D-amino acids for the enhancement of a binary biocide cocktail consisting of THPS and EDDS against an SRB biofilm.

Biofilms of sulfate reducing bacteria (SRB) are often responsible for Microbiologically Influenced Corrosion (MIC) that is a major problem in the oil and gas industry as well as water utilities and other industries. This work was inspired by recent reports that some D: -amino acids may be useful in the control of microbial biofilms. A D: -amino acid mixture with equimolar D: -tyrosine, D: -methionine, D: -tryptophan and D: -leucine was tested in this work for their enhancement of a biocide cocktail containing tetrakis (hydroxymethyl) phosphonium sulfate (THPS) and ethylenediamine-N,N'-disuccinic acid (EDDS). Desulfovibrio vulgaris (ATCC 7757) was cultured in ATCC 1249 medium. Its biofilm was grown on C1018 carbon steel coupons. Experimental results indicated that the triple biocide cocktail consisting of 30 ppm THPS, 500 ppm EDDS and 6.6 ppm D: -amino acid mixture (with equimolar D: -tyrosine, D: -methionine, D: -tryptophan and D: -leucine) was far more effective than THPS and EDDS alone and their binary combination. The triple biocide cocktail effectively prevented SRB biofilm establishment and removed the established SRB biofilm. The D: -amino acid mixture alone did not show significant effects in the two tasks even at 660 ppm.