Adsorption, Contamination Diagnosis And Associated Bioremediation Of C.I. Acid Red 14 In Soil

Azo dyes are widely used in many industrial fields,such as textile,leather,paper,plastics, rubber,food,etc.They have been considered as an extremely important pollutant in environment due to their high toxicity,complex composition,poor degradability and great solubility in water.At present,owing to wide usage of Azo dyes in China,the water and soil have been contaminated widely.In this study,using azo dye C.I.AR14 as example,we performed some basic research on their physical-chemical property,contamination diagnosis and associated bioremediation in soil.Firstly,physical-chemical properties of C.I.AR14 are studied,including soil adsorption, sorption kinetics,sorption thermodynamics and the effects of pH and salinity.The experimental results of adsorption of C.I.AR14 on DG06,GSE17200 and GSE17201 soils show the Freundlich model expresses the adsorption isotherm better than the Langmuir model. The adsorption capacity increase with GSE17200＜GSE17201＜DG06.Sorption kinetics indicates the pseudo-second-order model achieves adsorption of AR14 on the three soils well and DG06 has higher q_e,K₂ andνthan GSE17200 and GSE17201.Based on the pseudo-second-order model,the adsorption thermodynamic of AR14 on DG06 soil have been studied and the thermodynamics parameter ofâ–³G0 is determined andâ–³G0 value shows the adsorption process of AR14 on DG06 is mainly physical in nature.The effects of temperature, pH and salinity(NaCl)on adsorption have been investigated.The decrease in pH or the increase in salinity enhances the adsorption of AR14 by DG06,GSE17200 and GSE17201.Secondly,the study of contamination diagnosis mainly contains the effect assessment of C.I.AR14 to the enzyme in soils and germination and growth of plant.By studying the effect of C.I.AR14 to urease,surcease and dehydrogenase in soils,it is found that under the experimental concentration range,urease and dehydrogenase show strong endurance to C.I.AR14;surcease shows certain inhibition to C.I.AR14,and in higher concentration,this action is more significant.Within 20 days,the effect of C.I.AR14 to urease is "activation-recovery-stability" process,but the one of C.I.AR14 to dehydrogenase is "activation-stability" process.In addition,with the increase of dye concentration,the activities of urease and dehydrogenase also increase.The research on germination and growth of wheat and rice influenced by C.I.AR14 indicate wheat is more endurable to C.I.AR14 than rice and the inhibition of C.I.AR14 to root growth of two plants is more significant than the one of C.I.AR14 to seed germination.The half dose-response concentration(ECso)of C.I.AR14 to inhibition of seed germination of two plants is 8.41g/L and 6.32g/L respectively. The half dose-response concentration(EC₅₀)of C.I.AR14 to inhibition of root elongation of two plants is 7.78 g/L and 6.23g/L respectively.During the EC₁₀and EC₅₀,the inhibition of root elongation and seed germination of wheat and rice has a good linearity with C.I.AR14 concentration.At last,the bioremediation of the soil polluted by C.I.AR14 is studied,including solution system and soil system.The research about solution system shows when the wheat is in seedling,the combined system of GEM-Wheat decolorizes C.I.AR14 more completely than that by separate system.With the increase of biomass of two kind of organism,decolorization rate of C.I.AR14 is also enhanced,which shows a good linearity relationship with R_GEM= 0.9736 and R_wheat=0.9801 respectively.Under the experimental range,the increase of pH and temperature can enhance treatment efficiency of the combined system.In addition,the GEM-associated wheat system can keep the system pH values at the range from 5 to 6,which can provide a constant condition for C.I.AR14 biotreatment.It is found that alteration of environmental factors can influence the decolorization rate of C.I.AR14,which is mainly act on GEM of the associated system.The research about soil system show the combined system in soil basically shows similar action with the one in solution.The treatment of the combined system is better than the one of single system.The research of kinetics shows the biodegradation of C.I.AR14 in three soils fit first-order degradation kinetics well with relative coefficients R=0.9738-0.9987.The rate constant of degradation is k(Wheat+GEM)＞k_GEM＞k_wheat.Their half life of degradation(t₁/2)is followed respectively as:t_1/2wheat=177d(DG06), 257d(GSE17200)and 231d(GSE17201);t_1/2GEM=107d(DG06),117d(GSE17200)and 100d(GSE17201);t_{1/2(Wheat+GEM)}=55d(DG06),80d(GSE17200)and 77d(GSE17201)。In addition,it is found that in the experiment condition,GEM can propagate in three soils,and with the increase of time,the amount of microorganism gradually increase and get to stability.