Programme de bourses "Jeunes Chercheurs"

Factors affecting arsenic removal with SONO filters

Starting in the 1980-1990ies, the installation of tube wells In Bangladesh has made a source of drinking water available, which, in contrast to surface water resources, is mostly free of microbial contamination. On the other hand, groundwater drawn from shallow tube wells contains high amounts of arsenic, which partially exceed concentrations of 500 µg/L (drinking water limit for arsenic in Bangladesh is 50 µg/L). Consuming this water over longer time periods poses a serious health risk to the local population. Especially in rural areas of Bangladesh, drinking water supply is highly decentralized and ensured only by these contaminated wells. With 57% of the affected population (roughly 28 million) still exposed, cheap, easy to handle, reliable, and low maintenance filters to remove arsenic are a promising approach to mitigate the problem. The government of Bangladesh provisionally approved of several arsenic removal units of which the SONO 45-25 filter fulfills the requirements mentioned above and is the only filter unit developed and produced in Bangladesh.

The SONO 45-25 filter consists of two plastic buckets piled on top of each other. The water enters the top bucket, which contains the active part for arsenic removal, the so-called composite iron matrix (CIM), consisting of zero-valent iron (ZVI). During the contact with aerated water, ZVI is constantly corroded, yielding hydrous ferric oxide (HFO) type solid phases, which are excellent sorbents for arsenate (As(V)) and arsenite (As(III)), as well as reactive intermediates, which can oxidize As(III) to As(V). The resulting co-precipitation of Fe(III) and As(V) and adsorption of As(V) to HFO eliminates arsenic from the water to levels below 50 µL/g. In the bottom bucket fine particles, which are produced in the top bucket, are removed before the water leaves the filter. Although some of the general pathways for the removal of arsenic with this type of filter are known, the complex chemistry within the CIM is not yet fully understood. Several water constituents such as phosphate, calcium, and dissolved organic carbon (DOC) have a strong effect on arsenic removal but no comprehensive investigation of the combined effect of different natural water constituents on the CIM in SONO filters has been carried out yet.

The proposed research project aims to extend the current understanding of the processes that occur in SONO 45-25 filters during arsenic removal, in particular the formation of solid phases and the sequestration of arsenic from water into solid phases. In a long-term field study in Bangladesh, the effect of natural groundwater differing in calcium, iron, phosphate, and DOC content on filter efficiency and solid (trans-) formation will be evaluated. In close cooperation with the local partner and manufacturer of SONO filters, the filters will be adapted for aqueous and solid sampling of the CIM and these tested filters will be delivered to the participating households. The results from this study will be used to refine and calibrate the basic reactive transport model, which will be set up with the current knowledge. The mathematical model and the results of this project will facilitate predicting the filter performance for water compositions that have not been evaluated and further optimization of the current filter technology.

  
A technical assistant of SONO Research and Technology Ltd. (STR) takes a water sample from a contaminated tube well for determining the concentration of arsenic. (Source: Anke Neumann, Sept. 2009)

            
This SONO 45-25 filter has been in use for over 7 years, reliably removing arsenic from the applied groundwater to levels secure for drinking and cooking. Filter effluent is collected for residual arsenic concentration testing during the well water sampling campaign in September 2009. (Source: Anke Neumann, Sept. 2009)

Involved Persons and Institutions

Postdoctoral Researcher:
Dr. Anke Neumann
House 225/2, Road 6, Sector 2, Upashahar
6202 Rajshahi
Bangladesh
Email: anke.neumann@jenal.org

Supervisor:
Dr. Stephan Hug
EAWAG
Überlandstr. 133
8600 Dübendorf
Switzerland
Email: stephan.hug@eawag.ch

Local Research Partner:
Dr. Abul K. M. Munir
Sono Technology and Research Ltd. (STR)/ Manob Sakti Unnayan Kendro (MSUK)
77 Mahatabuddin Road
Courtpara, Kushtia
Bangladesh
Email: akmmunir2003@yahoo.com

Research Partner:
Prof. Abul Hussam
Department of Chemistry and Biochemistry
George Mason University
Fairfax, VA 22030
USA
Email: abulhussam@gmail.com