Emerging water quality and treatment trends for municipal drinking water
BY STEVEN J. DURANCEAU, PH.D., P.E.
Global environmental resources are at a crisis point. Water shortages, land degradation, air pollution, and global warming continue to take a serious toll on our planet. New threats are emerging in the form of increasingly severe natural disasters, plant and insect species invasions as a result of global trade, global atmospheric transport of trace pollutants, and urbanization. And as a result, all available drinking water supplies are susceptible to devastation.
More than 300 million people around the world live in areas with severe water shortages. Additionally, according to United Nations reports, thousands of people die each day because of poor-quality drinking water. Obviously, the situation is far better in the United States than in most countries, but our population growth has increased the demand for potable water supplies, and regulations continue to raise the standards of what qualifies as drinking water. As the population continues to grow, and traditional potable supplies diminish, water purveyors will have to develop lower-quality sources of water.
Thus, the engineering community must play a vital role in ensuring that this water is treated and distributed safely.
Treatment and management
As we move into the 21st century, it is important to realize that as scientists continue to improve their tools for detecting and identifying substances that can be measured in the environment, the number and type of chemicals and organisms known to exist in drinking water will increase. This knowledge will generate new debates regarding chronic health issues.
Continuous technological advances will result in even more complex regulations intended to protect the public from all known or perceived forms of acute and chronic toxicity. Human longevity will be more directly linked to all aspects of the environment, including water quality.
For the drinking water community, long-term water supply; distribution system repair, replacement, and rehabilitation; privatization; e-commerce; cross-connections; public perception; and vulnerability to and security from terrorism are some of the challenges that will redefine how drinking water professionals solve critical issues in the future.
And new research, changing regulations, and emerging treatment methods will support them along the way.
Water quality rules
In 1974, Congress passed the Safe Drinking Water Act (SDWA) to protect public health by regulating the nation’s public drinking water supply and protecting sources of drinking water. Administered by the U.S.
Environmental Protection Agency (EPA) and its state partners, the SDWA authorized the EPA to set enforceable health standards for contaminants in drinking water.
Since that time, Congress has revised and strengthened the SDWA to ensure the law’s continued effectiveness.
Today, regulations that include requirements for water quality are increasing and impacting water utility operations related to source water, treated water, and distributed water. For example, the most recent SDWA amendments, enacted in 1996, contain requirements for specific water quality parameters and increase opportunities for public participation in establishing standards for potable water.
The 1996 Rules include the following:
Chemical and Microbial Rules, which include the following: Lead and Copper Rule, Disinfectant/Disinfection By-Products Rule (DBPR), Surface Water Treatment Rules, and Total Coliform Rule;
Consumer Confidence Reports;
Source Water Assessments;
Drinking Water State Revolving Loan Fund;
State Capacity Development Strategies;
Operator Certification Revisions;
Public Notification Improvements;
Publicly Accessible Drinking Water Contaminant Databases;
Annual Compliance Report; and
Health Care Provider Outreach and Education.
Further, the EPA is developing interrelated regulations, the first of which were implemented recently (others will be implemented in the near feature) to control microbial pathogens and disinfectants/ disinfection by-products (D/DBPs) in drinking water. Collectively, these rules are known as the microbial/disinfection by-products (M-DBP) rules, and they direct that the principal of simultaneous compliance will remain for both Long- Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and Stage 2 DBPR. Therefore, water utility systems will be required to address the Stage 2 DBPR and LT2ESWTR requirements concurrently to protect public health and to optimize technology decisions. Utilities that have a better understanding of their existing disinfection methods, and the methods’ effects on distribution system water quality, will be in a much better position to respond to and to comply with these impending regulations.
Disinfection of drinking water was one of the major public health advances of the 20th century. One hundred years ago, typhoid and cholera epidemics were common throughout cities in North America. Disinfection was a major factor in reducing these epidemics, and it is an essential part of drinking water treatment today.
Treatment technologies for water disinfection include the following chemical and physical processes: Chlorination -Chlorine is used to treat microbes, as well as to improve tastes, odors, and color. Chlorination is a historically proven process and is one of the most effective disinfectant methods. Chlorinated disinfection by-products are well known, as much research has been performed during the past 20 years. Chlorine disinfection is practiced as the means for primary disinfection by most water purveyors in the United States.
Chloramination – This chemical process uses a combination of chlorine and ammonia as the treatment agent. It is mainly used as a disinfectant residual to maintain disinfection throughout a distribution system. Chloramines are becoming more popular as a low-cost method to reduce the formation of regulated disinfection by-products; however, implementation of chloramines increases operating costs since staff is needed to man and monitor additional system flushing and free chlorine maintenance activities.
Less is known about by-products resulting from chloramination. Recently, CalPASC, a Sacramento-based trade organization, claimed that chloramines contribute to pitting, pin-holes, and failure of copper pipe. Additionally, lead increases found in the drinking water of suburban Washington, D.C., homes has been linked to a change from chlorination to chloramination.
Needless to say, chloramines require additional scrutiny.
Chlorine dioxide – A chemical process used primarily for taste and odor control, chlorine dioxide has limited applications for primary disinfection because of the formation of chlorate and chlorite byproducts.
However, it will continue to be used for taste and odor enhancements.
Ozonation – A chemical process using ozone, ozonation helps to reduce the formation of disinfection by-products. It treats tastes, odors, and color. Ozone will continue to be used as a strong oxidant, and it is a highly effective Cryptosporidium inactivator. However, where bromide is present, the use of ozone is limited because of the formation of the disinfection by-product bromate.
Ultraviolet (UV) irradiation – This is a physical process in which ultraviolet wavelengths are used to kill pathogenic micro-organisms in water. UV irradiation is a new technology that the EPA believes is feasible for water disinfection. As of today, there are approximately 500 UV irradiation installations globally, yet only eight large installations are in the United States.
More information is needed to clarify how UV disinfection will be used as a method for compliance with the SDWA and what by-products exist, if any.
Membrane filtration – In this physical process, pathogens are removed by a semipermeable synthetic barrier. Membranes remove particles and pathogens, and in some cases viruses, from water supplies.
Membrane use is accelerating, as the technology offers distinct advantages over chemical processes for disinfection and for advanced treatment in general.
The EPA relies upon a multi-barrier approach to protect consumer drinking water. When one of the barriers is changed or a new barrier is applied by a utility, there can be detrimental changes in water quality if the action is not evaluated. There are inherent dilemmas in the balance between implementing disinfection without forming DBPs, as shown in Figure 1. Planning is the cornerstone of successful projects; water utilities should make informed water-quality-related decisions based on well-constructed bench-scale, pilot-scale, and demonstration-scale process testing.
And they should include considerations to down-stream systems (primarily the distribution system).
Xenobiotics and emerging contaminants
Water purveyors increasingly are faced with concerns regarding new contaminants. Research has revealed the increasing detection frequency of trace organic xenobiotic chemical residuals and newly identified micro-organisms in water. Xenobiotics refers to a group of emerging contaminants that collectively include pharmaceuticals and drug metabolites, personal care products, hormones, plasticizers, pesticides (including many that have been banned for decades), petrochemical by-products and metabolites, and other potential endocrine disrupting chemicals. There are increasing concerns that these compounds may disrupt physiological processes related to reproduction. R.H. Sakaji of the Department of Health Services for the State of California indicates that these chemicals should be of concern, and new studies are needed to validate existing occurrence data and to improve our understanding of the fate of these chemicals in the environment. (See R.H Sakaji, S. Book, R. Hulquist, and R. Haberman’s 2004 paper called Xenobiotics: What are They and Why Are We So Concerned About Them?” published in the Journal AWWA [96(5):58].) Research into the occurrence and impacts of these contaminants, including research on methods to remove them from drinking water, is ongoing. For example, several years ago, the U.S. Geological Survey sampled for 95 compounds at 139 locations in 30 states. One or more of the emerging contaminants were found at 80 percent of the sampling locations.
Additionally, based on investigations by the Johns Hopkins University Bloomberg School of Public Health, researchers recently observed that trichlocarban occurrence is greatly under-reported and suggested that the antimicrobial contaminant is present in 60 percent of U.S. water resources. Additional research is being conducted to identify effective treatment methods, potential health effect levels, and compliance criteria.
Membrane processes and disinfection
Advanced treatment using membrane processes has become increasingly popular as a solution to address both water-shortage and water-quality concerns. During the 1970s, membrane processes emerged as a limited and expensive technology that could be used to deal primarily with watersalinity issues. At that time, most membrane systems were custom-made, proprietary, and costly. This system-based approach limited the growth of reverse osmosis technologies until the advent of spiral-wound membrane element configurations, which allowed for competition and the subsequent reduced costs. Today, there are many instances where advanced treatment is more cost-effective than conventional treatment processes. It is important to note that treatment plants operating with membrane processes have decided advantages over other types of facilities when you factor in automation and security benefits.
The cumulative capacity and number of membrane filtration technologies in the United States for surface water treatment has skyrocketed from 0.1 million gallons per day (MGD) in 1991 to nearly 300 MGD today (see Figure 2). Additionally, vendor information indicates that the number and capacity of large, reverse osmosis plants for seawater desalination has increased significantly around the world. Today, systems with a capacity of up to 300,000 cubic meters per day are being constructed. Additionally, desalted seawater costs have decreased from $2.00 per cubic meter in 1998 to about $0.50 per cubic meter last year, according to Mark Wilf and C. Bartels’ article, Optimizing of seawater RO systems design,” published in the journal, Desalination. Membranes will continue to evolve as their capacity and performance improve. Many people in the water community believe that membranes will emerge as the first choice for treatment because they are readily available and affordable, they provide disinfection, and they solve multi-contaminant problems.
Furthermore, membranes have distinct advantages relative to removing emerging contaminants from water sources.
Membranes will continue to be used to treat surface water supplies for microbial and particulate reduction, controlling disinfection by-product precursors, removing pesticides and pharmaceuticals, and reducing hardness and salinity. Whether for filtration or desalination, membrane treatment clearly is on the rise.
Infrastructure needs – Much of the nation’s water pipelines, treatment plants, and other such facilities have exceeded their useful life, and the aging water distribution system infrastructure must be replaced at an accelerated rate. However, the price tag is steep. In 2001, the EPA released findings from its Drinking Water Infrastructure Needs Survey, that drinking water systems will need to invest $150 billion over a 20-year period to ensure clean and safe drinking water. The primary area of concern for upgrades is the distribution system, specifically pipelines.
Internal Distribution System Evaluations – Internal Distribution System Evaluations (IDSEs) are studies conducted by community water systems and will be used to select new compliance monitoring sites within a distribution system that more accurately reflect sites representing high total trihalomethane and haloacetic acid levels, which are disinfection by-products. IDSE results are not to be used by the EPA for compliance purposes. Systems conducting IDSE monitoring shall monitor for one year under a schedule determined by source water and system size. Large and medium water systems will be required to submit the results of the IDSE (including any monitoring) and the results of Cryptosporidium monitoring two years and two and a half years after rule promulgation, respectively (expected to be implemented in 2006-2008). The IDSE contains specific water-quality monitoring requirements. (See www.epa.gov /OGWDW/mdbp/st2aip.html for more information.) Security – Today, water purveyors find themselves facing new responsibilities linked to concerns over water system security and possible acts of terrorism. For example, the Public Health Security and Bioterrorism Preparedness and Response Act of 2002 requires that all community water systems serving more than 3,300 people perform vulnerability assessments to evaluate their susceptibility to potential threats and identify corrective actions. As a result, utilities have responded to this challenge and have hardened their facilities and practices to discourage acts of terrorism and vandalism. However, security will remain a significant component of water utility operations in the future, and expenditures related to security will continue to escalate as purveyors improve their infrastructure. (For more information on water system security, see www.epa.gov/safewater/ security.)
The advancement of drinking water regulations will not be without cost. There will be continual pressure on water purveyors to provide higher-quality service under more stringent conditions, affecting the cost of operations and the manner in which water is delivered to consumers. To replace many water communities’ deteriorated infrastructure, the users’ cost of water must be increased to attain the level of service that will be required, particularly as the number of immune-compromised and elderly individuals rises.
Changes outside of and within the water community will require more involvement by the public and will result in continual perception issues. Water purveyors will be held accountable for secondary, aesthetic water quality standards, mandated by regulation and carried out via litigation from organized consumer groups. Additionally, the water community will need to focus on distribution systems – and determine cost-effective methods for their repair, rehabilitation, and replacement – to maintain water quality at the tap and to meet consumer expectations of quality and security. These will be significant challenges that will be met with new and improved technologies. Solving the many water supply, treatment, and distribution challenges of the future will offer exciting and new opportunities to those of us fortunate enough to work within the drinking water community.
Steven J. Duranceau, Ph.D., P.E., is vice president and director of Water Quality and Treatment for Boyle Engineering Corporation in Orlando, Fla. He can be reached at 407-425-1100, or via e-mail at email@example.com.