Abstract:

Soil infiltration system is of great significance for the treatment of rural decentralized domestic sewage. However, the system can be blocked easily and the reaeration performance is poor, which limits the application. To improve the system permeability and the ammonia nitrogen removal rate, different proportions of mineral particles were added to the local brown soil to alter the porosity. The contaminations removal effects under different hydraulic loads were analyzed and the microbial response was revealed based on high-throughput sequencing and PICRUSt2 function prediction. The results showed that the {{\mathrm{NH}}_4}^{+}-N removal rate of the zeolite system (which completely replaced the soil) was 91.1% under the hydraulic load of 0.1 m³·m^-2·d^-1. The Unclassified_ f_ Enterobacteriaceae, Arthrobacter, Bacillus and other bacteria were naturally enriched, which rely on simultaneous nitrification aerobic denitrification achieving the highest nitrogen removal rate, but the phosphate removal rate was only 14%. When the soil proportion was 30%, the {{\mathrm{NH}}_4}^{+}-N removal rate was 93.4%, with the highest abundance of functional genes related to nitrification. It is a scientific ratio for constructing a nitrification module, and the phosphate removal rate increases to 25%. When the soil accounts for 50% or more, the gene abundance of nitrification function decreases and the anoxic environment increases, which is a suitable ratio for constructing a denitrification module. However, the functions of soil indigenous microorganisms are mainly nitrogen fixation and organic matter assimilation or utilization (Actinobacteria, Acidobacteria and Chl-oroflexi). It is thus difficult for the organic matter involved to be used for denitrification. This study provides a scientific basis for improving nitrogen purification efficiency, biodiversity and stability of brown soil area soil infiltration system, as well as theoretical support for future establishment and optimization of modular infiltration systems.

Key words: decentralized domestic sewage, soil/sand ratio, soil infiltration, functional microorganism, enzyme activity