Study on Effectiveness of Intervention of a Vertical Flow Constructed Wetland in between Septic Tank and Soak Pit for the Treatment of Septic Tank Effluent

Abstract

Septage comprises the solid and liquid constituents of any primary treatment system, including a Septic Tank. In this study, the wastewater collected from a septic tank is passed through a partially converted anaerobic filter, and a vertical flow constructed wetland (VFCW) before being sent to a soak pit. The main objective of this case study was to check the effectiveness of incorporating a VFCW between a septic tank and a soak pit to bring down the consequences created due to effluent seepage from soak pits to the groundwater. Conventionally, the effluent gets directly passed to soak pits after primary onsite treatment in the septic tank. The soak pit walls made of porous materials allow the gradual seepage of final effluent into the ground, polluting the groundwater reserves. We analyzed the septic tank effluent from 60 households wherein the effluent was let off into the soak pits. The various parameters analyzed with their averages were 393.83 ± 293.41 mg.L-1 for COD, 151.48 ± 94.37 mg.L-1 for BOD, 30.81 ± 13.05 mg.L-1 for NO3-, 23.35 ± 13.54 mg.L-1 for PO43-, 7.35 ± 0.31 for pH, 184.05 ± 163.20 mg.L-1 for TSS, 3.05 x 107± 2.04 x 108 CFU.100mL-1 for TC. Therefore, it is certain that the final effluent being sent into soak pits after primary treatment does not meet the Central Pollution Control Board (CPCB) discharge standards. In this case study, we were able to obtain final effluent values after VFCW treatment as 55.72 mg.L-1 for COD, 12.12 mg.L-1 for BOD, 10.2 mg.L-1 for NO3-, 3.74 mg.L-1 for PO43-, 7.41 for pH, 8.37 mg.L-1 for TSS, 379.27 mg.L-1 for TS and 51.9 CFU.100mL-1 for TC. With this case study, we were able to resolve this impediment by bringing down the values of all the parameters considered while analyzing under the limits of discharge standards set by CPCB. The removal efficiency of COD, BOD, NO3-, PO43-, pH, TSS, and TC after wetland was found to be 89.46%, 88.051, 63.484, 44.37%, 3.41%, 98.47%, 97.71%, 97.19% respectively. The study has proven that with the introduction of another decentralized treatment system between a septic tank and soak pit, it is safe to dispose of the effluent into soak pits, thereby reducing the chances of groundwater pollution considerably.