Study On Adsorption Technology For Emergency Treatment Of Sudden Copper Pollution In Rivers And The Decision Analysis

A lot of environmental risks have been accumulated with rapid growth of the previous extensive economy in our country,which led to frequent sudden heavy metal pollution accidents in rivers.Because of the imperfection of current emergency disposal technologies and decision-making system,pollution accidents have caused serious environmental,economic losses and adverse social impacts.Over all,some existed problems in the emergency water treatment were as follows: The pollutants were hard to remove from water effectively and completely;the high flow resistance and lower treatment efficiency were caused by the traditional treatment way of granular adsorbents which were closely packed in the woven bags;and the emergency response was not timely.To address the above essential issues,the study chose the one of priority pollutants in the “twelve-five” project of the China-the copper ion as the target pollutant,focused on the research of adsorption technology,and developed a novel fibrous adsorbent which was derived from the low-cost and abundant lignocellulosic biomass jute fiber by the microwave-assisted preparation process for enhanced heavy metal removal from water with low flow resistance.Besides,the study developed the adsorption reactors which can be rapidly assembled and enhance mass transfer efficiency of current granular adsorbents,and established an emergency decision-making model which revealed the response time effect.The study investigated the microwave-assisted preparation process of the carboxyl modified jute fiber adsorbent.The jute was rapidly pretreated with NaOH solution under microwave heating.According to the response surface methodology based on the single factor experiments,optimum pretreatment conditions were reaction time of 17 min,reaction temperature of 96℃ and alkaline concentration of 16%.Compared with alkali boiling under water-bath heating,reaction time was shortened by 70% and alkaline concentration was reduced from 20% to 16% in the microwave-assisted pretreatment process.The pretreated jute was grafted with Pyromellitic dianhydride(PMDA)under microwave heating.According to the response surface methodology based on the single factor experiments,the optimum grafting conditions were mass ratio between PMDA and jute of 2.8,reaction time of 18 min and reaction temperature of 120℃.The initial microwave-assisted grafting reaction rate was about 18.6 times as high as that under water-bath heating.The results show that the breaking strength of modified jute by the microwave-assisted method was larger than that of modified jute by the water-bath heating method.The study investigated the adsorption performance of carboxyl modified jute,and used adsorption models to analyze the above adsorption experimental data.The adsorption capacity of the carboxyl modified jute toward Cu(II)was 43.98 mg/g under the reaction conditions: the initial pH of 6.0±0.2,initial copper concentration of 100 mg/L and reaction temperature of 25℃.The co-ions(K(I),Na(I),Ca(II)and Mg(II))had less significant inhibitory effect on the adsorption performance of carboxyl modified jute toward Cu(II)which was not obviously affected by storage time.The carboxyl modified jute can be easily regenerated with EDTA-2Na solution and reused up to at least four times with 85% equivalent high adsorption capacity.The carboxyl modified jute can effectively remove some heavy metal ions which were in the blacklist of priority pollutants in the “twelve-five” project of the China.The sequence of adsorption capacity was: Ni(II)< Mn(II)< Cu(II)< Zn(II)< Cd(II)< Pb(II),and the adsorption capacity for Pb(II)was about 159.51 mg/g.The adsorption behavior of the carboxyl modified jute toward Cu(II)followed pseudo second-order kinetics model with a highly significant correlation;the whole adsorption process was mainly controlled by chemical adsorption.According to the Langmuir isotherm model with remarkably high adsorption capacity of 44.84 mg/g(4.23 mg/g for raw jute)under 25℃,the Cu(II)was adsorbed by monolayer adsorption on the carboxyl modified jute.The study investigated the adsorption processes for emergency treatment of sudden copper pollution in rivers,and developed adsorption processes of the fixed fiber,oscillation fluidized bed and fluidized bed for granular adsorbents.The fixed fiber adsorption process included fixed bed and fixed fiber curtain adsorption process.The dynamic adsorption capacity of carboxyl modified jute fixed bed was about 4.2 times as high as that of raw jute fixed bed.Thomas,Yoon-Nelson and BDST models could well estimate the dynamic adsorption capacity,50% and 10% breakthrough time of the process,respectively.The fixed fiber curtain adsorption process possessed stronger applicability on the site because it had the lower backwater height and smaller head loss than the adsorption dam,and could remove copper from water effectively.The dynamic adsorption capacity of 001*7 resin in the oscillation fluidized adsorption process was 65.80 mg/g under the optimum reaction conditions: fill opacity in the filter bags of 50%,operating velocity of 17 r/min,initial copper concentration of 100 mg/L and ratio between the bag space and water depth of 1:5.The dynamic adsorption capacity of the 001*7 resin in the fluidized adsorption process was 92.03 mg/g under the optimum reaction conditions: 001*7 resin dosage of 0.5 g/L,superficial liquid velocity of 1.18 cm/s and initial copper concentration of 100 mg/L.In order to estimate the adsorbents amount of the oscillation fluidized adsorption process and the fluidized adsorption process in the emergency water treatment,the mass transfer models for the above two processes were developed by the dimensional analysis method,respectively.Based on the correlative technical parameters from the above studies,the study established an emergency decision-making model which selected the emergency response time as the decision variable according to the law of pollutants diffusion in water and dynamic development tendency of environmental damages and pollution-control cost.The object function of the model was the minimum of total cost of emergency treatment which represented sudden water pollution loss.The water standard and emergency supplies preparedness time were chosen as constraint conditions.The study quantitatively evaluated the effect of the time for procuring,loading,transporting,unloading and assembling emergency supplies on the total cost by the scenario analysis method,which revealed the influence degree of the emergency preparedness implementation time and field conditions on the total cost of emergency treatment.The results can not only show serious consequences caused by the delayed emergency response clearly for relative responsible personnel,but also provide decision-makers with quantitative information support in the aspects of selection of strategic points and technical programs of emergency treatment and establishment of the emergency supplies depository.In conclusion,the results of this study enriched and improved the emergency disposal technologies and decision-making system for sudden heavy metal pollution in rivers,which had important significance in the society,economy and environment.