Use of dewatered sludge as microbial inoculum of a subsurface wastewater infiltration system: effect on start-up and pollutant removal

Abstract

Brown earth–based subsurface wastewater infiltration systems (SWISs) inoculated with/without dewatered sludge were constructed and operated under the same  conditions to boost the application of SWIS in brown soil areas. Start-up period of SWIS with dewatered sludge was 28 days, 12 days shorter than that of SWIS  without dewatered sludge. COD, NH₃-N and TN removal efficiencies of dewatered sludge as microbial inoculum for SWIS were higher than that of SWIS without  dewatered sludge under hydraulic loading rates (HLR) of 0.04, 0.07, 0.1 and 0.13  m³·m⁻²·d⁻¹. Effluent concentrations of COD, NH₃-N and TN in the SWIS  inoculated with dewatered sludge were 44.51±4.13, 7.35 ± 0.24 and 14.03 ± 0.31 mg·L⁻¹ under HLR of 0.13 m³·m⁻²·d⁻¹, which were simultaneously lower than  Chinese criteria for water discharge from municipal wastewater treatment plants.  The number of bacteria, nitrifying bacteria and denitrifying bacteria in dewatered  sludge as microbial inoculum for SWIS were higher than that in SWIS without  dewatered sludge under the same HLR. The results will be helpful in promoting the application of dewatered sludge as microbial inoculum in brown earth–based SWISs for the purpose of shortening start-up period, effecting high levels of pollutant  removal and recycling waste.

Keywords: subsurface wastewater infiltration system, dewatered sludge, start-up, inoculum