Table 1 Biocides used for this study, including their type and mode of action for inhibiting microorganisms.

Tetrakis(hydroxymethyl) phosphonium sulfate (THPS)

Quarternary phosphonium compound

Releases THP (trishydoxymethyl phosphine) which cleaves sulfur-sulfur bonds in the disulfide amino acids of microbial cell walls; damages cell membrane; removes iron sulfide deposits from the metal surface

^{34, 36,37,– 38}

Glutaraldehyde (GLUT)

Electrophilic

Contains reactive electron accepting functional groups that react with exposed amine thiol groups in membrane proteins of bacteria; potent crosslinker for amino acids; causes cell wall damage and cytoplasmic coagulation

^{38, 41, 42}

Benzalkonium chloride (BAC)

Lytic (membrane active)

Amphipathic in nature, surfactants that can penetrate bacterial cell wall and lyse the cells resulting in the loss of osmoregulation capacity

^{32, 38, 39}

GLUT/BAC (50/50)

Lytic + electrophilic

Combined actions of GLUT and BAC as they perform synergistically together

^{38, 47}