities were removed by centrifugation. The clarified supernatant was re-precipitated by adjusting its pH with caustic. It was shown that in the two steps process white MAP crystals could be obtained with over 85% recovery to be used for another applications. The economical analysis of the process has shown that ammonia in the digester effluents can be recovered at the cost of $7.5-8.0 kg(-1) NH4+-N. The rate of reaction is very fast and is completed almost in minutes. This simplifies the process design resulting in a smaller reaction vessel.

Ammonia↗
PubMed2001

Three years experience of operating and selling recovered struvite from full-scale plant.

The adoption of phosphorus removal at sewage treatment works (STW) creates two main problems. Firstly large amounts of sludge are produced and secondly the quantity of the effluent deteriorates due to the increase in the phosphorus load of the sidestream. Furthermore, these processes do not remove phosphorus in a form that would enable it to be recycled. Therefore in order to control these process difficulties and produce a recyclable phosphorus product a sidestream struvite crystallisation reactor was developed. The struvite was produced in a fluidised bed reactor using dewatered filtrate from anaerobic sludge digestion. Magnesium hydroxide was added in a magnesium to phosphate ratio of 1:1 and the pH was adjusted to between 8.2-8.8 with the addition of sodium hydroxide. A retention time of 10 days alowed the growth of pellets between 0.5-1.0 mm in size. The recovered struvite contained only minute traces of toxic substances and was sold to fertiliser companies for 27,000 yen tonne(-1). It is used to enhance existing fertilisers, which are widely used on paddy rice, vegetables and flowers.

Agriculture↗
PubMed2005

Auto-nucleation and crystal growth of struvite in a demonstrative fluidized bed reactor (FBR).

The experience of P removal by auto-nucleation and crystal growth of struvite (MAP) in a demonstrative plant is proposed. The demonstrative plant is located in a municipal wastewater treatment plant in northern Italy. The trials are a consequence of previous experimentation carried out using silica sand as seed material. Working in metastable conditions the auto-nucleation process is performed, and allows the control of the precipitation and the growth of MAP inside the FBR reactor. No scaling problems are observed in the collecting pipes. After the treatment of 650m3 of anaerobic supernatants, 0.28 tons of granulated crystalline MAP are produced. The chemical analysis shows its possible use in agriculture as fertilizer. Operative costs analysis confirms the SCP as a cheap way to remove and recover P from anaerobic supernatants.

Anaerobiosis↗
PubMed2006

Production and basic morphology of struvite crystals from a pilot-scale crystallization process.

A pilot-scale, struvite crystallization process was operated using anaerobic digester supernatants from two, full-scale, treatment plants as influent. It was found that the produced struvite crystals were easily separated from the process and were composed of very pure struvite (91.2 % to 94.1 % purity), with small amounts of calcium and carbonate, and traces of iron and aluminum. Most of the harvested struvite crystals, which were an aggregation of numerous fine crystals, were round, hard and larger than 1.5 mm in mean diameter. The crystal retention time in the reactor and the magnesium dosage in the supernatant appeared to have a significant effect on the crystal size, hardness and morphology.

Crystallization↗
PubMed2006

Exploring the determination of struvite solubility product from analytical results.

The solubility of magnesium ammonium phosphate hexahydrate (struvite) was determined in different water and wastewater solutions, by using the analytical results of the solubility tests conducted in the Environmental Engineering Lab at the University of British Columbia. The various factors affecting the struvite solubility such as pH, ionic strength and the temperature of the solutions were also studied in this project. The struvite solubility product values were found to vary significantly from one solution to another and over the range of the experimental conditions as well. For instance, the solubility product (Ksp) determined at 20 degrees C for anaerobic digester supernatant from the Penticton, B.C. Advanced Wastewater Treatment Plant, was found to vary from 8.46 x 10(-15) (pKsp =14.07) to 1.3 x 10(-13) (pKsp =12.89), over a pH range 6.45 to 8.97; while in the case of distilled water, with the same struvite crystals and at the identical temperature, it was found to vary from 5.21 x 10(-15) (pKsp=14.28) to 2.12 x 10(-13) (pKsp =12.67) over a pH range of 7.01 to 9.62. These results explore the possible reasons for widely varying struvite solubility reported in the literature. A possible correlation was also developed to correlate struvite solubility product with varying temperature. Furthermore, an attempt was made to establish a correlation between conductivity and calculated ionic strength of the solutions. A significant gap, between the values predicted by the correlation developed in this study and those predicted by the existing correlation, was also observed.

Bacteria, Anaerobic↗
PubMed2000

Stabilization and solidification of metal-laden wastes by compaction and magnesium phosphate-based binder.

Bench-scale and full-scale investigations of waste stabilization and volume reduction were conducted using spiked soil and ash wastes containing heavy metals such as Cd, Cr, Pb, Ni, and Hg. The waste streams were stabilized and solidified using chemically bonded phosphate ceramic (CBPC) binder, and then compacted by either uniaxial or harmonic press for volume reduction. The physical properties of the final waste forms were determined by measuring volume reduction, density, porosity, and compressive strength. The leachability of heavy metals in the final waste forms was determined by a toxicity characteristic leaching procedure (TCLP) test and a 90-day immersion test (ANS 16.1). The structural composition and nature of waste forms were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. CBPC binder and compaction can achieve 80-wt% waste loading and 39-47% reduction in waste volume. Compressive strength of final waste forms ranged from 1500 to 2000 psi. TCLP testing of waste forms showed that all heavy metals except Hg passed the TCLP limits using the phosphate-based binder. When Na2S was added to the binder, the waste forms also passed TCLP limits for Hg. Long-term leachability resistance of the final waste forms was achieved for all metals in both soil and ash wastes, and the leachability index was approximately 14. XRD patterns of waste forms indicated vermiculite in the ash waste was chemically incorporated into the CBPC matrix. SEM showed that waste forms are layered when compacted by uniaxial press and are homogeneous when compacted by harmonic press.

Hazardous Waste↗
PubMed2004

Accuracy of bladder stone detection using abdominal x-ray after spinal cord injury.

BACKGROUND: Bladder calculi are a common problem in those with spinal cord injury (SCI). Detection is important to prevent complications. OBJECTIVE: To determine the accuracy of bladder stone detection by abdominal x-rays. METHODS: X-ray reports from individuals with SCI with known bladder stones detected by cystoscopy were reviewed. MAIN OUTCOME MEASURES: X-ray reports noted the presence or absence of bladder stones. The stone variables evaluated were stone composition (crystallographic analysis), widest dimension of the largest stone (during cystoscopy), and the total volume (cm3) of the stone mass removed. RESULTS: Sixty-two consecutive x-ray reports from individuals with bladder stones were reviewed. The majority of stones were calcium phosphate (46.8%) or struvite (26.7%). Regarding stone composition, the detection by x-ray was 28.6% for struvite stones and 41.9% for calcium phosphate stones. Regarding diameter of largest stone, the detection by x-ray was 14% for stones < 0.5 cm, 0% for stones 0.5 cm to 0.9 cm, 33% for stones 1.0 cm to 1.49 cm, 33% for stones 1.5 cm to 1.9 cm, and 54% for stones > or = 2.0 cm. Regarding total volume of stones, the detection by x-ray was 0% for volumes < 0.2 cm3, 33% for volumes 0.2 cm3 to 0.39 cm3, 60% for volumes 0.40 cm3 to 0.59 cm3, 40% for volumes of 0.60 cm3 to 0.79 cm3, 0% for stones from 0.8 cm3 to 0.99 cm3, and 57% for volumes > or = 1.0 cm3. Overall, 13/62 (20.97%) of stones found during cystoscopy were detected by the x-ray. CONCLUSION: Abdominal x-ray is not a reliable method to detect bladder stones in individuals with SCI.

Adult↗
PubMed1995

Purification of chlorpromazine-sensitive GTPase from rat cerebral cortex.

The chlorpromazine-sensitive GTPase from the cell membrane of rat cerebral cortex was purified to homogenity by using DEAE Bio-Gel A agarose, hydroxyapatite and heparin agarose chromatography. The purified chlorpromazine-sensitive GTPase was purified 370-fold to obtain a final specific activity of 40 mumol GTP hydrolyzed2min/mg protein. The purified enzyme was inhibited by chlorpromazine but not by compound 48/80. Magnesium was required for its activity instead of calcium. The purified enzyme had an apparent pH optimum of 8.0, and molecular weight was estimated to be 58,000.

Animals↗
PubMed1995

A practical approach to nephrolithiasis.

Detailed metabolic evaluation and prophylaxis for all patients presenting with a first renal stone seems inappropriate. The crucial clinical problem lies in predicting which patients are likely to have a recurrence. Stone composition is an important guide for the physician's decisions concerning investigation and a rational choice of treatment.

Calcium↗
PubMed2004

Performance of magnesium ammonium phosphate precipitation and its effect on biological treatability of leather tanning industry wastewaters.

Leather tanning industry is one of the several industries discharging significant amount of nitrogen. Magnesium ammonium phosphate (MAP) precipitation is a promising pretreatment for leather tanning industry wastewaters for the control of toxic parameters; excess suspended solids as well as nitrogen which increase the cost and complexity of following biological treatment. Application of MAP precipitation, however, modifies the characteristics and biological treatability of wastewaters. In this study, characteristics and biological treatability of MAP precipitation effluent were experimentally investigated using the wastewaters obtained from a bovine leather processing plant. An experimental study involving the determination of COD fractions and kinetic parameters of biological treatment was conducted for both gravity settling and MAP precipitation. Results of the study indicated that MAP precipitation, in addition to high degree of nitrogen removal, yielded a soluble, readily biodegradable effluent which was also free from toxics. MAP precipitation provided an effluent COD of almost half of that of gravity settling. Reduced value of soluble residual microbial products (Sp) obtained with MAP precipitation effluent was an additional benefit.

Animals↗
PubMed2005

Extraction of selected heavy metals using modified clays.

In the present study, attapulgite, kaolinite, and montmorillonite KSF were modified using azeotropic distillation to condense 2-mercaptoethanol with the clay material. The resulting product was used as a coordinating agent to remove selected metal ions, e.g., copper(II), cadmium(II), silver(I), nickel(II), and lead(II) ions from standard aqueous solutions. Batch systems were used, and samples were shaken for two hours, and following filtration, metal content of the filtrate was measured by atomic absorption spectrometry. Without adjusting the pH, better than 90% of the metal ions could be removed.

Bentonite↗
PubMed2000

Characteristics of pharmaceutical grade phyllosilicate powders.

The purpose of this paper was to evaluate the possible use of three types of pharmaceutical grades of phyllosilicates as pharmaceutical excipients. Seven samples (two smectites, three palygorskites, and two sepiolites) were studied. A complete mineralogical and chemical characterization of each material was made and powder texture was established by image analysis of scanning electron micrographs. Powder flow properties were then determined and the influence of textural characteristics on powder rheology and particle packing was assessed. Mineral contents were adequate for the sepiolites (> 90% of main mineral) and smectites (78 and 95%), but should be improved on the palygorskite samples (around 50% of main mineral in two of the studied samples). According to the textural characterization, the samples presented almost equal size distributions, but exhibited two different morphologies (i.e., laminar for smectites and fibrous for sepiolites and palygorskites). Both sepiolites possessed high flowability, whereas this factor varied from medium to low in the other materials. The compressibility of smectites was adequate, whereas that of palygorskites was high and that of the sepiolites was low. All of the samples studied would be useful as solid dosage form excipients (some samples would require improvement of their flow properties or treatment to reduce the amount of mineral impurities).

Bentonite↗
PubMed1985

Beta dosimetry with newly developed graphite mixed TL detectors.

The characteristics of thermoluminescent dosemeters prepared from graphite mixed with sintered MgB4O7:Dy are presented for beta ray dosimetry. These dosemeters are attractive for beta ray dosimetry since the material combines low transparency with near tissue equivalence and high sensitivity, thus enabling skin dose to be assessed from low energy beta emitters in accordance with the ICRP recommendations. Results from practical field experiments are also presented.

Beta Particles↗
PubMed2004

Variations in dose response with x-ray energy of LiF:Mg,Cu,P thermoluminescence dosimeters: implications for clinical dosimetry.

In many medical procedures where accurate radiation dose measurements are needed, the variation of detector response with x-ray energy is of concern. The response of LiF:Mg,Cu,P TLDs to a range of x-ray energies was analysed in monoenergetic (synchrotron), diagnostic and therapy radiation beams with the aim of implementing this dosimeter into clinical practice where existing dosimetry techniques are limited due to lack of sensitivity or tissue equivalence (e.g. neonatal radiography, mammography and brachytherapy). LiF:Mg,Cu,P TLDs in different forms from two manufacturers (MCP-N: TLD Poland, GR200: SDDML China) were irradiated using x-ray beams covering 10 keV to 18 MVp. Dose readings were compared with an ionization chamber. The effect of different TLD types and annealing cycles on clinical utility was investigated. The measured energy response of LiF:Mg,Cu,P TLDs was fit to a simple model devised by Kron et al (1998 Phys. Med. Biol. 43 3235-59) to describe the variation of TLD response with x-ray energy. If TLDs are handled as recommended in the present paper, the energy response of LiF:Mg,Cu,P deviates by a maximum of 15% from unity and agrees with the model to within 5% or experimental uncertainty between 15 keV and 10 MeV. LiF:Mg,Cu,P TLDs of all forms have consistent and superior energy response compared to the standard material LiF:Mg,Ti and are therefore suitable for a wide range of applications in diagnostic radiology and radiotherapy.

Brachytherapy↗