Anaerobic-ion exchange (AN-IX) process for local-scale nitrogen recovery from wastewater

Significance Statement

Recovery and reuse of wastewater-derived nitrogen has numerous ecological, economic, and societal benefits. Nitrogen is an essential nutrient that, paradoxically, can trigger environmental problems such as algal blooms and groundwater impairment in the absence of source-control measures. Sustainable approaches for managing nitrogen discharges are urgently needed, particularly in environmentally sensitive watersheds. The Anaerobic/Ion Exchange Process (AN-IX) is a cost-effective technology that has dual benefits. Deployment of AN-IX can achieve nitrogen recovery for local-scale recycling (1-3,5) while simultaneously mitigating nitrogen discharges to the environment (4-7).  AN-IX capitalizes on the effectiveness of natural, low cost zeolites to sequester NH4+ ion under anoxic conditions (8). An exciting dimension to AN-IX is the capacity to concentrate nitrogen in a form that can support crop production, thus diminishing the need for commercial fertilizers and providing a sustainable local-scale approach for closing the nitrogen loop (1-3,5).

The AN-IX process is a unique and innovative coupling of anaerobic solids blanket treatment with anoxic ion exchange in an integrated, multiple-chamber reactor.  Anaerobic pre-treatment provides three critical functions: 1. ammonify organic-nitrogen to the ammonium ion form, 2. remove solids, reduce biological instability, and prevent clogging, and 3. elute reducing gases into the common reactor headspace to limit oxygen ingress and prevent ammonia oxidation.  Downstream of the anaerobic upflow chamber, ammonia removal by anoxic ion exchange can readily occur. This completely passive system is self-contained and does not require any aeration or energy inputs. Prototype systems that were continuously operated at field sites in Maryland (355 days) and Florida (662 days) yielded consistent and reliable capture of over 95% of wastewater nitrogen. The feasibility of direct coupling of anaerobic and anoxic systems was unequivocally demonstrated through proof-of-concept studies conducted on human wastewater from different sources in different climatic zones. The ammonia that was anoxically separated by AN-IX was directly recycled for propagation of Solanum lycopersicum (cherry tomato), an edible food crop (1-3).

The design of AN-IX is simple, even though the process itself is complex.  Importantly, AN-IX is a highly appropriate technology for local-scale deployment due to its low footprint and inherently passive operation. The fact that the system is self-contained and requires no day-to-day maintenance opens up possibilities for scalable nitrogen recovery in rural, urban and peri-urban settings. AN-IX provides a practicable solution for addressing a global priority for effective onsite nitrogen removal systems, with the added benefit of recovering nitrogen in a form that can be used for agricultural applications. Local-scale, on-site wastewater treatment systems are employed worldwide. Typically, the primary function of these systems is to control pathogens and biodegradable organics with minimal attention to nitrogen removal. In fact, over a quarter of US households rely on conventional septic systems for on-site wastewater management. Prominent geographic locations on the east coast of the US that are highly impacted by onsite wastewater nitrogen discharges include Cape Cod (MA), Long Island (NY), the Chesapeake Bay, and the state of Florida.  Other critical areas include San Francisco Bay, Puget Sound, and the Great Lakes. Water quality in these locations is severely impacted by nitrogen that is inadvertently discharged from hundreds of thousands of onsite systems. Clearly, there is a compelling need for cost-effective local-scale nitrogen recovery systems.  Fortunately, AN-IX is capable of filling this niche.  Field-scale research and process optimization are ongoing.

Previous studies cited:

  1. Smith, D. and Smith, N. (2015a)  Local-Scale Recovery of Nitrogen Recovery for Edible Plant Growth. Water Science and Technology, 1287-1292, 2015.
  2. Smith, D. and Smith, N. (2015b)  Nitrogen Recovery from Onsite Wastewater and Local Recycle. Uniting for Progress.  National Onsite Wastewater Recycling Association, November 3-6, 2015, Virginia Beach, Virginia.
  3. Smith, D. and Smith, N. (2015c)  Point-of-Generation Nitrogen Recovery from Wastewater. Water and Energy 2015, Opportunities for Energy and Resource Recovery in the Changing World.  Water Environment Federation, June 7-10, 2015, Washington, DC.
  4. Smith, D. and Smith, N. (2015d) Wastewater Treatment and Nitrogen Recovery at Point of Origin.  Third International Conference on Water, Energy and Environment (ICWEE), Sharjah, United Arab Emirates, March 2015.
  5. Smith, D. (2015) Point-of-Generation Nitrogen Recovery from Wastewater E3S Award.  Environmental Engineer and Scientist, Vol. 21, No. 2, Spring 2015, American Academy of Environmental Engineers and Scientists, Annapolis, MD.
  6. Smith, D. (2014) Multi-Chamber Treatment and Recovery Process.  US Tech H2.O, U.S. State Department, Washington, DC, March 2014.
  7. Applied Environmental Technology (2013) Energy and Nutrient Extraction from Onsite Wastewater. EPA SBIR Phase I Final Report.
  8. Smith, D. (2011) Chabazite Biofilter for Enhanced Stormwater Nitrogen Removal. Water Environ. Res., 83, 4, April 2011, pp. 373-384.

Anaerobic-ion exchange (AN-IX) process for local-scale nitrogen recovery from wastewater. Renewable Energy Global Innovations


About the author

Daniel P. Smith, Ph.D., P.E. BCEES

Applied Environmental Technology, USA; [email protected]

Dr. Smith is president of Applied Environmental Technology, a registered Professional Engineer, and is Board Certified by the American Academy of Environmental Engineers and Scientists. He holds a Ph.D. in Environmental Engineering and Science. Dr. Smith has been conducting applied research for several decades on numerous topics related to water quality, treatment systems, and environmental modeling. He is an expert on the fundamental science, engineering, and practice of local-scale treatment and resource recovery from sanitation wastewater using integrated physical, chemical and biological processes. He has developed technologies that incorporate anaerobic treatment, porous media biofiltration, reactive solid-state electron donors, and ion exchange with plant and microbial systems for media regeneration and nutrient recycle. Dr. Smith’s projects have won several Excellence in Environmental Engineering and Science Awards from the American Academy of Environmental Engineers and Scientists in Annapolis, Maryland, including Onsite Nitrogen Reduction with TwoStage Biofiltration (2009) and Point-of-Generation Nitrogen Recovery from Wastewater (2015). 

About the author

Nathaniel T. Smith, M.S, Civil and Environmental Engineering, EIT

Applied Environmental Technology USA; [email protected]

Nathaniel Smith holds B.S. and M.S. degrees in civil and environmental engineering. He has worked on several research projects focused on at-source treatment of human sanitation water for nitrogen removal and recovery. Topics of his research include anaerobic treatment, unsaturated porous media biofiltration, ion exchange, and denitrification bioreactors with solid state electron donors. He received his M.S. from the University of California, Davis, where his Master’s project addressed nitrogen removal from mixed, urine-enriched wastewater streams under low temperature conditions. In 2015, he was awarded the George and Rosemary Tchobanoglous Graduate Fellowship at the University of California, Davis. 

Journal Reference

Daniel P. Smith1, , ,Nathaniel T. Smith2
Show Affiliations
  1. Applied Environ2mental Technology, PO Box 576, Garrett Park, MD 20896, USA
  2. Civil and Environmental Engineering, University of Maryland, College Park, MD 20742, USA


An anaerobic-ion exchange (AN-IX) process was developed for point-of-origin recovery of nitrogen from household wastewater. The process features upflow solids-blanket anaerobic treatment (ammonification) followed by ammonium ion exchange onto natural zeolite. The AN-IX system is configured as a series of linked upflow chambers that operate passively without energy input, and is amenable to intermittent and seasonal operation. A 57 L prototype was operated for over 1.8 years treating actual wastewater under field conditions. Total nitrogen removal exceeded 96% through the first 160 days of operation and effluent ammonium nitrogen remained below detection for 300 days. Ion exchange chambers exhibited sequential NH4+-N breakthrough over extended operation and complete media exhaustion was approached at Day 355. The ammonium capacity of zeolite was estimated as 13.5 mg NH4+-N per gram dry weight. AN-IX is a resilient and cost effective process for local-scale nitrogen recovery and reuse, suitable for small scale and larger systems.

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