Adsorption Of COD From Landfill Leachate By Different Modified Straw Biochars

Landfill leachate is a kind of organic wastewater with complex water composition and high concentration of COD and ammonia nitrogen,its water quality and quantity change greatly,so the reduction of COD is an important treatment goal.Adsorption is a common means of physical and chemical treatment,selection of an efficient adsorbent is the key to deal with all kinds of wastewater by adsorption.In this study,the modified reed straw biochar and the rice straw biochar were made by different modifiers,then p Hpzc,SEM,FTIR and XRD analyses were applied to study the structures of two modified biochars.Also,the impact on the reduction of COD by different factors was studied to explore the absorption characteristic.And the two modified biochars were studied by orthogonal test to find the optimum condition.At the same time,the regenerative adsorption effect of the two biochars was studied.The main results were as follows:(1)With reed straw as raw material,the optimum carbonization temperature was 600?,the carbonization time was 2h,the carbon yield was 35.5%.The results of modificiations showed that the removal rate of COD by the unmodified reed biochar was 32.56%,and the removal rate reached 48.22% by the modified biochar with composite modification of Fe Cl3 and HCl.The p Hpzc of modified reed biochar was 8.4.The results showed a coarser surface,a more developed structure,a large number of acidic functional groups and a higher fibre crystallinity based on the characterization of modified reed biochar by SEM?FTIR?XRD.(2)With rice straw as raw material,the optimum carbonization temperature was 500?,the carbonization time was 2h,the carbon yield was 37.2%.The results of modificiations showed that the removal rate of COD by the unmodified rice biochar was 34.88%,and the removal rate reached 53.34% by the modified biochar with composite modification of Zn Cl2 and HCl.The p Hpzc of modified rice biochar was 6.5.The results showed a porous structure,a large number of folds,a large number of acidic functional groups and a higher fibre crystallinity based on the characterization of modified rice biochar by SEM?FTIR?XRD.(3)The adsorption test of modified reed biochar showed that the optimum parameters od adsorption at the COD concentration of 1500mg·L-1: p H=5,the dosage was 0.8g,adsorption time was 60 min,the reaction temperature was 40? and the removal of COD was about 67% under this condition.The degree order of four influencing factors on adsorption of the modified reed biochar was p H>intial concentration of COD> adsorption time>dosage.The kinetic experimental data of the adsorption of reed biochar fitted well the pseudo-second-order equation,the adsorption was mainly controlled by surface adsorption and intra particle diffusion,mainly belonged to chemical adsorption.The adsorption isotherm fitted the Langmuir isotherm,belonged to the monolayeradsorption.The recycled reed biochar could still adsorb the landfill leachate.(4)The adsorption test of modified rice biochar showed that the optimum parameters of adsorption at the COD concentration of 1500mg·L-1: p H=5,the dosage was 0.8g,adsorption time was 90 min,the reaction temperature was 40? and the removal of COD was about 75% under this condition.The degree order of four influencing factors on the adsorption of the modified rice biochar was p H>dosage>adsorption time>intial concentration of COD.The kinetic experimental data of the adsorption of rice biochar fitted well the pseudo-second-order equation,the adsorption was mainly controlled by surface adsorption and intra particle diffusion,mainly belonged to chemical adsorption.The adsorption isotherm fitted the Freundlich isotherm,belonged to the multilayersorption.The recycled rice biochar could still adsorb the landfill leachate.Both the reed and rice straw had a certain effect on the removal of COD from landfill leachate,the adsorption performance was improved to a certain extent after modification.The modified reed biochar and modified rice biochar had the ability to reduce the concentration of COD,and they were economical and efficient adsorbents.