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Issue link: http://wateronline.epubxp.com/i/164223
Feature Save Nutrients, Save The World While regulations demand that wastewater treatment plants get nutrients out of the water, the world's food supply may demand more — that we recover and reuse them. By Kevin Westerling N utrients are a nuisance in our environmental waters and, by extension, a nuisance to wastewater treatment plant (WWTP) operators, especially in the United States. Federal and state regulators have been steadily rolling out more — and more stringent — effluent limits on nutrients — namely, phosphorus and nitrogen. Aggressive action is certainly necessary; eutrophication caused by nutrients results in hypoxia (oxygen depletion) and harmful algal blooms that kill aquatic life and can lead to cyanosis ("blue baby syndrome") in humans. The aggressive way in which WWTPs are targeted, however, may seem unfairly strict and unbalanced considering the nutrient loadings of nonpoint sources, such as runoff from farmlands, which actually pollute receiving waters much more. But this burden taken on by wastewater utilities may also yield tremendous opportunity. Whereas the current focus mainly lies on simple (or not so simple) nutrient removal, often at great cost to the municipality, the next (r)evolutionary step will be the recovery and reuse of nutrients, particularly phosphorus. It's a virtual inevitability since phosphorus is a finite resource that otherwise must be mined from phosphate rock. Phosphorus is vitally important because, along with nitrogen and potassium, it's an essential component of (N-P-K) fertilizer. In short, it's needed to feed the world, and it's in danger of running out … someday. There is considerable debate as to when and how that may happen, with many factors to consider in the projection (see the sidebar on page 10 for details). 8 wateronline.com ■ Though even alarmists would admit that we're at least decades away from a phosphorus shortage, there is no denying the general direction of the trend. A finite resource coupled with a rising population, according to the basic law of supply and demand, will only create shortage and increase value. So it's feasible that wastewater plants could someday get rich from treating human waste, which is loaded with nutrients. Imagine that: urine as liquid gold! Before you balk, consider that one person's urine is enough to keep 3,000 to 10,000 square feet of farmland well-fertilized, depending on the type of crops grown.1 Even in its most basic forms — localized land application, for instance — the recycling of nutrients has enough value to help offset the very significant costs of sludge treatment. What opportunity might then be offered by more advanced recovery technologies, especially when considering the rising demand for fertilizer? And while the true mission of public utilities isn't to turn a profit per se, it is their mission to serve the community's needs in the most cost-effective way. Recovery and reuse of nutrients has the capability to simultaneously protect waterways from eutrophication, provide (and prolong) fertilizer production for crops, and save — or even earn — money for municipalities. The question then becomes, why aren't more wastewater facilities doing this? Some progressive utilities in the U.S. actually are, but it is much more prevalent in Europe. Here are some of the technologies and utilities that are leading the way. Water Online The Magazine