Effect Of Preparation Process And The Mechanisms On Phosphorus Removal By Zn-LDHs Modified Zeolite

In order to study the purification effect of phosphorus,laboratory-scale vertical-flow constructed wetland systems were constructed.Original and modified zeolites were used as substrate to treat contaminated water.Zeolite/Zn layered double hydroxides（Zn-LDHs）were synthesized with co-precipitated method using divalent metal compounds and trivalent metal compounds,under two different alkaline conditions.Combining on the results of adsorption test and microbiological test,the analysis of purification effect by modified zeolite and original zeolite provided a theoretical basis for the research of targeted removal of phosphorus in different forms.The purification experiment results showed that:（1）Zn-LDHs modified zeolites performed better than the original zeolites for phosphorus removal.The removal performances of ZnFe-LDHs（3:1）modified zeolites were best.The order of removal efficiencies for TP,TDP and SRP by Fe-LDHs modified zeolites were ZnFe（1:1）<ZnFe（2:1）<ZnFe（3:1）,the order of removal efficiencies for TP,TDP and SRP by Al-LDHs modified zeolites were ZnAl（2:1）<ZnAl（1:1）<ZnAl（3:1）.The removal rates of Fe-LDHs modified zeolites were superior to Al-LDHs modified zeolites with the same M²⁺.（2）The role of microorganisms influenced the removal rates of the zeolites,with the increase of concentration of Zn²⁺within a range;the microbial effect of the modified zeolite becomes greater.（3）The comprehensive ability of removing phosphorus was better when the LDHs-modified zeolites were synthesized at pH 11.Adsorption isotherm data were analyzed by Langmuir and Freundlich adsorption equations.The results showed that:（1）The phosphate adsorption behaviors on LDHs-modified zeolites could be described by Freundlich equation better,and the phosphate adsorption behaviors on original zeolites could be described by Langmuir equation better.（2）All the LDHs-modified and original zeolites had strong adsorption capacity of phosphate,and the LDHs-modified zeolites behaved better.The order of equilibrated adsorption capacity were ZnFe（1:1）<ZnFe（2:1）<ZnFe（3:1）,ZnAl（2:1）<ZnAl（1:1）<ZnAl（3:1）.（3）The ZnAl-LDHs-modified zeolites had a better adsorption capacity than the ZnFe-LDHs modified zeolites with the M²⁺:M³⁺=1:1.With the increase of concentration of Zn²⁺,the results were exactly opposite.To detect the number of phosphate bacteria on the substrates,MPN methods were used.The detection results showed that LDHs modification had a promoting effect on the growth of microorganisms.The surfaces of LDHs-modified and original substrates were covered with a trace amount of bio-film.The numbers of microorganisms had positive effects on bio-film formation and phosphorus removal effect.