Nitrogen removal from rural domestic wastewater by subsurface wastewater infiltration system: A review

Subsurface wastewater infiltration system (SWIS) has been widely used in rural decentralized sewage treatment due to its low cost, low energy consumption, high efficiency, and other advantages. Numerous researches have reported optimizing the SWIS nitrogen removal process, while the relevant mechanisms and optimization methods have not been well summarized. As such, this review aims to fill the above gaps as follows. Firstly, the SWIS nitrogen removal efficiency and mechanism are outlined, and the role of microorganisms is described in detail. Moreover, the issue of N 2 O emission in nitrogen removal was introduced. Secondly, the usage of different types of fillers in substrate improvement was summarized, highlighting the unique advantages of plants used in SWIS. A clear adjustment range and control method is proposed for system operating parameters such as hydraulic loading rate (HLR), organic loading rate (OLR), carbon-nitrogen ratio (CNR), temperature and dissolved oxygen (DO). Finally, the role of bioaugmentation in nitrogen removal was summarized. The part of conclusion and prospects evaluates the development and application of SWIS in rural areas.