Dechlorination of PCBs by electrochemical reduction with aromatic radical anion as mediator

Mediated electrochemical reduction was applied to the dechlorination of polychlorinated biphenyls (PCBs) in tetra-n-butylammonium perchlorate/dimethylformamide solution. Rapid and complete dechlorination was possible with biphenyl or naphthalene as the mediator, whereas the reaction was much slower with anthracene or 9,10-diphenylanthracene. The reaction rate was so high with naphthalene or biphenyl radical anion that differences in reactivity could not be observed between congeners. Side reactions, other than biphenyl formation, could occur depending upon the mediators and the substrates, but contributed less than 10% of the total products in the case of naphthalene-mediated dechlorination. Almost all chloride ion formed in the dechlorination remained in the cathode solution. The order of the reaction was determined to be 0.5 for the substrate and 1 for the mediator (naphthalene) in the dechlorination of 2-chlorobiphenyl; identical to results for the mediated dechlorination of 1-chloronaphthalene. The reaction rate in practical PCB dechlorination could be estimated with the use of the initial concentration of the mediator and chlorine content of the solution provided that the problem of the deactivation of the electrode surface could be solved.     

A review on the conversion of cassava wastes into value-added products towards a sustainable environment

The solid and liquid wastes generated from cassava-based industries are organic and acidic in nature, which leads to various global concerns—primarily global warming and biodiversity loss. But the conversion of these wastes into value-added products associated with environmental pollution control contributes to sustainable development. Generally, the thermochemical process such as pyrolysis and gasification and biochemical processes such as anaerobic digestion have been applied for the conversion of cassava waste into value-added products. This review addresses the valorization of cassava wastes, which fulfill almost all needs of the hour, such as energy (biofuel), wastewater treatment (adsorbents), bioplastics, starch nanoparticles, organic acid production, and antimicrobial agents. The major aim of this paper is to analyze and provide the disclosure of the efficiency of cassava-based industrial waste as a source to minimize the problem associated with conventional fossil fuels and through which mitigate the impact of global warming and climate change. Furthermore, recent research and achievements in the valorization of cassava waste have been highlighted.

     

Dechlorination of polychlorinated organic compounds by electrochemical reduction with naphthalene radical anion as mediator

Electrochemical reduction with electrochemically generated naphthalene radical anion in N,N-dimethylformamide was applied to the dechlorination of five representative POPs, namely HCB, lindane, DDT, PCP and aldrin. Rapid and complete dechlorination was possible for lindane and DDT to give nearly quantitative yields of benzene and 1,1-diphenylethane, respectively. HCB was reduced through complex reaction pathways to yield unknown products. Dechlorination of PCP and aldrin beyond dichlorinated compounds was difficult because of their very negative reduction potential. The reaction pathways for each dechlorination were proposed with the identification of intermediates.     

Dechlorination of pentachloroethane by commercial Fe and ferruginous smectite

Short-term experiments were conducted to investigate the effect of a commercial Fe and an iron-bearing clay mineral, ferruginuous smectite (SWa-1), on the degradation of pentachloroethane (PCA). After 3 h of contact time, SWa-1 catalyzed PCA dehydrochlorination to tetrachloroethene (PCE, 65% conversion), whereas commercial Fe promoted PCA stepwise dechlorination via dehydrochlorination (approximately 40% conversion) and subsequent PCE hydrogenolysis to trichloroethene (TCE). The addition of unaltered SWa-1 to commercial Fe led to a complete inhibition on TCE production, whereas the addition of reduced SWa-1 barely resulted in a 30% decrease.     

Dioxin analysis in stack emissions, slags and the wash water circuit during high-temperature incineration of chlorine-containing industrial wastes; Part 2

PCB's and polychlorobenzene sumps have been incinerated in a high-temperature installation. The working conditions, wastes, sampling methods and analysis of the stack emissions, slag and wash water are described. No 2,3,7,8-TCDD and only ppt-traces of some PCDD congeners were detected in the stack emission. The performance criteria of the incinerator and the more important sampling procedures are discussed.     

Palm oil and its wastes as bioenergy sources: a comprehensive review

Environmental Science and Pollution Research - Due to global warming and increasing price of fossil fuel, scientists all over the world have been trying to find reliable alternative fuels. One of...     

Nanogreen is the new future: the conversion of lignin and lignocellulosic wastes into nanomaterials

Environmental Science and Pollution Research - The lignocellulose biorefinery industry has assumed an important role within the current scenario. Lignin is an abundant and available biopolymer and...     

有机锡化合物降解机制的激光闪光光解研究

利用激光闪光光解技术进行了三苯基锡(TPT)与HNO2水溶液体系的355 nm紫外光光解研究,考察了其瞬态物种的生长和衰减等行为.瞬态吸收光谱分析结果表明,pH为1.5条件下,HNO2在355 nm紫外光照射下可产生羟基自由基(·OH),·OH与TPT的苯反应生成C6H6-OH加合物,其加合反应速率常数为3.3×109 L/(mol·s).     

DOC/SCR组合方式及关键参数对NOx转化效率的影响

在柴油机中等转速下,通过改变柴油机氧化催化器（DOC）和选择性催化还原催化器（SCR）的组合方式,以及改变喷嘴位置、两级SCR载体间距和催化剂成分,获得各种条件下的NOx转化效率,为优化组合方式和关键参数提供重要数据支撑。结果表明：增加尿素喷嘴与SCR入口的相对距离,NOx转化效率升高,喷嘴距离为45 cm较为合适;载体间距的增大,NOx转化效率先略有升高,后急剧下降,间距为2 cm较为合适;载体体积增大,NOx转化效率明显升高,在满足目标NOx转化效率的前提下,载体体积不宜过大;DOC与SCR的组合方式对NOx转化效率具有明显差异,前置DOC能够有效的提高NOx转化效率;在催化条件下,NOx转化效率由高到低排序为：铜基 > 钒基 > 铁基;对于复合催化剂而言,铜铁复合基>铁铜复合基。     

Adsorption of hydrogen sulfide by biochars derived from pyrolysis of different agricultural/forestry wastes

The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on three different biochars derived from agricultural/forestry wastes through pyrolysis at various temperatures (100 to 500 ºC) were investigated. In this study, the H₂S breakthrough capacity was measured using a laboratory-characterized using pH and Fourier transform infrared spectroscopy analysis. The results obtained demonstrate that all biochars were effective in H₂S sorption. The sorption capacity of the biochar for H₂S removal is related to the pyrolysis temperature and pH of the surface. Certain threshold ranges of the pyrolysis temperature (from 100 to 500 ºC) and pH of the surface are presented. It also concluded that the sorption capacity (for removing H₂S) of rice hull-derived biochar is the largest in three biochars (camphor-derived biochar, rice hull-derived biochar, and bamboo-derived biochar). These observations will be helpful in designing biochar as engineered sorbents for the removal of H₂S.Implications: This paper focuses on the adsorption of hydrogen sulfide (H₂S) by biochars derived from wastes. The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on three different boichars derived from agricultural/forestry wastes through pyrolysis at various temperatures were investigated. In this study, the H₂S breakthrough capacity was measured using laboratory characterization with pH and Fourier-transform infrared spectroscopy analysis. The results obtained demonstrate that all biochars were effective in H₂S sorption. The sorption capacity of the biochar for H₂S removal is related to the pyrolysis temperature and pH of the surface.     

Dechlorination of trichloroethylene by a steel converter slag amended with Fe(II)

This study aims to assess the feasibility of using slag, byproduct from iron and steel making industries, as a new reactive material for dechlorination reactions and to investigate dechlorination chemistries of the systems containing the slag and Fe(II). Initially, screening experiments were conducted to evaluate various systems containing slags with or without Fe(II). A combination of the steel converter slag and Fe(II) showed a potential to be developed as a reactive material to treat chlorinated organics. Further kinetic studies with the steel converter slag/Fe(II) systems revealed that the dechlorination capacity of the slag/Fe(II) system is comparable to that of zero-valent iron and generally higher than the cement/Fe(II) system. The slag/Fe(II) system can substantially dechlorinate trichloroethylene (TCE) in the neutral pH region, although the dechlorination rate was greatest in the pH region between 12 and 13. TCE reductions in the slag/Fe(II) system were observed to occur through reductive beta-elimination pathways that produce primarily acetylene and no chlorinated intermediates such as vinyl chloride. These results demonstrate that the steel converter slag with Fe(II) has sound characteristics for an alternative reactive medium for subsurface remediation.     

The use of anthracene as a model compound in a comparative study of hydrous pyrolysis methods for industrial waste remediation

Polycyclic aromatic hydrocarbons are very stable compounds and tend to bioaccumulate in the environment due to their high degree of conjugation and aromaticity. Hydrous pyrolysis is explored as a technique for the treatment of industrial water containing PAH, using anthracene as a model compound. The reactivity of anthracene under a range of temperatures and durations are studied in this paper. Aliquots of 1.0-10.0 mg of anthracene in a range of 1.0-5.0 mL of H₂O are subjected to hydrous pyrolysis under varied conditions of temperature, reagents and duration. The conditions include oxidising systems comprising distilled water, hydrogen peroxide and Nafion-SiO₂ solid catalyst in water; and reducing systems of formic acid and formic acid/Nafion-SiO₂/Pd-C catalysts to assess a range of redox reaction conditions. Oxygen in air played a role in some of the reaction conditions. Pyrolysed products were identified and quantified by the use of Gas Chromatography-Mass Spectrometry (GC-MS). The major products were anthrone, anthraquinone, xanthone from oxidation; and multiple hydro-anthracene derivatives from reductive hydogenation. The nature of reaction conditions influenced the extent of anthracene degradation. The products formed are more reactive (less stable) as compared to anthracene the starting material and will therefore be less persistent in the environment.     

Dechlorination and destruction of 2,4,6-trichlorophenol and pentachlorophenol using hydrogen peroxide as the oxidant catalyzed by molybdate ions under basic condition

The dechlorination and destruction of 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) under basic condition using hydrogen peroxide as the oxidant catalyzed by molybdate ions have been studied. Under ambient conditions of temperature and pressure, more than 95% of millimolar solutions of TCP and PCP can be converted to CO2 and CO, chlorinated and nonchlorinated carboxylic acid in 40 min. Up to 2.4 chloride ions per TCP and 3.5 chloride ions per PCP were released. TOC measurements indicated that 18% and 11% of the carbon was mineralized for TCP and PCP respectively after an hour of reaction. The results of ESR measurements suggested that the reaction possibly proceeded via the pathway with singlet oxygen.     

以绿化废弃物为原料的复合型抑尘剂的制备及其综合性能

针对建筑施工场地扬尘和绿化废弃物资源化率低的问题,利用绿化废弃物悬铃木枝条为原料制备羧甲基纤维素钠(CMC),将其与聚乙烯醇(PVA)和辛癸基葡糖苷(APG0810)进行复配,制备出了一种复合型抑尘剂.以黏结性、润湿性、抗风蚀性和生物毒性为指标,探究了各组分用量对各种性能的影响,并利用TOPSIS法对复合型抑尘剂的综合...     

Exo-pectinase production by Bacillus pumilus using different agricultural wastes and optimizing of medium components using response surface methodology

In this research, the production of exo-pectinase by Bacillus pumilus using different agricultural wastes was studied. Agricultural wastes containing pectin such as wheat bran, sugar beet pulp, sunflower plate, orange peel, banana peel, apple pomace and grape pomace were tested as substrates, and activity of exo-pectinase was determined only in the mediums containing sugar beet pulp and wheat bran. Then, effects of parameters such as concentrations of solid substrate (wheat bran and sugar beet pulp) (A), ammonium sulphate (B) and yeast extract (C) on the production of exo-pectinase were investigated by response surface methodology. First, wheat bran was used as solid substrate, and it was determined that exo-pectinase activity increased when relatively low concentrations of ammonium sulphate (0.12–0.21 %?w/v) and yeast extract (0.12–0.3 %?w/v) and relatively high wheat bran (~5–6 %?w/v) were used. Then, exo-pectinase production was optimized by response surface methodology using sugar beet pulp as a solid substrate. In comparison to P values of the coefficients, values of not greater than 0.05 of A and B ² showed that the effect of these process variables in exo-pectinase production was important and that changes done in these variables will alter the enzyme activity.     

Raw sugarcane bagasse as carbon source for xylanase production by Paenibacillus species: a potential degrader of agricultural wastes

Environmental Science and Pollution Research - Paenibacillus species isolated from a variety of natural sources have shown to be important glycoside hydrolases producers. These enzymes play a key...     

利用不同有机和无机固体废物配制人工土壤的研究

以生活污泥、牛粪、蚓粪、菌菇渣、粉煤灰、脱硫石膏、钢渣和煤矸石8种固体废物为原料配置人工土壤,探讨不同有机和无机固体废物配比对人工土壤性质的影响。结果表明,获得的人工土壤中,粒级0.250 mm的水稳性团聚体质量分数总体在20%~50%,接近或达到正常的自然土壤标准,制得的人工土壤为弱碱性,pH实测值在7.12~8.14。培养过程中,人工土壤中有机碳含量大大降低。生活污泥组、蚓粪组人工土壤在培养过程中呈现铵态氮向硝态氮的转化,而牛粪组人工土壤在培养过程中虽然有较多的有机氮被矿化,但同时也有较多的硝态氮被重新同化成有机氮。合成的人工土壤在物理、化学、养分和生物毒理学性质方面均已达到自然土壤相关参数的正常范围值,可以满足植物生长的要求。但由于部分固体废物原料重金属超标,则应尽量避免用于种植可食用类植物。     

Kinetics of ozone decomposition and oxidation of a model organic compound in water

The decomposition of ozone and oxidation of a model, polychlorinated organic compound, 2,3,4,5,6-pentachlorobiphenyl were studied. The parameters included self-decomposition of ozone at various pH values, mass transfer of ozone, and the rate of oxidation of 2,3,4,5,6-pentachlorobiphenyl. The decomposition of ozone follows a second-order reaction kinetics. Below pH 5, the rate of decomposition is not pH dependent and is slow. Above pH 5, the rate is pH sensitive and k_o is specific to the ionic strength of the solution. The decomposition of 2,3,4,5,6-pentachlorobiphenyl follows pseudo-first-order reaction kinetics. The decomposition rate varies with temperature, ozone, and substrate concentration in a complex manner even though the dependence of the rate on ozone and substrate concentration is first-order dependent.     

Biomass conversion of agricultural waste residues for different applications: a comprehensive review

Environmental Science and Pollution Research - Agricultural waste residues (agro-waste) are the source of carbohydrates that generally go in vain or remain unused despite their interesting...