Algae in lakes and reservoirs can create issues for drinking water plants including toxins, bad taste and unpleasant odors in the water. While there are a number of treatment methods used to deal with this problem, ozone treatment of the water has emerged as a proven and cost effective method.
Depending on where and how the ozone is applied to the process, the ozone can serve two purposes: primary disinfection and removal of algae related compounds that pose health or aesthetic risks to the drinking water plants customers.
The city of Oregon in Ohio was concerned about algae related issues from their intake in Lake Erie due to cyanobacteria that can produce microcystin, a toxin. Toledo had experienced a severe issue with this toxin that resulted in a 2014 temporary ban on the use of water from their drinking water plant. This cause Oregon to look for solutions before they experienced a similar problem.
In Oregon’s process, water from lake Erie will be treated with ozone and then go through biological filtration. The approach will remove algae-related toxins. The process works because ozone breaks down the toxins into molecules that are quickly digested by the biology living in the filter.
The process was first tested at the pilot scale for several months to prove that it worked well. The full scale system is expected to be in operation by the algae season of 2017. Other advantages include reduced use of chlorine, improved disinfection and reduced disinfection byproducts. Ozone also eliminates trace organic compounds.
The project is expected to cost $14 million, with funds mainly coming from the Ohio Environmental Protection Agency’s Water Supply Resolving Loan Account. Oregon’s water rates will increase about $2 to $3 more a month for the improved quality and safety.
Wilfred LePage, age 83 of Monroe, MI died Monday, January 27, 2014 in his home after a year long period of declining health.
Following service with the Marines during the Korean Conflict, he studied at Wayne State University. While in college he entered his career field of drinking water purification at the Mount Clemens Water Filtration Plant. In 1959 he accepted a supervisory position with the Monroe Water Department from which he retired in 1995.
Wilfred rose to international prominence in the water industry. He authored and published numerous technical papers largely on the application of ozone to drinking water treatment and, following invasion of the water system by the non-indigenous zebra mussel, on mussel mitigation. He traveled extensively at home and abroad while presenting his work.
He held leadership positions in several technical and scientific societies and received numerous high honors including the water industry’s coveted George Warren Fuller Award for his innovative work with ozone.
Public drinking water systems will need to start complying with LT2ESWTR if sampling results indicate source waters are at risk for cryptosporidium contamination. The protozoan is capable of causing serious gastrointestinal illness. Compliance generally means additional protective measures including watershed control, source relocation, pretreatment methods, filtration, and pathogen inactivation methods. Chlorination does not control the protozoan at practical application rates.
Systems serving less than 10,000 people will need to comply with the rules by September 2014 and systems serving 10-000 to 50,000 people need to comply by the end of this year. These systems had to already complete two years of monitoring to assess risk.
While there are numerous options for gaining credits to reduce the risk of cryptosporidium entering the distribution system, ozone is one of the pathogen inactivation options. The use of ozone has to be considered in the context of both economics, water quality issues and other source water treatment objectives.
Ozone is often most economical when it is also being used to solve other water treatment objectives and part of a multi barrier approach to water treatment. for example, if ozone is being used for taste and odor control, increasing ozone dose may be an economic option for additional LT2ESWTR credits. It should be noted that in cold water, the amount of ozone required may be high, so the best applications would be in areas where water temperature does not drop significantly.
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.
The City of Winfield drinking water department produces on average 2 MGD of water and has capacity of 6 MGD. The city has about 4,350 residential 715 commercial customers for its water.
The Winfield Water Treatment facility was operational in 1969, coinciding with the completion of the Winfield City Lake. Currently, all water treated by the City of Winfield is supplied by the city lake.
The city maintains around 130 miles of water distribution lines and 7.7 miles of raw water line from the lake to the water plant.
A 2005 water plant upgrade project included the construction of an ozone water treatment facility. Ozonation of water improves both the aesthetics of water in terms of taste, smell and appearance as well as improtant health criteria such a enhanced disinfection and the reduction of disinfection byproducts.
Winfield is a little unusual in that most ozone systems were supplied to much larger water treatment facilities.
During the 64th Annual U.P. Water Treatment System Operator’s Training, which is associated with the American Water Works Association. Manistique competed against 11 other communities in a drinking water taste off. Manistique’s water supply is drawn from the Indian River – something which sets Manistique apart form many of the other communities in the taste competition. It’s very hard for a surface water treatment plant to compete against groundwater systems. Manistique is the first surface water plant to win the competition in the U.P.
Last year the city upgraded it’s water treatment plant to use ozone and granular activated carbon filtration in order to meet new drinking water quality rules making it the first in the U.P. One of the primary uses for ozone water treatment is taste and odor improvement. What makes ozone especially attractive for this application is that it can simultaneously improve water taste while also imrpoving disinfection and removing other water impurities. This is the case in Manistique.
The Milwaukee Water Works is a national leader in providing safe, high-quality drinking water. The finished water is distributed to an estimated 830,000 residents of Milwaukee and 15 other communities in the metropolitan area meets or exceeds all federal and state drinking water standards.
Each year, the Water Works annually tests Lake Michigan water and fully treated water for more than 500 potential contaminants while the U.S. Environmental Protection Agency requires tests for just 91. Monitoring water quality cost $1.2 million in 2012. Monitoring of un-regulated chemicals and organisms is done as a precaution to ensure the water is safe, Couillard.
Multiple steps in the water treatment process are barriers that prevent contaminants from reaching household taps. Treatment begins with ozone, the primary disinfectant capable of killing parasites, including Cryptosporidium. Ozone water treatment also destroys harmful compounds as well as substances that could cause taste and odor problems. Particles are removed in filters before chlorine is added as a secondary disinfectant to prevent growth of bacteria and other potentially harmful microorganisms in water mains.
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.
Before a new water main or one that has recently under gone repair can be placed back into service, it must be flushed and disinfected. The conventional approach is to use high concentrations of chlorine for an extended period of time to kill the bacteria living in the biofilms attached to the water main surface. The disadvantage of this approach is that hypochlorite solutions need to be transported, stored and handled. These solutions are considered hazardous in some jurisdictions. In addition, the treated water must be dechlorianted prior to discharge, which requires another set of chemicals.
Ozone has been used in drinking water treatment for over 100 years and is a proven drinking water disinfectant. It has not been used extensively for the disinfection of water mains. The advantage of ozone use is that it can be generated on site from air and does not require any treatment prior to discharge. A question regarding the use of ozone for treating biofilms on water main surfaces is whether the ozone will penetrate the biofilm to inactivate all of the bacteria present.
Stantec Consulting and EPCOR Water Service Inc. of Edmonton, alberta, Canada conducted a laboraotry study to see if ozone would be effective against these biolfilms (Ozone Science and Engineering, 34: 243-251, Li Chang and Steve Craik). The study looked at HPC bacteria grown on concrete mortar substrates to simulate water main surfaces.
Ozone appears to be able to achieve a 1.7 log reduction of the biofilm at a CT value of 120 mg-min/l. Higher CT values did not appear to improve teh log reduction significantly. the study concluded that log reductions of less than 2.0 should be expected with ozone.
In the September 2006 issue of Opflow magazine published by the AWWA, ozone was also studied in treating water mains in Denver. In these tests the CT values were only 10-24 mg-min/l and the results were not as effective.
So, it appears that ozone may be an effective treatment for water mains that offers easier and safer application, but the ozone CT probably needs to be in the 120-240 mg-min/l range.
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.