Abstract: Domestic wastewater was infiltrated through a subsurface wastewater infiltration system (SWIS) for depth denitrification treatment after precipitation. Influence of carbon source addition on nitrogen removal， denitrification microbial activity， N₂O generation and conversion rate was analyzed. The results showed that carbon source was conductive to the promotion of microbial denitrification， but adding excess would promote substantial growth of other bacterial groups and inhibit the advantages of denitrification activity and nitrogen removal efficiency. When the organic content increased from 2.0% to 9.5%， removal efficiency for COD， NH⁺₄-N and TN decreased by 10.9%， 19.5% and 24%， respectively and N₂O generation and conversion rate declined. Correlation analysis showed that the nitrifier and denitrifier quantity exhibited significantly positive and negative correlation with N₂O conversion (R²=0.994 and 0.959)， respectively， suggesting that N₂O production was the result of the interaction of nitrification and denitrification， and mainly derived from nitrification process in upper layer.

Key words: subsurface wastewater infiltration system, domestic wastewater, carbon source, nitrogen removal, N₂O