| In recent years, with the development of production and progress of science and technology, a large number of chemicals have been synthesized to meet the need of human live, industry, agriculture and other areas. The large amounts production and use of organic compounds led to massive organic substances into environment inevitably, resulting in the organic pollution of water body more and more seriously. Organic pollutants have immeasurable effect on human as well as other organisms even at trace levels. Benzene, toluene, ethylbenzene, xylene (referred to as BTEX), chlorobenzene and nitrobenzene are typical organic matters that are widely used in many sectors of petroleum and chemical industry as important industrial raw materials and organic solvents. In this paper, the treatment method of these organic matters was studied preliminarily.Iron-carbon micro-electrolysis, also called interior micro-electrolysis, zero-valent iron or iron chips filtration, has been used to pre-treat industrial wastewater or contaminative groundwater due to extensive adaptability to wide variations of compositions of wastewater. It is based on the electrochemical reaction on the surface of electrodes. Iron-carbon micro-electrolysis pretreatment is low cost, high efficiency, no selection for pollutants and operational simplicity because it does not require chemical coagulant and external power as in the cases of coagulation and electrolysis. In this study, to resolve passivation and clogging problems in traditional micro-electrolysis, a new preparation method of iron-carbon micro-electrolysis packing was proposed to pre-treat organic wastewater.Using iron filings, activated carbon power and clay as raw materials, the granular iron-carbon micro-electrolysis packing was made by the method of calcination. The influences of clay, Fe/C mass ratio, packing diameter, clay proportion, additives and calcination temperature on the removal rate of benzene in simulated wastewater were investigated and the optimum conditions of preparation were obtained. The results showed that the adsorption effect of clay on benzene can be neglected, and iron-carbon micro-electrolysis contributed to mostly of the benzene removal. Packing diameter had no obvious effect on the removal rate in the ranges of 3mm～8mm. Adding ammonium carbonate, ammonium chloride, copper nitrate and manganese sulfate into packing didn't improve the removal rate significantly. The optimum condition of preparation was obtained when the Fe/C mass ratio was set at 6:1, clay proportion was set at 25% and calcination temperature was 300℃. The packing had some mass loss in the calcination process, the higher the calcination temperature, the more easily oxidized of the packing, the greater the mass loss. There was a relationship between the packing hardness and clay proportion. A high proportion of clay in the packing could increase the hardness and the packing were made easily.Typical organic compounds, such as benzene, toluene, ethylbenzene, xylene (referred to as BTEX), chlorobenzene and nitrobenzene were selected as model compounds. Through a series of experiments, the performance of micro-electrolysis packing on removal of organic pollutants in simulated wastewater was studied systematically. The conclusions showed that:The reaction of BTEX samples with iron-carbon micro-electrolysis packing can be described by pseudo-first-order kinetics in the ranges of 25mg/L-100mg/L and the rate constants of ethylbenzene and xylene were bigger than that of benzene and toluene. The reactions of benzene in the ranges of 25mg/L-500mg/L, toluene in the ranges of 25mg/L-250mg/L, ethylbenzene in the ranges of 25mg/L-100mg/L, and xylene in the ranges of 25mg/L-100mg/L can be described by pseudo-first-order kinetics. The effect of initial concentrations on rate constants wasn't significant except ethylbenzene. Initial pH had no obvious effect on the removal rate when the pH raged from 3 to 9. Temperature was an important parameter influencing the performance of the packing. It was observed that an increase in temperature could significantly raise the reaction rates in the ranges of 5℃-30℃. The removal rate was strongly packing amount dependent and an increase in the packing amount could significantly raise the removal rate as the packing amount increased from 5g/200ml to 40g/200ml. The flow-through column packed with packing was designed to remove BTEX solution of 200mg/L, 100mg/L,50mg/L and 50mg/L from simulated wastewater running for approximately 60d with approximately 60 min residence time. The packing had good performance and the removal rate could reach 80%-90% after running steadily. The accumulation of precipitates (corrosion products) on the packing surface may necessitate periodic backwash or cleanup steps using hydrochloric acid in the continuous column operation. There were no obvious agglomeration and clogging phenomena after running for 60 days. The passivation and clogging problems in traditional micro-electrolysis were resolved in some extent.The reaction of chlorobenzene solution with iron-carbon micro-electrolysis packing can be described by pseudo-first-order kinetics in the ranges of 50mg/L-200mg/L. Initial pH had no obvious effect on the removal rate when the pH raged from 3 to 9. Temperature was an important parameter influencing the performance of the packing. It was observed that an increase in temperature could significantly raise the reaction rates in the ranges of 5℃-30℃. The removal rate was strongly packing amount dependent and an increase in the packing amount could significantly raise the removal rate as the packing amount increased from 10g/200ml to 50g/200ml. The flow-through column packed with packing was designed to remove chlorobenzene solution of 200mg/L from simulated wastewater running for approximately 70d with approximately 120 min residence time. The packing had good performance and the removal rate was over 90% after running steadily. It could be seen that, the packing still had good performance and there were no obvious decrease on the removal efficiency of the packing after the long-time column experiment. The accumulation of precipitates (corrosion products) on the packing surface may necessitate periodic backwash or cleanup steps.The reaction of nitrobenzene solution with iron-carbon micro-electrolysis packing can be described by pseudo-first-order kinetics in the ranges of 50mg/L-200mg/L. The packing showed prominent activity to the reductive transformation of nitrobenzene to aniline. Furthermore, the aniline formation rate can be described by zero-order kinetics. The degradation performance was strongly pH dependent and a decrease of the initial pH values resulted in the increase of degradation efficiencies of nitrobenzene and formation rate of aniline. The optimum pH was 3.0 for the reductive degradation of NB in the tested pH ranges of 3-9. Temperature was an important parameter influencing the performance of the iron-carbon micro-electrolysis process. It was observed that an increase in temperature could significantly raise the removal rate of NB and formation rate of AN in the ranges of 5℃-30℃. The removal rate was strongly packing amount dependent and an increase in the packing amount could significantly raise the removal rate as the packing amount increased from 10g/200ml to 50g/200ml. The flow-through column packed with packing was designed to remove nitrobenzene solution of 500mg/L from simulated wastewater running for approximately 68d with approximately 120 min residence time. The packing had good performance and the removal rate was over 90% after running steadily. The degradation products of NB and the precipitates of iron oxides/hydroxides covered on the packing surface, which inhibited the contact between packing and NB, and thereby the activity of the packing surface was decreased and the further removal rate of NB was decreased accordingly. Throughout the operation, a decrease in the removal rate of NB resulted in the decrease of formation rate and concentration of aniline, showing positive correlation.The changes of the packing surfaces morphologies and matters before, during and after the. column experiment were analyzed by scanning electron microscopy (SEM) in conjunction with energy-dispersion spectroscopy (EDS). The results showed that carbon element decreasing after calcination indicated that some of the organic matters in the clay evaporated out of packing though high temperature calcinations. The content of iron element increased after calcination. Acid washing led to the cleaning of packing, and accordingly more reactant surface area was reactived for further surface reactions. Hydrochloric acid had effectively removed the absorbed precipitates, and thus the activity of packing was regenerated. After the long-term column experiment, there were mass losses of iron in the packing, and the extent of loss was dependent on the influent concentration, backwashing frequency and so on.
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