Introduction: Considering the problem of eutrophication of the water bodies, phosphate removal from water has emerged as a research of topical interest. The present study aims to investigate the efficacy of Canna lily-based constructed wetland to remove phosphate from wastewater. The translocation of phosphate in plant tissue and its biochemical transformation in sediments is also studied to understand its accumulation and recirculation within the system. Results: The removal of phosphate stabilized at around 50% in the present study and plant uptake was found to be the major removal mechanism. Average removal was 167 mg/m 2 day for total phosphate and 84 mg/m 2 day for available phosphate for an initial loading rate of 200 mg/m 2 day and 85 mg/m 2 day, respectively, at a HRT of 24 h. Most of the phosphate concentrated in above ground tissue of plant and its relative accumulation was maximum in flowers. Fractionation of phosphate in sediments confirmed removal by sediments with an accumulation of apatite phosphate (Ca and Mg bound), but release of non-apatite form (Fe and Al bound). Conclusion:The study concludes that Canna-based constructed wetland can be an effective tool for phosphate removal from wastewater and sediments particularly under tropical conditions. Regular harvesting of above ground tissue of Canna can result in nutrient export from the system, whereas autochthonous addition may result in recirculation.

The rotating biological contactor (RBC) process offers the specific advantages of a biofilm system in treatment of wastewater for removal of soluble organic substances and stabilisation of nitrogen compounds. Being a unique adaptation of the moving-medium biofilm system, it facilitates easy and effective oxygen transfer. However, process optimisation and adaptability under different conditions remain challenging tasks for the efficient use of this technology. Although modelling helps to study system performance under various external conditions, satisfactory mathematical representation is lacking due to the dynamic nature of the RBC system. In this work, it has been attempted to frame a mathematical model for a three-stage RBC process in simple and realistic ways. The model is based on the well-known principles of one-dimensional mass transfer and transport of substances. The biochemical conversion process is adopted from the Activated Sludge Model No. 3 which represents a mixed-culture biomass environment. Owing to the dynamic nature of oxygen transfer, which is the typical limiting substrate in municipal wastewaters, the boundary layer is assumed to be completely mixed and concentrations averaged over the entire volume. A part of the boundary layer is assumed to be exposed to air and the rest submerged in bulk liquid at all times. The model results are compared with laboratory-scale experimental data available at 25 'C. Sensitivity analysis is performed with the model to study the significance of variation of different system parameters or the surrounding environment. In essence, the model helps to explore the flexibilities within a RBC system and optimise the process design accordingly.

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