Subsurface wastewater infiltration systems for nitrogen pollution control.

ABSTRACT

Subsurface wastewater infiltration systems (SWISs) are suggested to be a cost-effective and environmentally friendly method for sewage treatment. However, a comprehensive summary of the relevant mechanisms and optimization methods for nitrogen (N) removal in SWIS is currently lacking. In this review, we first summarize the N transformation mechanisms in SWIS. The impact of operational parameters on the N removal efficiency is then delineated. To enhance pollutant removal and minimize resource wastage, it is advisable to maintain a wet-dry ratio of 11 and a hydraulic loading rate of 8-10 cm/day. The organic load should be determined based on influent characteristics to optimize the balance between sewage treatment and nitrous oxide (N2O) emission. Finally, various strategies and modifications have been suggested to enhance pollutant removal efficiency and reduce N2O emissions in SWIS, such as artificial aeration, supply electron donors, and well-designed structures. Overall, greater emphasis should be placed on the design and management of SWIS to optimize their co-benefits while effectively controlling N pollution. PRACTITIONER POINTS SWISs are often considered black boxes with their efficiency depending on hydraulic characteristics, biological characteristics, and substrate properties. Biological nitrification coupled with denitrification is considered to be the major N removal process. Increasing the reduction of N2O to the inert N2 form is a potential mechanism to mitigate global warming. Strategies such as artificial aeration, supply electron donors, and well-designed structures are suggested to improve N removal performance.