Formation kinetics and reaction behavior of pentavalent chromium formed in the cement kiln co-processing of solid waste.

Cement kiln co-processing is becoming the main strategy to dispose of hazardous waste containing Cr. A newly-discovered pentavalent Cr compound, which was proved to be formed during cement kiln co-processing of solid waste, is partly responsible for the water-soluble Cr released from the cement. However, the formation characteristics and the solubility of Cr(V) are still unclear to date. In this study, the reaction kinetics and further redox reactions of Cr(V) at high temperature were examined, and its crystal structure and solubility were also explored. At the temperature range of 1000-1200 °C, the formation rate of Ca5(CrO4)3O0.5 reached over 90 % within 10 min, and then slowly increased to near 100 % from 10 min to 10 h. shows that Ca5(CrO4)3O0.5 is formed by interface reaction at an early period, and by diffusion at a later period. The kinetic analysis indicates that Ca5(CrO4)3O0.5 is initially formed through an interface reaction and subsequently through diffusion. Ca5(CrO4)3O0.5 was identified and assigned as hexagonal crystal group (P63/m). Approximately 0.55 g and 0.15 g of Ca5(CrO4)3O0.5 dissolve in neutral water at 100 °C and 50 °C, and the concentrations of Cr(V) in water reach 550 and 150 mg/L, respectively. Additionally, this study finds that at the temperature range of 400-700 °C Ca5(CrO4)3O0.5 can be oxidized into CaCrO4, and at the temperature higher than 1400 °C, it can be further converted into Ca3(CrO4)2 and reduced into CaCr2O4. This study gives a deep insight into Cr oxidation-reduction reaction during thermal treatment of solid waste. These insights provide a comprehensive understanding of Cr oxidation-reduction reactions during the thermal treatment of solid waste, offering valuable guidance for waste management strategies.

The impact of predators of mosquito larvae on Wolbachia spreading dynamics.

Dengue fever creates more than 390 million cases worldwide yearly. The most effective way to deal with this mosquito-borne disease is to control the vectors. In this work we consider two weapons, the endosymbiotic bacteria Wolbachia and predators of mosquito larvae, for combating the disease. As Wolbachia-infected mosquitoes are less able to transmit dengue virus, releasing infected mosquitoes to invade wild mosquito populations helps to reduce dengue transmission. Besides this measure, the introduction of predators of mosquito larvae can control mosquito population. To evaluate the impact of the predators on Wolbachia spreading dynamics, we develop a stage-structured five-dimensional model, which links the predator-prey dynamics with the Wolbachia spreading. By comparatively analysing the dynamics of the models without and with predators, we observe that the introduction of the predators augments the number of coexistence equilibria and impedes Wolbachia spreading. Some numerical simulations are presented to support and expand our theoretical results.

Preparation of a novel iron oxychloride (FeOCl) auxiliary electrode in promoting electrokinetic remediation of Cr(VI) contaminated soil: An experimental and DFT calculation analysis.

The utilization of auxiliary electrode can improve substantially the electrokinetic remediation efficiency of heavy metal contaminated soil. The increase in the auxiliary electrode performance is the key to further promote the electrokinetic remediation efficiency. In this study, two kinds of auxiliary electrodes, pure FeOCl and doped FeOCl with W and S, were prepared and used in the electrokinetic remediation of Cr(VI) contaminated soil. The system equipped with the auxiliary electrode doped FeOCl brought more stable system current (202 mA) and more uniform electric field than blank group (130 mA). The reduction rate of Cr(VI) was increased by 50% due to the presence of Fe2+ and S2-. The accelerating migration of ions by auxiliary electrode was responsible for the improvement in electrokinetic remediation efficiency. Density functional theory (DFT) calculation showed that Cl vacancy formation energies of pure FeOCl, S-doped FeOCl (S/FeOCl) and W-doped FeOCl (W/FeOCl) were 1.29, 1.15 and 1.49 eV respectively, and the ion diffusion barriers were 0.093, 0.099 and 0.148 eV respectively. Calculation results indicated that the doping of S was conducive to the diffusion of Cl ions, and the bonding of W-Cl was stronger than Fe-Cl. The charging and discharging process of auxiliary electrode became easier due to the formation of lower vacancy in S-doped FeOCl, which could bring a higher current for the electrokinetic remediation system. The electrochemical performance of FeOCl doped with W and S was improved obviously. This study provided a further explanation for the positive role of auxiliary electrode in electrokinetic remediation system.

Oxidation and reduction reactions of (Al/FexCr1-x)2O3 caused by CaO during thermal treatment of solid waste containing Cr.

Solid solutions of (AlxCr1-x)2O3 and (FexCr1-x)2O3 are predominant compounds containing Cr in solid waste and are frequently formed during thermal treatment of solid waste. (AlxCr1-x)2O3 and (FexCr1-x)2O3 have superior thermomechanical properties and excellent corrosion resistance. However, oxidation and reduction reactions of the Cr in these solid solutions seriously affect their chemical stabilities and the environmental risks posed by the final products. In this study, first the reaction behaviors of (AlxCr1-x)2O3 and (FexCr1-x)2O3 at high temperatures were analyzed and whether the incorporation of Cr(III) in solid solutions can prevent Cr(III) from being oxidized was determined. Both (AlxCr1-x)2O3 and (FexCr1-x)2O3 without the presence of CaO exhibit good thermal stability at high temperatures. However, the participation of CaO induces Cr(III) oxidation in (AlxCr1-x)2O3 and (FexCr1-x)2O3 at 500-1000 °C. Cr(III) oxidation in these solid solutions is accompanied by the formation of CaCrO4 and Fe2O3 or Al2O3. Al2O3 combines with CaCrO4 and further forms a more stable Cr(VI) compound (e.g., Ca4Al6O12CrO4). While Fe2O3 combines with CaCrO4 at 1000-1200 °C. This is accompanied by the formation of CaCr2O4 and CaFe2O4, which effectively promotes the reduction of Cr(VI). Moreover, part of the CaCr2O4 transforms into a more stable phase (i.e., FeCr2O4) at 1200-1300 °C. Although the incorporation of Cr(III) in these solid solutions cannot prevent Cr(III) oxidation completely at high temperatures, the Cr(III) oxidation in these solid solutions is still suppressed compared with Cr2O3. The results of this study provide further insights into the oxidation and reduction reactions of Cr-hosting compounds during thermal treatment of solid waste.

Oxidation reaction behavior of Cr-hosting spinels during heating of solid wastes containing Cr.

Cr-hosting spinels are frequently formed during heating of solid wastes containing multiple metals, and its oxidation reaction (Cr(III) → Cr(VI)) is closely related with the toxicity of products. This study examined the reaction behaviors of Cr-hosting spinels (ZnCr2O4, CuCr2O4 and NiCr2O4) at high temperature and proposed possible oxidation mechanism. Cr-hosting spinels alone usually exhibit good thermal stability at high temperature. However, CaO can trigger the oxidation of Cr(III) in Cr-hosting spinels at 500-900 °C and ZnCr2O4 is easier to be oxidized than NiCr2O4 and CuCr2O4 at same condition. The oxidation of Cr-hosting spinels is accompanied with the formation of CaCrO4 and divalent metal oxides (ZnO, NiO and CuO). The broken and rebuilding of CrO bonds are key steps for Cr-hosting spinels oxidation, blocking the combination of free Cr with Ca and O atoms maybe more effective approach for suppressing Cr(III) oxidation. Furthermore, CaO can trigger the reduction of CaCrO4 into a new Cr(V) compound (Ca5(CrO4)3O0.5) at 900-1200 °C. As the temperature rising to 1300 °C, CuO reacts with CaCrO4 to form CuCrO2, in which Cu(II) and Cr(VI) are reduced into Cu(I) and Cr(III) respectively. This study provided some new knowledge for the reaction behavior of Cr-hosting spinels when solid wastes containing Cr were treated at high temperature.

Mosquito Control Based on Pesticides and Endosymbiotic Bacterium Wolbachia.

Mosquito-borne diseases, such as dengue fever and Zika, have posed a serious threat to human health around the world. Controlling vector mosquitoes is an effective method to prevent these diseases. Spraying pesticides has been the main approach of reducing mosquito population, but it is not a sustainable solution due to the growing insecticide resistance. One promising complementary method is the release of Wolbachia-infected mosquitoes into wild mosquito populations, which has been proven to be a novel and environment-friendly way for mosquito control. In this paper, we incorporate consideration of releasing infected sterile mosquitoes and spraying pesticides to aim to reduce wild mosquito populations based on the population replacement model. We present the estimations for the number of wild mosquitoes or infection density in a normal environment and then discuss how to offset the effect of the heatwave, which can cause infected mosquitoes to lose Wolbachia infection. Finally, we give the waiting time to suppress wild mosquito population to a given threshold size by numerical simulations.

Temperature dependent reduction of Cr(VI) to Cr(V) aroused by CaO during thermal treatment of solid waste containing Cr(VI).

Cr(VI) compounds at high temperature usually tend to decompose and reduce into Cr(III) due to thermodynamically instability for Cr(VI). This study found Cr(VI) could be reduced into Cr(V) instead of Cr(III) in the presence of CaO during heating solid waste containing Cr(VI). CaCrO4 is prepared and mixed with CaO as simulated solid waste containing Cr(VI). It was found that CaCrO4 reacted with CaO and formed a new product Ca5(CrO4)3O0.5 at temperature range of 800 and 1000 °C. The valence state of Cr in Ca5(CrO4)3O0.5 is determined to be +5 b y XPS analysis, and the color for new formed Cr(V) is observed in green, similar to Cr(III) compounds. The temperature and CaO are two keys to arouse the reduction reaction of Cr(VI) into Cr(V). In particular, the reduction of Cr(VI) into Cr(V) is strongly depended on temperature (800-1000 °C), this reaction can be balanced within 10 min, while prolonging sintering time has little help for promoting the reduction of Cr(VI) to Cr(V). Additionally, it was found Cr(V) can keep stable and not be re-oxidized into Cr(VI) at 800-1000 °C. Above results offers some new understanding and knowledge about the formation of Cr(V) in presence of much CaO or CaCO3 during heating solid waste containing Cr(VI).

Stable Introduction of Plant-Virus-Inhibiting Wolbachia into Planthoppers for Rice Protection.

Progress has been made in developing the maternally inherited endosymbiotic bacterium Wolbachia as a tool for protecting humans from mosquito-borne diseases. In contrast, Wolbachia-based approaches have not yet been developed for the protection of plants from insect pests and their associated diseases, with a major challenge being the establishment of artificial Wolbachia infections expressing desired characteristics in the hemipterans that transmit the majority of plant viruses. Here, we report stable introduction of Wolbachia into the brown planthopper, Nilaparvata lugens, the most destructive rice pest that annually destroys millions of hectares of staple crops. The Wolbachia strain wStri from the small brown planthopper, Laodelphax striatellus, was transferred to this new host, where it showed high levels of cytoplasmic incompatibility, enabling rapid invasion of laboratory populations. Furthermore, wStri inhibited infection and transmission of Rice ragged stunt virus and mitigated virus-induced symptoms in rice plants, opening up the development of Wolbachia-based strategies against major agricultural pests and their transmitted pathogens. VIDEO ABSTRACT.

Modeling the suppression dynamics of Aedes mosquitoes with mating inhomogeneity.

A novel strategy for controlling mosquito-borne diseases, such as dengue, malaria and Zika, involves releases of Wolbachia-infected mosquitoes as Wolbachia cause early embryo death when an infected male mates with an uninfected female. In this work, we introduce a delay differential equation model with mating inhomogeneity to discuss mosquito population suppression based on Wolbachia. Our analyses show that the wild mosquitoes could be eliminated if either the adult mortality rate exceeds the threshold [Formula: see text] or the release amount exceeds the threshold [Formula: see text] uniformly. We also present the nonlinear dependence of [Formula: see text] and [Formula: see text] on the parameters, respectively, as well as the effect of pesticide spraying on wild mosquitoes. Our simulations suggest that the releasing should be started at least 5 weeks before the peak dengue season, taking into account both the release amount and the suppression speed.

Incompatible and sterile insect techniques combined eliminate mosquitoes.

The radiation-based sterile insect technique (SIT) has successfully suppressed field populations of several insect pest species, but its effect on mosquito vector control has been limited. The related incompatible insect technique (IIT)-which uses sterilization caused by the maternally inherited endosymbiotic bacteria Wolbachia-is a promising alternative, but can be undermined by accidental release of females infected with the same Wolbachia strain as the released males. Here we show that combining incompatible and sterile insect techniques (IIT-SIT) enables near elimination of field populations of the world's most invasive mosquito species, Aedes albopictus. Millions of factory-reared adult males with an artificial triple-Wolbachia infection were released, with prior pupal irradiation of the released mosquitoes to prevent unintentionally released triply infected females from successfully reproducing in the field. This successful field trial demonstrates the feasibility of area-wide application of combined IIT-SIT for mosquito vector control.

Wolbachia spread dynamics in multi-regimes of environmental conditions.

Mosquito-borne diseases such as dengue fever and Zika kill more than 700,000 people each year in the world. A novel strategy to control these diseases employs the bacterium Wolbachia whose infection in mosquitoes blocks virus replication. The prerequisite for this measure is to release Wolbachia -infected mosquitoes to replace wild population. Due to the fluctuation of environmental conditions for mosquito growth, we develop and analyze a model of differential equations with parameters randomly changing over multiple environmental regimes. By comparing the dynamics between the stochastic system and constructed auxiliary systems, combined with other techniques, we provide sharp estimates on the threshold releasing level for Wolbachia fixation. We define the alarm period of disease transmission to measure the risk of mosquito-borne diseases. Our numerical simulations suggest that more frequent inter-regime transitions help reduce the alarm period, and the disease transmission is more sensitive to the average climatic conditions than the number of sub-regimes over a given time period. Further numerical examples also indicate that the reduction in the waiting time to suppress 95% of wild population is more evident when the releasing amount is increased up to a double of the wild population.

Assessing the efficiency of Wolbachia driven Aedes mosquito suppression by delay differential equations.

To suppress wild population of Aedes mosquitoes, the primary transmission vector of life-threatening diseases such as dengue, malaria, and Zika, an innovative strategy is to release male mosquitoes carrying the bacterium Wolbachia into natural areas to drive female sterility by cytoplasmic incompatibility. We develop a model of delay differential equations, incorporating the strong density restriction in the larval stage, to assess the delicate impact of life table parameters on suppression efficiency. Through mathematical analysis, we find the sufficient and necessary condition for global stability of the complete suppression state. This condition, combined with the experimental data for Aedes albopictus population in Guangzhou, helps us predict a large range of releasing intensities for suppression success. In particular, we find that if the number of released infected males is no less than four times the number of mosquitoes in wild areas, then the mosquito density in the peak season can be reduced by 95%. We introduce an index to quantify the dependence of suppression efficiency on parameters. The invariance of some quantitative properties of the index values under various perturbations of the same parameter justifies the applicability of this index, and the robustness of our modeling approach. The index yields a ranking of the sensitivity of all parameters, among which the adult mortality has the highest sensitivity and is considerably more sensitive than the natural larvae mortality.

Complex wolbachia infection dynamics in mosquitoes with imperfect maternal transmission.

Dengue, malaria, and Zika are dangerous diseases primarily transmitted by Aedes aegypti, Aedes albopictus, and Anopheles stephensi. In the last few years, a new disease control method, besides pesticide spraying to kill mosquitoes, has been developed by releasing mosquitoes carrying bacterium Wolbachia into the natural areas to infect the wild population of mosquitoes and block disease transmission. The bacterium is transmitted by infected mothers and the maternal transmission was assumed to be perfect in virtually all previous models. However, recent experiments on Aedes aegypti and Anopheles stephensi showed that the transmission can be imperfect. In this work, we develop a model to describe how the imperfect maternal transmission affects the dynamics of Wolbachia spread. We establish two useful identities and employ them to find sufficient and necessary conditions under which the system exhibits monomorphic, bistable, and polymorphic dynamics. These analytical results may help find a plausible explanation for the recent observation that the Wolbachia strain ωMelPop failed to establish in the natural populations in Australia and Vietnam.

Wolbachia spread dynamics in stochastic environments.

Dengue fever is a mosquito-borne viral disease with 100 million people infected annually. A novel strategy for dengue control uses the bacterium Wolbachia to invade dengue vector Aedes mosquitoes. As the impact of environmental heterogeneity on Wolbachia spread dynamics in natural areas has been rarely quantified, we develop a model of differential equations for which the environmental conditions switch randomly between two regimes. We find some striking phenomena that random regime transitions could drive Wolbachia to extinction from certain initial states confirmed Wolbachia fixation in homogeneous environments, and mosquito releasing facilitates Wolbachia invasion more effectively when the regimes transit frequently. By superimposing the phase spaces of the ODE systems defined in each regime, we identify the threshold curves below which Wolbachia invades the whole population, which extends the theory of threshold infection frequency to stochastic environments.

[Preliminary Study on the Structural Characteristics of Residue from Rice Straw Burning in Field].

Because of their special structural characteristics, straw burning residues (biochar) have important impacts on the soil carbon sequestration and the transport and transformation behavior of pollutants. In this paper, a series of qualitative and quantitative analysis methods such as scanning electron microscopy (SEM) , X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) have been used to study the basic physical and chemical properties and structural features of rice straw burning residues generating at different incineration intensity in field. The results show that: the basic physical and chemical properties of straw burning residues from field were closely associated with the burning intensity. The higher the burning intensity, the lower the TOC content. Meanwhile, the order degree of carbon atoms in the resulting residue increased. Wherein the fatty component of rice straw burning residues is gradually reduced with the burning intensity while the aromaticity of rice straw burning residues is gradually increased. In addition, the organic components in the straw burning residues from field have more significant contribution to the surface area.