Dechlorination Of Hexachlorobenzene Research Articles

Rapid mechanochemical dechlorination of hexachlorobenzene with zero-valent silicon as a novel additive: The attempt of zero-valent nonmetallic

The used of different zero-valent metals as reducing agents for dechlorination of polychlorinated biphenyl (PCB) based on mechanochemical method have been studied intensively, while few studies have been conducted on zero-valent nonmetallic reducing agents. Therefore, in this study, zero-valent silicon (ZVS), easily obtainable from photovoltaic panel waste in near future, has been used to serve the purposes as additive to dechlorinate persistent organic pollutants i.e., hexachlorobenzene (HCB). High-energy ball milling rapidly removes the passivated layer from the ZVS surface, exposing its fresh surface to release free electrons for the dechlorination of HCB at shortened time with eventually condensed amorphous carbon and hydrated silica as final products, safe to the soil. The degradation efficiency could achieve at 96.12% and dechlorination rate at 83.91% within only 60 min milling and 10% additive amount even if the concentration of HCB in simulated contaminated samples was as high as 5%. Various characterizations have been performed to fully analyze the intermediate phases and to understand the decomposition mechanism. Cyclic voltammograms (CV) curve and Tafel polarization scanning test as electrochemical evaluation method were performed to explore the involvement of electron release in the HCB remediation, for explaining the superior performance of ZVS compared to other additives based on radical dechlorination pathway. Overall, this work is expected to introduce a brand-new alternative toward practical application of mechanochemical remediation for the polluted soils, not only from environmental remediation perspective, but also the waste disposal.

Dithionite promoted microbial dechlorination of hexachlorobenzene while goethite further accelerated abiotic degradation by sulfidation in paddy soil

It is of great scientific and practical importance to explore the mechanisms of accelerated degradation of Hexachlorobenzene (HCB) in soil. Both iron oxide and dithionite may promote the reductive dechlorination of HCB, but their effects on the microbial community and the biotic and abiotic mechanisms behind it remain unclear. This study investigated the effects of goethite, dithionite, and their interaction on microbial community composition and structure, and their potential contribution to HCB dechlorination in a paddy soil to reveal the underlying mechanism. The results showed that goethite addition alone did not significantly affect HCB dechlorination because the studied soil lacked iron-reducing bacteria. In contrast, dithionite addition significantly decreased the HCB contents by 44.0–54.9%, while the coexistence of dithionite and goethite further decreased the HCB content by 57.9–69.3%. Random Forest analysis suggested that indicator taxa (Paenibacillus, Acidothermus, Haliagium, G12-WMSP1, and Frankia), Pseudomonas, richness and Shannon’s index of microbial community, and immobilized Fe content were dominant driving factors for HCB dechlorination. The dithionite addition, either with or without goethite, accelerated HCB anaerobic dechlorination by increasing microbial diversity and richness as well as the relative abundance of the above specific bacterial genera. When goethite and dithionite coexist, sulfidation of goethite with dithionite could remarkably increase FeS formation and then further promote HCB dechlorination rates. Overall, our results suggested that the combined application of goethite and dithionite could be a practicable strategy for the remediation of HCB contaminated soil.

Degradation behaviors and accumulative effects of coexisting chlorobenzene congeners on the dechlorination of hexachlorobenzene in soil by nanoscale zero-valent iron.

It is well known that many chlorinated organic pollutants can be dechlorinated by nanoscale zero-valent iron. However, in the real chlorinated organic compounds contaminated soil, the congeners of high- and low-chlorinated isomer often coexist and their dechlorination behaviors are poorly known, such as hexachlorobenzene (HCB). In this work, the degradation behaviors of three coexisting chlorobenzene congeners pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB) and 1,2,4-trichlorobenzene (1,2,4-TCB) and the influence of initial pH and reaction temperature on the dechlorination of HCB in HCB-contaminated soil by nanoscale zero-valent iron were studied. The amount and extent of accumulated coexisting chlorobenzenes was analyzed under different environmental conditions. The results indicate that nanoscale zero-valent iron can improve the degradation efficiency of highly toxic chlorinated benzenes and reduce the accumulative effects of highly toxic chlorinated benzenes on dechlorination of HCB. The accumulative effects of three coexisting chlorobenzene congeners on the dechlorination of HCB were ranked as follows: 1,2,4-TCB > 1,2,4,5-TeCB > PeCB.

Mechanochemical remediation of the chlorinated compounds contaminated soil depending on the minerals inside-the most reasonable approach

This study explored a possible destruction of hexachlorobenzene (HCB) as example of persistent organic pollutants (POPs) as well as the dechlorination mechanism by directly using minerals in the soil, such as antigorite, talc and olivine. Compared with a stable quartz phase of SiO2, all three Mg silicate minerals demonstrated certain degrading capacity for HCB with different efficiency order as: antigorite > talc > olivine > SiO2 at 2 h of milling time. Interestingly, olivine exhibited a better performance than antigorite at 4 h of milling time, giving destruction percentage of 92.7% over 89.0% even at high concentrated HCB up to 5% added. Raman and ESR characterizations of the ball milled sample with olivine indicated the formation of amorphous carbon and graphitic carbon, and the occurrence of free radicals was observed to play an important role in dechlorination and carbonization of HCB. The first identified effectiveness of directly using Mg silicate minerals, allowed no addition of active chemicals during the ball milling, therefore avoided the concern over extrinsic contaminations on the soil. Olivine was further utilized to deal with actual contaminated soil and showed unique advantages on application prospects.

Biochar and biochar-polylactic acid composite enhance biodegradation of hexachlorobenzene in soil by altering microbial community

It is of great scientific and practical importance to explore the mechanisms of accelerated degradation of hexachlorobenzene (HCB) in soil. However, the response of microbial community composition and structure, and their links to anaerobic reductive dechlorination in paddy soils remains unclear yet. We examined impacts of biochar and biochar-polylactic acid composite addition on the diversity, composition, and structure of soil prokaryotic community and their different contribution to HCB anaerobic dechlorination. The results showed that both biochar and biochar-polylactic acid composite addition could promote HCB dechlorination in paddy soils. Soil prokaryotic community richness and diversity were not significantly impacted by biochar but were remarkably affected by biochar-polylactic acid composite amendment. Random forest analysis and structural equation models indicated that the relative abundance of indicator taxa, soil Eh, and Fe2+ content best explained (p < 0.01) the HCB dechlorination with biochar addition, while soil Eh, Fe2+ content, and microbial diversity were the most important predictors of HCB dechlorination with biochar-polylactic acid composite addition. Together, our findings suggest that biochar amendment promoted anaerobic dechlorination of HCB in paddy soils by increasing the relative abundance of specific bacterial genera, while biochar-polylactic acid composite promoted HCB dechlorination by enhancing microbial community diversity. Therefore, biochar and biochar-polylactic acid composite showed distinct effect on the composition and diversity of soil prokaryotic community and different contribution to HCB dechlorination. Overall, our results suggested that biochar-polylactic acid composite could be used as soil remediation material to efficiently accelerate dechlorination of HCB.

Mechanisms of aerobic dechlorination of hexachlorobenzene and pentachlorophenol by Nocardioides sp. PD653.

We sought to elucidate the mechanisms underlying the aerobic dechlorination of the persistent organic pollutants hexachlorobenzene (HCB) and pentachlorophenol (PCP). We performed genomic and heterologous expression analyses of dehalogenase genes in Nocardioides sp. PD653, the first bacterium found to be capable of mineralizing HCB via PCP under aerobic conditions. The hcbA1A2A3 and hcbB1B2B3 genes, which were involved in catalysing the aerobic dechlorination of HCB and PCP, respectively, were identified and characterized; they were classified as members of the two-component flavin-diffusible monooxygenase family. This was subsequently verified by biochemical analysis; aerobic dechlorination activity was successfully reconstituted in vitro in the presence of flavin, NADH, the flavin reductase HcbA3, and the HCB monooxygenase HcbA1. These findings will contribute to the implementation of in situ bioremediation of HCB- or PCP-contaminated sites, as well as to a better understanding of bacterial evolution apropos their ability to degrade heavily chlorinated anthropogenic compounds under aerobic conditions.

Method development and mechanistic study on direct pulsed laser irradiation process for highly effective dechlorination of persistent organic pollutants

Chlorine-based compounds are typical persistent organic pollutants (POPs) that are widely generated in industrial production. This paper reports an effective and rapid pulsed laser irradiation technique for the dechlorination of hexachlorobenzene (HCB), a model pollutant, without additional catalysts or supports. The effects of the laser parameters, including the laser wavelength and power, on the dechlorination efficiency, were also investigated. The optimized results showed that a lower laser wavelength of 266 nm with 10 mJ/pulse power exhibited the highest dechlorination efficiency with 95% within 15 min. In addition, the laser beam effect was examined by designing the direct-pulsed laser single and multipath irradiation system. The results showed that improving the laser beam profile resulted in more than 95% dechlorination efficiency within 5 min. Thus, the dechlorination reaction proceeded much faster as the surface area that the laser beam came in contact with increased due to the multipath system than the single pathway. Gas chromatography identified benzene as the final product of HCB with pentachlorobenzene (PCB), tetrachlorobenzene (TeCB), trichlorobenzene (TCB), dichlorobenzene (DCB), and chlorobenzene (CB) as intermediate products. The mechanism of HCB dechlorination was explained by a comparison of theoretical calculations with the experimental results. The present study reports an advanced technique for the complete dechlorination of chlorobenzenes, which holds great application potential in environmental remediation.

Enhanced anaerobic degradation of hexachlorobenzene in a Hydragric Acrisol using humic acid and urea

Humic substances acting as an electron shuttle and nitrogen transformation process influence remarkably the electron transfer in anaerobic reaction systems and thus may affect the reductive dechlorination of hexachlorobenzene (HCB). In order to develop an efficient agricultural strategy for the remediation of organochlorine-contaminated soils, a batch incubation experiment was conducted to study the effects of humic acid, urea, and their interaction on the reductive dechlorination of HCB in a Hydragric Acrisol with high iron oxide content. After 44 d of anaerobic incubation, the five treatments, sterile control, control, humic acid, urea, and humic acid + urea decreased HCB residues by 28.8%, 47.8%, 64.7%, 57.8%, and 71.3%, respectively. The amendment of humic acid or urea significantly decreased soil Eh values and accelerated Fe(III) reduction to Fe(II), thus promoting markedly reductive dechlorination of HCB. Humic acid had a larger dechlorination effect than urea. Since there was a synergistic interaction between humic acid and urea that accelerated HCB dechlorination, the treatment having both amendments together was the most efficient for HCB dechlorination. The results showed that the combination of NH4+-N supplied by a fertilizer and humic substance is a feasible strategy for the remediation of organochlorine-contaminated soils with abundant iron oxide.

Biochemical characterization of NADH:FMN oxidoreductase HcbA3 from Nocardioides sp. PD653 in catalyzing aerobic HCB dechlorination.

Nocardioides sp. PD653 genes hcbA1, hcbA2, and hcbA3 encode enzymes that catalyze the oxidative dehalogenation of hexachlorobenzene (HCB), which is one of the most recalcitrant persistent organic pollutants (POPs). In this study, HcbA1, HcbA2, and HcbA3 were heterologously expressed and characterized. Among the flavin species tested, HcbA3 showed the highest affinity for FMN with a K d value of 0.75±0.17 µM. Kinetic assays revealed that HcbA3 followed a ping-pong bi-bi mechanism for the reduction of flavins. The K m for NADH and FMN was 51.66±11.58 µM and 4.43±0.69 µM, respectively. For both NADH and FMN, the V max and k cat were 2.21±0.86 µM and 66.74±5.91 sec-1, respectively. We also successfully reconstituted the oxidative dehalogenase reaction in vitro, which consisted of HcbA1, HcbA3, FMN, and NADH, suggesting that HcbA3 may be the partner reductase component for HcbA1 in Nocardioides sp. PD653.

Hydrodechlorination of hexachlorobenzene in a miniaturized nano-Pd(0) reaction system combined with the simultaneous extraction of all dechlorination products

The persistent organic pollutant hexachlorobenzene (HCB) and all 11 further chlorobenzenes were hydrodechlorinated at environmentally relevant concentrations in miniaturized reaction systems, catalyzed by low concentrated Pd(0)-nanoparticles, to examine differences in dechlorination rates and pathways. Using solid-phase microextraction coupled to gas chromatography-mass spectrometry allowed the simultaneous extraction and detection of reactants, intermediate products and fully dechlorinated benzene, regardless of their different physicochemical properties. Dechlorination of HCB with formation of intermediates mainly proceeded via pentachlorobenzene, 1,2,3,4-tetrachlorobenzene, 1,2,3-trichlorobenzene, 1,2-dichlorobenzene, and monochlorobenzene to benzene. Specific catalytic activities of Pd(0)-nanoparticles (100–3400 L g−1 min−1) differed depending on chlorination degree of chlorobenzenes and position of chlorine atoms. An inductive effect is assumed to favor a removal of the vicinal chlorine atom. The presented method permits the facile determination and comparison of nanomaterials’ specific catalytic activities and allows the elucidation of dehalogenation pathways. It further enables to specifically examine formed intermediates to assess their toxicity and biodegradability.

Degradation kinetics of hexachlorobenzene over zero-valent magnesium/graphite in protic solvent system and modeling of degradation pathways using density functional theory

Hexachlorobenzene (HCB), like many chlorinated organic compounds, has accumulated in the environment from agricultural and industrial activity. Because of its health risks and adverse impact on various ecosystems, remediation of this contaminant is of vital concern. The objective of this study is to evaluate the proficiency of activated magnesium metal in a protic solvent system to accomplish reductive dechlorination of HCB. Experimental results were compared with those predicted by quantum chemical calculations based on Density Functional Theory (DFT). Multivariate analysis detected complete degradation of HCB within 30 min at room temperature, the reaction having a rate constant of 0.222 min−1. Dechlorination was hypothesized to proceed via an ionic mechanism; the main dechlorination pathways of HCB in 1:1 ethanol:ethyl lactate were HCB → PCBz → 1,2,4,5-TCB; 1,2,3,5-TCB → 1,2,4-TriCB; 1,3,5-TriCB → 1,4-DiCB; 1,3-DiCB. The direct relationship between the decreasing number of Cl substituents and dechlorination reaction kinetics agrees with the ΔG values predicted by the computational model. This methodology shows promise for the development of a practical and sustainable field application for the remediation of other chlorinated aromatic compounds.

The effect of redox capacity of humic acids on hexachlorobenzene dechlorination during the anaerobic digestion process.

Hexachlorobenzene (HCB) dechlorination affected by humic acids (HA) was evaluated in terms of HA redox capacity, HA concentrations, and microbial community, as well as the correlation between HA redox capacity values and HCB concentrations. With addition of HA in the initial stage, redox capacity values increased by 2.19meq/L (80mg/L of HA addition, HA80), 2.51meq/L (120mg/L of HA addition, HA120), and 3.64meq/L (200mg/L of HA addition, HA200), respectively. The addition of HA could prominently enhance the HCB degradation rate. However, the concentration and the redox capacity of HA decreased during the anaerobic digestion process. Illumina MiSeq sequencing showed that microbial community affected by HA. Bacillus, Comamonas, and Pseudomonas were the predominant genera during the HCB dechlorination treatment. Moreover, Bacillus and Pseudomonas can improve HA electron transfer capability and promote the dechlorination of HCB.

Mechanochemical formation of chlorinated phenoxy radicals and their roles in the remediation of hexachlorobenzene contaminated soil

Mechanochemical degradation (MCD) is a promising eco-friendly method to dispose persistent organic pollutants (POPs). Mechanically induced free-radical attack was thought to be one of the key elements in initiating and accelerating the dechlorination and degradation of POPs. In this study, mechanochemical formation of free-radicals and their roles in the remediation of hexachlorobenzene (HCB) contaminated soil were explored using both of experimental analysis and quantum chemical calculations. It was found that chlorinated phenoxy radicals(CB-O) can be produced in the milling process and they played a vital role in the dechlorination of HCB, based on the results of electron spin-resonance (ESR) and X-ray photoelectron spectra (XPS). Two transition states of mechanochemical reaction along the formation of pentachlorinated phenoxy radical (PeCB-O) were located, with the energy barriers of 39.4 and 3.4 kJ/mol. The localized orbital locator (LOL), Mayer bond order and topological analysis were also implemented to depict the process in detail. Free-radical attack dominated dechlorination pathway of HCB in the MCD process was also verified by the Fukui function analysis. The study on the mechanically-induced generation of free-radicals and their associated modes of action on the degradation of HCB will provide a deep insight into mechanochemical remediation mechanism of POPs contaminated soil.

Erratum for Ito et al., "Identification of the hcb Gene Operon Involved in Catalyzing Aerobic Hexachlorobenzene Dechlorination in Nocardioides sp. Strain PD653".

Volume 83, no. 19, e00824-17, 2017, [https://doi.org/10.1128/AEM.00824-17][1]. Page 8, Fig. 3 legend, lines 6 and 7: “No-RT and genomic DNA, used as negative and positive controls, respectively, are presented in lanes − and +, respectively” should read “No-RT and genomic DNA, used as

Evaluation of carbon isotope fractionation during anaerobic reductive dehalogenation of chlorinated and brominated benzenes

Compound specific stable isotope analysis (CSIA) has been established as a useful tool to evaluate in situ biodegradation. Here, CSIA was used to determine microbial dehalogenation of chloro- and bromobenzenes in microcosms derived from Hackensack River sediments. Gas chromatography-isotope ratio mass spectrometry (GC-IRMS) was used to measure carbon isotope fractionation during reductive dehalogenation of hexachlorobenzene (HCB), pentachlorobenzene (PeCB), 1,2,3,5-tetrachlorobenzene (TeCB), 1,2,3,5-tetrabromobenzene (TeBB), and 1,3,5-tribromobenzene (TriBB). Strong evidence of isotope fractionation coupled to dehalogenation was not observed in the substrate, possibly due to the low solubilities of the highly halogenated benzene substrates and a dilution of the isotope signal. Nonetheless, we could measure a depletion of the δ13C value in the dichlorobenzene product during dechlorination of HCB, the sequential depletion and enrichment of δ13C value for trichlorobenzene in TeCB dechlorinating cultures, and the enrichment of δ13C during debromination of TriBB. This indicates that a measurable isotope fractionation occurred during reductive dehalogenation of highly halogenated chloro- and bromobenzenes in aquatic sediments. Thus, although more quantitative measurements will be needed, the data suggests that CSIA may have application for monitoring in situ microbial reductive dehalogenation of highly halogenated benzenes.

Identification of the hcb Gene Operon Involved in Catalyzing Aerobic Hexachlorobenzene Dechlorination in Nocardioides sp. Strain PD653.

Nocardioides sp. strain PD653 was the first identified aerobic bacterium capable of mineralizing hexachlorobenzene (HCB). In this study, strain PD653-B2, which was unexpectedly isolated from a subculture of strain PD653, was found to lack the ability to transform HCB or pentachloronitrobenzene into pentachlorophenol. Comparative genome analysis of the two strains revealed that genetic rearrangement had occurred in strain PD653-B2, with a genomic region present in strain PD653 being deleted. In silico analysis allowed three open reading frames within this region to be identified as candidate genes involved in HCB dechlorination. Assays using recombinant Escherichia coli cells revealed that an operon is responsible for both oxidative HCB dechlorination and pentachloronitrobenzene denitration. The metabolite pentachlorophenol was detected in the cultures produced in the E. coli assays. Significantly less HCB-degrading activity occurred in assays under oxygen-limited conditions ([O2] < 0.5 mg liter-1) than under aerobic assays, suggesting that monooxygenase is involved in the reaction. In this operon, hcbA1 was found to encode a monooxygenase involved in HCB dechlorination. This monooxygenase may form a complex with the flavin reductase encoded by hcbA3, increasing the HCB-degrading activity of PD653.IMPORTANCE The organochlorine fungicide HCB is widely distributed in the environment. Bioremediation can effectively remove HCB from contaminated sites, but HCB-degrading microorganisms have been isolated in few studies and the genes involved in HCB degradation have not been identified. In this study, possible genes involved in the initial step of the mineralization of HCB by Nocardioides sp. strain PD653 were identified. The results improve our understanding of the protein families involved in the dechlorination of HCB to give pentachlorophenol.

Effects of biochar on dechlorination of hexachlorobenzene and the bacterial community in paddy soil

Anaerobic reductive dechlorination is an important degradation pathway for chlorinated organic contaminants in paddy soil. This study investigated the effects of amending paddy soil with wheat straw biochar on both the dechlorination of hexachlorobenzene (HCB), a typical highly chlorinated contaminant, and on the structure of soil bacteria communities. Soil amendment of 0.1% biochar did not significantly affect the dechlorination of HCB in the soil. However, biochar amendment at higher application levels (5%) stimulated the dechlorination of HCB in the first month of anaerobic incubation and inhibited the dechlorination of HCB after that period. The stimulation effect may be ascribed to the graphite carbon and carbon-centered persistent radicals, which are redox active, in biochar. The inhibiting effect could be partly ascribed to the reduced bioavailability of HCB in biochar-amended soils. High-throughput sequencing revealed that the amendment of biochar changed the soil bacterial community structure but not the bacterial abundances and diversities. The relative abundance of Dehalococcoidaceae in the tested soils showed a significant relationship with the dechlorination percentages of HCB, indicating that Dehalococcoidaceae may be the main HCB-dechlorinating bacteria in the studied paddy soil. The results indicated that low application levels of biochar did not affect the dechlorination of HCB in the paddy soil, while high application levels of biochar mainly inhibited the dechlorination of HCB due to the reduced bioavailability of HCB and the reduced abundances of certain dechlorinating bacteria in the biochar-amended paddy soil.

Mechanochemical mechanism of rapid dechlorination of hexachlorobenzene

Recent researches indicate that mechanochemical treatment (MCT) is a promising method to degrade the environmental hazards, especially in the area of persistent organic pollutants (POPs) disposal. However, the mechanochemical dechlorination mechanism of POPs still needs to be further verified. In this mechanochemical process, hexachlorobenzene (HCB) was chosen as a model pollutant with aluminum and alumina (Al+Al2O3) powders as the co-milling regents. Both of the intermediate analysis and quantum chemical calculations were adopted to elucidate the free radical dechlorination mechanism of HCB. The solid residues were characterized by electron spin-resonance (ESR) spectroscopy, Fourier transform infrared (FTIR) spectra and X-ray photoelectron (XPS) spectra, which proposed that the radicals formed in the mechanochemical process were chlorinated phenoxyl radicals (CB-O). Four quantum chemical descriptors were selected in predicting the intermediates and reaction pathway: (i) atomic charge, (ii) electrostatic potential (ESP), (iii) frontier molecular orbitals (FMO) theory and (iv) dual descriptor. Then, a stepwise dechlorination mechanism based on CB-O was proposed. It was found that the intermediates and radical-related reactions in the mechanochemical dechlorination of HCB are quite different from that happen in a typical photocatalytic dechlorination process. Impacts of different radical reactions on the dechlorination of HCB were also compared at last.

Reductive dechlorination of hexachlorobenzene subjected to several conditions in a bioelectrochemical system

A microbial fuel cell (MFC) is a very promising way to remove organic pollutants. Hexachlorobenzene (HCB) is a widely used agricultural pesticide. In this study, single-chamber and membrane-less soil MFCs were constructed. The HCB was degraded to pentachlorobenzene (PeCB), tetrachlorobenzene (TeCB), and trichlorobenzene (TCB) in sequence by a reductive dechlorination process in soil MFCs. The influences of the external resistance, concentration of phosphate buffer, and electrode spacing in soil MFCs on the degradation rate and removal efficiency of HCB were analyzed. The results showed that the degradation rate and removal efficiency of HCB were increased when the external resistance decreased from 2000 to 20Ω, and also when the concentration of phosphate buffer increased. The anode area played a significant role in dechlorination of HCB. Altering the spacing of the reducing electrode resulted in a lower ohmic resistance in the soil MFCs. The ohmic resistance was negatively correlated with the removal efficiency and degradation rate (P<0.05). In conclusion, HCB removal efficiency could be enhanced by soil MFCs, the performance of which was improved by a decrease in external resistance and internal resistance, and an increase in phosphate buffer concentration, rather than just by shortening the electrode spacing.

Mechanochemical treatment of hexachlorobenzene: effect of additives

Mechanochemical (MC) methods have shown an excellent performance while decomposing a number of halogenated persistent organic pollutants (POPs). In this study, a number of MC degradation tests were performed on hexachlorobenzene (HCBz), using an all-dimensional planetary ball mill and applying selected additives, including CaO, CaO-SiO2, CaO-Al2O3, CaO-Al and Fe-SiO2. After 8 h of milling, up to 99.7% of the original HCBz was removed by processing with a combined CaO-Al additive. Different ratios of Al to CaO were compared and the highest (99.70%) destruction efficiency of HCBz was achieved after 3 h by the additive CaO-Al (11.1% added), considered to be the most practical pair. Sequential dechlorination of HCBz and polymerisation of the resulting residual benzene should be the main degradation pathway; this conclusion is reached by observing lower chlorinated intermediates and graphite and amorphous carbon as final products. Strong radical signals and micro-spheres as well as tribo-microplasma phenomena were induced by severe mechanical ball milling.