Critical evaluation of the use of the hydroxyapatite as a stabilizing agent to reduce the mobility of Zn and Ni in sewage sludge amended soils

The leachability of zinc (Zn) and nickel (Ni) was investigated in various soil types amended with sewage sludge and sewage sludge treated with hydroxyapatite. Sandy, clay and peat soils were investigated. For leachability tests, plastic columns (diameter 9 cm, height 50 cm) were filled with moist samples up to a height of 25 cm. Sewage sludge (1 kg) was mixed with 4.6 kg of clay and sandy soils and with 6.7 kg of peat soil. For sewage sludge mixtures treated with hydroxyapatite, 0.5 kg of the hydroxyapatite was added to 1 kg of the sewage sludge. Neutral (pH 7) and acid precipitation (pH 3.5) were applied. Acid precipitation was prepared from concentrated HNO(3), H(2)SO(4) and fresh doubly distilled water. The amount of precipitation corresponded to the average annual precipitation for the city of Ljubljana, Slovenia. It was divided into eight equal portions and applied sequentially on the top of the columns. The results indicated that the leachabilities of Zn in sewage sludge amended peat and clay soils were low (below 0.3% of total Zn content) and of Ni in sewage sludge amended sandy, clay and peat soil below 1.9% of total Ni content. In sewage sludge amended sandy soil, the leachability of Zn was higher (11% of Zn content). The pH of precipitation had no influence on the leachability of either metal. Treatment of sewage sludge with hydroxyapatite efficiently reduced the leachability of Zn in sewage sludge amended sandy soil (from 11% to 0.2% of total Zn content). In clay and peat sewage sludge amended soils, soil characteristics rather than hydroxyapatite treatment dominate Zn mobility.     

Poly(vinyl alcohol-co-lactic acid)/Hydroxyapatite Composites: Synthesis and Characterization

There is a wide range of applications where calcium phosphate and hydroxyapatite (HA) are used as biomaterials, e.g. as synthetic bone grafts, coating on metal prostheses (like hip endoprostheses or dental implants) and drug carriers. In the study, the design and synthesis of composites based on poly(vinyl alcohol-co-lactic acid)/hydroxyapatite (PVA-co-LA/HA) with potential for biomedical applications, they are presented. The hydroxyapatite particles were surface-grafted with l(+)-lactic acid in the presence of manganese acetate as catalyst, resulting in modified hydroxyapatite (HA_m) with improved capacity of bonding, respectively for the preparation of the composite based on PVA-co-LA/HA_m. FT-IR spectra further confirmed the existence of PLA polymer on the surface of HA particles. In synthesis of PVA-co-LA copolymer the different molar ratios PVA/LA (2/1, 1/1, 1/2), toluene/water: 1/2 (as azeotrope solvent mixture) and manganese acetate as catalyst, were used. The composite materials were synthesized in situ with 10 wt% HA, and respectively HA_m (reported to PVA and lactic acid components). The composite materials were characterized by FTIR spectroscopy, thermal analyses (DSC, DTG), ¹H-NMR spectroscopy, particle size distribution and zeta potential.     

Preparation and Adsorption Performance of Nano-hydroxyapatite-Enhanced Acrylamide Hydrogel Adsorbent

Journal of Polymers and the Environment - In this study, a hydrogel adsorbent was successfully synthesized using hydroxyapatite/acrylamide/β-cyclodextrin to adsorb heavy metal ions and dyes in...     

Simultaneous Determination and Optimization of Titan Yellow and Reactive Blue 4 Dyes Removal Using Chitosan@hydroxyapatite Nanocomposites

Journal of Polymers and the Environment - Chitosan (CS) and hydroxyapatite (HA) nanocomposites have been prepared and used for the simultaneous removal of Titan Yellow (TY) and Reactive Blue 4 (RB...     

无机稳定剂处理重金属污染土壤

以重金属污染土壤为研究对象，比较了铁屑、蒙脱石、碳酸钙和羟基磷灰石4种稳定剂对土壤中Pb，Zn，Cd，Cu 4种重金属的稳定效果。实验结果表明，4种稳定剂稳定效率的大小顺序为：羟基磷灰石﹥碳酸钙﹥蒙脱石﹥铁屑。当稳定剂质量分数为10%时，羟基磷灰石、碳酸钙、蒙脱石和铁屑对Pb，Zn，Cd，Cu 4种重金属的平均稳定效率分别为99.63%，98.53%，97.15%，86.95 %。未加稳定剂时，土壤中的Pb以残渣态为主，Zn以残渣态和可交换态为主，Cd以残渣态为主，Cu以残渣态和可交换态为主；加入稳定剂后，土壤中4种金属可交换态的所占比例（简称占比）均显著降低，还原态的占比明显增大，残渣态的占比略有增大，氧化态的占比基本保持不变。     

Removal of cadmium ion by means of synthetic hydroxyapatite

The reaction behaviour of synthetic hydroxyapatite [Ca10(PO4)6(OH)2] (HAP) toward cadmium ion was investigated for the Cd/Ca molar ratio in the range 1-0.005, by means of ions, pH measurements and XRD, SEM, IR techniques. The reaction behaviour between HAP and cadmium ion could be explained by a formation of an amorphous phase and/or a sorption mechanism.     

羟基磷灰石去除废水中的Fe3+

以天然磷矿粉制备的羟基磷灰石(HAP)作为吸附剂，处理模拟含Fe3+废水。实验结果表明，在HAP加入量为1.0g/L、初始模拟废水pH为3.00、反应温度为室温的最佳条件下，处理初始Fe3+质量浓度为150mg/L的模拟废水，反应90min后Fe3+去除率为99.89%，处理后模拟废水中Fe3+质量浓度为0.15mg/L，低于0.30mg/L，达到GB5749—2006《生活饮用水卫生标准》的要求。     

Phosphate recovery from phosphorus-rich solution obtained from chicken manure incineration ash

The recovery of phosphorus from waste is very important for Japan because Japan has no natural phosphorus resources. In order to recover phosphorus from incineration ash of chicken manure, an acid dissolution–alkali precipitation method was investigated. Phosphorus content in the ash was 8%. The ash was treated with hydrochloric acid to obtain phosphorus-rich solution. Phosphorus could then be recovered as a precipitant by adding sodium hydroxide solution into the phosphorus-rich solution and gradually changing the pH in the solution to 3, 4, and 8. At pH 3, a small amount of phosphorus was precipitated to remove iron, which would cause coloring of subsequent precipitants. At pH 4, 84% of the phosphorus in the original solution could be recovered as CaHPO₄ · 2H₂O with a purity of 92%. At pH 8, 8% of the phosphorus in the phosphorus-rich solution could be recovered as identified hydroxyapatite. A recovery rate of 92% phosphorus as CaHPO₄ · 2H₂O and identified as hydroxyapatite was achieved.     

碳酸盐对化学沉淀法回收废水中磷的影响

研究了溶液中CO_3~(2-)对磷酸铵镁(MAP)法和羟基磷酸钙(HAP)法磷回收率的影响,并对回收磷所得产物进行了傅立叶变换红外光谱和X射线衍射分析.实验结果表明:为使磷回收率达80%以上,MAP法回收磷时n(CO_3~(2-)):n(Mg~(2+))必须小于0.5,HAP法回收磷时n(CO_3~(2-)):n(Ca~(2+))必须小于0.2;溶液中的CO_3~(2-)浓度对MAP法回收产物没有明显影响,但HAP法回收磷产物中会出现大量碳酸钙.     

Theoretical assessment of phosphate amendments for stabilization of (Pb + Zn) in polluted soil

Contamination of the environment with toxic metals, such as lead (Pb), represents a serious concern for human health. Most of the studies on Pb stabilization were performed using various phosphorus-containing amendments that can reduce Pb mobility and bioavailability by the sorption and precipitation of new, stable pyromorphite-type minerals, presenting very low solubility and bioaccessibility. However, the presence of competing ions, such as zinc (Zn), can reduce stabilization efficacy. The role of chemical composition on the stability of immobilization products of Pb and Zn by the addition of hydroxyapatite (HAP) or fluoroapatite (FAP) has been examined in this paper. In this analysis we used a theoretical criterion which is based on calculation of the ion–ion interaction potential, representing the main term of the cohesive energy of the matrix/pollutant system. It has been demonstrated that the stability of the HAP matrix decreases and that the stability of the FAP matrix increases with the Pb immobilization in the presence of Zn. The results of this analysis point out FAP as an advantageous amendment for the immobilization of Pb in the presence of Zn.     

Streambed Sediment Geochemical Controls on In-Stream Phosphorus Concentrations during Baseflow

A spatially extensive geochemical data set of stream water and bed sediment composition across the Tamar catchment in south-west England was analysed to identify the key bed sediment properties that control the in-stream dissolved reactive phosphorus (DRP) concentrations during baseflow conditions. Linear regression analysis of the streamwater DRP concentrations and the distribution coefficient K _d for DRP revealed that the former is positively correlated with total SiO₂ and Al₂O₃, and negatively correlated with K₂O. The primary control on these major element distributions is the dominant bedrock geology. The data suggest that streamwater DRP concentrations are mainly controlled by adsorption to clay minerals. Where P concentrations in streamwater were considerably elevated by inputs from point sources, DRP concentrations are also controlled by precipitation of hydroxyapatite.     

Enhancement of Sedimentation Velocity of Heavy Metals Loaded Hydroxyapatite Using Chitosan Extracted from Shrimp Waste

In this study, synthesize hydroxyapatite (HA) suspensions sedimentation was used after usual terms as support for adsorption of heavy metals ions. Thus, the effectiveness of chitosan, produced from shrimp waste, in the flocculation of turbid suspensions resulting from the treatment of water contaminated with heavy metals was studied by adsorption on HA. Different particles sizes of HA were mainly controlled in this work (an average of granule size ranging from 1.6 to 63 μm). The results of Cu²⁺ and Zn²⁺ adsorption on HA showed relatively fast kinetics, with removal extent of 88–95 % by varying the initial total metal concentration. High removal rates were obtained for Cu²⁺. Chitosan was found to be able to eliminate by flocculation more than 98 % of turbid suspensions generated by metals adsorption on HA after only 30 min of sedimentation. Effects of pH and dose of chitosan on the coagulation–flocculation process were also studied. The optimal dose of chitosan was found between 0.2 and 2 mg/L which corresponds to an optimal pH ranging from 6 to 7.     

High rate mesophilic, thermophilic, and temperature phased anaerobic digestion of waste activated sludge: a pilot scale study

The paper reports the findings of a two-year pilot scale experimental trial for the mesophilic (35°C), thermophilic (55°C) and temperature phased (65+55°C) anaerobic digestion of waste activated sludge. During the mesophilic and thermophilic runs, the reactor operated at an organic loading rate of 2.2 kgVS/m(3)d and a hydraulic retention time of 20 days. In the temperature phased run, the first reactor operated at an organic loading rate of 15 kgVS/m(3)d and a hydraulic retention time of 2 days while the second reactor operated at an organic loading rate of 2.2 kgVS/m(3)d and a hydraulic retention time of 18 days (20 days for the whole temperature phased system). The performance of the reactor improved with increases in temperature. The COD removal increased from 35% in mesophilic conditions, to 45% in thermophilic conditions, and 55% in the two stage temperature phased system. As a consequence, the specific biogas production increased from 0.33 to 0.45 and to 0.49 m(3)/kgVS(fed) at 35, 55, and 65+55°C, respectively. The extreme thermophilic reactor working at 65°C showed a high hydrolytic capability and a specific yield of 0.33 g COD (soluble) per gVS(fed). The effluent of the extreme thermophilic reactor showed an average concentration of soluble COD and volatile fatty acids of 20 and 9 g/l, respectively. Acetic and propionic acids were the main compounds found in the acids mixture. Because of the improved digestion efficiency, organic nitrogen and phosphorus were solubilised in the bulk. Their concentration, however, did not increase as expected because of the formation of salts of hydroxyapatite and struvite inside the reactor.     

Determination of the Thermal Efficiency of Pre-boilover Burning of a Slick of Oil on Water

The burning rate of a slick of oil on a water bed is calculated by a simple expression derived from a one-dimensional heat conduction equation. Heat feedback from the flame to the surface is assumed to be a constant fraction of the total energy released by the combustion reaction. The constant fraction (χ) is named the burning efficiency and represents an important tool in assessing the potential of in situ burning as a counter-measure to an oil-spill. The total heat release, as a function of the pool diameter, is obtained from an existing correlation. It is assumed that radiative heat is absorbed close to the fuel surface, that conduction is the dominant mode of heat transfer in the liquid phase and that the fuel boiling temperature remains constant. By matching the characteristic thermal penetration length scale for the fuel/water system and an equivalent single layer system, a combined thermal diffusivity can be calculated and used to obtain an analytical solution for the burning rate. Theoretical expressions were correlated with crude oil and heating oil, for a number of pool diameters and initial fuel layer thickness. Experiments were also conducted with emulsified and weathered crude oil. The simple analytical expression describes well the effects of pool diameter and initial fuel layer thickness permitting a better observation of the effects of weathering, emulsification and net heat feedback to the fuel surface. Experiments showed that only a small fraction of the heat released by the flame is retained by the fuel layer and water bed (of the order of 1%). The effect of weathering on the burning rate decreases with the weathering period and that emulsification results in a linear decrease of the burning rate with water content.     

Calculation of carbon balances for evaluation of the biodegradability of polymers

Establishing carbon balances has been proven to be an applicable and powerful tool in testing biodegradability of polymers. In controlled degradation tests at a 4-L scale with the model polymer poly(-hydroxybutyrate) (PHB), it was shown that the degree of degradation could not be determined with satisfactory accuracy from CO₂ release alone. Instead, the course of degradation was characterized by means of establishing carbon balances for the degradation of PHB withAcidovorax facilis and a mixed culture derived from compost. Different analytical methods for determining the different carbon fractions were adapted to the particular test conditions and compared. Quantitative determination of biomass and residual polymer were the main problems in establishing carbon balances. Amounts of biomass derived from protein measurements depend strongly on assumptions of the protein content of the biomass. Selective oxidation of biomass with hypochlorite was used as alternative, but here problems arose from insoluble metabolic products. Determination of soluble components with the method of chemical oxygen demand (COD) also includes empirical assumptions but seems acceptable if the dissolved carbon fraction is in the range of some 10% total carbon. Results confirm both analytical assays and theoretical approaches, in ending up at values very close to 100%, within an acceptable standard deviation range under test conditions comparable to standard test practice.Paper presented at the Bio/Environmentally Degradable Polymer Society—Third National Meeting, June 6–8, 1994, Boston, Massachusetts.     

Review of the kinetics of alkaline degradation of cellulose in view of its relevance for safety assessment of radioactive waste repositories

The degradation of cellulose (a substantial component of low- and intermediate-level radioactive waste) under alkaline conditions occurs via two main processes: a peeling-off reaction and a basecatalyzed cleavage of glycosidic bonds (hydrolysis). Both processes show pseudo-first-order kinetics. At ambient temperature, the peeling-off process is the dominant degradation mechanism, resulting in the formation of mainly isosaccharinic acid. The degradation depends strongly on the degree of polymerization (DP) and on the number of reducing end groups present in cellulose. Beyond pH 12.5, the OH^- concentration has only a minor effect on the degradation rate. It was estimated that under repository conditions (alkaline environment, pH 13.3-12.5) about 10% of the cellulosic materials (average DP = 1000-2000) will degrade in the first stage (up to 10⁵ years) by the peeling-off reaction and will cause an ingrowth of isosaccharinic acid in the interstitial cement pore water. In the second stage (10⁵-10⁶ years), alkaline hydrolysis will control the further degradation of the cellulose. The potential role of microorganisms in the degradation of cellulose under alkaline conditions could not be evaluated. Proper assessment of the effect of cellulose degradation on the mobilization of radionuclides basically requires knowing the concentration of isosaccharinic acid in the pore water. This concentration, however, depends on several factors such as the stability of ISA under alkaline conditions, sorption of ISA on cement, formation of sparingly soluble ISA-salts, etc. A discussion of all the relevant processes involved, however, is far beyond the scope of the presented overview.     

Model of technological alternatives of production of sodium chromate (VI) with the use of chromic wastes

This article presents a mathematical model which describes the sodium chromate (VI) production process with the use of chromic waste as a substitution of natural raw materials. This model is a function of selected process parameters common for all of the examined alternatives and based on equations of material balance. Optimization of the elaborated technological alternatives of the production process with use of recycling of chromic waste has been evaluated by determining the extreme value of the quality indicator WJ. This indicator defines the quantity of waste created in the process. Optimization results enabled the selection of the optimal technological solution from all of the alternatives possible for use in industrial practice. Negative values of the indicator prove that there is the possibility of introducing to the process a larger quantity of waste than the one obtained in the process and transported to the storage heaps.     

Effects of chemical composition of fly ash on efficiency of metal separation in ash-melting of municipal solid waste

In the process of metal separation by ash-melting, Fe and Cu in the incineration residue remain in the melting furnace as molten metal, whereas Pb and Zn in the residue are volatilized. This study investigated the effects of the chemical composition of incineration fly ash on the metal-separation efficiency of the ash-melting process. Incineration fly ash with different chemical compositions was melted with bottom ash in a lab-scale reactor, and the efficiency with which Pb and Zn were volatilized preventing the volatilization of Fe and Cu was evaluated. In addition, the behavior of these metals was simulated by thermodynamic equilibrium calculations. Depending on the exhaust gas treatment system used in the incinerator, the relationships among Na, K, and Cl concentrations in the incineration fly ash differed, which affected the efficiency of the metal separation. The amounts of Fe and Cu volatilized decreased by the decrease in the molar ratio of Cl to Na and K in the ash, promoting metal separation. The thermodynamic simulation predicted that the chlorination volatilization of Fe and Cu was prevented by the decrease in the molar ratio, as mentioned before. By melting incineration fly ash with the low molar ratio in a non-oxidative atmosphere, most of the Pb and Zn in the ash were volatilized leaving behind Fe and Cu.     

Effect of Degree of Substitution of Octenyl Succinate Starch on Enzymatic Degradation

Octenyl succinate starch of degree of substitution (ds) 0.03, 0.07, and 0.11 was synthesized in an aqueous medium. These compounds were then tested for the susceptibility to enzymatic degradation. The multiple-enzyme regime of -amylase, amyloglucosidase, and pullulanase was chosen for the evaluation. This combination of enzymes had been proven to degrade 99.5% of unmodified starch to glucose and hence was chosen for this study. It was found that even small amounts of subsituent caused a considerable decrease in the extent of degradation. The net extent of degradation decreased with increasing ds. Surprisingly, the amount of glucose from all three substituted substrates was quite similar, suggesting the effect small amounts of subtituent had on the enzymatic activity.     

Characterisation of the physico-mechanical parameters of MSW

Following the basics of soil mechanics, the physico-mechanical behaviour of municipal solid waste (MSW) can be defined through constitutive relationships which are expressed with respect to three physical parameters: the dry density, the porosity and the gravimetric liquid content. In order to take into account the complexity of MSW (grain size distribution and heterogeneity larger than for conventional soils), a special oedometer was designed to carry out laboratory experiments. This apparatus allowed a coupled measurement of physical parameters for MSW settlement under stress. The studied material was a typical sample of fresh MSW from a French landfill. The relevant physical parameters were measured using a gas pycnometer. Moreover, the compressibility of MSW was studied with respect to the initial gravimetric liquid content. Proposed methods to assess the set of three physical parameters allow a relevant understanding of the physico-mechanical behaviour of MSW under compression, specifically, the evolution of the limit liquid content. The present method can be extended to any type of MSW.