Fate of Selected Heavy Metals in a Biological Wastewater Treatment System

Carried out by human activity, micropollutants are one of the major environmental concerns. Among these micropollutants, heavy metals occupy an important position. Indeed, many micropollutants from human activity, particularly in urban areas, are eliminated in the water masses, degrading their quality and disrupting their good ecological functioning. Their presence in wastewater is one of the main causes of water and soil pollution. The purpose of this study was to evaluate heavy metals content in wastewater at the wastewater treatment plant of AL-HOCEIMA city, located on the Mediterranean coast in the north of Morocco. To this end, two composite samples, 24 h to be representative, were taken (raw water and treated water). Water volumes were collected using refrigerated (4 °C) autosamplers equipped with Teflon bottle hoses to prevent contamination. The content of heavy metals such as Cu, Zn, Fe, Mn, Cd, Pb, As, Ni, Ba, Cr, Co and Hg in wastewater was determined by Inductively Coupled Plasma Spectrometry (ICP-OES). The results showed that the content of heavy metals (Cu, Zn, Fe, Mn, Cd, Pb, As, Ni, Ba, Cr, Co and Hg) at the inlet of the treatment plant is relatively low, because of the low industrial activity in the region. This clearly confirms the domestic nature of the city wastewater. The removal efficiency of heavy metals was directly proportional to their initial values in raw wastewater. The reduction of heavy metals was as follows: Cd < Cu < Fe < Mn < Cu < Pb < Ni < Co < Ba < Zn < Cr < Hg.