The equilibrium and rate of heavy metals interaction with aerobically digested sludge

Heavy metal that is discharged into sewerage system becomes concentrated in the sewage sludge. The sludge digester may become acclimated to very high level of trace metal over a long period of time. The goal of this research is to determine the kinetics and equilibrium aspects of the heavy metal and aerobically digested sludge interaction.; The dissolved organic matter (DOM) in wastewater treatment system has an important role in the uptake of heavy metals by aerobically digested sludge. Result show that the DOM contains two discrete acid groups for metal complexation. The acidity constant, pK_aA and pK_aB, are 6.5 and 9.7. The specific surface area of the aerobically digested sludge is 47 m 2/g. SS. The first layer adsorption constant (log K₁) is 4.8, and the multi layer adsorption constant (log K₂) is 3.3. pH _zpc of aerobically digested sludge is in the range of 2.5 to 3.5 by plotting zeta potential (mV) against pH. The pH_zpc is lower than operational digester pH; it means that bacteria have net negative charge. This condition will allow metals with positive charge become absorbable. The surface site density of aerobically digested sludge, S_T is 4.5 × 10−3 mole/g. SS. The acidity constant, pK _H is 5.9.; Six different type of metal such as Pb(II), Cd(Il), Cu(II), Zn(II), Ni(II) and Co(II) and different initial metal concentration were used in the kinetic experiment. The stability constant was calculated based on uptake rate and release rate constant results. The result of stability constant (log K _S) is in the order: Pb(II) > Cu(II) > Cd(II) > Zn(II) > Ni(II) > Co(II).; Batch equilibrium metal uptake by aerobically digested sludge experiment was conducted with different shaking time (equilibrium time) and different initial metal concentration. Results show that heavy metal uptake is very fast and reach equilibrium in only an hour. The stability constant was calculated and followed the order of: Cd(II) > Pb(II) > Cu(II) > Zn(II) > Ni(II) > Co(II).