Microbial control in industrial water recycle systems

Industrial water recycle systems (e.g. cooling and clarification systems) provide an ideal environment for the proliferation of microorganisms. Common microorganisms within these systems include algae, aerobic bacteria, anaerobic bacteria, and fungi. These microbes contribute to biological fouling and microbiologically influenced corrosion. These problems contribute to reduced cooling, routine cleaning, equipment replacement, and treatment. To reduce the potential for these problems, an effective microbial control program must be implemented. An approach that considers the modification of the existing microbial control program before implementing a new program was applied to the problem. When selecting a new microbial control technology, one must consider the technical suitability (compatibility with the system's microbial problem, pH, level of solid and organic constituents, and materials of construction) and the selection criteria (investment and operating costs, environmental impact, and safety concerns) for available technologies. Two process water systems with undesirable microbial contamination were studied at a polymer manufacturing facility (DuPont Co., Old Hickory, Tennessee). These two systems were a cooling water circulation system and a process water clarification and recycle system. An assessment of the DuPont cooling and clarification system cases was performed to determine the technical constraints for suitable microbial control technologies. Based on the cooling water recirculation system's algae and aerobic bacteria problem, basic pH (8.52±0.09), relatively low level of solid and organic constituents (11 ppm) and stainless steel construction, numerous technologies were identified as potential candidates for controlling microbial contamination. Based on the clarification system's aerobic and anaerobic bacteria problem, slightly basic pH (7.56±0.35), relatively high level of organic constituents (321±36 ppm), and concrete construction, numerous technologies were also identified for controlling microbial contamination. Using selection criteria identified in this study to further screen the microbial control technologies, rankings and recommendations were produced.