An Integrated Study On Constructed Wetland For Rural Sewage Treatment And Bioenergy Production

Inadequate sanitation,dwindling natural oil reserves,and global warming are aggravating issues in the world.Therefore,initiatives are being undertaken to address sanitation and to deflate the greenhouse gases and energy crisis.The 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.With this objective,biomass availability for bioenergy production could be ensured alternately by exploring non-conventional plant species constructed wetland vegetation for wastewater treatment and utilization of their biomass for Lignocellulosic ethanol production.Here,seven horizontal sub-surface flow constructed wetlands（HSFCWs）were entrenched,two were lined with either chemical（limestone,LS）or organic（sawdust,SD）substrates,five were cultured with divergent plant species as well as introduced biological（Ipomoea aquatica-IA）system in the floating-bed constructed wetland（FBCW）to enhance the performance of constructed wetlands（CWs）.Among the seven,two HSFCWs were left unplanted and packed with limestone（HSFCW-LS）,sawdust（HSFCW-SD）.Four species were selected for mono-and poly-culture,namely;Ipomoea aquatica（water spinach）,Canna indica（Indian shot）,Iris pseudacorus（yellow flag）,and Oryza sativa（rice）.These plants were grown individually as well as poly-cultured in HSFCWs,in order to measure the pollutants removal efficiency and plants growth parameters.Meanwhile,one FBCW was planted with Ipomoea aquatica（FBCW-IA）under natural conditions.Through this approach,sewage was fed to HSFCWs as an influent,and passed through these cultivated CWs and unplanted CWs for wastewater treatment.Every time same sewage wastewater was used as an influent in each fortified CW.Sewage wastewater was replaced weekly,for a total of 12 weeks of experimentation.Wastewater sampling was done for influent at the inlet in the beginning and that of effluent from the outlet after a week of treatments.Quality of raw wastewater during12 weeks of experimentation remained almost uniform and below the wastewater standards.Cumulative data of treated wastewater depicted that collectively,the CWs having polyculture or mixed plantation（HSFCW-MP）,as well as in monoculture HSFCW-IA and FBCW-IA achieved the highest performance in the removal of total nitrogen（TN）,NH4⁺–N,and total phosphorus（TP）with average removal efficiencies of 76,94 and 94.3%,respectively.Whereas,HSFCW-SD,Iris pseudacorus（HSFCW-IP）,and Canna indica（HSFCW-CI）performed better for FC and TSS with corresponding removal efficiency between 64%–77%respectively.While HSFCW-LS and HSFCW-OS showed average performance.Moreover,I.aquatica had 215 cm vine length,and C.indica had 273 g fresh weight per plant.Ipomoea aquatica also produced the highest biomass yield of 4.6 kg m^–2.This study concludes that the performance of the biological methods of macrophyte cultivation such as FBCW-IA,HSFCW-MP,and HSFCW-IA was significantly superior to chemical and organic substrates,so it could be a more effective,economical,and sustainable approach for sewage treatment.In addition,for bioethanol production,alkali–autohydrolysis combined pretreatment followed by enzymatic hydrolysis with two successive incubation periods（12 and 24 hours）were employed.It was found that prolonged incubation of hydrolysate for 24 hours increased the carbohydrate yield.Oryza sativa biomass rendered greater carbohydrate and bioethanol concentration(1.5 mg L^-1).Hence,the current research concludes that non-conventional CW plants have a robust potential to purify wastewater as well as to provide feedstock for Lignocellulosic ethanol production.