Comparison of the effects between tidal flow and subsurface flow wetlands on sewage treatment

The effects of multi-stage tidal flow(TF) and subsurface flow(SSF) wetlands on the treatment of sewage were compared. The results showed the removals of NH₄⁺-N (ammonia), TN(total nitrogen), SRP(soluble reactive phosphorus), TP(total phosphorus), CODCr(chemical oxygen demand) using the TF wetland increased by 22%, 5%, 1%, 1% and 5% respectively than using the SSF wetland, which suggested the TF wetland was capable of largely enhancing nitrification but slightly on denitrification. The maximum rate of phosphorus and CODCr removal took place in the 1^st unit of both TF and SSF wetlands. The removal rate of NH₄⁺-N in all units of the TF wetland was higher than the SSF wetland, while the first three units of the TF wetland were the dominated sink of TN accounting for 100% TN removal of the system; The 4^th unit contributed negatively to TN removal because the nitrification was strengthened by higher substrate(NH₄⁺-N) concentration, and the denitrification inhibited by lack of labile carbon.