EVALUATION OF MICROBIALLY-INDUCED CORROSION (MIC) OF MILD STEEL IN Aspergillus Niger CULTURES

Abstract

Microbially-Induced Corrosion (MIC) of mild steel in Aspergillus niger cultures at various temperatures (30, 40, 50 and 60^oC) and times (6, 12, 18 and 24 hours) has been investigated. The Aspergillus niger mycelia was cultured and its spores harvested from seven (7) days old slants, inoculated by washing the slants with 0.1% sterilized tween 80 into the 250ml Erlenmeyer flasks containing the cultures, and placed on a rotary shaker at 300rpm, pH4.0 and a temperature of 30^oC for 120 hours. The corrosion tests were conducted in a thermo-stated water bath containing eight beakers of Aspergillus niger cultures and the coupons. There was a general increase in corrosion rate with exposure time; the highest corrosion rate of 245mpy being attained at a temperature of 40^oC. Corrosion rates obtained at 50 and 60^oC were found to be lower than those at 30 and 40^oC. This might be due to the retardation in the growth of the fungi as the temperature was increased. The metabolic activities of the fungi might have produced some organic substrates which, directly or indirectly, were responsible for the observed degradation of the substrate. It was concluded that the rate of fungal growth, temperature and environment (corrodent) are the major factors affecting the corrosion rate of mild steel under the influence of these microorganisms.