Catalytic oxidation of o-chlorophenol over Co2XAl (X= Co,Mg, Ca,Ni) hydrotalcite-derived mixed oxide catalysts

• Superior catalytic activity observed for o-chlorophenol oxidation on Co₂MgAlO. • The reducibility, oxygen species and basicity influenced catalytic activity. • The organic by-products were generated in o-chlorophenol catalytic oxidation. A cobalt-based hydrotalcite-like compound was prepared using a constant-pH coprecipitation method. Cobalt-transition metal oxides (Co₂XAlO, X= Co, Mg, Ca and Ni) were investigated for the deep catalytic oxidation of o-chlorophenol as a typical heteroatom contaminant containing chlorine atoms. The partial substitution of Co by Mg, Ca or Ni in the mixed oxide can promote the catalytic oxidation of o-chlorophenol. The Co₂MgAlO catalyst presented the best catalytic activity, and could maintain 90% o-chlorophenol conversion at 167.1°C, compared only 27% conversion for the Co₃AlO catalyst. The results demonstrated that the high activity could be attributed to its increased low-temperature reducibility, rich active oxygen species and excellent oxygen mobility. In the existence of acid and base sites, catalysts with strong basicity also showed preferred activity. The organic by-products generated during the o-chlorophenol catalytic oxidation over Co₂MgAlO catalyst included carbon tetrachloride, trichloroethylene, 2,4-dichlorophenol, and 2,6-dichloro-p-benzoquinon, et al. This work provides a facile method for the preparation of Co-based composite oxide catalysts, which represent promising candidates for typical chlorinated and oxygenated volatile organic compounds.     

Organic Farming and Soil Carbon Sequestration: What Do We Really Know About the Benefits?

Organic farming is believed to improve soil fertility by enhancing soil organic matter (SOM) contents. An important co-benefit would be the sequestration of carbon from atmospheric CO₂. Such a positive effect has been suggested based on data from field experiments though many studies were not designed to address the issue of carbon sequestration. The aim of our study was to examine published data in order to identify possible flaws such as missing a proper baseline, carbon mass measurements, or lack of a clear distinction between conventional and organic farming practices, thereby attributing effects of specific practices to organic farming, which are not uniquely organic. A total of 68 data sets were analyzed from 32 peer-reviewed publications aiming to compare conventional with organic farming. The analysis revealed that after conversion, soil C content (SOC) in organic systems increased annually by 2.2% on average, whereas in conventional systems SOC did not change significantly. The majority of publications reported SOC concentrations rather than amounts thus neglecting possible changes in soil bulk density. 34 out of 68 data sets missed a true control with well-defined starting conditions. In 37 out of 50 cases, the amount of organic fertilizer in the organic system exceeded that applied in the compared conventional system, and in half of the cases crop rotations differed between systems. In the few studies where crop rotation and organic fertilization were comparable in both systems no consistent difference in SOC was found. From this data analysis, we conclude that the claim for beneficial effects of organic farming on SOC is premature and that reported advantages of organic farming for SOC are largely determined by higher and often disproportionate application of organic fertilizer compared to conventional farming.     

Sorptive domains of pine chars as probed by benzene and nitrobenzene

Chars were generated by pyrolyzing pine wood at temperatures between 300 °C and 700 °C for 6 h and at 500 °C for 10-300 min. Their organic content and surface acidity decreased, and BET surface area increased, with increasing pyrolytic temperature and time. The uptake of benzene and nitrobenzene increased with increasing pyrolytic temperature and time with isotherms characterized by a transition from less to more concave-downward. The isotherms with low-temperature and short-time chars were fitted to the dual Langmuir-partition model, whereas those with high-temperature chars to the dual-Langmuir model. Calculations suggest that the organic phases of chars functioned as partition media and the uptake of benzene and nitrobenzene on carbonized chars occurred first in micropores via pore-filling and later in larger pores through capillary condensation and adsorption. It is concluded that chars may be considered to consist of the partition domain, the high-energy micropores domain and the low-energy large pores domain.     

Predicting molybdenum toxicity to higher plants: Influence of soil properties

The effect of soil properties on the toxicity of molybdenum (Mo) to four plant species was investigated. Soil organic carbon or ammonium-oxalate extractable Fe oxides were found to be the best predictors of the 50% effective dose (ED₅₀) of Mo in different soils, explaining > 65% of the variance in ED₅₀ for four species except for ryegrass (26-38%). Molybdenum concentrations in soil solution and consequently plant uptake were increased when soil pH was artificially raised because sorption of Mo to amorphous oxides is greatly reduced at high pH. The addition of sulphate significantly decreased Mo uptake by oilseed rape. For risk assessment, we suggest that Mo toxicity values for plants should be normalised using soil amorphous iron oxide concentrations.     

Migration of C in the paddy soil-to-rice plant system after C-acetic acid breakdown by microorganisms below the plow layer

Migration of ¹⁴C derived from ¹⁴C-acetic acid was examined by using soils sampled from paddies in four administrative areas in Japan (Aomori, Yamanashi, Ehime and Okinawa) and rice plant in a tracer experiment to understand the fate of ¹⁴C in the paddy soil-to-rice plant system. The loss of ¹⁴C radioactivity levels derived from ¹⁴C-acetic acid was caused by soil microorganism breakdown. A part of the ¹⁴C fixation to soil was caused by microbial assimilation into the fatty acid fraction. ¹⁴C moved upward via two different types of ¹⁴C dynamics in soil: quick movement upward; and constant but slow movement upward. ¹⁴C was highly assimilated into the plant panicle and that was caused by the root-uptake and the transfer of ¹⁴C. Migration of ¹⁴C derived from ¹⁴C-acetic acid relied heavily upon changes of chemical forms and characteristics of ¹⁴C-compound as caused by microorganisms in soil.     

超临界水氧化法处理竹子溶解浆生产废水的实验研究

介绍了利用目前国内最大超临界水氧化中试反应器(2.2L+1.7L)对竹子溶解浆生产废水进行处理的试验,其反应装置处理水量可以达到900~1100L/d。分析了超临界水氧化过程中不同反应温度、时间、压力及其氧气浓度对该废水COD处理效率的影响。实验结果表明:在温度为500℃、压力为24MPa,氧化反应时间为60s时,其COD去除率达到99.2%;氧化反应时间为90s时,其COD去除率达到99.95%。处理后的排水能够达到国家规定的排放标准。同时对超临界水氧化反应过程中出现的反应机理及放热现象进行了探讨。     

阴阳极协同作用降解有机污染物的研究进展

电化学法催化降解有机污染物已引起广泛兴趣。在电极的作用下,电化学反应和化学催化作用结合,可导致有机分子的电催化降解。选用合适的阳极和阴极材料可以加速电化学反应速率,有助于有机物的电化学转化。本文介绍了阳极和阴极氧化有机物的原理,综述了近年来阴阳两极协同作用降解有机物的进展。     

汾河太原段有机污染物检测及评价

采用GC和GC/MS检测手段,定量出汾河太原段有机污染物46种,其浓度在ppb~ppm范围。采用多污染物评价方法,就有机物对健康和生态的潜在危害进行定量评价,结果表明,6个采样点的健康总环境影响度TAS和4个采样点的生态总环境影响度TAS分别大于1,对人体健康和生态有潜在危害。酚类是主要的危害健康污染物。1,4-二氯苯,1,3-二氯苯,萘是主要的危害生态污染物。      

Anaerobic degradation of xenobiotic organic contaminants (XOCs): The role of electron flow and potential enhancing strategies

In groundwater, deep soil layer, sediment, the widespread of xenobiotic organic contaminants (XOCs) have been leading to the concern of human health and eco-environment safety, which calls for a better understanding on the fate and remediation of XOCs in anoxic matrices. In the absence of oxygen, bacteria utilize various oxidized substances, e.g. nitrate, sulphate, metallic (hydr)oxides, humic substance, as terminal electron acceptors (TEAs) to fuel anaerobic XOCs degradation. Although there have been increasing anaerobic biodegradation studies focusing on species identification, degrading pathways, community dynamics, systematic reviews on the underlying mechanism of anaerobic contaminants removal from the perspective of electron flow are limited. In this review, we provide the insight on anaerobic biodegradation from electrons aspect — electron production, transport, and consumption. The mechanism of the coupling between TEAs reduction and pollutants degradation is deconstructed in the level of community, pure culture, and cellular biochemistry. Hereby, relevant strategies to promote anaerobic biodegradation are proposed for guiding to an efficient XOCs bioremediation.     

Comparison of constant volume balloons, model trajectories and tracer transport during ETEX

In the field phases of the European Tracer EXperiment (ETEX), an inert tracer was released for 12 h into the atmosphere and samples taken at several locations downwind. During the same time, several Constant Volume Balloons (CVB) (10 and 6 for ETEX first and second release, respectively) were launched into different altitudes and followed as far as 21–188 km, to indicate the initial dispersion directions of the tracer puff. A model simulating the CVB behaviour in hydrostatic meso-scale model forecasts is applied to ETEX data to demonstrate its capability to predict the tracer puff mean axis over long distances (−2000 km). CVB model results are first compared to air parcels trajectories and 2D (i.e. isentropic, isobaric and isodensity) trajectories. Then they are compared to the measured CVB trajectories and finally to the tracer puff trajectories. As expected, the CVB model and isodensity model trajectories are found to be identical. The 16 CVBs calculated trajectories nearly overlap the real ones over 21–188 km with mean absolute horizontal transport deviations less than 20 km (average value of 8.2 km). The corresponding relative transport deviations are less than 45% with an average value of 20.6%. Better predictions are obtained for the ETEX second release. During the 60 h following ETEX’s first release start, the simulated CVBs are mainly found in the area of the maximum surface concentrations of the released tracer, up to 2000 km. Up to 36 h after ETEX second tracer release start, the simulated CVB trajectories predict well the mean axis of the tracer puff, but failed later.