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

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 m(3).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 m(3).m(-2).d(-1), which were simultaneously lower than Chinese criteria for water discharge from municipal waste water treatment plants. The number of bacteria, nitrifying bacteria and denitrifying bacteria in dewatered sludge as microbial inoculum for SWTS were higher than that in SWTS 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.