Removal of lead and chromium from aqueous solution by bacillus circulans biofilm
Contamination of the aquatic environment by heavy metals is a worldwide environmental problem. The pollutants of serious concern include lead, chromium, mercury, uranium, selenium, zinc, arsenic, cadmium, gold, silver, copper and nickel, due to their arcinogenic and mutagenic nature (Leung et al., 2000). Many industries such as coating, automotive, aeronautical, steel, textile dyeing, leather tanning, electroplating and metal finishing generate large quantities of wastewater containing various concentrations of lead and chromium. Lead poisoning in humans may cause severe damage to the kidneys, nervous system, and reproductive systems, liver and brain (Leung et al., 2000). Severe exposure to lead is also associated with sterility, abortion, stillbirth and neonatal deaths. The hexavalent form of chromium is considered to be a group “A” human carcinogen because of its mutagenic and carcinogenic properties (Cieslak Golonka, 1996). Permissible limits for lead and chromium in drinking water given by Institute of tandards and Industrial Research of Iran (ISIRI) is 0.1 mg/L and 0.01 mg/L, respectively (ISIRI, 1053). These limits for water packaged (bottled) reported by this institute is 0.005 and 0.05 mg/L, respectively (ISIRI, 6694). In recent years, cancer rate has increased because of the precence of lead in drinking and natural waters. The international public health associations have reduced the permitted amount of lead in drinking water. For example, the European Community (EC) recommends a limit of 50 μg/L of lead in potable waters (Talebi and Safigholi, 2007). Thus it becomes mandatory to remove lead and chromium from drinking water and wastewaters.