Abstract
Different species of microbes form mixed-culture biofilms in cooling water systems. They cause microbiologically influenced corrosion (MIC) and biofouling, leading to increased operational and maintenance costs. In this work, two D-amino acid mixtures were found to enhance two non-oxidizing biocides [tetrakis hydroxymethyl phosphonium sulfate (THPS) and NALCO 7330 (isothiazoline derivatives)] and one oxidizing biocide [bleach (NaClO)] against a biofilm consortium from a water cooling tower in lab tests. Fifty ppm (w/w) of an equimass mixture of D-methionine, D-leucine, D-tyrosine, D-tryptophan, D-serine, D-threonine, D-phenylalanine, and D-valine (D8) enhanced 15 ppm THPS and 15 ppm NALCO 7330 with similar efficacies achieved by the 30 ppm THPS alone treatment and the 30 ppm NALCO 7330 alone treatment, respectively in the single-batch 3-h biofilm removal test. A sequential treatment method was used to enhance bleach because D-amino acids react with bleach. After a 4-h biofilm removal test, the sequential treatment of 5 ppm bleach followed by 50 ppm D8 achieved extra 1-log reduction in sessile cell counts of acid producing bacteria, sulfate reducing bacteria, and general heterotrophic bacteria compared with the 5 ppm bleach alone treatment. The 10 ppm bleach alone treatment showed a similar efficacy with the sequential treatment of 5 ppm bleach followed by 50 ppm D8. The efficacy of D8 was found better than that of D4 (an equimass mixture of D-methionine, D-leucine, D-tyrosine, and D-tryptophan) in the enhancement of the three individual biocides against the biofilm consortium.
Highlights
Large-scale cooling water systems are widely used to remove heat from industrial equipment using a heat exchanger in chemical manufacturing facilities, power plants and petroleum refineries (Wang et al, 2013)
Lab tests showed that 1 ppm (w/w) D-tyr and 100 ppm D-met individually enhanced the efficacy of low concentrations of tetrakis hydroxymethyl phosphonium sulfate (THPS) and ADBAC biocides, respectively in the mitigation of the Desulfovibrio vulgaris biofilm on carbon steel, achieving better efficacies than higher concentrations of THPS and ADBAC (Xu et al, 2012, 2014; Jia et al, 2017b)
confocal laser scanning microscopy (CLSM) images and NALCO 7330 against a field biofilm consortium on C1018 carbon steel coupons retrieved from a water cooling tower
Summary
Large-scale cooling water systems are widely used to remove heat from industrial equipment using a heat exchanger in chemical manufacturing facilities, power plants and petroleum refineries (Wang et al, 2013). D-amino acids can enhance the efficacy of some existing biocides against corrosive biofilms. Lab tests showed that 1 ppm (w/w) D-tyr and 100 ppm D-met individually enhanced the efficacy of low concentrations of THPS and ADBAC (alkyldimethylbenzylammonium chloride) biocides, respectively in the mitigation of the Desulfovibrio vulgaris (a sulfate reducing bacterium) biofilm on carbon steel, achieving better efficacies than higher concentrations of THPS and ADBAC (Xu et al, 2012, 2014; Jia et al, 2017b). CLSM images and NALCO 7330 (active components: 5-chloro-2-methyl-4isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one) against a field biofilm consortium on C1018 carbon steel coupons retrieved from a water cooling tower.
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