Laboratory experiments on simultaneous removal of K and P from synthetic and real urine for nutrient recycle by crystallization of magnesium-potassium-phosphate-hexahydrate in a draft tube and baffle reactor

The simultaneous removal of K and P from urine for nutrient recycling by crystallization of magnesium potassium phosphate hexahydrate (MPP) in a laboratory-scale draft tube and baffle reactor (DTBR) is investigated. Results show that mixing speed and hydraulic retention time are important operating factors that influence crystallization and crystal settlement. Slurry should be discharged at a crystal retention time of 11 h to maintain fluidity in the reactor. Further applications of the DTBR using real urine (pretreated by ammonia stripping and diluted five times) showed that 76% K and 68% P were recycled to multi-nutrient products. The crystals collected were characterized and confirmed mainly as a mixture of magnesium ammonium phosphate hexahydrate, MPP, and magnesium sodium phosphate heptahydrate. Results indicate that the DTBR effectively achieved the simultaneous recycling of K and P from urine to multi-nutrient products through MPP crystallization.     

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.     

Nitrogen and phosphorus removal for swine wastewater by ammonium crystallization and intermittent aeration process

Abstract

A process on crystallized precipitation of ammonium by adding magnesium salt and phosphate was carried out to improve C/N ratio in swine wastewater. After completion of crystallized precipitation of ammonium, an intermittent aeration process with aeration and non‐aeration periods alternated at interval of 1:1 hr day^‐1 is used for the improved swine wastewater (T‐N/BOD=0.14: BOD=8200 mg/liter and T‐N=1166 mg/liter). The results obtained from the experiment show that the removal ratios of T‐N and NH₄‐N are 91% and 99%, respectively. T‐P is not removed, while the removal ratio of PO₄‐P is 60% as 3% of CaCl₂ liquid is added. The results also indicate that dilution with water is effective to improve the removal of phosphorus even if raw swine wastewater contains high concentrations of T‐N, T‐P, BOD, and TOC.     

磷酸铵镁沉淀法回收尿液中N和P的实验研究

以源分离尿液为研究对象,在氨氮含量为2 850 mg N/L的微稀释尿液中,投加MgCl2·6H2O和Na2HPO4·12H2O,以磷酸铵镁沉淀法回收N和P。通过正交实验确定影响磷酸铵镁沉淀反应的因素依次为: pH值、PO3-4∶NH+4、Mg2+∶NH+4、温度。在搅拌速度=100 r/min、反应温度=15℃、反应时间=10 min的条件下,实验分别考察了pH值、PO3-4投加量、Mg2+投加量对磷酸铵镁沉淀法去除N、P的影响,结果表明最佳工艺条件为pH=9.5,Mg2+∶NH+4∶PO3-4=1.3∶1.0∶1.0。最佳工艺条件下尿液中的NH+4-N可从2 850 mg/L降低到约125 mg/L;剩余磷酸盐浓度约7 mg/L。SEM及XRD分析表明,沉淀物的主要成分为呈斜方晶系的磷酸铵镁晶体。     

磷酸铵镁沉淀法预处理垃圾渗滤液

探讨了用磷酸铵镁沉淀法预处理垃圾渗滤液时,沉淀剂种类、pH值、物质摩尔配比和反应时间等因素对氨氮去除效果的影响。得出了处理氨氮浓度为2 677.34 mg/L的垃圾渗滤液时,在兼顾所用镁盐量尽量低和处理出水氨氮或磷酸盐的残留量都比较低的较佳实验条件为:沉淀剂种类为:MgSO4.7H2O和Na2HPO4.12H2O,反应时间为20 min,pH=9.5,n(Mg)∶n(P)∶n(N)=1.3∶1.15∶1.0。在较佳实验条件下,垃圾渗滤液的NH3-N去除率为97.05%,处理出水PO34--P含量为8.35 mg/L,NH3-N含量为75.86 mg/L。对所得沉淀物进行了成分分析和X-衍射光谱、扫描电镜表征,表明大部分沉淀物为磷酸铵镁物质。     

Effects of acidifying reagents on microwave treatment of dairy manure

Dairy manure, acidified using organic acids (acetic, oxalic, and citric acid) were treated with microwave enhanced advanced oxidation process (MW/H₂O₂-AOP). The effect of a mixture of oxalic acid and commonly used mineral acids (sulfuric and hydrochloric acid) on MW/H₂O₂-AOP was also examined. Substantial amounts of phosphorus were released under MW/H₂O₂-AOP, regardless of organic acid or mineral acid used. All three organic acids were good acidifying reagents; however, only oxalic acid could remove free calcium ion in the solution, and improve settleability of dairy manure. The MW/H₂O₂-AOP and calcium removal process could be combined into a single-stage process, which could release phosphate, solubilize solids and remove calcium from dairy manure at the same time. A mixture of oxalic acid and mineral acid produced the maximum volume of clear supernatant and had an ideal molar ratio of calcium to magnesium for effective struvite (magnesium ammonium phosphate) crystallization process. A single-stage MW/H₂O₂-AOP would simplify the process and reduce mineral acid consumption compared to a two-stage operation. The results of a pilot scale study demonstrate that MW/H₂O₂-AOP is effective in treating manure and recovering resource from dairy farms.     

改性蛭石结合鸟粪石沉淀法回收垃圾渗滤液中氨氮的实验研究

研究了使用氯化镁改性蛭石,利用磷酸铵镁沉淀的原理,在垃圾渗滤液中按比例加入PO43-,处理垃圾渗滤液中氨氮的同时,在蛭石上生成磷酸铵镁沉淀,以便于磷酸铵镁沉淀的回收利用。结果表明,筛取蛭石粒径为60～80目,配制浓度20%的氯化镁溶液浸泡改性蛭石20 min,取25 g改性蛭石,100 mL垃圾渗滤液调节pH为9,按n(NH4+)∶n(PO34-)=1∶1.2的比例加入PO43-离子,垃圾渗滤液中氨氮去除率为85.06%,实验并对磷酸铵镁沉淀进行了结构成分分析,为垃圾渗滤液中氨氮的处理及磷酸铵镁沉淀的回收提供了一种新的方法。     

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.     

鸟粪石结晶法回收垃圾渗滤液氨氮研究

采用MgSO₄·7H₂O和Na₂HPO₄·12H₂O使NH₃-N生成MgNH₄PO₄·6H₂O（鸟粪石）结晶沉淀法回收渗滤液中NH₃-N。考察了pH值、反应时间、药剂配比对NH₃-N去除率的影响。结果表明,鸟粪石结晶回收NH₃-N反应的适宜pH值为9～9.5之间,过高的pH会破坏鸟粪石晶体结构,导致固定氨从MgNH₄PO₄中游离出来,不利于氨氮的去除。在pH值为9.5、反应时间为25 min、Mg²⁺∶NH⁺₄∶PO^3-₄=1.5∶1∶1.5的最佳条件下,渗滤液中NH₃-N浓度由初始3 500 mg/L,经结晶沉淀后降低至175 mg/L,去除率达95%。鸟粪石结晶沉淀过程中几乎不吸收重金属,同时回收了氨氮,其沉淀产物鸟粪石是一种优良的缓释肥原料。     

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.     

铁炭微电解-MAP沉淀法联合预处理垃圾渗滤液

采用铁炭微电解-磷酸氨镁(MAP)沉淀法对垃圾渗滤液进行预处理,实验结果表明,铁炭比为5∶1,pH值为3,反应时间为3 h时,铁炭微电解的COD的去除率为47.5%;在投加药剂n(Mg2+)∶n(PO43-)∶n(NH4+)为1.4∶1∶1,pH值为9,反应时间为1 h的条件下,垃圾渗滤液氨氮去除率达到79.7%。     

Capturing the lost phosphorus

Minable phosphorus (P) reserves are being depleted and will need to be replaced by recovering P that currently is lost from the agricultural system, causing water-quality problems. The largest two flows of lost P are in agricultural runoff and erosion (∼46% of mined P globally) and animal wastes (∼40%). These flows are quite distinct. Runoff has a very high volumetric flow rate, but a low P concentration; animal wastes have low flow rates, but a high P concentration together with a high concentration of organic material. Recovering the lost P in animal wastes is technically and economically more tractable, and it is the focus for this review of promising P-capture technologies. P capture requires that organic P be transformed into inorganic P (phosphate). For high-strength animal wastes, P release can be accomplished in tandem with anaerobic treatment that converts the energy value in the organic matter to CH₄, H₂, or electricity. Once present as phosphate, the P can be captured in a reusable form by four approaches. Most well developed is precipitation as magnesium or calcium solids. Less developed, but promising are adsorption to iron-based adsorbents, ion exchange to phosphate-selective solids, and uptake by photosynthetic microorganisms or P-selective proteins.     

响应面分析法优化稀土废水MAP沉淀法脱氮

经过预处理后的稀土生产废水,其氨氮浓度大幅降低,但并未达到中华人民共和国《稀土工业污染物排放标准》（GB26451-2011）中氨氮浓度限值。实验通过响应面分析法中的Box-Behnken实验设计（BBD）,取pH、n（Mg）：n（N）、n（P）：n（N）3因素,采用Design-Expert 8.0.6,建立合适的剩余氨氮浓度及剩余总磷浓度模型,得到回归方程,并分析模型各项指标,各因素及其相互作用对剩余氨氮浓度及剩余总磷浓度的影响。利用预测模型预测最佳实验条件,在最佳实验条件下验证预测结果,并对沉淀物进行X射线衍射（XRD）分析。结果显示,二次响应模型适用于剩余氨氮浓度及剩余总磷浓度,2个模型均拥有较好的拟合程度、可信度及精密度,最优反应条件为：pH=9.88、n（Mg）：n（N）=1.50：1、n（P）：n（N）=1.38：1时,剩余氨氮浓度为46.58 mg/L,剩余总磷浓度为7.85 mg/L。在最优条件下所得到的沉淀物并非纯净的MgNH₄PO₄·6H₂O,还有Mg₃（PO₄）₂·22H₂O生成。     

Modelling of phosphorus removal from aqueous and wastewater samples using ferric iron

Batch laboratory scale experiments were conducted to investigate the removal of phosphate from aqueous and municipal wastewater samples by addition of FeCl(3).6H(2)O. The effect of pH, Fe-dose and initial phosphate concentration were assessed. Optimum phosphate removal, 63% for 1:1 molar addition of Fe(III) was observed at pH 4.5. However, a 155% excess of Fe-dose was necessary for complete phosphorus removal. Phosphorus removal from municipal wastewater was slightly higher than that observed for the aqueous solutions. A chemical precipitation mathematical model was developed and tested with the available experimental data. The model included a total of 15 chemical reactions and 4 solid phases with the option of single-phase precipitation or two-phase co-precipitation. The resulting system of non-linear algebraic equations was solved numerically, using the Wijngaarden-Dekker-Brent method.     

原位水解生成的羟基氧化铁凝聚吸附除磷效能与机制简

将不同摩尔比Fe³⁺与OH^-（[Fe³⁺]：[OH^-]=1：0、1：1、1：2和1：3）反应获得原位水解生成的羟基氧化铁（in situ FeO_xH_y）,研究了具有不同水解程度的羟基氧化铁对凝聚吸附除磷效能与机制。研究显示,In situ FeO_xH_y对磷的去除率随铁投量增大而升高,且均在中性pH范围内具有最佳除磷效果;在相同铁投量条件下,磷去除率随着[OH^-]：[Fe³⁺]的升高而降低;当体系碱度较低时（pH<6）,引入OH^-可促进Fe³⁺水解而提高除磷效果。4种羟基氧化铁均可在15 s内可快速吸附磷,且吸附过程符合准二级动力学模型;Freundlich模型均可很好地描述磷在4种羟基氧化铁表面的吸附行为。磷酸盐吸附后,In situ FeO_xH_y表面Zeta电位明显降低,且[Fe³⁺]：[OH^-]为1：0的羟基氧化铁降低最为显著。结合MINITEQ计算软件磷酸盐、铁盐形态分析结果显示,对于碱度较低的体系,通过投加一定量OH^-可促进Fe³⁺水解,进而使得其更易与水中H₂PO₄^-与HPO₄^2-结合,生成具有多核羟基的磷酸铁络合物,进而提高除磷效果。     

Fenton法处理垃圾渗滤液MBR-NF浓缩液

采用Fenton法处理MBR-NF浓缩液,考察了FeSO4·7H2O投加量、n(H2O2)/n(Fe2+)投加比、初始pH对渗滤液MBR-NF浓缩液处理效果的影响,并在最佳实验条件下,探讨浓缩液富里酸(FA)、亲水性有机物(HyI)组分在Fenton氧化前后组成的变化。研究结果表明,在FeSO4·7H2O投加量为0.055 mol/L、n(H2O2)/n(Fe2+)投加比为4、初始pH为7.58时,对COD、腐植酸(UV254)、色度(CN)的去除率分别为79.6%、93.7%和97.8%。Fenton氧化后,浓缩液中有机物组分含量发生了较大变化,腐植酸含量下降,HyI成为渗滤液溶解性有机物主要成分。紫外-可见光谱表明,Fenton法对FA去除效果较好,而对HyI氧化效果较差;傅立叶红外光谱显示,经Fenton氧化后,FA的结构发生了明显变化,而HyI则变化不明显。     

Absorption of NO and NO2 in Caprolactam Tetrabutyl Ammonium Halide Ionic Liquids

ABSTRACT

To explore environmentally benign solvents for the absorption of NO and NO₂, a series of caprolactam tetrabutyl ammonium halide ionic liquids were synthesized. The solubility of NO and NO₂ was measured at temperatures ranging from 298.2 to 363.2 K and atmospheric pressure, and the following trend in the solubility of NO and NO₂ in ionic liquids with various halide anions was observed, respectively: F > Br > Cl and Br > Cl > F. Moreover, as the temperature increased from 308.15 to 363.15 K and the mole ratio of caprolactam increased from 2:1 to 6:1, the solubility of NO increased. Alternatively, the solubility of NO₂ decreased as the temperature increased from 298.15 to 363.15 K, and the mole ratio of caprolactam increased from 2:1 to 6:1. The absorption and desorption of NO and NO₂ was practically reversible in the ionic liquids, which was characterized by nuclear magnetic resonance. The method, which is at least partially reversible, offers interesting possibilities for the removal of NO and NO₂.

IMPLICATIONS Basic ionic liquids with amino groups were synthesized and used to capture CO₂, SO₂, and H₂S, and to promote hydrogenation of CO₂. In this paper, the authors used caprolactam tetrabutyl ammonium halide ionic liquid (IL) as absorbing medium in which NO_x could be absorbed. NO_x desorbed from the absorbent could be efficiently reduced by right catalysts at high temperature. The absorbed NO and NO₂ gas could be desorbed at higher temperature, allowing the ionic liquids to be reused several times without loss of capability. It was believed that caprolactam tetrabutyl ammonium bromide (CPL-TBAB) ILs may be useful for NO_x removal reagent for pollution control.     

臭氧辅助UV/Fenton法处理电镀添加剂生产废水

采用臭氧辅助光芬顿法处理电镀添加剂生产废水,考察双氧水、FeSO₄·7H₂O、pH和反应时间等因素对废水COD和UV₂₅₄去除的影响。实验结果表明,pH=4,臭氧通入量为0.25 g,双氧水的投加量93.3 mL/L,FeSO₄·7H₂O投加量为5.3 g/L,最佳反应时间为30 min,COD和UV₂₅₄去除率分别达到92.64%和87.95%。这表明,臭氧辅助光芬顿法对电镀添加剂生产废水处理效果显著,处理时间大大减少。     

Synthesis of a novel slow-release potassium fertilizer from modified Pidgeon magnesium slag by potassium carbonate

A novel slow-release potassium fertilizer (SPF) was synthesized using Pidgeon magnesium slag (PMS) and potassium carbonate, which could minimize fertilizer nutrient loss and PMS disposal problems. Orthogonal experiments were conducted to determine the optimum conditions for synthesis. The potassium (K)-bearing compounds of SPF existed mainly in the form of crystalline phases Ca_1.197K_0.166SiO₄, K₂MgSiO₄, and K₄CaSi₃O₉, and in the noncrystalline phase. The active silicon content of SPF was 2.09 times as much as that of magnesium slag, and the slow-release character of SPF met the requirement for partly slow-release fertilizer in the national standard (GB/T23348-2009). The best models for describing the K release kinetics in water and 2% citric acid were the Elovich model and the first-order model, respectively. The heavy metal contents of SPF conformed to the national standard for organic–inorganic compound fertilizers, and the leaching mass concentrations of heavy metals and Fluorine were far lower than the limit values of the identification standard for hazardous waste identification for extraction toxicity (GB5085.3-2007), and also met the class II quality standard for ground water. The environmental risk of SPF is therefore very low, but because SPF is alkaline, its effect on soil pH should be taken into account.

Implications: PMS is the solid waste resulting from the production of magnesium metal by Pidgeon’s reduction process. Utilization of PMS in the high-technology and high-value areas may promote the high-efficiency development of worldwide collection metallic magnesium industry and contribute to the reduction of emissions of fine dust to air. This paper presents one of the new techniques in the use of PMS as a slow-release fertilizer by adding K₂CO₃. The product can serve as a very cost-effective and reliable artificial fertilizer.     

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.