Effect of water clarification using moringa oleifera on corrosion resistance in patinable steel pipeline

ABSTRACT

In Brazil, it is common to apply chemical coagulants during the drinking water treatment stages, the most used among them is aluminum sulfate (Al2(SO4)₃), considered harmful to health and may cause neurological diseases. During the rainy season, the levels of suspended particles in the water increase, making it necessary to add a higher dosage of conventional coagulant, thus generating a high commercial cost for the pipelines, which may even not reach the consumer in a properly treated form. Considering some negative aspects of the application of this type of coagulant, the present work investigates the Moringa oleifera seed as a potential natural coagulant to be used during the water treatment process. Immersion corrosion tests were carried out (30, 60 and 90 days) and subsequently, Open Circuit Potential (OCP) and Linear Polarization (PL) electrochemical tests applied to CST COR 400 weathering steel samples (coated with epoxy paint, without coating (neutral) and with the presence of a weld bead) originating from a water main piping. Optical microscopy (OM) analyzes and powder characterization were also carried out using Fourier transform infrared (FTIR) reading. The studies concluded that for biocoagulation and clarification of raw river water, the dosage of 200 mg/ 200 ml is the most appropriate, as it did not change pH and turbidity, being within potability standards. In the immersion corrosion tests, the steel with epoxy paint protection had a balance in terms of mass loss, the opposite happened with the neutral sample. The FTIR identified the slight presence of elements such as bromide that helps in the oxidative process and in greater quantities the presence of aldehyde and amines that help in the process as corrosion inhibitors.

Keywords:
Water pipeline; Water clarification; Corrosion; Moringa oleifera