REMOVAL OF HEAVY METALS FROM WASTEWATER WITH AGRICULTURAL WASTES

Heavy metals, also known as trace metals, are one of the most persistent pollutants in wastewater.The discharge of high amounts of heavy metals into water bodies leads to several environmental and health impacts. The exposure of humans to heavy metals can occur through a variety of routes, which include inhalation as dust or fume, vapourisation and ingestion through food and drink. Some negative impacts of heavy metals to aquatic ecosystems include death of aquatic life, algal blooms, habitat destruction from sedimentation, debris, increased water flow, other short and long term toxicity from chemical contaminants. Abundant amounts of heavy metals present in soils cause reduction in quality and quantity of food preventing plants, growth, uptake of nutrients, physiological and metabolic processes. Severe effects on animals may include reduced growth and development, cancer, organ damage, nervous system damage, and in extreme cases, death. To help mitigate the negative impacts of heavy metals on the health of humans, animals and the environment, a variety of remediation processes exists, Oghenerobor Akpor (۲۰۱۴). This remediation has been introduced to remove the toxic metals in the water ranging from the expensive chemical treatment to the low cost biosorption. The chemical treatment for wastewater required mixture of chemical compound to reduce the metals pollutant. Some treatment methods developed such as coagulation, flocculation, reverse osmosis, membrane separation, ion-exchange, solar photo degradation and ozonation were conducted either to remove or degrade the pollutants in wastewater to harmless form. The hazardous state of the toxic metals is changed into a stable and safe state so that the threat to human and the environment is reduced. However, the conventional methods were rather expensive, as higher cost was needed during the operation. Moreover, the conventional methods tend to have residuals and incomplete removal of the pollutants posing another problem, Chiban et al. (۲۰۱۲). Recently, scientists have been studying on using inexpensive adsorbents to remove heavy metals in the water. The low cost adsorbentsused to practice adsorption activities were usually waste products from another production like agriculture, industrial and food production, which can be obtained abundantly. The most popular heavy metals are lead (Pb), zinc (Zn), mercury (Hg), nickel (Ni), cadmium (Cd), copper (Cu), chromium (Cr), and arsenic (As). Although these heavy metals can be detected in traces; however, they are still hazardous. Table ۱ summarizes some heavy metals, focusing on their major sources, health effects, and the permitted quantity in drinking water. The aforementioned metals and others such as silver (Ag), iron (Fe), manganese (Mn), molybdenum (Mo), boron (B), calcium (Ca), antimony (Sb), cobalt (Co), etc. are commonly available in wastewater and need to be removed.