Publication: Removal of iron, manganese and natural organic matter from synthetic groundwater by using limestone and zeolite immobilized with iron oxidising bacteria (iob)
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Date
2023-02-01
Authors
Lee Wen Si
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Abstract
Groundwater is one of the alternatives to surface water that can be used to complement the growing water consumption caused by population growth and industrialization. However, with the high content of heavy metals present in the groundwater, treatment is needed to treat the pollutants. In this study, a column study is conducted to observe the elimination of iron (Fe), manganese (Mn) and natural organic matter (NOM) in the groundwater under different retention times by using limestone and zeolite immobilised with iron-oxidising bacteria (IOB). The IOB is isolated from the existing sand filter collected from Kampung Chap Water Treatment Plant, Bachok. Rossellomorea sp. representing an IOB was found from the isolation process and was further cultured in the laboratory for immobilization into the limestone and zeolite as replacement materials for the sand filter. When the limestone assisted with the Rossellomorea sp., the elimination of Fe and Mn was 98% and 86%, respectively, while zeolite assisted with Rossellomorea sp., the elimination of Fe and Mn was 99% and 89%, respectively. The result shows that the limestone and zeolite immobilized with IOB are higher than the limestone without IOB (Fe: 86%; Mn: 82%) and zeolite without IOB (Fe: 94%; Mn: 94%). The presence of Rossellomorea sp. enhances the Fe oxidation, resulting in increased ferric iron precipitation in the column media. The removal of NOM also increases when Rossellomorea sp. is immobilised because the Rossellomorea sp. consumes the NOM as a carbon source. When the flow rate increased from 2 mL/min to 4 mL/min, the breakthrough time was reduced due to low retention time. The Thomas model and Yoon-Nelson model were performed to evaluate the adsorption behaviour revealing that a mechanism of adsorption and ion exchange occurred, in which the elemental compositions of Fe and Mn in the limestone and zeolite were increased after the experiment. The SEM and BET analysis demonstrate the pore size of the zeolite increased from 12.3 nm to 24.87 nm when Rossellomorea sp. was immobilised, whereas pore size and surface area were not discovered in the limestone after immobilisation which pore and surface area were covered by the IOB. The SEM analysis also demonstrates the formation of ferric precipitation on the surface of limestone and zeolite that is retained in the column. The total coliform (MPN) increases due to the Rossellomorea sp. present that promotes the growth of coliform bacteria. In conclusion, the immobilisation of limestone and zeolite with Rossellomorea sp. is a sustainable and potential technique to extract the Fe, Mn and NOM in the groundwater.