investigation of using fixed activated sludge system for removing heavy metals (cr, ni and pb) from industrial wastewater

in this research the operation of fixed activated sludge system for treatment of wastewater containing heavy metal compounds, by use of fas pilot ,a plaxy glass tank with three section; these section are downward-flow aerated reactor, upward-flow aerated reactor and gravity sediment unit, length and width and height of each part was respectively 15.7cm, 31.5cm , 51.5 cm and feeding with the synthetic wastewater containing proteins, lipids, carbohydrates and heavy metal compounds (chromium, lead and nickel) was studied. the aerated reactor is equipped with media made of pvc with surface area equal to 81.34 m2/m3. the obtained results show that cod removal percentage in the fas has been about 96% and the acclimation time for microorganisms in this system is short. at each stage increasing the concentration of heavy metals lead to a decrease both in cod and mlss, and again the cod and mlss increase, after the microorganisms acclimate with changes, but do not increase from the best previous stage condition of cod removal percentage, and the cod removal percentage has a downward movement. heavy metals removal percentage in fixed activated sludge at the concentration of 1 mg/lit is 84%, 75% and 80%, respectively, and by increasing concentration of heavy metals at 5 mg/lit, the removal percentage is 90%, 84% and 87%, respectively. by increasing concentration of heavy metals at 10 mg/lit, the removal percentage is 85%, 95% and 92%, respectively, and by increasing concentration of heavy metals at 50 mg/lit; the removal percentage is 86%, 96% and 95.1%, respectively. by increasing concentration of heavy metals at 100 mg/lit, the removal percentage is 86%, 97.6% and 97%, respectively. finally the microorganisms practically lose their efficiency to remove the heavy metals and cod at the concentration of 400 mg/lit of chromium, lead and nickel.