Innovative process for iron and arsenic removal from water
In Bangladesh, groundwater is predominantly used as drinking water. The high iron content in the water causes it to turn red and taste bad. Even worse is arsenic, which is also contained in the groundwater and which can neither be seen nor tasted, and which is one of the strongest poisons. Levels in Bangladesh and many parts of the world often exceed WHO recommendations of 10 µg/l many times over. For this reason, groundwater should not be drunk without treatment.
The removal of iron and arsenic from groundwater is actually technically very simple. In Bangladesh, the SIDKO and SONO filters work on a two-stage principle. First, iron is oxidized and thus precipitated, and then the arsenic adsorbs to filter media. The method is simple and functional, but has the disadvantage that the process is very slow, so very large filters are needed and/or only small amounts of water can be cleaned. In the case of SIDKO filters, this is only about 1,000 L per day, despite the considerable size of the systems (reference to page). SONO and SIKDO operate with outdated technology, are difficult to maintain and are far too expensive due to their short service life. Therefore, AGAPE e.V. has developed its own household filters in cooperation with the Institute of Geosciences at the University of Heidelberg (GEOW).
In another collaboration with GEOW, we have tried an innovative technique - electrocoagulation. In this process, very low electric current (max. 12.6 mA) is applied to iron plates immersed in the water to be treated. The current dissolves iron from the plates and chemical iron complexes are formed as flakes, which take arsenic with them and sink to the bottom very quickly. The clear water is arsenic-free. At the same time, other substances such as iron, manganese and phosphorus are removed, which have a negative effect on taste, appearance or also on health in higher levels.
The process was successfully tested in the laboratory as part of a master's thesis (M.Sc. Daniel Müller, GEOW). All basic conditions and end substances were examined to ensure that no other substances harmful to health are produced during the process. Electricity and water, aren't they mutually exclusive or dangerous? No, the amount of current used was below the safety extra-low voltage in all tests. One could even touch the electrodes or reach into the water without hesitation during operation.
Figure 1: Experimental setup of the flow-through treatment This compact plant setup can replace the SIDKO filters in Bangladesh in the future (source: www. geow.uni-heidelberg.de).
We then tested the process under real conditions in Hamburg, since use in Bangladesh is not possible for the time being due to Corona. There is a groundwater damage case with more than 14,000 µg/l arsenic, i.e. more than 50-100 times higher than in Bangladesh. With the method, even such high levels of arsenic could be completely removed within a few hours. This clearly demonstrates the high efficiency of the method and suggests that it is suitable for Bangladeshi conditions.
Fig. 2: Test setup in a barrel. This plant setup is to be used on a test basis in Bangladesh in 2021 to treat the entire daily water consumption for families. (Source: www. geow.uni-heidelberg.de): When electricity is applied, iron dissolves from the metal plates and forms large solid flakes with the pollutants, which settle quickly. The water is free of arsenic and heavy metals.
Both prototypes are ready and waiting to be shipped to Bangladesh. Our plan for 2021 is to supply at least 50 households with such barrel systems and two schools with the flow-through system. The production of the systems is very simple and cheap and shall be done in Bangladesh from now on.