Study On Preparation Of The Modified Biomass Materials And The Adsorption Performance Of Arsenic And Its Treatment Technology

To meet the requirement for the response of the frequently occurred water pollution,the development of efficient,low-cost adsorbents is necessary.This study focused on the natural biomass materials: sawdust and spent coffee grounds.The different chemical modifications are used to synthesis the biomass based adsorbents—modified sawdust and modified coffee cellulose adsorbents.The adsorptive performances were examined in details,and the adsorption mechanism is also investigated to better understand the bonding structure between pollutants and adsorbent.The fixed bed and the combined adsorption-membrane techniques are constructed to provide the technical support for the sudden water pollution accidents.The raw sawdust is used as a matrix,epichlorohydrin(ECH)and diethylenetriamine(DETA)are used as reagents to prepare the modified sawdust adsorbent.The optimized synthesis condition is: The optimal ratio of the modified sawdust dosage and ECH is 1:3(It means for every one gram of the modified sawdust,3 m L ECH will be added accordingly),The optimal ratio of the modified sawdust dosage and DETA is 1:1(It means for every one gram of the modified sawdust,1 mL DETA will be added accordingly).The temperature of the esterification and crosslinking reactions is 90? and 70?C,respectively.The results revealed that the grafted amino group is beneficial for the loading of iron compound.The temperature of etherification reaction and ECH dosage is essential for the synthesis of modified sawdust.The optimal solution pH for adsorption process is between 5 and 6.The maximum adsorption capacity for As(III)and As(V)is 13.2,46.1 mg/L,respectively,which have the remarkable advantages compared with the reported biomass materials.The spent coffee ground is used as a matrix,5% NaClO solution is used to extract the pure coffee cellulose from the spent coffee grounds.Polyethyleneimine(PEI)and glutaraldehyde are used as reagents to prepare the modified coffee cellulose adsorbent.The optimized synthesis condition is: 5% PEI solution is reacted with coffee cellulose for 120 min;0.1% glutaraldehyde is used as crosslinker to react with coffee cellulose for 240 min.the optimal Fe(NO3)3 solution is 500 mg/L.Unlike of the modified sawdust,the alkaline aging process is not conducted after complexing with Fe(III),because complexation with Fe(III)could greatly increase the surface Zeta potential of modified coffee cellulose,so as to facilitate As(V)adsorption.The modified coffee cellulose shows bad adsorption performance for As(III)because of the absence of alkaline aging process.The batch experiments revealed that pH is a key factor for the adsorption process,and the weak acidic condition is beneficial for arsenic adsorption on modified coffee cellulose.The maximum adsorption capacity for As(V)is 91 mg/g.After As(V)adsorption,the successive adsorption of Cu(?)is further achieved with the maximium adsorption capacity of 200 mg/g.The simulation for the statical and dynamic adsorption of biomass materials is conducted,and the adsorption mechanism is discussed according to the properties of adsorbents.The results indicated that: arsenic adsorption on the modified biomass materials is spontaneous,and the adsorption kinetics could be best fitted with pseudo-second-order equation,indicating the chemisorptions in nature.Langmuir equation could best fit the arsenic adsorption on both modified materials,indidcating the monolayer adsorption in nature.As to the mechanism for arsenic adsorption on modified sawdust,the loaded iron oxyhydroxides are mainly responsible for As(III)adsorption,while the grafted amino groups is mainly responsible for As(V)adsorption.The mass transfer mechanism indicated that: the internal mass transfer coefficient [kLa]d constitutes the most proportion of the global mass transfer coefficient [k La]g,indicating the main mass transfer resistant comes from the phys-chemical reaction between arsenic and adsorbent,and the arsenic diffusion into the inner pores of sawdust.For the modified coffee cellulose,the markable change of Zeta potentials of coffee cellulose is observed during the synthesis process.After modification,the surface Zeta potential is siginificantly increased to 41.6 mV,indicating the strong affinity towards negatively charged As(V).The mechanism study revealed that the successive adsorption of As(V)and Cu(?)is achieved by the electrostatic attraction and the surface complexation between copper and amino groups.The fixed bed technique is desighed to simulate the adsorption dam for the treatment of sudden water pollution accidents.The modified sawdust is packed into the adsorption column,and the effects of different bed depths and flow rates are studied to better understand the adsorption performance.Different dynamic adsorption models are used to summarize the basic adsorption parameters,which is important for the potential application in the sudden water pollution accidents.In order to separate the exhausted adsorbents from the reactor,the combined adsorption-UF membrane technology is designed.The mechanic stirring and aeration stirring are compared for the removal efficiency of total arsenic.The results revealed that aeration stirring can make more uniformly mixture than mechanic stirring.Moreover,the increased concentration of dissolved oxygen could accelerate the oxidation of As(III)to As(V),thus enhancing the total arsenic removal efficiency.The simulative arsenic contaminated water samples are prepared.For the initial concentration of 0.1 mg/L arsenic solution,the arsenic concentration in the effluent is below the standard concentration of drinking water in China.The retaining efficiency for the exhausted adsorbents is about 100%.The UF membrane module also has high removal efficiency for TOC and suspended solids in the water.The permeate flow slightly decreased with the running time,indicating the adsorbent is no easy to attach onto the membrane surface,and the less possibility for the membrane fouling is expected.The frequency for the backwashing process is greatly reduced.In summary,this study revealed that the modified biomass materials and techniques are suitable for the remediation of arsenic related sudden water pollution accidents.