Q
I am reading about a lot of activity in wastewater recycling projects, including for potable drinking water. Can it be done safely and what might that mean for POU/POE and bottled water consumption? — U.S.
A
There really are many large scale projects being developed and already underway aimed at converting wastewater into drinking water. The historic droughts in Texas and the Southwest have triggered a lot of interest in recovering wastewater, especially because populations have been increasing so that the demand for public water has increased. Southern California has been a leader for many years in recovering wastewater for potable and non-potable applications.
Introduction
All water has always been reused. In the natural cycle water evaporates to the atmosphere from the Earth’s surface; it ultimately falls as rain and snow, some of which runs off from land and collects in rivers and lakes and oceans, and some of which percolates into underground aquifers. Shallow aquifers and surface waters are often interconnected. Increasingly the water is being withdrawn and used for irrigation, industrial processes or drinking water and then the resultant wastewater is usually treated and discharged back to the environment to reenter the cycle. Although it is estimated that there are at least 326 million trillion gallons of water in or on the Earth, 98 percent is brackish or in the oceans. Of the remaining two percent freshwater, most is locked in polar icecaps and glaciers, about 0.36 percent is in the ground and only about 0.036 percent is in lakes and rivers. The rest is in transition in the atmosphere as water vapor. The problem is that the available freshwater isn’t always located in sufficient quantities where people who need it live.
Human technology has stepped in to make more water available. Dams have been built to store it and canals and pipelines to move it. Water treatment technology is now available to take water of any quality from any source and convert it into water of necessary quality for any purpose, including drinking.
Water reuse
Sanitary wastewater is available as a source for essentially 100 percent reuse. It contains recoverable nitrogen, phosphorus nutrients and biosolids for agriculture and oils and grease as potential biofuels. It can be fermented anaerobically to produce methane for energy. The treated water can be produced for crop irrigation and cooling water and high quality drinking water, depending upon the level of treatment that is provided.
The goal is to change the identity of the water from wastewater to water of appropriate quality for the intended use so that it is acceptable and safe for human contact. The natural water cycle does this by biological degradation of contaminants and sedimentation in rivers and lakes, evaporation and precipitation and by filtration and storage time in groundwater. These remove many minerals, chemicals and microbial contaminants by several mechanisms. Water treatment processes simulate and accelerate the natural purification processes (for a price), but they can also provide a supplement for more reliable, efficient and environmentally friendly supply.
Direct and indirect potable reuse
There are two general categories of potable reuse water: Indirect reuse (IPR) and direct reuse (DPR). The essential difference between IPR and DPR is the lack of an environmental phase before or after treatment prior to delivery to consumers.
Either deliberate (planned) or inadvertent (unplanned) IPR has been practiced since the beginning of civilization particularly with respect to surface water use. Natural runoff and animal human waste discharges into upstream surface waters are diluted and transported downstream to be withdrawn and put to use for irrigation or human consumption, usually with subsequent treatment in the last approximately 150 years. Most river surface water supplies in the U.S. have been treating more or less contaminated upstream water by “conventional processes” to produce safe drinking water that meets national drinking water quality standards. Only about one percent of that municipal water is used for human consumption for food preparation or drinking water.
IPR and DPR recent history
The Montebello Forebay Groundwater Recharge Project has been in operation in Los Angeles since 1962. It is a planned IPR project where 50,000 acre feet (16.3 billion gallons) per year of treated wastewater is spread and percolated to an aquifer where it is stored and withdrawn for drinking water. This is a soil aquifer treatment (SAT) process. Several other more recent spreading or injection projects have been in successful operation in Southern California.
The most recent is in the Orange County Water District where half of the 70 million gallons per day of production of advanced treated water is injected as a salt water intrusion barrier. The rest is percolated from lakes into the groundwater where it is stored and transported and subsequently withdrawn by water suppliers and distributed without further treatment. The Orange County process consistently produces water with total organic carbon (TOC) levels in the range of 0.15 mg/l and removes dioxane that is probably the most difficult organic chemical to treat, to non-detect or less than 1 ppb. A low TOC means that the production of disinfection by-products would also be low. This would also cap the potential for contaminants that would be present at levels of concern.
The first large scale DPR project was initiated in Windhoek, Namibia, South Africa in 1968 — it has been modified and expanded since then. Singapore has had a IPR/DPR “NEWater” project in operation for 10 years and is expanding its production. Singapore’s Public Utilities Board also bottles its NEWater and provides it at no cost for plant visitors and at public events. DPR processes are being considered in several locations in the U.S.
Treatment processes
Conventional drinking water treatment processes for surface waters in the U.S. consist of coagulation, flocculation, sedimentation, sand filtration and disinfection by a form of chlorine. Conventional treatment is very good at removing particulates and some chemicals and bacteria and viruses and some protozoa. Typical TOC levels of conventional finished water are at the several mg/l level. Conventional treatment is not designed to effectively remove many industrial chemicals. It will produce disinfection byproducts and protozoa removal requires very effective filtration or disinfection modifications because chlorine is not totally effective for protozoa, especially cryptosporidium.
Planned potable reuse technologies are more intensive than conventional treatments because they start with sanitary wastewater, which is a frankly contaminated source. However, they are capable of ultimately producing even higher quality drinking water than surface water conventional treatment systems. They are specifically designed to remove essentially all microbial and chemical contaminants with very high effectiveness and they focus on multiple barrier treatment trains to assure excellent reliability even in the event of diminished performance of one of the barriers.
There are multiple treatment configurations that can be used to produce high quality potable drinking water from impaired sources. The components can include several of the following technologies: Starting with secondary or tertiary treated wastewater, soil aquifer treatment, granular carbon, sequences of membrane treatments including microfiltration, ultrafiltration or nanofiltration with reverse osmosis and disinfection systems including chlorine, ozone, chlorine dioxide and ultraviolet light. More costly advanced oxidation technologies can be used to remove trace organic chemicals like residual pharmaceuticals or recalcitrant chemicals like 1,4-dioxane. Advanced oxidation involves technologies that produce hydroxyl free radicals from hydrogen peroxide or ozone and ultraviolet light. Hydroxyl free radicals have a free electron and they are the most reactive free radicals available. With higher costs, they have the capability of destroying essentially any organic chemical and converting it to carbon dioxide and water if a sufficiently high dosage is produced.
Health implications
The principal concern in any water system is eliminating microbial risks. Trace chemical removal is also highly desirable and practiced, but there is a consensus that risks, if any, of consumption of parts per billion and parts per trillion of a few residual organics is not significant. Planned reuse projects are designed to consistently achieve these results so they can produce water that is at least as safe as and probably better than conventional drinking water that meets drinking water regulations.
Public concerns and reactions
In spite of the proven successes of planned IPR and DPR technologies and the high quality product water that they produce, it is natural for many consumers to have some misgivings because of the sanitary wastewater source, i.e. the “yuck factor.” Planned IPR systems also provide a greater perception that the treated water has lost its original wastewater identity because there has been an intervening environmental phase, such as storage in the ground, or placement in a surface reservoir prior to being retreated in a conventional drinking water plant. It would not be surprising that some consumers who are supportive of the IPR and DPR reuse project and intellectually satisfied that the water is safe to drink might be reluctant to do so and would gravitate to POU treated water or to bottled drinking water.
In fact, this is not an unusual situation among some consumers in many conventional public systems, either because of undesirable taste or media fed perceived, although unlikely, risks from the public water supply. One small poll in an IPR location indicated that among strong supporters, about 40 percent of respondents stated that they were drinking bottled water and another 40 percent stated that they had a POU device in their home. The types of devices were not specified, but it is likely that many of them were just taste and odor carbon filters so they would not have much of an effect on the finished water composition. So, clearly the IPR/DPR issues are of perception rather than actual water quality and safety.
All water is recycled either in the natural cycle or via human technological intervention. IPR and DPR systems are increasing because the need for high quality water is increasing in parts of the U.S. experiencing shortages. The technologies are proven to be successful and reliable and drinking water quality is at least as good as or better than from conventional surface water supplies. Consumers are supportive when they understand the need for an adequate and reliable water supply. Additionally, more intensive treatment of wastewater protects the environment by reducing the discharges to surface waters. Nonetheless, some consumers will be reluctant to drink the water in their homes because of concerns about the history and proximity of the impaired source water. These concerns may subside in time with familiarity, but it is not surprising that some people then will opt to consume POU or bottled water.
Dr. Joseph Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.
