In-situ Remediation Of Polychlorinated Biphenyl (PCB) Contaminated Sediments By Activated Carbon And Its Biological Effects

"Black carbon" is a reductive carbon mixture produced by incomplete combustion of biomass or fossil fuels,and its physicochemical properties are stable.It has a strong absorption and stabilization effect on many pollutants,especially for persistent and hydrophobic organic pollutants such as polycyclic aromatic hydrocarbons,polychlorinated biphenyls,DDT and so on.It is the main contributor to environment for"self purification".Activated carbon and "black carbon" have similar chemical composition and physicochemical properties.And because of the activation treatment,the adsorption stability of activated carbon is stronger than black carbon,so it is widely used in the purification treatment of waste water and waste gas,however,the direct application of activated carbon to the external environment(such as contaminated sediments,etc.)has rarely been reported for pollution control.The main reason is that the adsorption and stabilization efficiency of activated carbon(especially for long time treatment),as well as the effect of activated carbon on natural environment,especially native organisms and ecological environment,is not clear.In this study,the passive sampling technique of low density polyethylene(LDPE)film was selected as the main method to evaluate the effect of treatment.And the effects of different dosage,different treatment time and different activated carbon on the treatment of PCBs contaminated sediment were studied,and the effect of activated carbon on the larva of benthic Chironomus was studied.The main conclusions are as follows:(1)By measuring the physicochemical properties of activated carbon,some conclusions can be found.The surface of coal-based activated carbon has a spherical and convex structure,and the surface of nut-shell activated carbon has irregular particles.Both of their surfaces have pore structures.There are some functional groups on both AC's surfaces,such as hydroxyl,nitro,and carbonyl,and only coal-based activated carbon has-N-H group.The BET specific surface area and total pore volume of single-site adsorption of coal-based activated carbon are 388.71 m2/g and 0.25 cm3/g respectively,which were greater than those of the nut-shell activated carbon's 204.16m2/g and 0.12 cm3/g.The contribution rates of the micropores and mesopores to the pore volume for two AC samples are all at a relatively high level,and the sum of the contribution rates by micropores and mesopores pore volume is 91.70%and 90.50%,respectively for coal-based activated carbon and nut-shell activated carbon.(2)After the aging,the total pore water concentration of PCBs in the top three is two chlorinated biphenyls,72.17?g/L,three chlorinated biphenyls,1?g/L and four chlorinated biphenyls 0.68?g/L.The effect of 2 kinds of activated carbon on the treatment of PCBs decreased with the increase of the number of chlorine atoms in PCBs.The reason may be that the more the number of chlorine atoms(especially the ortho substituted chlorine atoms),the larger the PCB molecule,the more difficult it is to match the micropores in the activated carbon,and the adsorption and adhesion is weakened.With the same dosage of activated carbon,the total pore water concentration of PCBs can be reduced to 0.001?g/L with the increase of treatment time,and the decrease of low chlorinated biphenyl concentration by activated carbon is higher than that of perchlorinated biphenyl.When the treatment time is the same,the higher the amount of activated carbon,the lower the pore water concentration of PCBs,the higher the removal rate of PCBs,and the removal rate increased significantly when the dosage is between 5%and 10%.With the increase of treatment time,the removal rate of activated carbon to PCBs can rise from 50%to 90%in the month of 1?6.In 6?12 months,the removal rate gradually tends to be gentle with time,which can reach more than 95%.According to the fitting results of the two stage kinetic equation,the adsorption effect of 2 kinds of activated carbon on different PCBs is different.The adsorption capacity of the nut-shell activated carbon to two chloro biphenyl and three chlorinated biphenyl is greater than the coal based activated carbon,which may be related to different surface functional groups on 2 kinds activated carbon.(3)Compared with 2 kinds of activated carbon,the negative effect of nut-shell activated carbon on biological indexes is slightly less than that of coal based activated carbon.When the activated carbon dosage is more than 5%,it may have a significant negative effect on biological activity.The control experiment showed that the negative effects of PCBs on organisms including the slow action of Chironomid larvae,insensitivity to external stimuli,a significant decrease in survival rate and the activity of SOD enzymes,and a significant increase in the activity of CarE enzymes,but little influence on the volume and wet weight of Chironomus larvae.After adding activated carbon to the PCBs contaminated sediment,the volume of the insect body became larger,the weight of the worm increased slightly and the body shape became shorter,and the survival rate of the Chironomus larvae was higher than that in 12 months,when the activated carbon dosage was 5%,the survival rate of the coal based group was 48.67%,and the nut-shell group was 55%.After 12 months,the activity of the Chironomus larva SOD enzyme activity in the 2.5%and 5%experimental groups increased from 93.34 U/g to 170.53 U/g,and the SOD enzyme activity in the 10%and 20%experimental groups decreased.The activity of the CarE enzyme of the Chironomus larva in the 2.5%,5%and 10%experimental groups dropped from 75.35 U/g to 42.80U/g,when the dosage was 20%,the activity of CarE enzyme increased.The reason for the development of bioindicators to healthy trend after adding activated carbon may be that the adsorption of activated carbon reduces the PCBs content in the sediment.The biological index of the nut-shell group was healthier than that of the coal based group.(4)In summary,the effect of nut-shell activated carbon on the treatment of two chlorinated biphenyl and three chlorinated biphenyl in sediment is better than that of coal based activated carbon,and the negative effect of coal based activated carbon on biological indexes is greater than that of nut-shell activated carbon.When activated carbon is used for sediment treatment in the field,it is recommended to add nut-shell activated carbon,and the dosage is 5%.