Physical and biological removal of Microcystin-LR and other water contaminants in a biofilter using Manganese Dioxide coated sand and Graphene sand composites.

Sand as a filter media is often challenged by the presence of organics in the form of natural organic matter, metal ions, and various micropollutants in the source water. It is mainly due to the presence of limited active adsorption sites and low surface area that governs an ineffective adsorption potential of the sand material. Herein, graphitized sand was synthesized to tackle the above limitations using two sugar solution sources: a) brewery effluent (as a low-cost solution) (GS1) and; b) sucrose solution (GS2). GS1 showed 68%, 60%, and 99% higher maximum adsorption constant (qmax) for divalent metal ions: iron, copper, and manganese, respectively as compared to raw sand (RS). Coating of MnO2 over the graphitized sand (GSMs: GS1M and GS2M) further helped in Microcystin-LR (MC-LR) removal (3%-9%) when inoculated with MC-LR-degraders, but was not as effective in removing metals, organic carbon and nitrogen when compared to just graphitized sand (GS1 or GS2). Inoculating GS and GSMs (for both sugar sources) not only helped in higher MC-LR removal (10%-15% more) but also enhanced the removal of other water contaminants including metals, organic nitrogen, and carbon. GS1 showed 20% and 50% more MC-LR removal than the sand material when tested at a low and high initial concentration of MC-LR (5 µg/L and 50 µg/L). The highest breakthrough period was obtained for GS1 filter using 1 mg/L Rhodamine-B dye, which was 12 times (48 min) more than the raw sand filter and almost 2.5 times (second best, 21 min) than GS1M. After three cycles of regeneration and reuse of GS1 filter, a decrease of just 14% in saturation adsorption capacity indicated its high reusability aspects.