Biological Nitrogen Removal Julian van der Made Department of Earth and Environmental Engineering Summer 2018 What are different forms of Nitrogen? Nitrogen form Symbol Occurrence and function Dinitrogen Gas or Atmospheric Nitrogen N2 Most common form of nitrogen and makes up over 70% of the atmosphere. Cannot be used by plants, but can be transformed into ammonia by nitrogen-fixing bacteria or Haber-Bosch process Ammonia/Ammonium NH3/NH4+ Can be used directly by organisms as nitrogen source. Not easily leached from the soil into water Nitrate NO3- Can be used by organisms as nitrogen source. Easily leaches out of soil into water Nitrite NO2- Bio-available, but can also be toxic to aquatic life and babies Nitrous Oxide N2O Gaseous and produced as intermediate during denitrifictation. Strong greenhouse gas Organic N C-NH2 (C is a complex organic group) Nitrogen as part of organic compounds. Microorganisms break these compounds down and release ammonia The Problem: Nitrogen Pollution Gaseous nitrogen compounds can cause air pollution such as smog The environmental effect of too much nitrogen in the water Nitrogen pollution sources Eutrophication, Algal Blooms, and Dead Zones http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/problems_in_environ men t/pollutionrev4.shtml Example: Gulf of Mexico Dead Zone One of the largest dead zones forms in the Gulf of Mexico every spring. Each spring as farmers fertilize their lands preparing for crop season, rain washes fertilizer off the land and into streams and rivers. Gaseous Nitrogenous Pollution: Greenhouse Gas Nitrous oxide is an gaseous intermediate formed during denitrification It is a powerful greenhouse gas, with a 100-year global warming potential that is about 300 times stronger than that of carbon dioxide. The biggest contributor to nitrous oxide emissions is the agricultural sector Gaseous Nitrogenous Pollution: Acid Rain Nitrates and Nitrites: Human Health Effects Nitrates and nitrites can occur in our drinking water, especially in industrial or agricultural areas. When ingested, nitrates can be converted into nitrites in the body. Nitrites react with human hemoglobin, reducing their capacity to carry oxygen, leading to something known as ’Blue Baby Syndrome’. A 2010 report on nutrients in ground and surface water by the U.S. Geological Survey found that nitrates were too high in 64 percent of shallow monitoring wells in agricultural and urban areas. Removing Nitrogen with Biological Wastewater Treatment Background: Redox Reactions Example: Zn-Cu Battery Cu2+ + 2e- Cu (reduction half-reaction) Zn Zn2+ + 2e- (oxidation half-reaction) Overall: Cu2+ + Zn Cu + Zn2+ Another Redox Example H2 2H+ + 2eF2 + 2e- 2F- What is being reduced and what is being oxidized? Who is the electron acceptor and who is the electron donor? Biological Wastewater Treatment: Microbial Redox Reactions Objective: Remove pollutants in water through microbial conversion into benign relatively benign forms Concept: Microbes oxidize electron donors and reduce electron acceptors to produce energy. By providing the correct electron donors/acceptors, pollutants can be consumed by microbes. Oxidation States of Nitrogen Oxidation state describes the degree of oxidation (or loss of electrons). The more negative the oxidation state, the more reduced the form, and thus the more electrons this form can donate Nitrogen Form Oxidation State NH3/NH4+ -III N2 0 N 2O +I NO +II NO2- +III NO3- +V Reduced/ Electron Donor Oxidized/ Electron Acceptor Engineering Biological Nitrogen Removal N(0) N(+I) Organic Carbon Organic Carbon Denitrification N(-III) N(+II) O2 Organic Carbon N(+III) Nitrification Organic Carbon N(+V) O2 N(+III) Picture of traditional WW plant Nitrification Tank O2 must be supplied Denitrification Tank Organic carbon must be supplied In a traditional biological nitrogen removal, nitrogen is removed in two steps: 1. First, ammonia (-III) is fully nitrified to nitrate (+V) using oxygen as the terminal electron acceptor. 2. Second, nitrate is removed through denitrification with organic carbon as the electron donor. NH3 NO3- N2 Increasing Efficiency in Nitrogen Removal N(0) N(+I) Organic Carbon Organic Carbon Denitrification N(-III) N(+II) O2 Organic Carbon N(+III) Nitrification Organic Carbon N(+V) O2 N(+III) Nitritation and Denitritation 25% savings in aeration energy and 40% savings in organic carbon requirement! Modified from Welsh et al., 2014 Anammox: A more efficient route for nitrogen removal 19 NH4+ + NO2- N2 + H2O Anammox: More Increases in Efficiency N(0) N(+I) Anammox: Anaerobic Ammonia Oxidation Organic Carbon Organic Carbon Denitrification N(-III) N(+II) O2 Organic Carbon N(+III) Nitrification Organic Carbon N(+V) O2 N(+III) N2 N2O Denitrification NO Denitritation Anammox NH4+ NO2- Denitratation NO3- Nitratation Nitritation Nitrification -3 reduced -2 -1 0 +1 +2 +3 62.5% savings in aeration energy and 100% savings in organic carbon requirement! +4 +5 oxidized Industrial Wastewater high in NO3 and NH4+ Denitratation and Anammox N2 N2O Denitrification NO Denitritation Anammox NH4+ NO2Nitritation reduced -2 -1 0 +1 NO3- Nitratation Nitrification -3 Denitratation +2 +3 100% savings in aeration energy and 60% savings in organic carbon requirement! +4 +5 oxidized Denitratation and Anammox for Industrial Wastewater Objective: Using glycerol as an external carbon source, halt the denitrification process at a point of maximum NO2- accumulation in the effluent by manipulating process controls or influencing microbial processes. Takeaways Currently, management on nitrogen in linear. Dinitrogen gas is fixed industrially using the Haber-Bosch process for industrial and agricultural practices. However, removing these reactive nitrogen species from our waste streams is not as actively managed, leading to pollution problems such as greenhouse gas effect by nitrous oxide or algal blooms Biological nitrogen removal offers a solution to some of the nitrogen problem, by providing the correct electron acceptors or donors for microbes to convert the pollutants to nitrogen gas.
