Evaluation of the removal performance in long-term operation of bioaugmented subsurface wastewater infiltration systems under a high hydraulic loading rate

To enhance the pollutant removal performance of a subsurface wastewater infiltration system (SWIS) used in decentralized treatment of domestic sewage, two nitrogen removing strains were isolated from a SWIS with high removal efficiency and inoculated into another SWIS. Three SWISs were analyzed: a sterilized SWIS (system 1), a control SWIS (system 2), and a bioaugmented SWIS (system 3). Under the conditions of 0.28 m(3)/m(2) center dot d hydraulic loading rate and 716 d running time, the removal capacities of COD, NH4+-N, TN and TP of system 3 were 167.19 +/- 14.21 mg/L middot d, 23.85 +/- 0.74 mg/L middot d, 25.21 +/- 0.96 mg/L middot d and 6.46 +/- 0.06 mg/L middot d, respectively. Correspondingly, the removal efficiencies of COD, NH4+-N and TN were 89.63%, 92.69%, and 86.95%, respectively, which were 6.41%, 6.45%, and 11.48% higher than those of system 2 and 63.01%, 55.15%, and 51.27% higher than those of system 1. The concentrations of COD, NH4+-N, TN and TP of system 3 stabilized at depths of 130 cm, 110 cm, 150 cm, and 130 cm, respectively. Additionally, both the number of nitrifying/denitrifying bacteria and the nitrate/nitrite reductase activity (NRA/NIRA) showed that the nitrogen removal zone was 90-130 cm deep. The coefficients of determination (R-2) between NO3--N concentrations and the number of denitrifying bacteria/NR activities in system 3 showed the greatest correlation, which were 0.97 at 150 cm and 0.92 at 90 cm. Bioaugmentation by the re-inoculation of strains isolated from a SWIS into new SWIS could be an ideal method to improve the performance and service life of SWISs. (C) 2021 Published by Elsevier B.V.

Automated summary

The study focused on enhancing the pollutant removal performance of subsurface wastewater infiltration systems (SWIS) by re-inoculating nitrogen removing strains, demonstrating that the nitrogen removal zone at depths of 90-130 cm showed the highest efficiency.