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.
Recent news regarding the algae related water quality problems in Toledo have raised issues about the potential for algae blooms and the release of toxic chemicals from the algae elsewhere in the US and especially in Northwest Ohio.
Celina, another town in Ohio, uses Grand Lake as its water source, which has encountered problems with the algae blooms and the toxins they release since 2009. Celina, however, has updated treatment system to deal with these issues.
The city uses two methods of water treatment to make its water safe, ozone and granular activated carbon treatments. Ozone is a powerful oxidant and highly effective disinfectant. It is a technology that has been in continual commercial use for more than 100 years and has distinct properties that allow disinfection of even heavily compromised water streams.
The GAC treatment is an extremely versatile technology and in many cases has proved to be a cost effective option. GAC absorption is particularly effective in treating low concentration waste streams and in meeting stringent treatment levels. GAC is known to remove a wide variety of toxic organic compounds to non-detectable levels.
As with any water treatment technology, suitability on a specific application normally depends on costs as they relate to the amount of carbon consumed.
Normally, this blog focuses on ozone and advanced oxidation technologies for water and air treatment. An interesting non chemical water treatment for algae control might be of interest to the readership of the blog.
Algae blooms can create both aesthetic and other problems for tanks, ponds and lakes. Chemical treatments are routinely used, but require adding toxic chemicals to the water and in safe doses might not always be effective. An alternative is the use of ultrasound.
The complex pattern of ultrasonic vibrations through the water causes the algae vacuole cell wall to resonate and break, much like a glass breaking from a high pitched sound. The broken vacuole wall eliminates algae’s ability to grow and reproduce, while the same vibrations are harmless to humans, animals, fish and other aquatic plants. The discovery that ultrasound waves in water kill algae was made over sixty years ago in submarine sonar experiments. the Navy discovered that surfaces impacted by the sonar waves did not accumulate algae as other areas not covered by algae did. This eventually led to the study of the phenomenon for algae control.
It is important to note that ultra sound alone might not be enough to solve all of the problems associated with a pond or lake. Even if the algae is killed, the pond might not contain enough bacteria or oxygen to break down the organic matter found in the water, including the algae killed by the ultra sound system. So, proper control of algae requires a balanced ecosystem which has sufficient oxygen and proper bacteria present in conjunction with the ultrasound.
Another issue is that some algae do not have the same physical structure as other algae and thus are not affected by ultrasound. Prior to applying ultrasound, the algae in a given body of water should be tested to make sure that it does not contain these algae species.
Although the method has some limitations, ultrasound algae control offers an economical treatment option for small bodies of water that has been used in a wide range of ponds, lakes and water treatment facilities.
City and community leaders in Waco had a chance to tour the site of the new drinking water treatment facility. The plant began its water pretreatment process last summer, but officials said they only recently starting running the ozone disinfection process. Ozone is a well proven option for reducing taste and odor problems in drinking water. Since then, officials with Waco’s Water Utility Services said they have noticed a difference in the smell and taste of the city’s water. Waco has had problems with taste and odor for many years prior to the improvements.
The problem came from algae growing in Lake Waco, the city’s main water source. Officials said when the algae die after being deprived of sunlight, they release a chemical compound called Geosmin which can affect the smell and taste of the water.
The addition of the dissolved air flotation (DAF) pretreatment plant means more of the algae can be removed before the water reaches the water treatment plant. Ozone then removes the dissolved compound Geosmin via oxidation. Officials said the pretreatment plant has brought the cost of water treatment down between 20 and 30 percent, because fewer chemicals are now needed at the main treatment plant. While costs have gone down, capacity has gone up from approximately 60-million gallons to 90-million gallons a day.
McKinney, TX residents noticed a metallic or earthy taste and smell to their water. The change is the result of a winter algal bloom at Lake Lavon. This is less common than a mid-summer algal bloom, which arrives in late July and into August. During a bloom, lab analysis can show high levels of geosmin and MIB, organic compounds released during the decomposition of algae that are responsible for the water’s undesirable taste and odor.
McKinney is served by the North Texas Municipal Water District (NTMWD) receives raw water supplies from: Lavon Lake, Jim Chapman Lake, Lake Texoma, Lake Tawakoni, and Lake Bonham for treatment and distribution to the region served. NTMWD is pursuing the implementation of ozonation, a process that uses ozone as a disinfectant, to meet new state and federal guidelines going into effect in 2012, and the new treatment method will also will also significantly reduce and/or eliminate taste and odor issues caused by algal blooms. Dallas, Fort Worth and Arlington have all had success with ozone for algal taste and odor issues. The organization’s current treatment process can only lessen these issues.
Ozonation is very effective for inactivating Cryptosporidium, bacteria and other naturally-occurring organisms. Ozonation also can reduce the formation of trihalomethanes (THMs), which result from the interaction of chlorine and naturally-occurring organic material in the source water. Additional benefits of this process is that it helps to alleviate taste and odor issues in treated drinking water, such as those experienced during algal blooms in Lavon Lake.
A preliminary engineering study for the utilization of ozonation as a primary disinfectant at the NTMWD Wylie Water Treatment Plants has been completed by the NTMWD staff and consulting engineer. The study provides the framework for the engineering design of ozonation facilities to be constructed at the Wylie Water Treatment Plant to meet the Texas Commission on Environmental Quality Stage 2 Disinfection Byproducts rules. A design contract has been executed with a consulting engineer, and the design has commenced. A purchase order has been issued for procurement of ozone generation equipment. The NTMWD anticipates completion of the design to allow for construction bids to be brought to the NTMWD Board of Directors for consideration in the fall of 2010. The project is estimated to cost $140-$150 million and will take several years to construct and place into operation. The current schedule includes implementation of the ozonation treatment process taking place in stages during the latter part of 2013 and early 2014.