Assessing the performance of a disposable electrochemical biofilm test kit on monitoring drainage sludge biofilm corrosion and its biocide treatment.

Drainage sludge is abundant with corrosive microbes which can contribute to soil corrosion of buried pipelines. In this work, the microbiologically influenced corrosion (MIC) of a drainage sludge biofilm against X65 carbon steel was confirmed by significant uniform corrosion (0.03 mm/a uniform corrosion rate) and more severe pitting corrosion (18% greater) on X65 coupons with nutrient enrichment without venting at 37 ℃ compared to the aerobic sludge at room temperature. A new biofilm/MIC test kit was employed to assess the aerobic sludge biofilm, and it was determined to be mildly corrosive against carbon steel after incubating 5 mL of aerobic sludge at room temperature for 7 d in the 10 mL biofilm test kit vial. Tetrakis-hydroxymethyl phosphonium sulfate (THPS), a green biocide was also tested in the biofilm/MIC test kit for its mitigation of the aerobic sludge biofilm and its corrosion against the X65 carbon steel working electrode. The biofilm test kit successfully monitored the sludge biofilm's sanitization efficacy. It was found that 100 ppm THPS was effective in inhibiting biofilm growth, and 400 ppm THPS in treating pre-established sludge biofilm by achieving 10% corrosion rate reduction. Thus, the biofilm/MIC test kit was found to be sensitive in detecting MIC and can be used as a convenient tool in assessing biofilm corrosivity and its mitigation efficacy.