Removal Of Cr (VI) And Pb(II) In Wastewater By Using Pyrolytic Excessed Sludge Residues As A Sorbent

The excessed sludge and anaerobic digestion sludge were taked as research object in the paper. Impacts of pyrolysis temperature and react time on properties of residue prepared by sludge pyrolysis were investigated. After that,the Cr(VI)and Pb(II) wastewater are treated by using sludge residue .Some factors such as contact time, solution pH and adsorbent dose were presented to perform Cr(VI) and Pb(II) removal from water.Furthermore,the satured sludge residues were desotped and the effect of desorption acid, contact time and acid concentration on desorption capacity of residues were studyed. Finally, the adsorption mechanism of the aerobic sludge adsorbent was also studied. Following main conclusions are obtained:1) With the increase of pyrolysis temperature and react time, the yield of sludge residues decreased. Iodine and adsorption capacity of residues is not correlated with prylosis temperature and time. There is an optimal parameter. The residues prepared by phosphorus–rich sludge in 700℃have the biggest adsorption capacity to Cr (VI) and Pb(II).2) With the contact time extend,the removal efficiency of Cr(VI)and Pb(II) increased. when the solution pH increased, the removal efficiency of Cr(VI)decreased ,and removal rate of Pb(II) increased. Adding adsorbent dose, removal efficiency of Cr(VI)and Pb increased but the adsorption capacity decreased. In the wastewater of Cr(VI)200mg/L, the maximum capacity of pyrolysis residue for Cr(VI) sorption was 13.9mg/g at pH=4.0, contact time 3.0h and adsorbent dose of 20g/L. When the initial concentration of Pb(II) wastewater is 200mg/L, the biggest capacity was 9.63mg/g at pH=5.0, contact time 3.0h and adsorbent dose of 20g/L.3) The Cr (VI) and Pb (II) sorption process can be depicted by the pseudo-second-order kinetic. Langmuir model and Freundlich model were well fitting to the isotherm data, and the former appeared to be better. It is showed that the adsorption process is controed by reaction speed of many processes by Weber-Morris model.4) Compared with nitrate, hydrochloric acid has a higher desorption rate to pyrolysis residues. And desorption rate increase, when the contact time is extended or the concentration of hydrochloric is improved. With 0.05mol/L hydrochloric acid to desorpt 3h, the desorption rate of Cr (VI) and Pb(II) can separately reach up to 71% and 64%. The process of desorption can be depicted by the pseudo-second-order kinetic.5) The mechanisms of Cr (VI) and Pb (II) removal by pyrolysis residues included electrostatic adsorption, surface complexation, and aperture adsorption.The above results indicate that the pyrolysis sludge residue can be employed as an effective, safe and economically feasible adsorbent in treatment of heavy mental wastewater.