Science & Technology

India is likely to be water scarce in future therefore rain water harvesting, water conservation, water pollution control, recycling and reuse of treated wastewater is necessary. Various methods have been developed to treat wastewater. Among them, constructed wetland systems (CWS) have gained importance as natural alternative to other physicochemical treatment methods for treating domestic wastewater. In the present study, performance of a two stage constructed wetland system treating domestic wastewater was evaluated. The study involved use of three locally available materials as wetland substrate as well as artificial aeration and addition of microbial consortium of Pseudomonas aeruginosa and Bacillus sp. in two stage CWS. The two stage CWS consisting of unplanted CWS followed by a planted CWS were used in the study. The gravel, sugarcane bagasse and rice-husk were the main media in unplanted CWS. The Ranunculus sceleratus, Veronica anagallis-aquatica and Eichhornia crassipes macrophytes were used in planted CWS. The systems were operated in batch mode with and without recirculation. The domestic wastewater with COD 224–352 mg/L, BOD 140–220 mg/L, TN 8.7–11.9 mg/L, TP 1–1.7 mg/L and bacterial count 2.80 x 10¹⁰-8.0 x 10¹⁰ CFU/100 mL was treated in CWS. The rice-husk followed by macrophyte species reduced the total nitrogen to zero whereas gravel and sugarcane bagasse followed by the plants reduced total nitrogen to a very low value of 0.6–1.1 mg/L at an overall detention time of 6 days. There was no significant removal of total phosphorus in unplanted CWS. Simultaneous removals of COD (50–100%), BOD (42–100%), TN (79–100%), TP (86–100%) and bacterial count (> 99%) were observed. Overall, Veronica anagallis-aquatica was more effective than Eichhornia crassipes and Ranunculus sceleratus. The results show that treated effluent from CWS was meeting standards for discharge in the environment.