By Kevin Flis
It's spring and the algae are in bloom, but harmful algal blooms are far from the only threats to drinking water. Fortunately, there are advanced treatment technologies to handle some of the most persistent contaminants today, including algal toxins, Cryptosporidium, and 1,4-dioxane.
Drinking Water Week, celebrated each spring in the U.S. (May 6-12 in 2018), is an opportunity to reflect on the importance of safe, clean drinking water and to consider the steps we should be taking to safeguard this precious resource. Humans currently withdraw triple the volume of water that we withdrew 50 years ago, and withdrawals continue to increase.1 In fact, global demand for water is predicted to rise by 55 percent between 2000 and 2050.2 With one-third of the world’s population experiencing water scarcity at least one month per year, building water resilience — our ability to ensure safe, clean water amid growing demand and increasingly variable supply — is more important than ever.
A Challenging Landscape For Water Utilities
Globally, water and wastewater systems are under growing pressure. Aging or stressed infrastructure is leading to cracked pipes and water main breaks that result in massive water loss and increase the risk of contamination. In the U.S. alone, the American Water Works Association has estimated that it will cost nearly $1 trillion over the next 25 years to repair and expand drinking water systems to meet the demands of a growing population.3 At the same time, there has been an increase in contamination of freshwater sources with toxins and chemicals, including harmful algal blooms (HABs). While ever more stringent water quality regulations are a positive move to protect precious water sources, they also place demands on utility budgets at a time when there is continued pressure to lower operating costs.
When it comes to drinking water treatment plants, HABs, groundwater contamination, and more stringent Cryptosporidium inactivation regulations are among the burning issues on the minds of plant managers. Municipalities are turning to innovative and comprehensive solutions to address these new challenges and ensure water security into the future.
Responding To HABs
HABs are a significant concern for water treatment plants. They have increased in frequency, duration, and intensity in the last two decades as a result of climate change. Rising temperatures and an increase in annual levels of sunlight are creating a shift in various ecosystems, turning lakes, ponds, and reservoirs into breeding grounds for algae. This reality is compounded by agricultural and industrial activities that introduce growth-stimulating nutrients into waterways. Concerns related to freshwater HABs range from the innocuous, but unpleasant, taste and odor of compounds that find their way into drinking water, to fish kills and algal toxins that are harmful to human health. These consequences have increased the pressure on water utility operators to closely monitor for the onset of HABs and prepare to respond.
Several hot spots for algal blooms on Lake Erie created a crisis in 2014 when toxins produced by the greencolored scum contaminated the drinking water source for 400,000 people in Toledo, OH and Monroe, MI.4 Similar problems in New York led the state to seek $65 million in funding to tackle toxic algal blooms in Skaneateles and 11 other upstate lakes.5
HABs in drinking water sources bring a myriad of unknowns for water treatment plants — from algal toxins to extra organic matter clogging up intake mechanisms. In the context of HABs, the term “algae” refers to a broad range of organisms, but especially to dinoflagellates, diatoms, and cyanobacteria. Cyanobacteria, often referred to as “blue-green algae,” are the most relevant to freshwater HABs. Drinking water utilities have experienced problems associated with cyanobacteria for years, as they release nonhazardous but nuisance byproducts when the blooms break down. These byproducts impart an earthy-musty taste and odor to drinking water.
Effective Treatment Of HABs — Three Phases, One Integrated Solution
A three-phase approach enables drinking water plants to effectively manage HABs. First, a separation technology known as dissolved air flotation (DAF) is used as pretreatment to remove the algae. This approach is effective, as it works with the algae’s natural tendency to float and concentrate on the surface where it can be removed. The system begins by dissolving air under pressure into water. Releasing the pressure via a special device creates millions of micro-bubbles that attach to the algae and other floc in the water and float it to the surface for removal. The resulting floated sludge is then removed by hydraulic means, and the purified water is removed from the bottom of the basin by laterals. The system can dramatically improve the quality of the water produced at a lower cost.
The second stage in tackling HABs is to provide ozone to oxidize the algal toxins generated by the algae while eliminating microcystins (a class of toxins produced by certain freshwater cyanobacteria) in the drinking water. Ozone is an excellent barrier treatment solution because it lyses the cell of the cyanobacteria and microcystin to destroy these contaminants. In addition to its powerful ability to oxidize these toxins, ozone is a sustainable method of treatment that can provide other key benefits for water utilities, such as improving the taste, odor, and appearance of the final purified water. Pollutants, colored substances, odors, contaminants of emerging concern (CECs), and microorganisms are directly destroyed by oxidation without creating harmful chlorinated byproducts or significant residues. Furthermore, ozone has the ability to provide all of these treatment solutions in a single unit process step — a simpler, less costly solution than implementing a menu of treatment options. Advanced ozone systems are engineered to produce large quantities of ozone reliably and efficiently and can be customized to fit seamlessly into local conditions and processes.
The final stage in the treatment of HABs is filtration — designed to filter out any remaining particles downstream from the ozone treatment process with an underdrain media filter as a final barrier to generate purified water. Alternatively, there are scenarios where ozone alone (with an existing filtration step already in place) or ozone-filtration are effective barrier treatment processes for HABs.
The true efficiency and optimization of these processes is realized through the implementation of an overarching control strategy that ties them all together. By breaking down the traditional compartmentalization of these technologies, and enabling them to effectively communicate with one another, an intelligent system is created, which meets performance requirements. Simultaneously, the system continuously seeks opportunities to reduce wasted consumption of power and consumables.
UV disinfection water treatment system
Groundwater Remediation And 1,4-dioxane
Nearly 40 percent of the world’s drinking water is sourced from the ground through wells or boreholes.6 Increasing levels of micropollutants — newly detected chemicals and chemicals with recently discovered potential health effects — pose a significant challenge for drinking water treatment plants drawing from groundwater sources. One of the most complex of these emerging contaminants is 1,4-dioxane, a compound used in a variety of industrial, manufacturing, and agricultural operations. A toxic substance, 1,4-dioxane is considered a potential threat to human health, and the U.S. EPA has classified it as a probable human carcinogen.
Prior to the emergence of 1,4-dioxane and other similar contaminants, municipal groundwater sources were relatively clean and, for the most part, required only small doses of chlorine for disinfection without any additional treatment. Stringent new drinking water standards to address these potent compounds demand a new approach. 1,4-dioxane is particularly difficult to remove since it does not readily bind to soils and is resistant to naturally occurring biodegradation processes.
AOPs Tackle The Most Challenging Water Contaminants
The use of an advanced oxidation process (AOP) is an ideal approach to treating 1,4-dioxane and other contaminants. AOP is the combination of two or more processes to generate or increase the number of hydroxyl radicals (OH radicals). These OH radicals contribute to the oxidation of undesirable substances and have a considerably higher oxidation potential compared to other oxidants. Flexible solutions are available that combine the key components of ozone, hydrogen peroxide, chlorine, and UV light in various combinations. The choice of treatment technologies depends on the target contaminant and onsite conditions, such as footprint, flow rate, and energy costs.
Water technology providers like Xylem focus on a solutions-based approach that evaluates which of these combinations can deliver the performance required to address each water utility’s particular challenges at the lowest possible cost. The ability to provide an integrated solution is rooted in a strong, well-resourced applications team supported by a full laboratory and fleet of AOP pilots. This allows the technology provider to test any combination of the AOP systems mentioned in advance of a full-scale design. The next step is to custom-design the AOP process to complement the existing process and ultimately ensure maximum reliability with the highest possible efficiency. Leading water technology providers offer a comprehensive suite of AOP treatment solutions and are key partners in implementing a system — taking the project from lab testing through onsite piloting and into full-scale implementation, including process guarantees.
Responding To Emerging Cryptosporidium Inactivation Requirements
Cryptosporidium, or crypto, is the leading cause of waterborne disease outbreaks in the U.S., impacting almost 750,000 people each year with potentially severe symptoms. The EPA’s Long Term 2 Enhanced Surface Water Treatment Rule addresses the health effects associated with crypto in surface water used as a drinking water supply. As the chlorine-resistant crypto parasite is easily inactivated with a low UV dose, many drinking water plant operators are turning to UV disinfection to provide safe drinking water for their communities.
Surface water affected by algal bloom
Municipalities across the U.S. that have installed UV disinfection technology in response to regulations introduced in 2006 are now required to resample surface water for Cryptosporidium levels under the EPA’s latest rule. Many municipalities are finding that levels of crypto have increased, and thus additional treatment is needed. By selecting UV disinfection, water utilities can have peace of mind that they will be effectively protected against crypto and Giardia, another parasite that gives rise to waterborne disease outbreaks.
The latest low-pressure UV lamp technologies and a low-dose approach to UV reduce the overall costs of UV disinfection. These factors make UV the number-one treatment process choice for Cryptosporidium and Giardia disinfection.
The City of West Palm Beach Water Treatment Plant, for example, is the first plant in Florida to add a UV disinfection system to its treatment processes. Their final UV disinfection solution includes Low-Pressure High-Output (LPHO) lamp technology that ensures the lowest lifecycle cost. Currently producing 47 MGD, the facility treats water from East Clear Lake for potable use by the City of West Palm Beach and surrounding communities. Upon completion of the major upgrade project, the plant will serve over 110,000 people, with a maximum treatment capacity of 50 MGD. The addition of a UV treatment solution will enhance the treatment plant’s protection against crypto, providing 100 percent redundancy in the disinfection process with an additional barrier to pathogens, improving the safety, reliability, and quality of the water produced by the city. Furthermore, UV disinfection will reduce the plant’s dependency on chlorine, which will positively impact the environment.
In another example, two major drinking water plants in the City of Columbus, OH — the Dublin Road Water Plant (80 MGD) and the Hap Cremean Water Plant (125 MGD) — are installing UV systems to provide an additional treatment barrier for crypto and ensure safe, clean drinking water for Ohio residents. The UV disinfection solutions selected for these projects were based on their low power consumption from the LPHO lamp technology.
Against a backdrop of climate change, increased demand, aging infrastructure, and an evolving regulatory environment, building resilient water treatment operations must be a priority for plant managers. Through implementation of DAF, ozone, filtration, AOP, or UV disinfection, we have the capacity to tackle these treatment challenges head-on, protecting our drinking water supplies and safeguarding the environment while lowering operating costs.
About The Author
Kevin Flis has been working in the water and wastewater industry for over 10 years, in roles including operations, project management, application engineering, up-front project engineering, project design, and market development. He holds a Bachelor of Science degree in chemical engineering from Iowa State University. As business development manager with Xylem, Flis focuses on developing solutions for utilities that can deliver secure water supplies, including water reuse, surface water treatment, groundwater remediation, and monitoring and control.