Effects of Extracts of Alchornea Cordifolia on Biocorrosion Control on Sewer Concrete

Abstract

Concrete infrastructures that make up the sewer system exposed to sewer waste waters are often subjected to microbial corrosion. The biogenic sulfuric acid produced by the activity of sulfur-oxidizing bacteria A.thiooxidans attacks concrete in sewers leading to loss of concrete mass and deterioration.  The aim of this study was to control concrete biodegradation using plant extracts of Alchornea Cordifolia. Concrete samples were corroded for 26 months in real sewer wastewater conditions. The influence of biogenic sulfuric acid on the biocorrosion of concrete samples was determined in terms of weight loss, pH, sulfate concentration variation, chemical composition changes, and formation of corrosion by-products. Recorded corrosion rates before coating were between 0.071996mpy – 1.168546mpy. Changes in sample morphology, ettringite and gypsum formed were observed by X-ray diffraction and SEM methods with corrosion progression.Phytochemicals analysis of extracts samples confirmed the presence of tannins, saponins, flavonoids, and terpenoids produced in plant tissues. GC-MS analysis of the ethanolic extracts identified 26 compounds. The most dominant being Eugenol.  Biocorrosion control determined the effects of extracts on concrete corrosion in sewer waters. A marked decline in the rates of corrosion with each extract's coating was recorded for extracts coated concretes (0.002589mpy -0.003256mpy). An increase in inhibition efficiency with an increase in extract concentration was observed and was in the range of   50% A.Cordifolia extracts gave the highest inhibitor efficiency. X-ray diffractive analysis and scanning electron microscopy showed morphological variations in concrete before and after coating. Results of ANOVA showed inhibitor concentration as having the most significant effect on the extracts' corrosion inhibition.