MICROBIOLOGICAL AND ELECTRO CHEMICAL STUDIES ON THE FORMATION OF BIOFILMS AND THEIR EFFECTS ON FERROUS METALS

Abstract

Biofilms were developed on the mild steel surfaces under natural Gulf Suez Sea water after 15 days in GPC (General Petroleum company) with black and rusty layer. Biofilm bacteria which included SMC- SRB and aerobic bacteria were collected from the mild steel surfaces then isolated and enriched using Postgate medium B and C.Thus SMC-SRB was obtained. Characteriiation of the biofilm aerobic bacteria was done using API NE20.The biochemical tests proved that the 18 isolates were related to Pesudomonaceae. Total carbohydrate was determined by phenol/ sulfuric acid reactions as an indicator of polysaccharide within the biofilm. The total carbohydrate concentrations ranged from 0.1 to 9.8 g/cm2 . Minimal inhibitory concentration (mic) for three compounds; Cetyl trimethyl ammonium bromide, WF-209 and 320-XC were detected for SMC-SRB and biofilm aerobic bacteria using sulfide determination and gradient plate technique. Mic was 10 ppm for CTAB, 320-XC and 30 ppm for WF-209. Potentiodynamic polarization curves were carried on the mild steel in the presence of biofilm bacteria under different temperatures and concentrations of the previous mentioned biocide. The results revealed that both SMC­ SRB and biofilm aerobic isolates had the ability to induced corrosion on the mild steel surfaces. X-Ray, SEM (Scanning Electron Microscope) and Sterio microscope technique were used to detect the effect