Removal of Manganese and Arsenic from Groundwater using Manganese Oxide Coated Sand
Manganese (Mn) and arsenic (As) are common natural groundwater contaminantsin Bangladesh and many other countries. WHO (2004) recommendedhealth-based drinking water guideline values of0.4 mg/l and 0.01 mg/l for Mn and As, respectively. Removal of dissolved Mnby filtration through granular media (sand) could be an effective treatment method forMn removal from drinking water. This research work was focused evaluation of the effectiveness of different Mn-oxide coated media (synthetic media, prepared media, green sand) in removing Mn and As from water.
Laboratory investigations have been carried out to assess removal of Mn and As in three different types of Mn-oxide coated media: (a) “prepared” Mn-oxide coated filter media (prepared by passing Mn-bearing water through filter columns made up of “Sylhet” sand), (b) “synthetic” Mn-oxide coated media (prepared by treating “Sylhet” sand with MnNO¬3, H2O2and NaOH), and(c) commercially available Mn-bearing “green sand”. The average Mncontentof the “prepared” filter media was about 7,550 mg/kg; average Mn contents of “synthetic” media and “greensand”were 25,250 mg/l and 14,400 mg/kg, respectively.
The three types of Mn-oxide coated filter media have been found to be very effective in removing dissolved Mn from groundwater over a wide range of initial Mn concentration and pH.Results of both column and batch experiments showed that Mn removal efficiency increases with increasing Mn-content of the filter media. Mn removal efficiency also increases with increasing Mn in the influent water and increasing pH (in column experiments). Synthetic Mn-coated media, with the highest Mn content among the 3 media, performed best in removing Mn at higher flow rates. However, the other media (“prepared” media and greensand) also performed wellat slower flow rates. A contact time of about 1.5 minutes was found to be sufficient for almost complete removal of Mn under the experimental conditions employed in this study. Removal of Arsenic [As(III)] in Mn-oxide coated filter media has been found to be strongly dependent on pH and phosphate concentration. Removal of As decreased with increasing pH, especially at pH beyond 7.5.