Global warming, climate change, and the resulting drive to adopt far more environmentally conscious attitudes to our dwindling natural resources has become the universal catch cry of the early 21st century.1, 2, 3 This new societal ethos is welcome and, as responsible citizens in our various corners of the world, dialysis providers must also rapidly embrace this global movement and put our own house in order. Despite widespread endemic drought conditions worldwide, most hemodialysis (HD) clinics still ignorantly discard daily to the sewer huge volumes of a reusable high-quality resource: dialysis process-derived water.
The dialysis process generates 2 very different water-related components. The first of these is reverse-osmosis reject water, whereas the second is spent dialysate effluent.
Reject water, highly filtered and purified, is formed by predialysis water filtration before exposure to blood products. In retrospect, applying the term “reject” to water of such high quality is at least a misnomer and, at worst, counterproductive because the word has connotations of badness or impurity. Although far from true of reject water, it may explain our thoughtless dialysis practice of completely discarding reject water to the sewer without considering its potential uses.
Meticulous particulate, carbon, and reverse-osmosis filtration is essential to the dialysis process.4 In the 1970s, aluminum,5 chloramines,6 endotoxin,7 and other substances were shown to pass into the patient from the dialysate across the dialyzer membrane. To protect from unwanted toxins carried in the water required to create dialysate in single-pass systems, reverse-osmosis water filtration became a standard requirement. After prefiltration, the reverse-osmosis process rejects to drain any remaining dissolved solutes. The high-volume effluent thus produced is known as reject water. Although the higher solute concentration of reject water increases its conductivity, reject water is otherwise better than mains water and despite its higher conductivity, most reject water is well within the US Environmental Protection Agency standards for potable drinking water.8
Whereas reject water is a predialysis effluent, spent dialysate effluent is formed after blood contact. After reverse-osmosis purification, accepted water mixes with a chemical concentrate in single-pass dialysis systems to form a serum-compatible bicarbonate-buffered dialysate that removes electrolytes, solutes, and uremic metabolic wastes from blood across the dialyzer membrane. The dialysate effluent thus formed is then uniformly drained to the sewer by all dialysis services worldwide.
To our embarrassment, despite 5 decades of HD, one of the first reports of dialysis water conservation is only now just appearing. In this issue of American Journal of Kidney Diseases, Tarrass et al9 report from Morocco a desalination trial of unsegregated reverse-osmosis reject water and dialysate effluent for reuse in landscape and irrigation programs. They report the water quality achieved, technical problems faced, and costs incurred by desalinating a combined effluent and compare the latter with standard Moroccan seawater desalination costs. They correctly criticize the current worldwide dialysis practice of the profligate wastage of dialysis wastewater, both reject water and dialysate effluent, and estimate that in Morocco alone, the combined effluent wastage from some 80,000 facility-based 4-hour treatments is approximately 50 million US gallons per year. In arid and drought-stricken regions, such losses are no longer supportable, and this Moroccan initiative is timely.
Although the Moroccan study focuses on combined reject water and dialysate effluent, 2 recent Australian studies have reported several reuse projects for reject water alone in both facility-based10 and home HD.11 These investigators claimed that given similar use patterns, the annual US equivalent reject water generation would be approximately 27 gigaliters, sufficient to provide all yearly water requirements for a US city of approximately 175,000, for example, Salt Lake City, Utah.12 In these reports, facility-based reject water has provided water for sterilizer steam generation, janitor stations, maintenance, and landscape care, whereas home HD–generated reject water has supplied home toilets, laundries, gardens, and stock watering. Even an income-generating reject water–powered commercial carwash facility is under consideration in the Australian initiative.13
Tarrass et al9 propose using combined effluent for irrigation, agricultural, and landscape use after desalination. To first confirm chemical suitability and microbiological safety, they analyzed the combined effluent and compared it with the agricultural wastewater standards of both the World Health Organization14 and the United Nations Food and Agriculture Organization.15 With the expected exception of the sodium and chloride concentration of the combined effluent, and thus its conductivity, the chemical analysis is well within the limits of both standards. However, because dialysate effluent presupposes patient blood contact, they applied the Association for the Advancement of Medical Instrumentation culture method16 of trypticase soy agar incubated at 36°C for 48 hours to their combined effluent. The resultant cultures also were within these standards. Although more stringent dialysis water sterility standards are now recommended to include incubation at room temperature for up to a week with Reasoners 2A or tryptone glucose-extract agar,17 this applies to in-feed and not effluent water. For dialysate effluent use in agricultural irrigation or landscaping, Association for the Advancement of Medical Instrumentation compliance seems more than adequate, particularly because bacterial colony counts have been well within both World Health Organization and United Nations Food and Agriculture Organization recommendations.
Concerns may surface that environmental bacterial or viral contamination may occur in effluent fluids of patients infected with viral hepatitis, acquired immunodeficiency syndrome, or other infectious diseases. Although there is no evidence that contamination poses a practical risk, the reuse of reject water alone, as proposed from Australia, rather than recycling a combined wastewater effluent that incorporates patient-contact dialysate effluent would avoid all contamination risk. Reject water use alone may also be both more practical and less expensive to install.
Although Tarrass et al9 compared the costs of combined reject water and dialysate effluent desalination by nanofiltration (US $0.70/cubic meter) or reverse osmosis (US $0.74/cubic meter) with those for commercial seawater desalination, desalination is unnecessary for reject water use alone. Desalination uses considerable power,18 and although the Moroccan study costs dialysate effluent desalination at 20% to 30% less than the desalination of seawater, the predicted expenditure is still high and would add significantly to dialysis budgets.
Equipment advances now also curb dialysis water use more efficiently. Installing better pretreatment technology minimizes reject water losses, but only with large capital and maintenance investments that, although economical for larger systems, are not as cost-effective for comparably smaller dialysis-system reverse osmosis. Although early HD reverse-osmosis systems rejected up to 75% of feed-water,19 later models can recycle the excess permeate back to the feed-water and reduce reverse osmosis wastage to approximately 20%. However, in the real world, many operational reverse-osmosis systems are the old varieties, and even with recirculation, water will always be wasted. Because budget restrictions will also prevent any rapid replacement program for many dialysis services, reject water reuse will likely remain valid and valuable in the medium future.
Newer prepacked or on-line dialysate generation systems20 and renewed interest in sorbent technology both for dialysate regeneration21 and in wearable kidney prototypes22 may alter future dialysis water use, with one currently emerging sorbent system already reducing total dialysis-related water use to 6 L/treatment.21 The potential impact of these technological advances on global dialysis-related water use is immense.
Whether through bulk effluent or separated reject water and dialysate effluent collection, there is a clear challenge to rethink our dialysis wastewater policies, and we must rapidly explore the potential for innovative wastewater reuse. For the reject water–only reuse model, little beyond some do-it-yourself hardware and a weekend plumbing project seems necessary to redirect reject water to wiser uses. For the whole-of-effluent model, in which conductivity issues demand additional desalination, cost may yet prove inhibitory. However, both demand urgent consideration.
This is an important report because it identifies “the elephant in our room.” As policy-makers realize the potentials for dialysis wastewater reuse, regulatory bodies will follow, requiring dialysis services to include a wastewater reuse program in their charter. This is as it should be. The Tarrass report in this edition of American Journal of Kidney Diseases provides our wake-up call. Let us hope it leads to further innovative reuse ideas for one of nature's most precious resources—water.
FULL TEXT
