## 5 Household Filter for Arsenic Removal for Drinking Water  
A major and impactful outcome from the various reported approaches for treatment of groundwater for removal of arsenic is their adoption in designing potable household filters that have been successfully used for treatment of groundwater as a source of domestic drinking water, particularly in under-developed countries. Several designs of arsenic filters have been developed, proposed and evaluated. Yet, there are still emerging new developments in this area. One of the most successful domestic treatment units is the SONO filter which is a two-bucket system [158]. The composition of the upper bucket includes a composite iron layer (4-5 cm thick) of a mixture of metal iron and iron hydroxides. This layer is then covered with sand layers. Also, sand and charcoal layers are included in the lower bucket for removal of the iron hydroxides and residual organic matter. Figure 5 shows that the arsenic contaminated groundwater passes through coarse sand, composite iron matrix (CIM), brick chips and wood charcoal [158]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Treatment Process As(V)** & **Removal Efficiency** & **As Concentration** \\ \hline Oxidation and Filtration & & \\ \hline Aeration and filtration & \(>\)90\% & 300 \(\mathrm{\SIUnitSymbolMicro g}\)As(III)/L \\ \hline Fe\({}_{2}\)O\({}_{3}\) filter & \(>\)95\% & 100–400 \(\mathrm{\SIUnitSymbolMicro g}\)As(III)/L \\ \hline As(III) oxidation by (OCI\(-\)) & & \\ and Fe precipitation & & \\ \hline Co-precipitation & & \\ \hline Enhanced lime softening & 90\% & \\ \hline Enhanced coagulation/filtration with & \(<\)90\% & \\ album & & \\ \hline Enhanced coagulation/filtration with & 95\% & \\ ferric chloride & & \\ \hline Adsorption & & \\ \hline Iron doped activated carbon & \(>\)95\% & 311 \(\mathrm{\SIUnitSymbolMicro g}\)As/L \\ \hline Hybrid activated alumina & \(>\)95\% & 2–20 \(\mathrm{\SIUnitSymbolMicro g}\)As/L \\ \hline Iron based sorbents & Up to 98\% & \\ \hline Layered double hydroxide & & \\ (LDH) & Up to 96\% & 300 \(\mathrm{\SIUnitSymbolMicro g}\)As(V)/L \\ \hline Modified zeolites & Up to 99\% & 100–400 \(\mathrm{\SIUnitSymbolMicro g}\)As/L \\ \hline Modified clays & Up to 80\% & 0.15 \(\mathrm{\SIUnitSymbolMicro g}\)As \\ \hline Laterite and limonite & Up to 95\% & 500 \(\mathrm{\SIUnitSymbolMicro g}\)As/L \\ \hline Adapted and modified from [75]. & & \\ \end{tabular}
\end{table} 
Table 3: Treatment efficiencies reported for some arsenic removal processes. The SONO filter which is manufactured in Bangladesh utilizes a composite iron matrix (CIM) to remove arsenic by complexation reactions on the metal surface as follows [158]:  
\[\text{FeOH}+\text{H}_{2}\text{AsO}_{4}-\rightarrow\text{FeHAsO}_{4}-+\text{H}_{ 2}\text{O}\text{ and}\]  
\[\text{FeOH}+\text{HAsO}_{4}{}^{2-}\rightarrow\text{FeAsO}_{4}{}^{2-}+\text{H}_ {2}\text{O}\]  
These reactions occur without the need for any pre- or post-chemical treatment. Also no regeneration is required and no toxic wastes are produced [158]. The resulting spent material from the arsenic removal process is a solid self-contained iron-arsenate cement which is non-toxic and does not leach out when in contact with rainwater. The arsenic concentrations in contaminated groundwater used in one study ranged from 5-4000 \(\mu\)g/L, but these were reduced to 3-30 \(\mu\)g/L after treatment [158]. The treated waters from the filter were found to meet the limits of 10 \(\mu\)g/L and 50 \(\mu\)g/L set by WHO and the Bangladesi government, respectively.