酸性条件下剩余污泥中Ca2＋和Mg2＋溶出对磷回收的影响

为了在酸性条件下实现剩余污泥中磷的高效回收，对pH=3时剩余污泥水解酸化过程中氨氮、正磷酸盐和钙镁离子的溶出现象以及磷回收进行了研究分析。结果表明：当pH=3时，所溶出的氨氮、镁离子和钙离子与磷酸盐的摩尔比均大于1，能满足采用鸟粪石沉淀法或者羟磷灰石沉淀法回收磷的要求；但所溶出的钙镁离子的摩尔比大于1，会对鸟粪石沉淀法回收磷的顺利进行有较大影响；有无外加镁剂对磷回收率影响不大。采用改型后的镁型强酸性阳离子交换树脂进行离子交换可以得到较高纯度的鸟粪石沉淀产品，通过XRD检测其纯度为95％以上。     

Modeling the crystallization of magnesium ammonium phosphate for phosphorus recovery

The crystallization of magnesium ammonium phosphate (MAP) is one of the main processes for recovering P and N from wastewater. Chemically defined solution systems were designed; the saturation indices (SIs) of the solution systems with respect to MAP were derived by using a geochemical aqueous model Program, PHREEQC 2.11; the effects of the solution conditions were evaluated using thermodynamic theories. The concentrations of P and Mg in the tested solutions were 10-600 mg l(-1) and 24-720 mg l(-1), respectively, the molar ratios of N/P and pH values of the solutions varied in the ranges of 1-40 and 6.0-12.0, respectively. The temperature of all the tests was set at 25 degrees C. The test results show that the SI value of MAP is the logarithmic functions of the concentrations of P, ammonium-N and Mg, and increases with the increase of the concentration of each element. The SI value of MAP is a polynomial function of pH value of the solution, and the optimum pH value for the crystallization of MAP is 9.0 but increases slightly with the increase of the N/P. Moreover, the SI value of MAP is a power law function of the ionic strength of solutions but decreases with its increase. The adjustment of the Mg concentration and the control of solution pH are two effective methods for the control of the crystallization of MAP. The results obtained from the research can be used to guide the design and control of MAP crystallization process for the removal and recovery of P.     

Phosphate recovery from greenhouse wastewater

A study was conducted to investigate the suitability of phosphate recovery from greenhouse wastewaters by using precipitation/crystallization process. More than 90% of the phosphate could be removed from the greenhouse wastewater. Various calcium phosphate salts were obtained in the process; hydroxyapatite [Ca5(PO4)3OH] could be the main product from the precipitates. Phosphate removal was affected by the presence of magnesium ion in wastewaters. An increase of magnesium concentrations in wastewaters decreased phosphate removal rates. The chemical contents of precipitates in terms of calcium, magnesium and phosphate were affected by calcium to magnesium molar ratio. Higher calcium contents were obtained at wastewaters with high calcium to magnesium molar ratio. An addition of magnesium did not affect the potassium contents in the precipitates. K-struvite, MgKPO4 x 6H2O, was not the major product in the precipitate, even with addition of a large quantity of magnesium.     

Phosphate Recovery from Greenhouse Wastewater

A study was conducted to investigate the suitability of phosphate recovery from greenhouse wastewaters by using precipitation/crystallization process. More than 90% of the phosphate could be removed from the greenhouse wastewater. Various calcium phosphate salts were obtained in the process; hydroxyapatite [Ca₅(PO₄)₃OH] could be the main product from the precipitates. Phosphate removal was affected by the presence of magnesium ion in wastewaters. An increase of magnesium concentrations in wastewaters decreased phosphate removal rates. The chemical contents of precipitates in terms of calcium, magnesium and phosphate were affected by calcium to magnesium molar ratio. Higher calcium contents were obtained at wastewaters with high calcium to magnesium molar ratio. An addition of magnesium did not affect the potassium contents in the precipitates. K‐struvite, MgKPO₄·6H₂O, was not the major product in the precipitate, even with addition of a large quantity of magnesium.     

碳酸根对磷酸钙沉淀反应回收磷的影响

以模拟的厌氧消化液为处理对象，通过小试实验，考察不同初始磷浓度Cp、Ca／P物质的量比、pH和温度下，碳酸根（CO3 2-）对磷酸钙沉淀反应回收磷的影响；利用扫描电镜（SEM）、x射线衍射仪（XRD）和傅里叶变换红外光谱（FT．IR）对沉淀产物进行表征。结果表明，高浓度的CO3 2-对以磷酸钙沉淀反应去除和回收磷的效率影响较大；Cp相同时，CO3 2-浓度（CCO3^2-）越大，P的去除率越低，低C，（20mg／L）时尤为显著；当CCO3^2-相同时，随着Cp的增大，反应速率加快，P的去除率逐渐升高，但升高幅度越来越小；增大Ca／P比和pH能提高P的去除率，降低CO3 2-对磷酸钙沉淀反应的抑制作用，综合考虑实际效果，应选择Ca／P比为3．33，pH为9．0作为适宜的反应条件；升高温度对降低CO3 2-对磷酸钙沉淀反应的抑制作用贡献不大。在Cp为60ITIg／L，Ca／P比为1．67，pH为9．0，温度为20℃的条件下，当CCO3^2-为0时，得到的沉淀产物主要为羟基磷灰石HAP；当CCO3^2-为30mmol／L时，得到的沉淀产物为磷酸钙和碳酸合磷灰石的混合物。     

Retention of Cd, Zn and Co on hydroxyapatite filters

This study qualifies and quantifies the immobilization of Cd, Zn and Co, (used as models of bivalent metal ions due to their relevant toxicity) in filters of synthetic hydroxyapatite (HAP) [Ca5(PO4)3OH]. They were flushed with solutions containing Cd (1 x 10(-5)M), Zn and Co (1 x 10(-4)M) at constant pH (8.6) and ionic strength (0.01 M). The concentration of these metal ions in the outlet was measured by ICP-OEM spectroscopy. The software PHREEQC (version 2.4.2) was used to model sorption process and the potential effect of salinity (KCl), pH, alkalinity (NaHCO3) and hardness (CaCl2) over the efficiency of the treatment. Results showed an excellent retention capacity of HAP for Cd, Zn and Co. Sorption data were successfully described considering a mix model of surface complexation onto phosphate surface groups, ionic exchange in surface calcium sites and the precipitation of ZnO. Co exchange and surface complexation constants (Kex and Kc) were taken from previous experiments, while KexCd=0.32 and KcCd=0.63 were estimated from our modeling results. Predictive values of metal ion sorption show that: (a) an increase in hardness does not play a significant role in the retention capacity of these metals on HAP; (b) an increase in alkalinity promotes the precipitation of MeCO3 which could alter the hydrodynamic of the column; (c) a decrease in pH and an increase in salinity inhibit ZnO precipitation enhancing Zn and Cd adsorption and decreasing Co retention on HAP.     

Nutrients removal and recovery by crystallization of magnesium ammonium phosphate from synthetic swine wastewater

With synthetic swine wastewater, lab-scale batch experiments were carried out to investigate the effects of pH value, magnesium dosage, calcium and carbonate concentrations on magnesium ammonium phosphate (MAP) crystallization. The morphology of the precipitates obtained was observed by using scanning electron microscopy with energy dispersive X-ray analysis, and the composition of the precipitates was analyzed with X-ray diffraction. The results show that the optimum pH value for MAP crystallization is in the range of 9.5-10.5; the phosphorus removal efficiency increases with the increase of Mg/P molar ratio; the optimum Mg/P molar ratio is 1.4, and excessive Mg dosage does not show significant effect on the efficiency improvement of MAP crystallization; the co-existing of Ca in solution disturbs the morphology and purity of the MAP product, and amorphous calcium phosphate will form when Ca increases to a certain concentration; CO3(2-) can affect the P removal efficiency, but does not obviously affect the morphology and purity of MAP.     

Mechanisms of phosphorus removal by cement-bound ochre pellets

Hydrous ferric oxide (here termed ‘ochre’) sludge, an abundant waste product produced from the treatment of acid mine drainage (AMD), was used in this study for the removal of phosphorus (in the form of phosphate ions) from contaminated waters. The phosphorus uptake capacities of both raw and pelletized AMD solids were compared using batch and column tests. Addition of a cement binder to the AMD solids during pellet production led to significantly increased P-loading of the resultant solids compared to the raw sludge. Additionally, the pellets were found to continue to remove P in tests up to 7 d in duration whereas the unbound AMD sludge appeared to approach equilibrium with phosphate solution after approximately 60 min of contact time. In line with previous studies P uptake by the AMD solids was found to be primarily via adsorption. By contrast calcium phosphate precipitation was found to be the dominant removal mechanism for the cement-bound ochre pellets with a relatively small proportion of removal attributable to the AMD solids. SEM–EDX analysis of the surface of used pellets showed a Ca:P molar ratio close to that of hydroxyapatite (HAP). Continuous column tests on these pellets showed a rapid decrease in P removal capacity by the pellets over time, attributable to the formation of a passivating HAP surface layer.     

不同Ca/P比下碳酸根对磷酸钙沉淀反应回收磷的影响

以模拟污水处理厂污泥厌氧消化液为处理对象,进行磷酸钙沉淀除磷小试实验,考察了不同Ca/P物质的量比下碳酸根(CO2-3)对磷酸钙沉淀反应回收磷的影响;利用扫描电镜(SEM)、X射线衍射仪(XRD)和傅里叶变换红外光谱(FTIR)对沉淀产物进行表征。结果表明,磷酸钙沉淀反应是一个快速过程,CO2-3的存在并未改变这一显著特征。磷酸钙沉淀反应过程中,CO2-3的存在降低了磷的去除率,改变了沉淀物形貌、结构和组分;实验设定范围内,磷酸钙的过饱和度越高,越难形成晶体态羟基磷灰石((Ca5(PO4)3OH,HAP);当pH值为9.0,Ca/P比为1.67时,CO2-3取代HAP晶格中的PO3-4,形成碳磷灰石(CHAP);当pH值为9.0,Ca/P比为3.33和5.01时,CO2-3和PO3-4之间竞争,形成碳酸钙(CaCO3);增大Ca/P能有效提高磷的去除率,降低CO2-3对磷酸钙沉淀反应的抑制作用,但综合考虑实际效果,选择Ca/P比为3.33作为适宜的反应条件。     

Removal of aqueous lead by poorly-crystalline hydroxyapatites

The use of a phosphorus amendment in altering Pb to a chemically less mobile phase is a promising strategy based on minimizing ecotoxicological risk and improving time and cost efficiency. This study evaluated crystalline and poorly-crystalline hydroxyapatite sorbents on removal of aqueous Pb in response to reaction time, solution pH, and Pb concentration. Batch experiments were conducted using a commercially-available crystalline hydroxyapatite (HA), and two poorly-crystalline hydroxyapatites synthesized from gypsum waste (CHA) and incinerated ash of poultry waste (MHA). Poorly-crystalline hydroxyapatites had greater capacity for Pb removal from a solution with a wider pH range as compared to a crystalline hydroxyapatite. The maximum sorption capacity of Pb determined by the Langmuir model was 500 mg g⁻¹ for CHA, 277 mg g⁻¹ for MHA and 145 mg g⁻¹ for HA. Removal of aqueous Pb by CHA was not dependent on solution pH, with a 98.8% reduction throughout the solution pH range of 2–9, whereas aqueous Pb removal by HA and MHA was pH-dependent with less removal in the neutral solution pH. Poorly-crystalline hydroxyapatites may provide an effective alternative to existing remediation technologies for Pb-contaminated sites.     

Copper complexation by dissolved organic matter and uncertainty assessment of their stability constants

The interaction of Cu with dissolved organic matter (DOM, extracted from an organic forest floor) was investigated and the resulting data was evaluated in terms of their uncertainty. The speciation of Cu over ‘free’ Cu (as analysed by diffusive gradients in thin films (DGT)), dissolved Cu–DOM complexes and precipitated Cu–DOM was determined as a function of pH (3.5, 4.0 and 4.5) and Cu/C ratio. The dissolved organically bound fraction was highest at pH 4.5, but this fraction decreased with increasing Cu/C ratio, which was observed for all pH levels. In the range of Cu/C=7×10⁻⁵–2.3×10⁻² (mol/mol) the precipitated fraction was very small. The speciation of both Al and Fe was not affected by increasing Cu concentrations. From a continuous distribution model using the Scatchard approach, we calculated the optimal fit and corresponding upper and lower 95% uncertainty bounds of the overall stability constants (K_o) with the shuffled complex evolution Metropolis (SCEM) algorithm. Although the optimal equation fitted the data very well, the uncertainty of the, according to literature, most reliable approach to establish stability constants, was still large. Accordingly, the usually reported intrinsic stability constants exhibited large uncertainty ranging from logK_i=6.0–7.1 (optimal 6.7) for pH 3.5, logK_i=6.5–7.1 (optimal 6.8) for pH 4.0, and logK_i=6.4–7.2 (optimal 6.8) for pH 4.5 and showed only little effect of pH.     

In vitro and in vivo studies of lead immobilization by synthetic hydroxyapatite

Apatite appears a useful compound for removing lead from water, due to its ability to immobilize the metal by precipitation. In dilute solution, dissolved hydroxyapatite [HA, Ca1O(P04)6(OH)2] provided phosphates that were reactive with aqueous lead (molar ratio HA/Pb= 1/10) forming precipitates at around pH 6. These dissolved at a more acidic pH (3). Solid HA in contact with Pb2+ions, led to the formation of pyromorphite [Pblo(P04)6(OH)2], identified by X-ray diffraction and insoluble at pH tested (3-8). The amount of pyromorphite increased with the weight ratio of HA/Pb. When this one increased from 1 to 1000, lead precipitated as pyromorphite rose from 19 to 99%. In vivo experiments on rats confirmed the in vitro results. In fact, lead bioavailability assessed by intestinal perfusion was unchanged in the presence of dissolved HA, whereas it was significantly lower in the presence of solid HA, evaluated by gastric intubation, at a weight ratio equal to 10 (amount of lead absorbed decreased by 60%). Apatite could bean effective means of immobilizing lead in drinking or sewage, since accidental pyromorphite ingestion does not yield bioavailable lead.     

Copper complexation by tannic acid in aqueous solution

The speciation of titrated copper in a dissolved tannic acid (TA) solution with an initial concentration of 4 mmol organic carbon (OC)/l was investigated in a nine-step titration experiment (Cu/OC molar ratio = 0.0030–0.0567). We differentiated between soluble and insoluble Cu species by 0.45 μm filtration. Measurements with a copper ion selective electrode (ISE) and diffusive gradients in thin films (DGT) were conducted to quantify unbound Cu(II) cations (‘free’ Cu) and labile soluble Cu complexes. For the DGT measurements, we used an APA hydrogel and a Chelex 100 chelating resin (Na form). Insoluble organic Cu complexes (>0.45 μm) was the dominant Cu species for Cu/OC = 0.0030–0.0567 with a maximum fraction of 0.96 of total Cu. At Cu/OC > 0.0100, Cu-catalysed degradation of aggregate structures resulted in a strong increase of free Cu and (labile) soluble Cu complexes with a maximum fraction of 0.28 and 0.32 of total Cu, respectively. Labile (i.e. DGT-detectable) soluble Cu complexes had a relatively high averaged diffusion coefficient (D) in the APA hydrogel (3.50 × 10⁻⁶– 5.58 × 10⁻⁶ cm² s⁻¹).     

Extraction of arsenic in a synthetic arsenic-contaminated soil using phosphate

An environment-friendly and cost-effective extraction method has been studied for the removal of arsenic from contaminated soil. A yellow-brown forest soil was contaminated with arsenic(V) and used as a model soil. Among various potassium and sodium salts, potassium phosphate was most effective in extracting arsenic, attaining more than 40% extraction in the pH range of 6–8 with minimum damage to the soil properties. Exchange mechanism is proposed for the extraction of arsenic from soil by phosphate. Sequential extraction shows that phosphate is effective in extracting arsenic of Al- and Fe-bound forms. Arsenic of residual form was not extracted. Arsenic was efficiently extracted by phosphate solution of pH 6.0 at 300 mM phosphate concentration and at 40°C.     

Repeated use of MAP decomposition residues for the removal of high ammonium concentration from landfill leachate

The residues of magnesium ammonium phosphate (MAP) decomposed by heating under alkali conditions were repeatedly used as the sources of phosphate and magnesium for the removal of high ammonium concentration from landfill leachate. Up to 96% of ammonium in MAP powder could be released under the following conditions: NH4(+):OH- molar ratio, 1:1; temperature, 90 degrees C; heating time, 2 h. Fourier transform infrared spectra and X-ray diffraction analysis of MAP before and after heating demonstrated that MAP was mainly transformed to amorphous magnesium sodium phosphate (MgNaPO4), which makes it possible for the NH4(+) to replace Na+ in MgNaPO4 to form more stable struvite. Successful ammonium removal was achieved by using the MAP decomposition residues as the sole phosphate and magnesium sources. The ammonium removal decreased gradually following the increase of MAP reuse cycles, and in the 6th cycle, ammonium removals of 84% and 62% were achieved for synthetic wastewater and landfill leachate, respectively. Analysis of the surfaces of MAP powders acquired at different reuse cycles using scanning electron microscopy with energy dispersive X-ray suggested that the existence of calcium, kalium and aluminum ions in landfill leachate might have inhibited the formation of MAP through competition with ammonium ions for phosphate ions. It is estimated that reuse of MAP for 3 cycles could save about 44% chemical costs.     

天然沸石同步去除水中氨氮和磷酸盐

通过静态吸附实验考察了浙江缙云产天然沸石对溶液中氨氮和磷酸盐的同步去除能力及机制,结果表明,天然沸石对溶液中氨氮的吸附过程较好地满足拟二级动力学模型、Langmuir和Dubinin-Radushkevich等温吸附模型。天然沸石对磷酸盐的去除能力随溶液中初始氨氮浓度的增加而增加。当溶液pH由7.0增加到9.0时,天然沸石对氨氮的吸附能力随之增加,而当pH由9.0增加到10时,天然沸石对氨氮的吸附能力则下降。当溶液pH低于7.5时,天然沸石对溶液中的磷酸盐无去除能力,当溶液pH位于7.5～9.0时,天然沸石对磷酸盐的去除能力随pH的增加急剧增加,当溶液pH大于9.0时,天然沸石对磷酸盐的去除能力随pH的增加则呈下降趋势。天然沸石对溶液中氨氮和磷酸盐的同步去除过程是自发进行、吸热及熵增加的过程。天然沸石对溶液中氨氮的吸附机制为离子交换,对磷酸盐的去除机制则为化学沉淀作用。     

利用白云石回收污泥厌氧消化液中的磷

为经济有效地从污泥厌氧消化液中回收磷,构建了以白云石提供钙镁源的磷回收方法,探讨了磷回收的工艺条件与效果。通过盐酸酸化厌氧消化液以降低其碳酸盐含量,同时利用白云石溶于冷稀盐酸的特性使其钙镁缓慢释放到酸化的厌氧消化液中形成第一步磷回收体系,考察体系酸化pH、白云石与厌氧消化液的固液比以及反应pH对白云石的钙镁释放和磷回收效果的影响;第一步磷回收后的上清液为第二步厌氧消化液磷回收提供钙镁源,研究投加钙磷摩尔比对磷回收效果的影响。实验结果表明,当固液比为5.0时,在酸化pH为4.0～4.5且酸化溶出时间为10 h以及反应pH为9.0的条件下,第一步磷回收产物以磷酸钙盐沉淀为主,厌氧消化液磷回收率及回收产物含磷率（以P2O5计）分别达到99.43%和38.49%;第一步磷回收后的上清液按一定的钙磷摩尔比投加到酸化后的厌氧消化液中进行第二步磷回收,当投加钙磷摩尔比为0.20时,在反应pH为9.0的条件下,回收产物同时含有磷酸钙盐和磷酸铵镁,厌氧消化液中氮、磷回收率分别达到13.19%和90.90%,回收产物氮、磷含量（以P2O5计）分别为0.26%和39.58%;经XRD、XRF、ICP及SEM等分析表征,2步磷回收的产物以磷酸钙盐和磷酸铵镁为主要成分,杂质少。研究表明,利用白云石为钙镁源,通过分别构建不同的磷回收体系可以分步从污泥厌氧消化液中经济有效地回收磷,且磷回收率和回收产物含磷率高。     

The Effects of Magnesium and Ammonium Additions on Phosphate Recovery from Greenhouse Wastewater

Phosphorus recovery from greenhouse wastewater, using precipitation-crystallization, was conducted under three levels of calcium concentration, 304 mg/L (7.6 mmol/L), 384 mg/L (9.6 mmol/L), and 480 mg/L (12 mmol/L), and also with additions of ammonium and magnesium into the wastewater. Jar test results confirmed high phosphate removal, with more than 90% of the removal achieved with a pH as low as 7.7. Under the low calcium concentration, ammonium addition affected the chemical reactions at pH lower than 8.0, where struvite was produced; when the pH was raised to 8.8, other calcium compounds dominated the precipitation. Under the medium calcium concentration, ammonium and magnesium addition helped struvite precipitation in the low pH range. Hydroxyapatite (HAP) was the main product. Under the high calcium concentration, ammonium addition showed no effects on the precipitation.     

石灰沉淀法除砷的影响因素

以Ca(OH)2溶液为沉淀剂,处理模拟含砷废水砷酸钠溶液,考察了pH值、Ca/As摩尔比、自由沉降时间和反应温度等因素对石灰沉淀法除砷效果的影响。结果表明,在pH值为12,Ca/As摩尔比为6,沉降时间为48 h,反应温度为25℃时,石灰沉淀法除砷的效率可达到99.05%;此外,对高浓度的含砷废水,在石灰沉淀法除砷工艺中添加简单无机盐絮凝工艺,可显著降低出水总砷浓度,达到污水综合排放标准的要求。     

The effects of magnesium and ammonium additions on phosphate recovery from greenhouse wastewater

Phosphorus recovery from greenhouse wastewater, using precipitation-crystallization, was conducted under three levels of calcium concentration, 304 mg/L (7.6 mmol/L), 384 mg/L (9.6 mmol/L), and 480 mg/L (12 mmol/L), and also with additions of ammonium and magnesium into the wastewater. Jar test results confirmed high phosphate removal, with more than 90% of the removal achieved with a pH as low as 7.7. Under the low calcium concentration, ammonium addition affected the chemical reactions at pH lower than 8.0, where struvite was produced; when the pH was raised to 8.8, other calcium compounds dominated the precipitation. Under the medium calcium concentration, ammonium and magnesium addition helped struvite precipitation in the low pH range. Hydroxyapatite (HAP) was the main product. Under the high calcium concentration, ammonium addition showed no effects on the precipitation.