Bioelectrochemical acidolysis of magnesia to induce struvite crystallization for recovering phosphorus from aqueous solution

A novel struvite crystallization method induced by bioelectrochemical acidolysis of magnesia(MgO) was investigated to recover phosphorus(P) from aqueous solution using a dual-chamber microbial electrolysis cell(DMEC). Magnesium ion(Mg~(2+)) in the anolyte was firstly confirmed to automatically migrate from the anode chamber to the cathode chamber, and then react with ammonium(NH+4) and phosphate(PO_4~(3-)) in the catholyte to form struvite. Recovery efficiency of 17.8%–60.2% was obtained with the various N/P ratios in the catholyte. When MgO(low solubility under alkali conditions) was added into the anolyte, the bioelectrochemical acidolysis of MgO naturally took place and the released Mg~(2+)induced struvite crystallization in the cathode chamber for P recovery likewise.Besides, there was a strong linear positive correlation between the recovery efficiency and the MgO dosage(R~2= 0.935), applied voltage(R~2= 0.969) and N/P ratio(R~2= 0.905). Increasing the applied voltage was found to enhance the P recovery via promoting the MgO acidolysis and the released Mg~(2+)migration, while increasing the N/P ratio in the catholyte enhanced the P recovery via promoting the struvite crystallization. Moreover, the electrochemical performance of the system was promoted due to more stable anolyte pH and lower pH gradient between the two chambers. Current density was promoted by 10%, while the COD removal efficiency was improved from 78.2% to 91.8% in the anode chamber.     

Monodisperse amino-modified nanosized zero-valent iron for selective and recyclable removal of TNT: Synthesis, characterization, and removal mechanism

Nitroaromatic explosives are major pollutants produced during wars that cause serious environmental and health problems. The removal of a typical nitroaromatic explosive, 2,4,6-trinitrotoluene (TNT), from aqueous solution, was conducted using a new recyclable magnetic nano-adsorbent ([email protected]₂NH₂). This adsorbent was prepared by grafting amino groups onto [email protected]₂ particles with a well-defined core-shell structure and demonstrated monodispersity in solution. The removal performance of the nano-adsorbent towards TNT was found to be 2.57 and 4.92 times higher than that towards two analogous explosives, 2,4-dinitrotoluene (2,4-DNT) and 2-nitrotoluene (2-NT), respectively, under neutral conditions. The difference in the removal performance among the three compounds was further compared in terms of the effects of different conditions (pH value, ionic strength, humic acid concentration, adsorbent modification degree and dosage, etc.) and the electrostatic potential distributions of the three compounds. The most significant elevation is owing to modification of amino on [email protected]₂ which made a 20.7% increase in adsorption efficiency of TNT. The experimental data were well fit by the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model, indicating multilayer adsorption on a heterogeneous surface. The experimental results and theoretical considerations show that the interactions between [email protected]₂NH₂ NPs and TNT correspond to dipole-dipole and hydrophobic interactions. These interactions should be considered in the design of an adsorbent. Furthermore, the adaptability to aqueous environment and excellent regeneration capacity of [email protected]₂NH₂ NPs makes these remediation materials promising for applications.     

The evaluation of potential purification of a horizontal subsurface flow constructed wetland treating greywater in semi-arid environment

The potential purification of an horizontal subsurface flow constructed wetlands (HSSFCW) treating greywater in a Moroccan primary school was investigated according to the monitoring of water quality parameters over a period of 100 days through two simultaneous stages: first, an internal three dimensional grid of sampling ports; secondly, an entry and exit. The calibration of the relaxed TIS concentration model based on tank in series hydraulic assumption with experimental data gave the frequency distribution profiles of K-rate constant values for the three parameters: BOD₅, COD and TN, whose maximum values are respectively 50 m/yr, 70 m/yr, and 42 m/yr. The HSSFCW system has higher K-rate coefficient for all the three parameters at the bottom layer compared with the surface layer, with increasing K-rates over length. The analysis of bacteriological and chemical results has shown that the HSSFCW could not completely remove all pollutants (especially TN and TP), but it could be used successfully to upgrade the quality of greywater to an acceptable level. However, we predict that there will be an increase in removal efficiencies with time bearing in mind that the system is newly implemented.     

Transformation of phosphorus during drying and roasting of sewage sludge

Sewage sludge (SS), a by-product of wastewater treatment, consists of highly concentrated organic and inorganic pollutants, including phosphorus (P). In this study, P with different chemical fractions in SS under different drying and roasting temperatures was investigated with the use of appropriate standards, measurements, and testing protocol. The drying and roasting treatment of SS was conducted in a laboratory-scale furnace. Two types of SS samples under different treatment temperatures were analyzed by ³¹P NMR spectroscopy. These samples were dried by a vacuum freeze dryer at ?50 °C and a thermoelectric thermostat drying box at 105 °C. Results show that the inorganic P (IP) content increased as the organic P content decreased, and the bio-availability of P increased because IP is a form of phosphorous that can be directly absorbed by plants. ³¹P NMR analysis results indicate the change in P fractions at different temperatures. Non-apatite P was the dominant form of P under low-temperature drying and roasting, whereas apatite P was the major one under high-temperature drying and roasting. Results indicate that temperature affects the transformation of P.     

Phosphorus loss from different farming systems estimated from soil surface phosphorus balance

The phosphorus load originating from crop production and animal husbandry is a major contributor to the eutrophication of lakes, rivers and coastal waters. The P losses to surface waters may, however, differ drastically due to the diversity of agricultural production systems practised under contrasting environmental conditions. To assess the most problematic types of agriculture, we need information on the P load from different alternative farming practices. Such information cannot, however, be obtained solely from field runoff experiments, as the number of treatment combinations required to account for all relevant farming systems and environmental conditions far exceeds our research capabilities. To facilitate the comparison of P loads, we therefore need reasonably simple models. A key factor controlling the P load from agriculture is the past and present use of nutrients in fertilizers and manure in relation to a crop's uptake, i.e. the soil-surface balance of P. Here, we present a simple empirical model that relates the P surplus (or deficit) in a farm to the edge-of-field losses of algal-available P. Based on long-term fertilizer trials, the model first estimates the change in soil-test P of top soil with the aid of the soil-surface balance of P. Soil-test P is then used to approximate the concentration of dissolved reactive P in surface runoff and drainage flow, as adjusted for different P application types. The loss of particulate P is obtained from typical erosion rates. The model can be applied in life-cycle analyses and in assessing future developments. We illustrate use of the model by calculating the loss of algal-available P from conventional and organic crop and dairy farms located on clay and fine sand soils.     

催化技术去除柴油机排放碳颗粒的研究进展

综述了柴油机排放碳颗粒催化燃烧中运用的贵金属催化剂、过渡金属催化剂、(类)钙钛矿催化剂以及催化技术与低温等离子体技术协同作用的最新研究进展,介绍了上述催化剂和催化技术的作用机理,并探讨了它们在实际应用中存在的问题和应用前景。     

利用焦炭吸附进行燃煤烟气脱硫脱氮技术的研究

介绍一种干法烟气脱硫脱氮工艺方法 ,利用一种非常容易获得炭质吸附材料经过简单的工艺处理后 ,达到燃煤烟气脱硫脱氮效果 ,整个过程不产生二次污染     

滤料可溶氨对测定水体中氨氮影响的消除

本文介绍了常用滤料中可溶性氨含量和对水体中氨氮含量测定的影响。根据实验结果，作者提出了消除影响的一些具体措施。     

碱性黑液酸析前后还原糖去除率的研究

用3,5-二水杨酸法测黑液里还原糖含量。通过正交试验法，探讨了黑液质量分数、反应温度、硫酸质量分数及搅拌时间对黑液酸析前后还原糖去除率的影响，得出的最佳工艺条件是：黑液质量分数为10％．反应温度为700℃，硫酸质量分数为10％，搅拌时间35min。     

移动式旋风颗粒层除尘器的设计研究

本文阐述了一种新型二级垂直移动式颗粒层除尘器，它的关键技术采用独创的床外清灰及气流输送、滤料循环系统．该除尘器１９９１年已获国家实用新型专利，它的适用范围广，除尘效率高，无二次污染。适用于粉尘、烟气等污染源的治理，使排放浓度达标．