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Various layered double hydroxides (LDHs) were prepared by the co-precipitation method using the most common divalent and trivalent metal precursors. The resulting LDHs were studied for their performance in removing phosphate from aqueous test solution. The results have clearly demonstrated the influence of Ca and Mg as precursor metals in synthesizing LDH compounds for removing phosphate. For the same LDH's dose, more phosphorus was removed by Ca-based LDHs than Mg-based LDHs. Real effluent from a wastewater treatment plant with high phosphate concentration (3.4-10.4 mg-P/L) can also be treated with >90% removal by both Ca-and Mg-based LDHs depending on the selection of suitable dose. For Ca-based LDHs, the main removal process was observed to be as calciumphosphate precipitation. Due to the loss of layered structure after first sorption/precipitation operation, Ca-(Fe or Al)-LDHs cannot be regenerated for reuse. However, Mg-based LDHs showed potentially applicable for the regeneration and reuse due to their stable nature in aqueous phase than Ca-based LDHs. On the other hand, when choosing CaMg-based LDHs for the phosphorus removal, the nature of Ca dissolution from such LDHs needs to be taken into account although they were demonstrated to be reusable with the efficiency of phosphate removal up to 64% at the fourth cycle.

Arsenic (As) causes health concerns due to its significant toxicity and worldwide presence in drinking water and groundwater. The major sources of As pollution may be natural process such as dissolution of As-containing minerals and anthropogenic activities such as percolation of water from mines, etc. The maximum contaminant level for total As in potable water has been established as 10 µg/L. Among the countries facing As contamination problems, Bangladesh is the most affected. Up to 77 million people in Bangladesh have been exposed to toxic levels of arsenic from drinking water. Therefore, it has become an urgent need to provide As-free drinking water in rural households throughout Bangladesh. This paper provides a comprehensive overview on the recent data on arsenic contamination status, its sources and reasons of mobilization and the exposure pathways in Bangladesh. Very little literature has focused on the removal of As from groundwaters in developing countries and thus this paper aims to review the As removal technologies and be a useful resource for researchers or policy makers to help identify and investigate useful treatment options. While a number of technological developments in arsenic removal have taken place, we must consider variations in sources and quality characteristics of As polluted water and differences in the socio-economic and literacy conditions of people, and then aim at improving effectiveness in arsenic removal, reducing the cost of the system, making the technology user friendly, overcoming maintenance problems and resolving sludge management issues.

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BACKGROUND: Layered double hydroxide compounds (LDHs) have been applied for the removal of oxyanions including arsenate (As(V)). However, the aim of this present research is to develop a LDH to treat arsenite (As(III)). Both batch and column sorption studies were conducted to assess the effect of LDH dosage, contact time, solution pH and initial As(III) concentrations on the As(III) removal performance. The potential re-use of this sorbent was also investigated.