A novel and an eco-friendly approach for organic dyes degradation using Spirulina platensis cultivated water

Waste water recycling may cater to the water scarcity problems which are prevailing in our daily life. The conventional studies in photocatalytic degradation of organic dyes use some specifically synthesized metal-oxide nanoparticles as photocatalyst, which may leave its traces as residue in degraded water. In this prototypical study, we have reported for the first time about light induced organic dyes degradation of methylene blue (MB), malachite green (MG) and congo red (CR) carried out using a novel photosensitizing agent, Spirulina platensis cultivated water (Spcw). The aim of the present study is to probe a simple, novel, an eco-friendly and a cost effective degradation of dyes without using any chemicals. It was observed that 15 ppm MB, 70 ppm MG and 6 ppm CR got degraded to 100% within 2, 1 and 3 h respectively. The presence of trace amount of elements such as Ca, Cu, Fe, K, Mg, Mn, Na, Mo, Co and Zn and phycobiliproteins found in the Spcw were analyzed using Fourier Transform Infra-Red (FT-IR) Spectroscopy, Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopy (SEM-EDX), UV-vis Spectroscopy, microscopic studies and mineralization studies with TOC, TSS, BOD and COD analysis. The results obtained from various control experiments with fresh medium and dark treatment clearly confirms that the light induced organic dyes degradation occurs only in the Spcw under sunlight irradiation. The effect of pH was studied with the Spcw added dye solutions and also in the degraded water from highly acidic to basic conditions to find the optimum pH. The kinetics of the light induced organic dyes degradation follows pseudo- first order reaction and the mineralization studies of the degraded water meets the water quality standards. The reason behind the photosensitization activity is due to the presence of traces of metal ions and light absorbing phycobiliproteins released during natural cell lysis process.