Effects of domestic sewage from different sources on greenhouse gas emission and related microorganisms in...

Reusing domestic sewage for crop irrigation is a promising practice, particularly in developing countries, since it is a substitute for chemical fertilizer and reduces water contamination. More attention was paid to the effect of sewage irrigation on crop yield and soil nutrients, but little attention was paid to greenhouse gas (GHG) emission from straw-returning paddy fields. In this study, a soil column monitoring experiment was conducted to assess the effects of untreated domestic sewage (dominated with ammonia) and treated domestic sewage (dominated with nitrate) irrigation on methane (CH₄), nitrous oxide (N₂O) emission, and related soil microorganisms in straw-returning paddy fields. Results showed that straw-returning dramatically promoted CH₄ emission but had little effect on N₂O emission. Both untreated and treated domestic sewage irrigation decreased CH₄ emission of straw-returning paddy whether nitrogen fertilizer applied or not. The mitigating effect of treated sewage irrigation on CH₄ emission was greater than untreated sewage irrigation. CH₄ emission had a significant correlation with the abundance of soil methanogens and methanogens/methanotrophs. N₂O emission increased with untreated or treated domestic sewage irrigation, although the total N input, including the N carried by sewage water, was the same for all treatments. No significant correlation between N₂O and denitrification functional genes was found in this study. Treated domestic sewage irrigation reduced the global warming potential (GWP) by 66.7%, but untreated domestic sewage had no evident influence on the GWP. Results indicated that treated domestic sewage irrigation could significantly inhibit CH₄ emission and the GWP by decreasing the ratio of methanogens to methanotrophs, and is promising in mitigating GWP from straw-returned paddy fields.