Yellow phosphorous is an important raw material in the chemical industry. However, during the production of yellow phosphorous, high concentrations of carbon monoxide and other impurities are released. Without appropriate purification and removal, this off gas has potential to cause severe pollution problems once released. Purified yellow phosphorous off gas can be beneficially reused as a raw material in chemical production for synthesis of high value-added chemical reagents. In this paper, the significance of purification and reutilization of yellow phosphorous off gas are explored. The principles, processes, and main characteristics of the technologies for purification and reuse of yellow phosphorus off gas (including technical measurements of impurity reduction, relevant engineering cases, and public acceptance of the technologies) are summarized. In view of the existing problems and scientific development requirements, this paper proposes several recommendations for green production based on the concept of recycle economics. We conclude that advanced purification and comprehensive reutilization can be an effective solution for heavy pollution resulting from yellow phosphorous off gassing.
To recycle the sludge resource from sewage treatment plants and solve the problem of odor pollution, the sludge was converted into an adsorbent by carbonized pyrolysis and the process was optimized by orthogonal experiments. The capability for odor removal as well as the structure of the adsorbent was studied with H2S as a target pollutant. The results indicate that the main factor affecting the deodorization performance of the adsorbent is the activating time. The sludge adsorbent sample SAC1 prepared under optimum conditions exhibits the best deodorization performance with a H2S breakthrough time of 58 min and an iodine value nearly that of the coal activated carbon. The breakthrough time of H2S is much longer than that on the coal activated carbon. On the other hand, characterization results from X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS) and scanning electron microscope (SEM) techniques show that SAC1 is composed of mainly graphite carbon with lower oxygen content on the surface. The bulk of SAC1 exhibits a honeycomb structure with well developed porosity and a high specific surface area of 120.47 m2·g-1, with the average pore diameter being about 5 nm. Such a structure is in favor of H2S adsorption. Moreover, SAC1 is detected to contain various metal elements such as Zn, Fe, Mg, etc., leading to a superior deodorization property to that of coal activated carbon.
C60, as one of carbon nanomaterials widely used in various fields, could be released into the water environment thus exerting some potential health risks to human beings. This work examined the behavior of aqueous stable colloidal nano-C60 (nC60) aggregates under different environmental conditions including Polyethylene glycol octylphenol ether (TX100) micelles concentration, pH, and reaction time when exposed to TX100 micelles. Results show that the nC60 aggregates became more dispersive and restored the capability of generating the singlet oxygen when exposed to TX100 micelles. With the increase of TX100 concentration, smaller average size of nC60 aggregates was observed in dynamic light scattering (DLS) analysis, the fluorescence intensity of TX100 was more quenched by nC60 aggregates, and the kinetic rate constant of generating the singlet oxygen for nC60 aggregates was improved. The mean size of nC60 aggregates in the presence of TX100 had no obvious variations when the pH ranged from 4 to 8. The longer reaction time between nC60 aggregates and TX100 led to a higher kinetic rate constant of generating the singlet oxygen. Collective data suggest that variations in physicochemical properties of nC60 aggregates are strongly dependent on the surrounding media under different environmental conditions and directly govern nC60’s transport behavior and potential toxicity.
This work explores the feasibility of Jerusalem artichoke stem (JAS), an agricultural waste, as an alternative precursor for fabrication of mesoporous activated carbon (MAC) via conventional ZnCl2 activation. The as-prepared JAS-MACs were characterized by thermogravimetric, nitrogen gas adsorption isotherm and high resolution scanning electron microscopy analysis. The interacting effects of chemical dosage, activation temperature and time on the mesoporosity, mesopore volume and carbon yield were investigated, and further optimized by response surface methodology (RSM). The Brunauer-Emmett-Teller surface area, mesoporosity and mesopore volume of the JAS-MAC prepared under optimum condition were identified to be 1631 m2·g-1, 90.16% and 1.11 cm3·g-1, respectively. Compared with commercial activated carbons, this carbon exhibited a comparable monolayer adsorption capacity of 374.5 mg·g-1 for Methylene Blue dye. The findings suggest that RSM could be an effective approach for optimizing the pore structure of fabricated activated carbons.
The interaction of the fly ash and NaOH, in an open reflux hydrothermal system at 100°C, has been explored by several researchers and formation of fly ash zeolites has been confirmed based on the X-ray diffraction analysis of the residues. However, this method does not reveal much about the characteristic transitions (viz. elemental, electro-negativity and cation exchange capacity) of the residues. In this situation, resorting to Fourier transform-infrared radiation (FT-IR) spectroscopy on the residues obtained from two-stage hydrothermal treatment process, described in this manuscript, appears to be a novel idea to establish transitions in chemical bonds (viz., -Si-OH-Al-, OH-Na, OH-Al-), crystallinity and cation exchange capacity of these residues. Based on extensive studies, it has been demonstrated that FT-IR spectroscopy is extremely useful for 1) detection of chemical bonds in the residues, 2) evaluation of zeolites in the residues and 3) also establishing the superiority of the two-stage interaction of the fly ash with NaOH for synthesizing better fly ash zeolites (viz., Na-P1 and Hydroxysodalte) as compared to those obtained from the conventional single-stage treatment of the fly ash.
An “Oxygen-enriched” highly reactive absorbent was prepared by mixing fly ash, lime and a small quantity of KMnO4 for simultaneous desulfurization and denitrification. Removal of SO2 and NO simultaneously was carried out using this absorbent in a flue gas circulating fluidized bed (CFB). The highest simultaneous removal efficiency, 94.5% of SO2 and 64.2% of NO, was achieved under the optimal experiment conditions. Scanning Electron Microscope (SEM) and Accessory X-ray Energy Spectrometer (EDX) were used to observe the surface characteristics of fly ash, lime, “Oxygen-enriched” highly reactive absorbent and the spent absorbent. An ion chromatograph (IC) and chemical analysis methods were used to determine the contents of sulfate, sulfite, nitrate and nitrite in the spent absorbents, the results showed that sulfate and nitrite were the main products for desulfurization and denitrification respectively. The mechanism of removing SO2 and NO simultaneously was proposed based on the analysis results of SEM, EDX, IC and the chemical analysis methods.
Under both pyrolysis and combustion condition, HCl removal efficiency for medical waste with Ca-based additives was semi-quantitatively studied by means of TG-FTIR. Additionally, the difference of HCl removal efficiency for PVC and medical waste was compared. Experimental results showed that: 1) Thermal degradation of medical waste mainly took place in two steps under both pyrolysis and combustion condition; 2) HCl emitted at both two steps and HCl concentration increased with the increased of Cl ratio in the medical waste; 3) for the same additive, HCl concentration decreased with the increased of additives amount, that is to say, HCl removal efficiency of medical waste increased as the increased of Ca/Cl molar ratio. Fourth, when Ca(OH)2 was used as additive, HCl removal efficiency for medical waste combustion was a little higher than that for medical waste pyrolysis, but either CaCO3 or CaO was used as additive, it was just opposite, more specifically, when CaCO3 was used as additive with Ca/Cl=1.3, HCl removal efficiency was 5.49% under pyrolysis condition, but that was only 4.24% under combustion condition. Fifth, under the same Ca/Cl molar ratio, HCl removal efficiency for PVC was higher than that for medical waste under both pyrolysis and combustion condition, more specifically, when Ca(OH)2 was used as additive with Ca/Cl=1, HCl removal efficiency was 64.51% for PVC, but that was only 27.66% for medical waste pyrolysis with 4% Cl under pyrolysis condition.
Concentrations of the heavy metals Cu, Ni, Pb, Zn, Cd, and Cr were examined in surface water and sediment from the Luan River inChina,. With a decline in Cu and Ni concentration found in surface water at downstream stations. This finding suggests that water currents are a major explanatory factor in heavy metal contamination. The abundance of Cr, Pb, and Cd observed in the middle reaches of the river indicates heavy metal contamination in local areas, although there was an obvious decrease in concentrations in the water downstream of the Daheiting Reservoir. The significant rising trend in Cu, Pb, and Ni seen the sediment farther away from the river also suggests that anthropogenic activities contribute to heavy metal pollution Sediments were therefore used as environmental indicators, with sediment assessment was conducted using the geo-accumulation index (Igeo) and the potential ecological risk index (RI). The Igeo values revealed that Cd (3.13) and Cr (2.39) had accumulated significantly in the Luan River. The RI values for most (89%) of the sampling stations were higher than 300, suggesting that sediment from the Luan River poses a severe ecological risk, with the potential ecological risks downstream higher than that in the upper and middle streams. Good correlations among Pb/Ni, Pb/Cd, Cu/Pb, and Cu/Cd in the water and Cr/Ni in the sediment were observed. Cluster analysis suggested that Cd may have various origins, being derived from anthropogenic sources.
Solution culture was conducted in order to understand accumulation characteristics and chemical forms of Pb in Arenaria orbiculata (A. orbiculata) and the response of root exudates to Pb addition. The results showed that: 1) Pb contents in the shoot and root of A. orbiculata increased with increasing in Pb concentrations in solution. 2) The contents of Pb chemical forms under Pb addition followed as: HAc extractable fraction (FHAC)>HCl extractable fraction (FHCl)>NaCl extractable fraction (FNaCl)>ethanol-extractable fraction (FE)>water extractable fraction (FW). 3) Increased Pb level in the medium caused increases in Pb contents in the four subcellular fractions of shoots and roots, with most accumulation in FIV (Fraction IV, soluble fraction) in shoots and FI (Fraction I, cell wall fraction) in roots. 4) Contents of soluble sugar and free amino acid of root exudates increased with increasing Pb concentration in solution. Significantly positive correlations between Pb and contents of soluble sugar and free amino acid were observed. 5) With Pb concentrations in solution, low molecular weight organic acids (LMWOAs) contents followed the tendency: tartaric acid>acetic acid>malic acid>citric acid. Significantly positive correlation was observed between Pb and citric acid contents. The results indicate that soluble sugars, free amino acid and citric acid in root exudates of A.orbiculata facilitate the absorption and accumulation of Pb, which exist in NaCl-, HCl- and HAc- extractable Pb forms, FI and FIV fractions, resulting in tolerance of A.orbiculata to Pb.
We investigated phytotoxicity in seven plant species exposed to a range of concentrations (0– 500 mg·kg−1 soil) of di-n-butyl phthalate (DnBP) or bis (2-ethylhexyl) phthalate (DEHP), two representative phthalate esters (PAEs) nominated by USEPA as priority pollutants and known environmental estrogens. We studied seed germination, root elongation, seedling growth, biomass (fresh weight, FW) and malondialdehyde (MDA) content of shoots and roots of wheat (Triticum aestivum L.), alfalfa (Medicago sativa L.), perennial ryegrass (Lolium perenne), radish (Raphanus sativus L.), cucumber (Cucumis sativus L.), oat (Avena sativa) and onion (Allium cepa L.), together with monitoring of plant pigment content (chlorophyll a, b and carotinoids) in alfalfa, radish and onion shoots. Root elongation, seedling growth and biomass of the test species were generally inhibited by DnBP but not by DEHP, indicating a lower level of phytotoxicity of DEHP than of DnBP. MDA contents of four species were promoted by PAE exposure, but not in alfalfa, ryegrass or onion shoots, indicating lower sensitivity of these three species to PAE pollutants. Plant pigment contents were clearly affected under the stress of both pollutants, implying the potential damage to the photosynthetic system of test plants, mainly by decreasing the content of chlorophyll a and b. Results of DnBP and DEHP phytotoxicity to the primary growth of test plants has provided information for the assessment of their environmental risk in the soil and also forms a basis for the further analysis of their toxic effects over the whole growth period of different plant species.
Soil moisture variability in natural landscapes has been widely studied; however, less attention has been paid to its variability in the urban landscapes with respect to the possible influence of texture stratification and irrigation management. Therefore, a case study was carried out in the Beijing Olympic Forest Park to continuously monitor the soil in three typical profiles from 26 April to 11 November 2010. The texture stratification significantly affected the vertical distribution of moisture in the non-irrigated profile where moisture was mostly below field capacity. In the profile where irrigation was sufficient to maintain moisture above field capacity, gravity flow led to increased moisture with depth and thus eliminated the influence of texture. In the non-irrigated sites, the upper layer (above 80 cm) exhibited long-term moisture persistence with the time scale approximating the average rainfall interval. However, a coarse-textured layer weakened the influence of rainfall, and a fine-textured layer weakened the influence of evapotranspiration, both of which resulted in random noise-like moisture series in the deeper layers. At the irrigated site, frequent irrigation neutralized the influence of evapotranspiration in the upper layer (above 60 cm) and overshadowed the influence of rainfall in the deeper layer. As a result, the moisture level in the upper layer also behaved as a random noise-like series; whereas due to deep transpiration, the moisture of the deep layer had a persistence time-scale longer than a month, consistent with characteristic time-scales found for deep transpiration.
There is no alternative to the world’s water resources, and their increasing scarcity is making it difficult to meet the world population’s water needs. This paper presents a sustainable water resources system (SWRS) and analyzes the operating mechanism that makes it possible to evaluate the status of such a system. A SWRS can be described as a complex coupling system that integrates water resources, social, economic and ecological systems into a whole. The SWRS’s operating mechanism is composed of dynamic, resistance and coordination components, and it interacts with and controls the system’s evolution process. The study introduces a new approach, set pair analysis theory, to measure the state of a SWRS, and an evaluation index system is established using the subsystems and operating mechanism of a SWRS. The evaluation index system is separated into three levels (goal level, criteria level and index level) and divides the index standard into five grades. An evaluation model of the SWRS based on set pair analysis theory is constructed, and an example of SWRS evaluation in Shanghai is presented. The connection degrees of the index in the three levels are calculated, and the connection degree of the goal index is calculated to be 0.342, which classifies the city’s SWRS condition as grade 2. The sustainable use of water resources in the region is determined to be at a relatively adequate level that meets the requirements of sustainable development.
Since the reform and opening-up, China’s economy has achieved remarkable development and so does the urbanization. However, there is an unavoidable contradiction between urban sprawl and the protection of arable land and the environment. By redefining the urban sprawl boundary, this paper is to provide a solution for the conflict above on the China’s urbanization context. The ideal boundary, moderate boundary and limit boundary are defined for urban sprawl in space. Taking Nanjing city as a case, the three urban sprawl boundaries are estimated in this paper based on the calculation of agricultural land resources value in Nanjing. The results show that 1) the integrated value of agricultural (cultivated) land resources in Nanjing is 1.55 × 107 CNY·hm−2, the economic value accounts for only 8.74% of the integrated value, while 91.26% of the integrated value has not revealed itself due to the existing institutional arrangements, policy distortions, and imperfect land market; 2) it is difficult to define the ideal and moderate boundaries due to the relatively low price of North Nanjing. In South Nanjing the land price is expensive and the ideal, moderate and limit boundaries are expanded to Jiangning, Qixia, and Yuhuatai; 3) the city scale of South Nanjing should be limited within 5.82 × 104 hm2, which is roughly the same as the designated size of 5.81 × 104 hm2 in the urban planning. It is suggested that the rational scope of urban expansion should be controlled within the moderate boundary.
In this study, China’s current macro-environmental policies as well as their implementation and management tools are analyzed. By using the basic economic methodology, detailed studies are conducted focusing on the implementation effect of contemporary China’s typical environmental policy of the total pollutant discharge quantity control type, and also the two types of environmental management tools are compared from the perspective of implementation costs and policy uncertainty. By introduction of distributed management tools into the implementation of environmental policies, market-oriented means and the methods of economic analysis are introduced into environmental policy decision-making mechanisms, which could afford a new method for changing the current relatively low efficiency of environmental policy, solving the problem of “government failure” in environmental policy implementation, and providing a new way to make environmental policy system more flexible and more efficient. It is of great practical significance to solve China's current structural, complex and accumulative environmental problems.
Microbial desalination cell (MDC) is a promising technology to desalinate water and generate electrical power simultaneously. The objectives of this study were to investigate the desalination performance of monovalent and divalent cations in the MDC, and discuss the effect of ion characteristics, ion concentrations, and electrical characteristics. Mixed salt solutions of NaCl, MgCl2, KCl, and CaCl2 with the same concentration were used in the desalination chamber to study removal of cations. Results showed that in the mixed salt solutions, the electrodialysis desalination rates of cations were: Ca2+ >Mg2+>Na+>K+. Higher ionic charges and smaller hydrated ionic radii resulted in higher desalination rates of the cations, in which the ionic charge was more important than the hydrated ionic radius. Mixed solutions of NaCl and MgCl2 with different concentrations were used in the desalination chamber to study the effect of ion concentrations. Results showed that when ion concentrations of Na+ were one-fifth to five times of Mg2+, ion concentration influenced the dialysis more profoundly than electrodialysis. With the current densities below a certain value, charge transfer efficiencies became very low and the dialysis was the main process responsible for the desalination. And the phosphate transfer from the anode chamber and potassium transfer from the cathode chamber could balance 1%–3% of the charge transfer in the MDC.
Aerobic granules were formed in a conventional, continuous flow, completely mixed activated sludge system (CMAS). The reactor was inoculated with seed sludge containing few filaments and fed with synthetic municipal wastewater. The settling time of the sludge and the average dissolved oxygen (DO) of the reactor were 2 h and 4.2 mg·L-1, respectively. The reactor was agitated by a stirrer, with a speed of 250 r·min-1, to ensure good mixing．The granular sludge had good settleability, and the sludge volume index (SVI) was between 50 and 90 mL·g-1. The laser particle analyzer showed the diameter of the granules to be between 0.18 and 1.25 mm. A scanning electron microscope (SEM) investigation revealed the predominance of sphere-like and rod-like bacteria, and only few filaments grew in the granules. The microbial community structure of the granules was also analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Sequencing analysis indicated the dominant species were α, β, and γ-Proteobacteria, Bacteroidetes, and Firmicutes. The data from the study suggested that aerobic granules could form, if provided with sufficient number of filaments and high shear force. It was also observed that a high height-to-diameter ratio of the reactor and short settling time were not essential for the formation of aerobic granular sludge.
Optimization of an integrated anaerobic-aerobic bioreactor (IAAB) treatment system for the reduction of organic matter (Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) concentrations) in Palm Oil Mill Effluent (POME) to legal standards with high methane yield was performed for the first time under thermophilic condition (50°C–55°C) by using response surface methodology (RSM). The experiments were conducted based on a central composite rotatable design (CCRD) with three independent operating variables, organic loading rates in anaerobic compartment (OLRan) and mixed liquor volatile suspended solids (MLVSS) concentration in anaerobic (MLVSSan) and aerobic compartments (MLVSSa). The optimum conditions for the POME treatment were determined as OLRan of 15.6 g COD·L-1·d-1, MLVSSan of 43100 mg·L-1, and MLVSSa of 18600 mg·L-1, where high aerobic COD, BOD and TSS removal efficiencies of 96.3%, 97.9%, and 98.5% were achieved with treated BOD of 56 mg·L-1 and TSS of 28 mg·L-1 meeting the discharge standard. This optimization study successfully achieved a reduction of 42% in the BOD concentrations of the final treated effluent at a 48% higher OLRan as compared to the previous works. Besides, thermophilic IAAB system scores better feasibility and higher effectiveness as compared to the optimized mesophilic system. This is due to its higher ability to handle high OLR with higher overall treatment efficiencies (more than 99.6%), methane yield (0.31 L CH4·g-1 CODremoved) and purity of methane (67.5%). Hence, these advantages ascertain the applicability of thermophilic IAAB in the POME treatment or even in other high-strength wastewaters treatment.
We investigated the performance of a 15.3 L capacity anaerobic baffled reactor (ABR) toward the treatment of low-strength domestic wastewater. The start-up period of the ABR was finished within approximately 130 days at a temperature below 25°C. The average CODCr in the effluent was 165 mg·L-1, and the corresponding CODCr removal efficiency of the ABR was 52.3%. During the third stage (from day 130 to day 233) of ABR operation, the average CODCr in the effluent reached 71 mg·L-1, which meets the secondary discharge requirement of the Integrated Wastewater Discharge Standard (GB 18918-2002, China). Moreover, partial microbial separation was observed along the five ABR compartments through scanning electron microscopic images. The geometric mean diameter of bioparticles in the five compartments increased from 0.050 mm to 0.111, 0.107, 0.104, 0.110, and 0.103 mm during the start-up stage. After operation for 179 days, the corresponding diameters further increased to 0.376, 0.225, 0.253, 0.239, and 0.288 mm, respectively. The fractal dimensions of the bioparticles indicated that these particles have smoother surfaces and more compact structures during ABR operation. Morphological analysis of the bioparticle sections demonstrated that the bioparticles have a pore volume of 30%–55%. The highest porosity was observed for the bioparticles in the second ABR compartment, whereas the lowest fractal dimension of bioparticle section was observed in the fifth compartment.
Hydrogen sulfide emission in sewer systems is associated with toxicity, corrosion, odour nuisance and high costs treatment. In this study, a novel method to inhibit sulfide generation from sewage by means of glutaraldehyde supplementation has been suggested and evaluated under anaerobic conditions. Different concentrations of glutaraldehyde at 10, 15, 20, 30 and 40 mg·L-1 have been investigated. Besides, the possible impacts of glutaraldehyde supplementation on an activated sludge system and an appraisal of the economic aspects are presented as well. As observed from the experimental results, a dosage of 20 mg·L-1 glutaraldehyde resulted in a significant decrease of the sulfide production by 70%–80% in the simulated sewage. Moreover, the impacts of additional glutaraldehyde at 20 mg·L-1 on activated sludge, in terms of chemical oxygen demand removal and oxygen uptake rates, were negligible. From an economical point of view, the cost of the commercial glutaraldehyde products required in the operation, which was calculated on the basis of activated sulfide removal avoidance, was around €3.7–4.6 S·kg-1. Therefore it is suggested that glutaraldehyde supplementation is a feasible technique to abate the sulfide problems in sewer systems. Yet further research is required to elucidate the optimum “booster” dosage and the dosing frequency in situ accordingly.