Comparative effectiveness of chlorine and chlorine dioxide biocide regimes for biofouling control

The effectiveness of chlorine (Cl₂) and chlorine dioxide (ClO₂) in controlling biofouling of 304L stainless steel heat exchanger tubing was compared using an experimental trough system. Three combinations of dose and contact time were evaluated. Chlorination coupled with a dispersant was also tested. Three criteria were used to assess the degree of fouling; organic carbon and dry weight of the fouling material accumulated on metal specimens and the visual appearance of this material on the specimens. These parameters correlated well with one another and therefore, collectively provided an effective means of evaluating biocide efficacy.Metal specimens in all troughs receiving biocide treatment were much less fouled than those in the trough receiving no biocide. Continuous application of Cl₂ at about 0.15 ppm was more effective than four 15-min 1 ppm Cl₂ applications per day. Both of these treatment regimes were more effective than a dose of about 1 ppm for 1 h day⁻¹. Use of a dispersant in combination with Cl₂ showed no significant reduction in the amount of biofouling material accumulation, although a difference in the texture of this material was observed. Unlike the Cl₂ results, low-level continuous ClO₂ treatment at 0.15 ppm resulted in biofouling similar to that when 1 ppm of ClO₂ was used for 1 h day⁻¹. Overall, ClO₂ was significantly (P < 0.05) more effective in controlling biofouling than Cl₂.