sediment, runoff, and nutrients all deposit into the gulf of mexico, sometimes originating as far north as minnesota. the large number of pollutants entering the outlet causes massive problems, sometimes in ways that one would not expect. for example, it might be surprising to learn that a large inflow of nutrients like nitrogen and phosphorus have adverse consequences for the ecosystem of the gulf of mexico.

when an excess of nitrogen and phosphorus enter a large body of water, an algal bloom occurs. as these algae blooms grow, two things happen: the algae on the surface prevent light from reaching aquatic plants below the surface, causing these plants to die, and the algae also die. bacteria break down the dead organisms, a process that requires the use of oxygen. this results in a deficit of oxygen, creating a dead zone where plants and animals cannot exist.

such a dead zone exists in the gulf of mexico, and it is at its largest size since measuring began in 1985 — roughly the size of new jersey. the large size is concerning considering the massive impacts the dead zone has on the gulf of mexico and the gulf coast area.

besides disrupting the ecosystem, the dead zone poses economic problems to the area. seafood is a large industry in the region, and fish kills represent a major threat to this industry.

the dead zone is projected to grow, and it certainly will not shrink without some sort of change occurring.

one way to reduce the amount of nutrients that reach waterways is to implement nutrient removal techniques in wastewater treatment facilities.

in washington, d.c., dc water has introduced enhanced nitrogen removal facilities that allow the blue plains treatment plant to significantly reduce the amount of nitrogen discharged into the potomac river; they claim that these new facilities have prevented over 144 million pounds of nitrogen from entering the potomac river.

dc water is also constructing a new tunnel system that will prevent sewer overflows from being flushed into waterways without first being treated. with rising concerns over excess nutrients in water ecosystems, wastewater treatment facilities around the united states are facing pressure from local, state, and federal governments to implement nutrient removal processes similar to those utilized by dc water.

besides discharges from wastewater treatment plants, runoff also represents a major source of nutrients in waterways. phosphorus and nitrogen are the main components of fertilizers and make their way into rivers, lakes, and other bodies of water as a part of agricultural runoff. runoff is classified as a non-source pollution and is therefore unregulated, so it has been difficult to track and prevent the amount of nutrients entering waterways through this route.

however, this does not mean that it is impossible to reduce the amount of runoff that reaches bodies of water.

investing in green infrastructure can prevent an abundance of nutrients in waterways and has other benefits like reducing flooding. green infrastructure includes rain gardens, bioswales, permeable pavements, and rainwater harvesting. incorporating green infrastructure alongside traditional infrastructure can help reduce the amounts of nitrogen and phosphorus reaching waterways.

—

citations:

“gulf of mexico ‘dead zone’ is the largest ever measured.” national oceanic and atmospheric administration. august 2, 2017. https://www.noaa.gov/media-release/gulf-of-mexico-dead-zone-is-largest-ever-measured.

“removing nitrogen from wastewater protects our waterways.” dc water. 2017. https://www.dcwater.com/nitrogen-reduction.

“tunnel dewatering pump station and enhanced clarification facility.” dc water. 2017. https://www.dcwater.com/projects/tunnel-dewatering-pump-station-and-enhanced-clarification-facility.

“what is green infrastructure?” environmental protection agency. july 03, 2018. https://www.epa.gov/green-infrastructure/what-green-infrastructure.

the energy in wastewater treatment most commonly comes from carbon containing organic matter. bacteria convert organic matter into methane, a combustible fuel that can be burned to generate power. in addition to carbon containing organic matter, there is also nitrogen in wastewater. unfortunately, current treatment processes don’t recover energy from waste nitrogen. but what if we could convert waste nitrogen into a combustible gas, just like converting organic matter into methane? it turns out we can! that’s where the rockets come in. bacteria are capable of converting waste nitrogen into nitrous oxide… yeah, nitrous oxide. the same stuff your dentist gives you, although dentists usually call it “laughing gas”. it’s also the same gas racecar enthusiasts use to supercharge their engines, although they call it “nitrox”. it’s also the same gas that has been used for decades in rockets. in fact, space ship one, the first privately manned spaceplane that is paving the way for sub-orbital space flights open to the public, used nitrous oxide in its rocket motors. it’s powerful stuff and we can get it for free from wastewater! at stanford we are developing a way to get bacteria to convert waste nitrogen into nitrous oxide, thus enabling energy recovery from both waste carbon and nitrogen. by producing nitrous oxide, we could essentially “supercharge” wastewater treatment, kind of like a nitrox turbocharged racecar.

wastewater treatment may not take us to the moon, but it can provide a serious amount of free and clean energy. considering that the treatment of wastewater consumes 3% of u.s. energy supply and wastewater treatment plants are often the highest energy expenditure for cities, generating power from wastes seems like a really good idea.