Studies on rhizospheric bacteria of phragmites in constructed wetlands

Abstract

Treatment of different wastewater using macrophytes vegetated constructed wetland reveals its potential in terms of significant reduction in BOD, COD, suspended solids, total solids, total nitrogen, heavy metals along with remediation of xenobiotics, pesticides and polyaromatic hydrocarbons. The rhizosphere of macrophytes such as Phragmites, Typha, Juncus, Spartina and Scirpus serves as an active and dynamic zone for the microbial degradation of organic and sequestration of inorganic pollutant resulting in successful treatment of domestic, textile and other effluents. Up to 2049 6648 mg metal per gram dry weight of plant biomass are found to accumulate in plant parts i.e. shoots and roots. Major metal removal mechanisms are bioaccumulation in plant parts, phytoextraction and phytostabilization. Different wastewaters treated through this technology are industrial, domestic, dairy, pesticides, PAHs, and xenobiotics containing effluents. The present study enables usability and effectiveness of RSM for constructed wetland modeling and its optimization in wastewater treatment studies. Treatment of domestic wastewater using constructed wetland system vegetated with Phragmites australis was studied at lab scale. Response surface methodology (RSM) a mathematical model was employed for analyzing the effect of independent factors (inlet flow rate, outlet flow rate, retention time) on wastewater parameters e.g. electrical conductivity, BOD5, COD, nitrates, phosphates, total solids, suspended solids, heavy metals in order to maximally treat wastewater. All independent variables were standardized using central composite design matrix utilizing different run orders. Average hydraulic loading of wastewater was 0.0104- 0.0208 cm3/day in each system. Treatment of wastewater was best obtained with 22.5ml/min of inlet and 9ml/min of outlet and 12.5 hrs of retention time. A reduction of 60- 67% was obtained in some parameters like total solids, BOD5, COD, and heavy metal concentration as compared to the control unplanted system.