Advanced Treatment Of Landfill Leachate After Biochemical Process With Ca-Al-LDH

In recent years, bio-treatment of landfill leachate has been widely used in manylandfills. This biochemical effluent is hard to be advanced treated for its various kindsof pollutants. It leads to the appearance that the concentrations of pollutants in theeffluent are still high and there are even many priority pollutants in it. So it is urgentlyrequired to find a method which is low-cost, efficient and reused in the application ofadvanced treatment.Recently, the method of adsorption has been used in the advanced treatment oflandfill leachate. The objective of this article is to investigate the possibility of anadsorption material, Ca-Al-LDH, formed in the biochemical effluent with someamount of AC and Ca(OH)2in the basis of the effluent’s characteristic and theprinciple of LDH’s co-precipitation. At the same time, with the Ca-Al-LDH formed inthe leachate, the concentrations of COD and organic matters also can be reduced. Inorder to explore the efficiency and mechanism in the removal of the organic mattersby Ca-Al-LDH, this article employed the contrast experiments and many kinds of testmethods like UV254, EEM and FTIR. All the results were indicated as followed:(1) The removal of organics in leachate by Friedel’s salt (Ca-Al-Cl-LDH) wasvery efficient. The maximum removal efficiencies of COD, UV254and TOC were57.67%,70.46%and63.97%, respectively. When the dosage of Ca-Al-Cl-LDH wasless than10g/L, the products in solid phase were CaCO3because of its dissolution.While the dosage was more than10g/L, it existed mainly in Ca-Al-LDH. Theformation of Ca-Al-LDH is beneficial to the removal of the dissolved aromaticcompounds, such as fulvic-like acid and humic-like acid. Ca-Al-LDH has a selectivityto the removal of the fulvic acid-like compounds with small molecular weight andmore carboxylic groups.(2) There was little of N-compounds removed by the addition of theCa-Al-Cl-LDH. The maximum removal rates of NO3-N, NO2-N and NH3-N were42.58%,20%and35.08%. The removal of the total Nitrogen was only37.95%. Fromthe point of NH3-N compounds, with the addition of Ca-Al-Cl-LDH, the pH value of the leachate was increased which might cause the decrease of the NH3-N. On theother hand, the adsorption of Ca-Al-LDH could make more NH3-N removed.(3) The Ca-Al-LDH can be synthetized with some amount of CaCl2andAlCl3·6H2O added to the leachate when pH was adjusted to10.5. So the Ca-Al-LDHcould be in situ formed in the biochemical effluent, and the concentration of COD(about60%) also could be reduced simultaneously. Considering of theindustrialization of the Ca-Al-LDH, AC and Ca(OH)2were used to replace CaCl2andAlCl3·6H2O. And when the dosage of AC was more than5g/L and the mass ratio ofAC and Ca(OH)2was3, Ca-Al-LDH could be formed. So the LDH compound couldbe synthetized by low-cost Ca-Al material like AC, and can be used in the advancedtreatment of landfill leachate after biochemical process.(4) Treatment of landfill leachate with AC and Ca(OH)2, the maximum removalrates of COD, UV254and TOC were73.85%,85.81%and74.71%, respectively. Theconcentration of COD left was less than100mg/L, which reached the dischargestandard of the leachate in China. The treatment efficiency of leachate with AC andCa(OH)2was much better than that with Ca-Al-Cl-LDH. Moreover, when the dosageof AC less than5g/L, the removal rate was larger than Ca-Al-Cl-LDH. Both of thephenomenon might be attributed to the stronger adsorption during the formation ofCa-Al-LDH, combined with the coagulation，adsorption and hydration of the AC.(5) The in-situ synthesis of Ca-Al-LDH with AC and Ca(OH)2in leachate couldremove many kinds of organic matters, for instance, the visible fulvic-like acid andhumic-like acid. Furthermore, the formation of Ca-Al-LDH was beneficial to theremoval of UV fulvic-like acid.With the different dosage of AC, the variation ofinorganic ion in leachate was different from the addition of Ca-Al-Cl-LDH. When ACadded to the leachate, the concentration of Cl-, Al3+and Ca2+decreased apparently andall the metal ions and inorganic anions were employed effectively.By means of the addition of different reagents to the leachate, only in theseconditions with10g/L Ca-Al-Cl-LDH, CaCl2and AlCl3·6H2O at pH=10.5and10g/LAC, Ca-Al-LDH was well formed. When the solid products were Ca-Al-LDH, theremoval of organic matters was much better than those were not. That is to say, the formation of Ca-Al-LDH was beneficial to the removal of the organics, especially forthe aromatic organics, such as visible fulvic-like acid, humic-like acid and UVfulvic-like acid. And Ca-Al-LDH has a selectivity for the removal of fulvic acid-likecompounds with more carboxylic groups.(6) The desorption of the solid phase in ultrasonic suggested that the removal ofhydrocarbons, alcohols and aromatic compounds was due to the surface adsorption ofCa-Al-LDH. The FTIR results indicated that the formation of Ca-Al-LDH wasbeneficial to the removal of aromatic organics and alcohols. In other circumstances,the removal of organic matters was lower.