Arsenic Removal by Adsorption and Multilayer Sand Filtration

Arsenic Removal by Adsorption and Multilayer Sand Filtration

Seeram Apoorva, Apoorva (TU Delft Civil Engineering and Geosciences)

Delft University of Technology

CIE 5050-09

2018-12-13

The presence of Arsenic in the groundwater, and eventually in the drinking water is a serious problem in many of the Asian countries. Due to it high toxicity to its removal is very essential. There are many removal technologies for the removal of arsenic such as adsorption, coagulation-filtration, membrane filtration, ion exchange and precipitation. Adsorption is one such technology which is mainly used as it’s a very simple technique. the extent of adsorption is affected by pH, nature of the adsorbent, surface area of the adsorbents. Iron is widely used for the removal of Arsenic from groundwater. The iron which is present in dissolved form in groundwater needs to first get oxidised to hydrous ferric oxides as flocs which provide adsorption sites for arsenic. In this study the effect of pH and Iron dosage on the arsenic removal by adsorption with the available dissolved Iron in the groundwater. The effect of pH on arsenic removal by floc formation of iron with a series of Jar tests were done for Arsenite and Arsenate. Also, the removal of arsenic in a multilayer sand bed (3 layers with Anthracite, Sand and Garnet) was evaluated at three different pH. It was found that pH plays a very important role on Arsenic removal. Arsenite removal was increased with pH whereas Arsenate removal decreased with increase in pH. At pH 5 and at high Fe concentrations, the removal decreases but the effective iron or the iron that flocculated to greater than 0.45µm was quite similar. This was also seen in the particle counter analysis. Iron concentration of 5mg/l was enough to remove Arsenate upto 90% whereas Arsenite needed higher doses of upto 20mg/l to reach 90%. Clear increase in the flocculation was observed in particle counts with the increase of iron concentration. Before the dosing of Iron Arsenic oxidation was seen in the filter bed maybe due to the presence of Arsenic Oxidising Bacteria (AOB). High oxidation efficiency was seen Sand and Garnet layer. The oxidation of Arsenite to Arsenate before dosing iron in the filter was less at pH 8. High resistance was observed in the filter bed within 3 days after backwashing although the removal was quite stable in the three days. After dosing of Iron, high removal of arsenic was seen in Anthracite layer due to the high adsorption of Iron in the Anthracite layer.

Arsenic
Adsorption
Sand Filtration

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