Report on Arsenic-Free Water Filters
Introduction
Arsenic concentration in water varies depending on the source. This report is based on the discussion of the measures of reducing the levels of arsenic in the tube-well water. In this case, three criterions are selected for the study. Each of the methods chosen will enumerate its merits and demerits that suit the application.
Problem
Arsenic is semi-metal element found in the periodic table. It is an odorless, tasteless element that occurs naturally in water, rocks and soils, air, plants and animals.
Arsenic poisoning from various water sources such as well present a significant problem across the globe. The number of lives lost due to arsenic poising is immense and mind-boggling. A large number of the population from such regions as Himalayas and Ganges deltas are affected by the unremitting natural disaster. Apart from death, arsenic poisoning has crippled both physical and mental capabilities. The current existing filtration designs do not eliminate arsenic from contaminated water. Arsenic-free water filter methods address the problem of arsenic contamination. It provides an effective solution by providing appropriate filtration method.
Scope
There are many ways to reduce the concentration of arsenic in water to the acceptable levels. Three criterions used to solve this problem are discussed in this report. These are; coagulation and filtration, membrane technologies, and passing contaminated water over charcoal and sand. We shall look at each of them regarding quality, efficiency, and simplicity. The discussion technique involves; explanation of functionality, efficiency, quality and importance1
Discussion
Criterion 1: Coagulation and filtration method
Explanation
This is the most documented method of arsenic removal. It involves coagulation and filtration using either lime softening or salts. This water treatment will effectively remove many any suspended and dissolved particles in water apart from arsenic. These include; iron, manganese, turbidity, phosphates, and fluorides. The removal of this constituent of water leads to quality improvement yielding to esthetic and healthy benefits. The conditions for removing arsenic are different from removing other constituents such as fluorides and phosphates. Ferric and aluminum salts are commonly used for arsenic removal. Examples of such salts are; ferric chloride, alum, and ferric sulfate. The most excellent arsenic removers among these salts are ferric or aluminum with over 99% removal and a concentration of less than 1µg/L4
In coagulation and filtration method, arsenic is removed through three main mechanisms. Firstly, is through precipitation where the insoluble salts such as Al (AsO4) or Fe (AsO4) are formed. Secondly, is the co-precipitation, and it involves the incorporation of arsenic species into the phase of the growing metal hydroxide. The last mechanism is adsorption, and this is the electrostatic the arsenic to the insoluble surfaces of the metal hydroxide3. Here, the co-precipitation and adsorption are the key stage mechanisms of arsenic removal. After coagulation and sedimentation, the arsenic load is removed through filtration through a 1.0-micron filter. This yields an efficiency of over 96%. The following data in figure 1shows the use of Fe-Mn oxidation in arsenic removal in three municipalities in Bangladesh
Data
Figure 1: use of Fe-Mn in three municipalities in Bangladesh5
Interpretation
If is evident that the efficiency of iron removal is much more than that of arsenic. This method is average arsenic removal on the three municipalities.
Criterion 2: Membrane Technique
Explanation
Selectively permeable membranes are available and consist of a membrane structure that allows some molecules to pass and rejects the rest3. Filtration done with membranes has an advantage of removing many contaminants from water such as salts, various heavy metals and bacteria. There are two types of membrane filtration; low-pressure membranes which include ultrafiltration and microfiltration4. Another membrane filtration technique is high-pressure filtration such as Reverse Osmosis and Nanofiltration. The low-pressure filtration has nominal pore sizes that operated by pressures of 10-30 psi2. The high-pressure membrane has operating pressures of 150-250 psi or sometimes higher than these2
Data
Figure 2: Pore sizes of different membranes and material size subject to filtration4
Interpretation
In figure: 1 shown above, it is evident that the reverse Nanofiltration (NF) and osmosis (RO) membranes have the pores that are reliable in removing arsenic. The two membranes are operated in lateral designs where a small amount of water is allowed to pass through the membrane. This system applies to applicable to household systems where the small amount of treated water is needed for cooking. New generation of membranes has been designed, and they operate at pressures ranging from 40-400 psi4 and rejection efficiency of 96-99%.
The advantages of membrane filtration are; ability to lower the concentration of other components of water, simple disposal of used membranes, minimal operational maintenance, cheap and safe since no chemicals are involved. The disadvantages are; low rate of recovery, relatively high cost of input and operation, and risk of membrane4
Criterion 3: Removal of Arsenic by passing water through Wood Charcoal.
Explanation
In an experiment performed by Purenovic1, he found out that a greater percent up to 98% removal in the process. The process involved the passing of water through charcoal at different flow rates. In details, the experiment comprised the following; the arsenic contaminated water is allowed to pass through sequential layers sand and wood charcoal at the regulated rate of flow. This setup consists of three pitchers of 11 liters each by volume that are placed one over the other in a vertical orientation placed on a bamboo tripod. The top most pitcher has a small hole at the bottom and contains arsenic water. The middle layer has some layers of wood charcoal and the sand. The pitcher also has a small orifice at the bottom and screen that prevent the sand from leaking. The charcoal piece size range from 1-1.5 cm and the weight of layers vary from 606gm to 754 gm. and 457 gm. The layer of sand weighs 4480 gm. The water is allowed to flow at different rates, and the bottom pitcher collects the filtered water. Arsenic removal is observed to be removed in the contaminated water passed through the wood charcoal. The results are shown in Table 1 below.
Data
Interpretation
These values show a high efficiency of the process at the lowest flow rate. This method is cheap and safe because the materials used for construction are locally available, and no chemicals are added in the process. However, with the small rate of flow, the method is only applicable for use in small scale.
Conclusion
Summary
Conclusions
The removal of arsenic in drinking water makes safe for drinking. From the methods of removal discussed above, it is evident that arsenic can be reduced to 99% purity in water. In this case, several methods are currently in used for doing the same. However, the method varies depending on the quality, cost and efficiency of removal. From the data given, it can be concluded that the appropriate method that should be adopted is the use of charcoal and sand.
Recommendations
Despite the fact that all the method discussed above is useful, a factor of the economy must be incorporated. Of the three methods regarding, quality and efficiency, the use of charcoal and sand are highly recommended. It is simple, chemical free and affordable.
Work Cited
Purenovic, Milovan. "Alternative Technology for Arsenic Removal from Drinking Water". Hemijska industrija 61.5 (2007): 238-245. Web.
Ruiping, Liu et al. "Arsenic Removal Through Adsorption, Sand Filtration And Ultrafiltration: In Situ Precipitated Ferric And Manganese Binary Oxides As Adsorbents". Desalination 249.3 (2009): 1233-1237. Web.
Negrea, A., et al. "Removal of Arsenic from underground water to obtain drinking water." Chem. Bull 54 (2009): 82-84.
Ahmed, M. Feroze. "An overview of arsenic removal technologies in Bangladesh and India." Proceedings of BUET-UNU International Workshop on Technologies for Arsenic Removal from Drinking Water, Dhaka. 2001
Johnston Richard, and Han Heijnen. "Safe water technology for arsenic removal." Technologies for arsenic removal from drinking water (2001): 1-22.
