The City of Tyler has released the results of an independent review of its water treatment process conducted by Enprotec/Hibbs & Todd, Inc. The study looked at the causes and possible remedies for high levels of haloacetic acids in the water. Haloacetic acids are a disinfection byproducts (DBP) which are regulated by the US EPA. They are formed when organic compounds in raw water react with chlorine to form chlorinated organic compounds such as haloacetic acids and trihalomethanes. In October of 2015 the city had received notification of high haloacetic acid levels in its drinking water.
The study recommended some operational changes to reduce the haloacetic acid levels, but some of the issues are due to the age of the water plant where the acid levels are the highest. The facility was constructed in 1950s before the onset of increased regulations on water quality. A newer facility uses ozone as a pre-treatment. The study recommends utilizing the ozone at the older water treatment plant, thereby reducing the amount of byproducts created by chlorine.
Ozone has been used extensively in the US and Europe to reduce the formation of chlorine based DBP’s.
The Emporia City, KS Commission approved a request authorizing the Public Works Department to proceed with an Ozone Equipment purchase Wednesday afternoon during an active session. The current equipment at the Water Treatment Plant uses atmospheric air and bubble diffusers and was installed in 1995, with an expected life of 15 to 20 years. The Ozone equipment and process is the primary disinfection action at the Water Treatment Plant. The equipment, which is slated to be installed in 2016, with a project construction cost estimate of $2.6 million.
Ozone equipment installed 20 years ago was primary based on air feed as the source of oxygen for ozone generation. Using air as the feed gas results in lower concentration ozone of 1-3 percent ozone. Newer oxygen fed ozone generators produce ozone at 10 percent concentration. Higher concentration ozone dissolves more readily in water for more efficient use of the ozone produced.
There is also a reduction in the size of the generator to produce the same mass of ozone, normally indicated in pounds/day. The reduction in the nitrogen levels also minimizes damage tot he generator due to the formation of nitric acid.
As a result of these advantages newer ozone systems have shifted to some form of oxygen feed, either from liquid oxygen supplied by gas companies or made on site using oxygen concentrators. The latter take air and remove the nitrogen to get to oxygen levels of 93%.
The first ozone systems were installed 20-30 years ago and are now being upgraded as the one in Emporium is later next year.
Natrona County’s drinking water is taken from the North Platte River and is treated at the Central Wyoming Regional Water System (RWS) with the primary disinfectant being ozone. The facility produces up to 25 million gallons of water per day. RWS uses chloramines as their secondary disifectant to keep bacteria from growing in the delivery system, including the pipes in your house.
At the RWS plant, after raw water is drawn from a well field that’s under the influence of the river, water is filtered and then ozone is used as their primary disinfectant.
Ozone is used because it’s better at killing giardia and other protozoan parasites like cryptosporidium (crypto) than chlorine. Protozoan parasites have hard outside surfaces. When chlorine is used in the process it requires longer contact times to kill bacteria.
Both RWS’ water plants is located low in the valley by the river. Once water is processed, it’s pumped uphill to high capacity tanks for storage. RWS operates 22 tanks. The system of high capacity tanks sits above the populations they serve and employ gravity to provide water pressure.
RWS’ water plant uses closed-system computers to operate their plants. Operators are able to gather information in real time from water flow and chemical analysis sensors, and use the computers to operate valves, introduce chemicals and automatically fill tanks. Supervisory control and data acquisition (SCADA) systems are common in the industry. Because their SCADA systems are closed systems, there’s no remote access to them from the Internet and operators must be on site to manage the plant.
The cost of the RWS facility in the range of $40-$50 million not including tanks or the distribution system. Tanks start at more than $1 million. Add the cost of miles and miles of underground lines, lift pumps, taps and other plumbing to the cost of the water plant and the total cost is much higher.
The Long Term 2 Enhanced Surface Water Treatment Rules, know as LT2ESWTR was promulgated in 2006 obligating large drinking water utilities to comply with the rules by 2012. The rule was designed to prevent cryptosporidium, a difficult to kill pathogen from entering the drinking water supply. An incident in Milwaukee resulted in thousands of people becoming ill and others to die. It was considered a serious threat that was not treated by the standard disinfection method of chlorination.
The AWWA has reported on both the monitoring results and treatment methodologies employed by these utilities in the August issue of the associations journal.
The LT2ESWTR required utilities to first monitor their water for the presence of cryptosporidium. Based on these results, utilities were placed in bins associated with the observation of cryptosporidium being in present in the source water. The more pathogen found, the more aggressively the utility had to treat its water. Reservoirs ad lakes showed the lowest occurrence with 3.2% of samples showing the organism while rivers and other flowing water sources showed up to 11% of samples with the pathogen. The average was about 6.4% of all surface water sources had the organism.
If utilities fell into the higher risk bins, i.e. they observed higher levels of cryptosporidium, they were required to use EPA methods referred to the microbial tool box. Utilities assigned in the higher risk bins used a variety of methods to treat the water. These methods begin at the water source where plans to control the watershed are intended to prevent the organisms from entering the source water. Various filtration methods were employed by the utilities to filter out the organisms. Finally, some utilities upgraded their disinfection processes to inactivate the organism. One of the more popular methods was ultraviolet light or UV.
Unfortunately, the AWWA survey only looked at 38 utilities with 24 actually reporting results. So the study did not provide good statistical information on how the various methods are being used. For example, the particular utilities contacted had not used ozone, although ozone is used to control cryptosporidium, especially were water temperature is higher and their are other reasons for using ozone. For example, in reservoirs and lakes, algae can create significant taste and odor challenges for a water utility while also having to deal with cryptosporidium. So employing ozone water treatment in these cases can provide both taste and odor removal as well as pathogen reduction.
The Milwaukee outbreak lead to a detailed study of the drinking water systems in this country that use surface water. A well designed plan involving considerable public comment resulted in an enhancement of the safety of drinking water. Although the process took over a decade, the results will be enjoyed for many years to come.
Big Bend Water District (BBWD) is the supplier of potable water to the community of Laughlin, the sole source of which is the Colorado River. “The BBWD has over 15,000 acre feet per year as an allotment, but historically Laughlin rarely uses more than 5,000 acre feet of that allotment. BBWD can treat a maximum of 15 million gallons per day. Over a 12-month period, the average per-day flow through the treatment plant is three to four million gallons a day. Intake for the BBWD is located in the Colorado River just north of the Laughlin Bridge; most of the water in the river is a result of snow melt in the Rocky Mountains.
The job of the treatment plant is to remove impurities from the water and make it safe for drinking. The BBWD uses ozone as a disinfectant at the facility. Ozone is generated on-site and prevents the formation TTHMs, which the EPA limits in water.
Trihalomethane – or TTHM – is a by-product of chlorine, when it is used to disinfect drinking water. Ozone can remove some of the precursor compounds that form TTHM and reduces the total amount of chlorine that can form them. While more expensive to generate than other oxidants the tradeoff is a lot less taste and odor issues and much lower TTHMs. BBWD treats with chlorine, the EPA requires the district to maintain a disinfectant residual in the system because it is a surface water system.
Ann Arbor’s Drinking Water Treatment Plant’s primary source of water comes from the Huron River. Ann Arbor is one of only seven facilities using an inland river as a drinking water source in Michigan. About 85 percent of the water comes from the river, while 15 percent comes from wells located at the city’s airport. The plant pumps on average more than 15 million gallons of water per day to some 125,000 city water customers.
Because the city uses surface water as it primary source, the water goes through a complete treatment process that consists of rapid mixing for quick dispersion of chemicals being added, flocculation to give the chemical reaction time it needs, settling to allow the removal of solids by gravity, and filtration.
The city also softens the water using lime, removing calcium and magnesium. Ozone is used as the primary disinfectant and chloramines as a secondary disinfectant. Fluoride is added to the water for dental protection, and phosphate is added to stabilize the water.
City officials are evaluating replacing portions of the plant that date back to the 1930s, and which could cost tens of millions of dollars.
Spartan periodically posts information about water plants around the world that use ozone. Most people, and even some water professionals, are not aware of the widespread use of ozone in drinking water treatment as well as other applications.
A recent study in the Journal Ozone Science and Enginnering has shown that electrolysis followed by volatilization can remove Br from drinking water and as a result lower the formation of bromate from ozone water treatment.
This is an important issue since a large number of water sources contain Br ion. Ozone can react under the proper conditions of pH, Br ion concnetration and other factors to form bromate. Bromate is regulated by the EPA as a possible carcinigen and it is limited in driking water to less than 10 ppb. Recent studies have indicated that the correlation between bromate and cancer may be weaker than thought, but the regulatory limitation remains in palce. As a result, ozone use has been limited to water sources with low Br levels.
A complication with the process is that electrolysis can produce chlorine whcih also reacts with ozone. Dechlorinating agents need to be added and the amount of ozone required adjusted to compensate for the ozone demand of the water. When this was done, the study showed that the reductions in bromate formation due to ozone were proportional to the reduction in the Br ion levels in the water.
Theoretically at least, it should be possibel to mitigate bromate formation due to ozonation by pretreating the water using electrolysis to reduce Br levels. This would expand the range of source water that could benenfit from ozone drinking water treatment.
The City of Santa Barbara’s Cater Water Treatment Plant is being upgraded
in response to stricter federal drinking water regulations. The $20 million ozone water treatment project is about 80 percent complete. The work should be completed by the end of January.
Ozone will replace chlorine in the pre-treatment of water at the plant. Besides meeting stricter federal regulations the city’s water taste should also improve. Ozone is finding increasing use by municipalities to meet increasingly stringent regulations for both pathogen control as well as a reduction in disinfection byproducts that can be associated with teh use of chlorine, especially at the pretreatment stage of the process.
A municipal drinking water system in a new high-tech industrial zone in South Korea has contracted for an ultraviolet (UV) advanced oxidation process (AOP) treatment technology. This is the firts time such a technology will be applied in Korea for drinking water.
The water treatment facility will treat more than 26 million gallons per day, and will be the first step in the development of the new $3 billion Sihwa Multi-Tech Valley project, a government-backed regional industrial development initiative being implemented by the K-Water municipality. The new hub for the enterprise is due to be completed by 2016, and aims to attract high-tech industries across the IT, chemicals and R&D sectors.
UV reactors and AOP technology will be used in the existing plant, Siheung wastewater treatment plant, for the removal of micro pollutants and disifection.
AOP is being used around the world to address problems associated with micro pollutants such as pesticides, personal care products and pharmaceuticals that find their way into drinking water sources.
Salt lake City uses ozone at two of its facilities: Little Cottonwood (LCW) and Point of the Mountain (POM). LCW has Utah’s first and largest ozone drinking water treatment system, two ozone generators each sized at 3,750 lb/day of ozone. The facility can treat 143 MGD of water. The plant can dose ozone at 3.5 ppm during times when taste and odor control are required or as low as 1 ppm during normal operation. The ozone provide a 0.5 log reduction of Giardia. the system became operational in 2009.
The new POM plant can produce up to 950 lbs/day of ozone delivering an ozone dose of 3 ppm. It is capable of treating 70 MGD. This system also employs a UV disinfection system down stream of the ozone to allow achievement of the LC2ESWT rule as well as stage 2 disinfectants/disinfection byproducts rule. POM thus has a multi-barrier treatment system with complementary technologies.
Both of the improvement projects were part of a $250 MM capital program. The improvements now allow Salt Lake City to meet future regulations while providing its customers with high quality good tasting water. The large financial commitment illustrates the foresight of the water districts leadership.