Nitrogen and Phosphorus Treatment Can Be Sustainable During on‐Site Wastewater Disposal

• Published in: Ground water 2023-07, Vol.61 (4), p.586-598
• Main Authors: Robertson, William D., Elgood, Richard J., Van Stempvoort, Dale R., Brown, Susan J., Schiff, Sherry L.
• Format: Article
• Language: English
• Subjects: Capital costs; Denitrification; Energy costs; Groundwater; Nitrogen; Nitrogen - analysis; Oxidation-Reduction; Phosphates; Phosphorus; Removal; Septic tanks; Septic wastewater; Sewage; Sustainability; Tin; Waste Disposal, Fluid; Wastewater; Wastewater disposal
• ISSN: 0017-467X; 1745-6584
• DOI: 10.1111/gwat.13316

Monitoring of a seasonal‐use, on‐site wastewater disposal system (septic system) in Canada, over a 33‐year period from 1988 to 2021, showed that during recent sampling the groundwater plume had TIN (total inorganic nitrogen) averaging 12.2 mg/L that was not significantly different than early values, representing 80% removal, whereas SRP (soluble reactive phosphate), although higher than early values averaging 0.08 mg/L, was still 99% lower than the effluent concentration. Evidence suggests that the anammox reaction and possibly also denitrification contribute to TIN removal, whereas SRP removal is primarily the result of mineral precipitation. Most of the removal occurs in close proximity to the drainfield infiltration pipes (within about 1 m) demonstrating that reaction rates are relatively fast in the context of typical groundwater plume residence times. This long‐term consistency demonstrates that sustainable nutrient treatment can be achieved with conventional on‐site wastewater disposal systems that have low capital costs and require minimal energy input and maintenance. Groundwater monitoring that encompasses three decades of operation of a household septic system, has revealed remarkably consistent nutrient removal that is insightful with respect to potential removal processes. Considering that 25% of the U.S. population treats wastewater in septic systems and that on‐site wastewater treatment is likely to gain momentum on the road to a net‐zero‐society, this demonstration of sustainability should garner considerable interest.