Entry for October 10, 2006

The use of alternative oxidants and disinfectants has been adopted by many large municipal drinking water systems.  These include Detroit, Los Angeles, Boston, Orlando, Dallas, Fort Worth, New York, Las Vegas among others.  Smaller municipal systems have been slower to adopt these technologies due to the perceptions of cost and complexity.  The reality is that these technologies would greatly benefit smaller systems by allowing them to improve water quality at modest cost and with high reliability.

 

Chlorine has been the principal oxidant and disinfectant for most drinking water plants.  The early use of chlorine greatly improved public health and it remains an excellent choice as a secondary disinfectant.  The use of alternative oxidants and disinfectants should be viewed as a complement to chlorine, minimizing adverse effects of chlorine while maintaining the advantages.

 

Recent US EPA regulations regarding water quality have strived to improve protection from water borne pathogens while minimizing adverse byproducts of the disinfection process.  One approach to achieving these twin objectives is to use multiple barriers such as multiple disinfectants, membranes and other technologies. 

 

An example would be to use ozone as a preoxidant and primary disinfectant while using chlorine as a secondary disinfectant.  The advantage of this approach is that the use of ozone minimizes the amount of chlorine required.  This in turn reduces the formation of chlorinated organics such as trihalomethanes while maintaining an easily measured and long lived disinfectant in the distribution system.  In addition, ozone is an excellent agent for inactivating pathogens that are difficult for chlorine to control such as cryptosporidium.  Ozone also offers other benefits such as taste and odor control.

 

Such benefits are acknowledged by the US EPA, the AWWA, major engineering organizations and many large municipal drinking water systems.   Smaller systems for the most part do not benefit from these technologies.  Some of these systems and their consultants might not be familiar with the technologies.  In other cases there might be a perception that costs or complexity make the technology inappropriate for a smaller system.

 

At one time the cost and complexity of advanced water treatment systems may have been beyond the reach of smaller water treatment plants, but this is no longer the case.  The reliability of these alternative systems has increased substantially from their early introduction.  Ozone generators for example now have lifetimes of 15-20 years in the field with on stream factors of 99.5%.  UV and membrane systems have also greatly improved in terms of reliability and cost.  With the advent of computer controls and improved instruments, little operator attention is required for routine operation.

 

The costs of these long lived systems add on the order of 10 cents per thousand gallons of water treated.  Given that customers pay on the order $5 per thousand gallons of water from public drinking water systems the cost of improved water quality seems trivial.  It is even more impressive when one considers purchasing 16 ounces of water for a dollar.   

 

Nevertheless, the investment in these advanced treatment technologies is not being made by smaller water systems.  At least part of the problem is the reluctance on the part of regulators to pressure these smaller systems to bring their plants fully into compliance with existing regulations.  This reluctance is probably due to the large up front investment in the equipment and installation.  Although these costs when spread out only amount to pennies per gallon, finding the initial funding can be difficult.  Government funded revolving loan programs can be an important part of the solution here.

 

Smaller water systems and their customers can benefit from advanced water treatment technologies that are both reliable and cost effective.  The federal and state governments through enforcement and provision of loans can make these improvements a reality.

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