Removal of AOX in Activated Sludge of Industrial Chemical Dyestuff with Bimetallic Pd/Fe Particles

Pd/Fe bimetallic particles were synthesized by chemical deposition and used to remove absorbable organic halogens (AOX) in the activated sludge of a chemical dyestuff wastewater treatment plant. Bath experiments demonstrated that the Pd/Fe bimetallic particles could effectively remove AOX. It indicated several factors, such as Pd loading, the amount of Pd/Fe used, initial activated sludge pH, and reaction time, which could affect the removal effect. The results showed that increasing the Pd content in Pd/Fe particles, from 0.01 to 0.05 wt %, significantly increased the removal efficiency of AOX in activated sludge. The Pd/Fe particles had a much higher removal efficiency of AOX in the activated sludge than bare Fe particles. A slightly acidic condition with a Pd content of 0.05% and 10 g/L of Pd/Fe was beneficial to the process of removing AOX in activated sludge. In detail, the removal efficiency of AOX in the activated sludge could reach 50.7% after 15 days of reaction with 10 g/L of Pd/Fe (Pd loading 0.05 wt %) and at an initial pH of 6.0 during the experiments. It also showed that the control samples without Fe0 and Fe/Pd additions only removed 7.9% of AOX under the same conditions. Meanwhile, the concentrations of AOX in the supernatant of activated sludge were lower than the initial AOX concentration in the supernatant during the activated sludge remediation with Pd/Fe bimetallic particles. The results indicated that the AOX removal from the activated sludge matrix might be mainly due to the Pd/Fe bimetallic particles, and not just by phase transfer.

Adsorption behavior and mechanism of 2,4,6-trichlorophenol on nut shell activated carbon

The adsorbable organic halides (AOX) produced during chlorine dioxide bleaching are highly toxic and difficult to degrade. Currently, AOX generation is mainly reduced by controlling conditions during bleaching. Studies on AOX removal in the natural environment are rarely reported. In this study, the adsorption of 2,4,6-trichlorophenol (2,4,6-TCP) on nut shell activated carbon was investigated. The effects of activated carbon dosage, adsorption time, and temperature on the removal of 2,4,6-TCP were examined. The optimal adsorption conditions was activated carbon dosage 0.20 g × L-1, adsorption time 130 min, and temperature 25 °C. The removal efficiency of 2,4,6-TCP was 91.5%. The adsorption kinetics and isothermal adsorption were studied, and a thermodynamic equation was established. The adsorption was more consistent with a pseudo-second-order kinetic model and Freundlich adsorption isotherm model. Thermodynamic studies showed that the adsorption of 2,4,6-TCP on activated carbon was a spontaneous exothermic process. These findings provide a new method for AOX removal in natural environments.

Bioremediation of AOX from pulp and paper industry wastewater and AOX contaminated soils

Bleaching of paper pulp with chlorine/ chlorine derivatives leads to formation of severalorganochlorine compounds. These compounds are collectively termed as "Adsorbable OrganicHalides" (AOX). Toxic effects of AOX are well documented. Analysis of various wastewaters,soils irrigated with wastewater and sludge show significant levels of AOX. This is a potentialthreat to the environment. Physical and chemical methods of AOX removal are not economical.Hence, bioremediation technology needs to be developed for effective, ecofriendly andeconomical management of AOX containing waste. With this aim, anaerobic biofilm reactors(7.2L) were developed in our laboratory. Anaerobic cultures degrading chlorophenols wereenriched and a consortium of such enrichments was used as the inoculum for the reactors. Thereactors were fed with nutrient medium and run at 20 days HRT and at 30 °c. Degradation of 2,4dichlorophenol (2,4 DCP) was studied at 100 ppm, 300 ppm and 600 ppm and 96.7, 74.5 and56.8 % dechlorination was observed, respectively. Anaerobic degradation at varyingconcentration of AOX from bleach composite wastewater (BCWW) was studied. Reactors fedwith 12.5, 25, 50 and 75 % BCWW v/v showed 62.9, 56.5, 55.9 and 27.1% AOX degradation,respectively. The results suggest feasibility of treating the BCWW stream separately in anaerobicreactor and then mixing the effluent with composite wastewater. The treatment will ensureprevention of AOX pollution. Fish toxicity bioassays are being carried out to study safe disposalof treated wastewater in natural water bodies. Aerobic cultures degrading different chlorophenolswere isolated. Using a consortium of these cultures bioremediation studies on AOX contaminatedsoils have been initiated.

Adsorptive removal of adsorbable organic halogens by activated carbon

Current research mainly focuses on the reduction of adsorbable organic halogen (AOX) sources, while studies on AOX monitoring and management in the environment are scarce. Organic pollutants in water are mainly fixed by sediments. Thus, in this paper, activated carbon was used to simulate the adsorption of AOX by sediments. AOX volatilization and degradation were also studied to exclude their effect on adsorption. Micromolecule chlorides were more easily volatilized and degraded than chlorobenzene and chlorophenol. The adsorption of activated carbon to AOX in bleaching wastewater was also studied and the optimum conditions for AOX removal were elucidated (particle size, 62 µm; time, 120 min; pH, 2.5; temperature, 40°C; and activated carbon dosage, 1.75 g l −1 ). AOX adsorption by activated carbon is a chemical process. Hence, the chemical compositions of the bleaching effluent with and without adsorption were analysed by GC-MS. The results revealed that activated carbon exhibits a good AOX removal effect, thereby providing a theoretical basis for monitoring the AOX distribution in the environment.

AOX removal from industrial wastewaters using advanced oxidation processes: assessment of a combined chemical–biological oxidation

In this paper, the abatement of adsorbable halogenated organic compounds (AOX) from an industrial wastewater containing relatively high chloride concentrations by a combined chemical and biological oxidation is assessed. For chemical oxidation, the O3/UV, H2O2/UV and photo-Fenton processes are evaluated on pilot scale. Biological oxidation is simulated in a 4 h respirometry experiment with periodic aeration. The results show that a selective degradation of AOX with respect to the matrix compounds (expressed as chemical oxygen demand) could be achieved. For O3/UV, lowering the ratio of O3 dosage to UV intensity leads to a better selectivity for AOX. During O3-based experiments, the AOX removal is generally less than during the H2O2-based experiments. However, after biological oxidation, the AOX levels are comparable. For H2O2/UV, optimal operating parameters for UV and H2O2 dosage are next determined in a second run with another wastewater sample.