Appraisal of a simple arsenic removal method for ground water of Bangladesh

Abstract

A simple three‐pitcher (locally known as ‘3‐kalshi') filtration assembly made entirely from readily available local materials is tested for its efficacy in removing arsenic from the groundwater of Bangladesh. In a 3‐ kalshi assembly, the first kalshi has iron chips and coarse sand, the second kalshi has wood charcoal and fine sand, and the third kalshi is the collector for filtered water. About 240 L of arsenic contaminated groundwater and groundwater spiked with high concentrations of both As(III) and As(V) were filtered. Analytical measurements were performed by using anodic stripping voltammetry (ASV) for trace level As(III) and As(total) and redox potential. Atomic absorption spectrometry with graphite furnace and Zeeman background correction (AASGF‐Z) and inductively coupled plasma atomic emission spectrometry (ICPAES) were used to validate measurements of arsenic and measure 24 other metals before and after filtration. Total Fe, ionic conductivity, E_h, pH, temperature and flow rates were measured at various stages of the filtration process. It has been shown that more toxic As(III) can be removed from 800 ppb to below the detection limit of 2 ppb. The As(total) can be removed to a concentration below 10 ppb for most samples even at the highest input concentration of 1100 ppb As(total). The dissolved iron concentration decreased from an average 6000 ppb to 200 ppb. Calculations based on compound formation and arsenic adsorption on hydrous ferric oxide show that, with a constant input of dissolved iron the arsenic removal capacity increases linearly with each filtration. Although the role of metallic iron was difficult to quantitate, it provided excess soluble iron in the filtering media of the second kalshi. The wood charcoal was used to remove any organic impurities that may be present in groundwater. The redox potential change shows speciation of iron in agreement with literature data. The decrease in conductivity by 35% of the original value indicates substantial removal of dissolved ions. This is also supported by ICPAES measurement. The filtered water remained crystal clear for months and free from most toxic metal ions. The daily capacity of the 3‐kalshi system varies from 42–148 L/day. The final water quality meets and exceeds the guideline values suggested by USEPA, World Health Organization and Bangladesh. We suggest the use of this simple setup to make potable water.

Key words:

• Arsenic removal
• groundwater
• Bangladesh

Notes

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