Identification, Documentation and Control of Biological Contamination in Middle Distillate Fuel

Abstract

The present study was initiated under a contract with the New Zealand Defence Scientific Establishment to document the nature, extent and possible sources of microbial contamination of middle distillate fuel (‘Dieso’) held in storage tanks at Devonport, Auckland, and to study possible methods for control of such contamination. Thirty-one fungal species and five bacteria were isolated during the period 1982-1984. The principal contaminants were the fungi Cladosporium resinae (the anamorph of Amorphotheca resinae Parbery), Penicillium corylophilum and Paecilomyces variotii. All three fungi produced dark mycelial mats at the water/diesel fuel interface in laboratory studies. Interactions between these fungi were observed. In the presence of Bushnell.-Haas mineral salts/diesel fuel phases Cladosporium resinae predominated while in seawater/diesel fuel phases Penicillium corylophilum predominated. All New Zealand and Australian isolates of C. resinae grew profusely in Bushnell-Haas mineral salts/diesel fuel phases. The biostatic/biocidal effects of chemicals on the predominant fungi in diesel fuel were studied in laboratory and field tests during 1984-1985. The most effective biocides in controlling C. resinae were benomyl, imazalil and Kathon 886. Imazalil had no effect on Paecilomyces variotii but when used in combination with benomyl a synergistic effect occurred at 100 ppm. Biobor JF, DEGME and EGME performed poorly in laboratory tests regardless of the amount of water present, but gave temporary inhibition of C. resinae in the field tests. Isolates from tanks treated with Biobor JF and DEGME grew well in the presence of these compounds in the laboratory. DML-7 and Proxel AS inhibited C. resinae and Penicillium spp. in both laboratory and field tests at a high dose of 300 ppm but were less effective against P. variotii. The effects of the biocides on engine performance and carbon deposits on engine components were studied. Recommendations for control of microbiological contamination of stored diesel fuel are given. In electron microscope studies no difference was observed in the intracellular structures between jet and diesel fuel isolates of C. resinae and the non-hydrocarbon utilizing Cladosporium cladosporioides.