Arsenic phyco-remediation by Cladophora algae and measurement of arsenic speciation and location of active absorption site using electron microscopy

Provision of clean drinking water remains a world-wide necessity, especially so for arsenic-affected regions where numerous physico-chemical methods have been developed for water remediation including adsorption, ion exchange, biosorption, solar stills, etc. Of these, several methods employ regeneration of media necessitating arsenic monitoring on a continuous basis, hence involving skilled operation or alternatively removal of arsenic-enriched concentrated brine into the environment. This study investigated the possibility of employing living algae for phyco-remediation of arsenic-enriched water rejects. Locally available algal species like Cladophora, Hair algae, Spirogyra were screened for arsenic uptake potential. It was found that Cladophora species can survive in an arsenic concentration of up to 6 mg/L in water and at a concentration of 80 g/L Cladophora can biosorb nearly 100% arsenic from water in a contact time period of up to 9-10 days after which desorption starts. HPLC coupled with ICPMS was used for arsenic speciation using both anionic and cationic chromatographic exchange systems and it was found that Cladophora species has a presence of arsenite, arsenate, arsenosugar, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). Electron microscopy investigation further confirmed the biosorption of arsenic by Cladophora algae.