Microbiologically influenced corrosion in hydronic heating systems

Open-loop hydronic heating systems have been found to provide a breeding ground for bacteria, including bacteria associated with microbiologically influenced corrosion (MIC) Microbiologically influenced corrosion of brass fittings, which may contain up to 8% lead in potable water applications, has been linked to high copper and lead levels in water samples taken from the hydronic-loop tubing. The contamination is likely concentrated in slime deposits found within the tubing. These slime deposits can enter the potable water supply, resulting in potential copper and lead exposure levels considerably above Environmental Protection Agency (EPA) guidelines. The authors recommend that hydronic heating systems incorporate a closed-loop design to prevent personal exposure and to provide for use of corrosion-inhibiting additives. © ASM International.