Effect of amended soil and hydraulic load on enhanced biological nitrogen removal in lab-scale SWIS

To characterize the effect of amended soil on nitrogen removal in subsurface wastewater infiltration system (SWIS), culture, grass carbon, and zeolite were mixed to produce microbial inoculums, and then the optimal microbial inoculums, nutrient substance, cinder, and original soil were mixed to produce the soils through bioaugmentation. Results indicate that the microbial inoculums (culture + 50% grass carbon + 50% zeolite) and the amended soil (12.5% microbial inoculums + 25% nutrient substrate + 12.5% cinder + 50% original soil) have the optimal biogenic stimulating properties, and the adsorption capacity of the amended soil are 1.216 mg-P g −1 and 0.495 mg-N g −1. The laboratory soil column experiment indicates that the efficient mode of nitrogen removal in lab-scale SWIS is adsorption–nitrification–denitrification and the nitrification/denitrification can be enhanced by the application of the amended soil. On average, the SWIS filled with amended soil converts 85% of ammonia nitrogen (NH 4 +-N) to NO x −-N and removes 49.8–60.6% of total nitrogen (TN), while the system filled with original soil removes 80% of NH 4 +-N and 31.3–43.2% of TN at 4–8 cm day −1. Two systems are overloads at 10 cm day −1. It is concluded that the microbial activities and nitrogen removal efficiencies are improved in SWIS after bioaugmentation.