Comparison of floating-bed wetland and gravel filter amended with limestone and sawdust for sewage treatment

Advancements in the design and technology of constructed wetlands for efficient removal of wastewater contaminants are ever in progress to develop situation-based economical systems. Here, we entrenched two horizontal sub-surface flow constructed wetlands (HSFCW) with either chemical, viz. limestone (HSFCW-LS) or organic, viz. sawdust (HSFCW-SD) substrates, and compared them with biological method, viz. growing of water spinach in floating-bed-constructed wetland (FBCW-WS) to enhance the performance of CWs. Same sewage wastewater was used as influent in each fortified CW replicated thrice. Sewage was replaced weekly, for a total of 12 weeks of experimentation. Sampling of raw sewage from influent was undertaken at the inlet in the beginning, and that of treated effluent from the outlet after a week of treatments. Quality of raw sewage used weekly during experimentation remained almost uniform and near to the wastewater standards. Cumulative data of treated wastewater depicted that the FBCW-WS achieved the highest performance in the removal of total nitrogen (TN), ${NH}_4^{+}$–N, and total phosphorus (TP) with average removal efficiencies of 75.9, 90.5, and 94.3%, respectively. Whereas, HSFCW-SD performed better for ${NO}_3^{-}$–N, FC, and TSS with corresponding removal efficiency of 77.5, 64.3, and 74.2% while HSFCW-LS showed average performance. This study concludes that performance of biological method of macrophyte cultivation (FBCW-WS) is significantly superior to chemical and organic substrates, so it could be more effective, economical, and sustainable approach for sewage treatment.