Arsenic contamination is the biggest natural calamity for Bangladesh. What type of initiatives can be taken by Bangladeshi Government now?
Arsenic contaminates groundwater across much of southern, central and eastern Bangladesh. Groundwater from the Holocene alluvium of the Ganges, Brahmaputra and Meghna Rivers locally exceeds 200 times the World Health Organization (WHO) guideline value for drinking water of 10 µg/l of arsenic. Approximately 25% of wells in Bangladesh exceed the national standard of 50 µg/l, affecting at least 25 million people. Arsenic has entered the groundwater by reductive dissolution of ferric oxy-hydroxides, to which arsenic was adsorbed during fluvial transport. Elevated concentrations are associated with fine sands and organic-rich sediments. Concentrations are low near the water table, rise to a maximum typically 20–40 m below ground, and fall to very low levels between about 100 and >200 m. Alternative arsenic safe technologies are-
i. Deep Tube well: The deep aquifers in Bangladesh have been found to be relatively free from arsenic contamination with some exception like geological depression in Sunamganj & Narail Districts and arsenic contaminated West Bengal District North 24 Parganas adjoining Bangladesh district western part of Jessore. The critical issue is the definition of deep tubewell. Most of water supply professionals often get confused with ‘Deep Tubewell’ and ‘Deep Aquifer’. However, ‘Deep Tubewell’ has been defined as well with depth of 500 ft or more. During deep tubewell installation, to avoid cross contamination, annular space has to be sealed properly with sodium bentonite or clay ball and PVC pipe joint has to be sealed by plastic tape to avoid leakage.
ii. Shallow Tubewell: Arsenic occurs mainly in groundwater of the valley-fill sequence deposited during the Holocene marine transgression. Groundwater from Pleistocene and older aquifers is largely free of arsenic. Considering the higher cost of ‘Deep Tubewell’, it is possible to find safe zone for shallow tubewell screen positioning in a heterogeneous geological setting even. Brown sand capped by red bed ‘Palaeosol’ produces arsenic safe water (Source: PhD thesis of Mattias von Bromssen, KTH, 2010) and it exist within variable shallow zone in almost half of Bangladesh.
If arsenic safe natural source of water is not available, treatment plant or surface water based options can be approached.
i. Arsenic Removal Plant: Community or household based AIRP can be installed attached to arsenic enriched hand tubewell to remove both arsenic and iron. The removal efficiency will be good if arsenic concentration of source water ranges within 150 µg/l. The mandatory issue is arsenic & iron ratio at 1:40 and phosphate less than 3 mg/L (though DPHE and UNICEF has recently started to allow up to 5 mg/L).
ii. Apart from AIRP, a number of household based treatment units have been applied in last two decades including DPHE-DANIDA Bucket Treatment Unit, Steven’s Institute Technology, Adorsho Filter, GARNET Home Made Milder, SONO Filter, Alcan Activated Alumina Filter, Shapla Filter & so on and community treatment unit including SIDCO Plant, READ-F, SKYHYDRANTS, RO Plant & so on.
iii. Pond Sand Filter: PSF is such technology which filtrate surface water through simple gradational sand. The O&M and microbial issue is still a big challenge for this option.
From a management perspective (as opposed to treatment) there may be some value in introducing soil and groundwater management techniques to prevent the acidification of acid sulfate soils and therefore mitigating arsenic mobilisation in the groundwater and it's possible transport to surface water. In Australia, acid sulfate soils became a problem with increased farming and development (e.g. residential canal development), particularly in the states of QLD and NSW, although there isn't the sme arsenic risk here as there is in Bangladesh. Both states reacted with some legislation to manage acid sulfate soils, including measures such as liming when soils are tilled to a certian depth and managing water tables in drainage line by locks and gates and some shallow bore water level management. The response was quite successful, but apart from regulation and legislative solutions, there were also some voluntary initiatives and information dissemination which also worked very well and targeted small land owners/farmers and other small developments. This was complimented by some fairly extensive mapping which allowed developers and land owners to assess if they fall in an acid sulfate soil zone themselves. I think mapping was key to both informing people of risk areas and empowering them to address the issue as they developed/used the land and water. If you're interested in what's been done in Australia on acid sulfate soils, some of the links below might be of interest:
https://www.qld.gov.au/environment/land/soil/acid-sulfate/
https://www.qld.gov.au/environment/land/soil/acid-sulfate/east-trinity/
http://envirodevelopment.com.au/_dbase_upl/soil_mgmt_guidelines_v3_8.pdf
http://www.dsdip.qld.gov.au/resources/policy/spp-guidelines-oct-02-v2.pdf
http://www.clw.csiro.au/acidsulfatesoils/atlas.html
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