Wednesday, October 29, 2008

Another IST Implementation with Problems

There was an article posted this last weekend to the web site about a recent switch-over from chlorine to industrial strength bleach at a major waste water treatment plant for the city. Not only was the chlorine replaced, but the sulfur dioxide used to dechlorinate the water discharged from the facility was replaced with safer sodium bisulfite.

Lack of a Reliable Supply of Bleach 

The Metro Wastewater Reclamation District has been working on this switch over since 2000 and the work was speeded up after the 2001 terrorist attacks made clear to management that the potential risks of handling the two PIH chemicals were too high. Even so there are still rail cars of sulfur dioxide and chlorine sitting behind fences and armed guards while the agency continues to try to certify its new process. That process is handling most of the waste treating work at the facility.

The problem stopping the complete switch to the bleach/bisulfite process, according to the director of operations and maintenance, is the lack of a “dependable, long-term supply of sodium hypochlorite”. Industrial strength bleach (sodium hypochlorite) degrades over time and the degradation is accelerated by heat. This means that the long distance transportation of bleach is not practical, especially by rail. Even if the facility must maintain a supply of chlorine and sulfur dioxide as a backup treatment option, the volume on hand will be greatly reduced, as will the number of railcars of these TIH chemicals shipped into the facility.

Cost of Replacement 

The new storage and handling equipment for the bleach and bisulfite process cost the facility $11 Million. Increased operating costs are projected at about $1 Million per year. Even so the Metro Wastewater Reclamation District management feels that that increased cost is “offset by the benefits in improved site safety”.

Moving the Hazard The one point that this article, and many discussions of replacing chlorine treatment with bleach treatment, fail to address is the fact that chlorine is still the actual disinfection agent. The two processes use roughly equal amounts of chlorine. The bleach is just easier and safer to transport and handle. Most commercial production of bleach uses chlorine as a raw material.

The chlorine is shipped to the bleach production facility by rail car. So switching water treatment and waste water treatment facilities to bleach does little to reduce the number of rail shipments of chlorine. If the bleach production facility is located further from areas of large populations than is the treatment plant, there is a net gain in safety and security. If the rail routing to the bleach production facility avoids more urban areas than the routing for the treatment facility there is a net gain in safety and security. If the opposite is true in either case the result may be an overall decrease in safety and security.

IST Benefit Calculations 

Inherently safer technology is not necessarily easy to identify. Switching from chlorine to bleach could result in less safety and security, not more. It all depends on the circumstances. If there is no net gain in safety or security, the added costs do not produce any benefit to society.

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