Preventing Chilled-Loop Bacteria Contamination
September 19, 2011
A dairy in California had a large process-chilled loop that frequently became contaminated with milk products, providing a food source for bacteria. Because the chilled loop is considered a potential source of food contact, the bacteria in the chilled water had to be maintained below detectable limits to comply with regulatory requirements.
For 20 years, the dairy had used traditional biocides to battle the problem. However, the technologies either failed to prevent biological fouling, caused corrosion or, too often, resulted in excessive treatment costs. Detectable levels of bacteria required immediate emergency maintenance that increased operating costs and, at times, caused unscheduled downtime. Yet, failure to take immediate action could result in even greater product loss, a shutdown mandated by state or federal regulators, or even the outbreak of a bacteria-related illness among consumers that could trigger huge revenue losses.
During the two decades, the dairy tried several non-oxidizing and oxidizing biocides to remedy the problem. The non-oxidizers proved to be ineffective in terms of cost and efficacy because they did not penetrate the slime layers that formed in the specific conditions of the chilled-water loop. The result was a rapid recovery of bacteria levels in the circulated water. Frequent high-dose shock treatments were used to maintain system hygiene, but the treatments were expensive and significantly increased organic loading.
The oxidizing biocides used were all classified as “surface burning agents.” Organic loading in the chilled water created a heavy demand on these products. Feeding the oxidizing biocides at dosages required to meet this demand and achieve a successful kill created significant corrosion throughout the system.
Looking for an effective and less costly approach, the dairy purchased and installed a Model P-6E electrochemical chlorine-dioxide gas generator from PureLine, Irvine, Calif., to produce a pure gas stream using just one precursor. The system converts Purecide 25 sodium chlorite to a chlorine dioxide solution, then strips the chlorite from the solution using an eductor and stripping column. The resulting pure chlorine dioxide gas is immediately introduced into the water or airstream for treatment.
The chlorine dioxide did not add to the organic loading or produce significant corrosive salts, introduce outside fluids or affect system pH. Pure chlorine dioxide proved to be a highly efficient kill agent even at low dosages and was compatible with the existing treatment formulations. The system penetrated and eliminated the slime without attacking system metallurgy. PureLine’s online controls automatically monitor the system for any contamination, so it was easier to maintain the cleanliness and prevent emergency maintenance or shutdowns.