Although heavy metals are essential for microbial growth at low concentration level, they can exert toxic effect at higher levels. The continuous discharge of them into the aquatic environment will in future limit the multiple uses of waster as well as increasing the frequency of chronic diseases in the human population. One of the most important sources rich in heavy metals is leachate coming from landfills of domestic solid wastes. This is an engineered method of disposing solid waste by spreading and compacting it to smaller volumes thus reducing associated environmental hazard to a minimum. Leachate typically contains high concentrations of organic and inorganic pollutants which can vary seasonally and annually as the waste age.
So, this study aimed at removing heavy metals from leachate using biological treatment. This was done by treatment of leachate biologically using adapted sewage flora followed by immobilized selected strain Acinetobacter sp. bacteria at different detention time.
The results revealed that selected strain of Acinetobacter sp. [beeds] was effective for biodegradation of chromium more than other metals then followed by cadmium, nickel, and lead. However, efficiency of sewage flora for degradation of selected metals was higher than beeds as  represented by degradation percent and rate of degradation, this was due to adaptation phases of sewage microorganisms on leachate.
The study recommended that leachate must be treated first in adapted sludge unit to decrease high concentration of these metals then followed by activated beeds unit for complete removal of these metals.