Characterization of heavy metals and toxic elements in raw sewage and their impact on the secondary treatment of the Marrakech wastewater treatment plant

The purpose of this study is to follow the evolution of the concentration of heavy metals (cr+6,cu and ni) and toxic elements (sulfides and phenols) in raw water at the inlet of the wastewater treatment plant of marrakech (morocco) and to evaluate their impact on the performance of secondary treatment with activated sludge. for this purpose,analyzes of heavy metals and toxic elements as well as other physicochemical parameters were carried out at the entry of the wwtp in 2013.the toxic elements were an annual average of 0.19 mg /l for cr+6,3.21 mg /l for cu,1.98 mg /l for ni,3.58 mg/l for phenol and 2.24mg /l for sulfides. the raw effluent pollution parameters are,ph 7.9,conductivity of 2711.99μs /cm,temperature 25.28° c,cod of 1051.67 mg o2 / l,bod5 of 516.58 mg o2 /l,an ss of 416.53 mg /l,global nitrogen (ngl) of 90.55 mg / l,and 11.20 mg /l for total phosphorus (pt).the results of analyses at the exit of secondary treatment provided good elimination efficiency throughout the year for all biological treatment parameters: 90% for chemical oxygen demand (cod),97% for 84% for suspended solids (ss),87% for global nitrogen (ngl),and 55% for total phosphorus (pt). however,during the month of april,the purification performance of the biological treatment was affected by the abundant presence of toxic elements that far exceeded the standards recommended by the moroccan authorities. the purification yields were affected and reached minimum levels of 74%,94% 75%,49% and 40% respectively of cod,bod5,ss,ngl and (pt). © 2017,university of mohammed premier.