Adsorption Mechanism And Technology Of Aromatic Organic Contaminants In Bio-treated Coking Wastewater

Coking industry is one of the most important sources of pollutants in Chinese aquatic environment.According to the statistics,the coking wastewater amount is about 400 million tons per year,almost 2%in the national industrial wastewater.Also,many kinds of aromatic organic compounds(AOCs)emerge in the effluent from wastewater plant,which cannot degrade completely during biological treatment.Hence,in terms of the purification of water and security of environment,there is an increasing demand for developing more effective ways to remove such residual AOCs from the effluent.Adsorption is always and widely employed in water treatment,and presents a promising prospect in treating effluent from biologically treated coking wastewater.However,beside the toxicants in waters,there are a large quantity of soluble microbial products(SMPs)and other background contaminants(such as,humic acids)in the effluent from biologically treated coking wastewater.The fouling of these compounds to adsorbents could seriously impact the stability of adsorption technology.Considering these,the current study is to investigate the "anti-fouling"performance of adsorbents,to study the mechanisms of "anti-fouling",and to develop the suitable adsorption technology treating effluent from biologically treated coking wastewater.The main works and conclusions are as follows:(1)The "anti-fouling" of commercial granular activated carbon(GAC,F400)is rather poor.The adsorption capacities and kinetics of phenolic pollutants onto F400 dramatically decreased by 70?80%when the adsorbent was pre-fouled with the model background contaminant(tannic acid,TA)compared to that without TA preloading.The parameters KF of AOCs onto GACs before and after TA-loading were linearly related to the micropore surface areas of GACs,suggesting the blockage of micropore in GACs by TA.Additionally,the adsorption properties(adsorption capacities and kinetics)of AOCs on TA-loaded GACs were significantly affected by AOCs functional groups.Compared with phenolic pollutants,the adsorption of aniline was less influenced by TA-loading.The adsorption disparity with preloading should be attributed to the multi-adsorption mechanisms,such as hydrophobic effect,?-? interaction and hydrogen bonding.(2)The aminated resin NDA80 has superior "anti-fouling" property.NDA80 was the aminated product of hypercrosslinked resin NDA79.The adsorption capacities and kinetics of phenolic pollutants onto NDA79 and NDA80 decreased significantly after loaded with TA.The parameters KF of AOCs onto resins before and after TA-loading were also linearly related to their micropore surface areas.However,in contrast to NDA79,the slopes for NDA80 were all smaller,and the intercepts for NDA80 were all larger.The adsorption kinetics properties of phenolic pollutants onto NDA80 were superior to that onto NDA79.The surface diffusion coefficients(DS)of phenol and ?-nitrophenol on NDA79 decreased to 32%and 42%after loaded with 120 ?mol/g TA,respectively.Differently,the values of DS of phenol and p-nitrophenol on NDA80 remained 66%and 73%respectively after the same loading with TA.In addition,NDA80 was proved to have superior properties of anti-contamination on lab scale and pilot scale in treating the effluent from biologically treated coking wastewater.(3)The superior "anti-fouling" property of NDA80 originates from the existence of amino groups on the mesomacropore.After loaded with 120 ?mol/g TA(with the surface area of the micropores decreasing by 71%),the adsorption affinities(Ka)of phenol and p-nitrophenol per unit specific surface area on NDA80 increased by 76%and 67%,respectively.Differently,the values of Ka on NDA79 remained almost constant before and after the same loading with TA.On the basis of our previous study that the hydrogen bonging between amino groups on modified resin and adsorbates was an important driving force,it can be concluded that the amination modification might have taken place at the mesomacropore regions of the resin rather than at the micropore regions which were easily blocked.The adsorption sites of amino groups were not easily blocked by background contaminants,leading to the superior "anti-fouling" property of NDA80.(4)The performance of NDA80 on actual effluent was excellent.In the present work,the technological condition towards the actual effluent was investigated.Besides,100 L/h pilot-scale experiment was conducted.Although the quality of influent fluctuated largely in pilot-scale experiment,the total COD reduction was steady.Meanwhile,the chromaticities of effluent in all batches were all below a degree of 5,and marked accumulation was not observed.The analysis of the resin after 71 days of repeated use showed that their surface areas were dramatically decreased,but the removal of COD per specific surface area by NDA80 increased by about 35%,corresponding to the results that the resin aminated at the mesomacropore regions has superior "anti-fouling" property.