Fluoride Action Network

Fluoride Removal from Groundwater by Adsorption Technology. The occurrence, adsorbent synthesis, regeneration and disposal.

Source: Dissertation | October 4th, 2017 | By Abdulai Salifu
Location: Ghana
Note from Fluoride Action Network:
“Since all methods [to remove fluoride] produce a sludge with very high concentration of fluoride that has to be disposed of, only water for drinking and cooking purposes should be treated, particularly in the developing countries.”
Reference: Fluorosis (see Interventions), World Health Organization

Excerpts from dissertation titled : Fluoride Removal from Groundwater by Adsorption Technology. The occurrence, adsorbent synthesis, regeneration and disposal.

Over 90 % of rural domestic water requirements in the Northern region of Ghana for instance (which was the area of focus of this study), is met from groundwater resources. Fluoride contamination of the groundwater in some parts of the region has, however, exposed the population in the fluoritic communities to fluoride-related health hazards. This has also resulted in the closure of otherwise many very useful drilled boreholes (wells) for water supply, in order to avoid the incidence of fluorosis and other related health effects. The closure of drilled (expensive) boreholes due to presence of excess fluoride do not only represent huge economic cost, but also hampers efforts of providing safe drinking water to the populace. As a consequence the population is forced to use unsafe surface water sources that are associated with the incidence of otherwise preventable, diseases such as cholera and diarrhea. Even though groundwater remains the most important source for rural water supply in the Northern region of Ghana, little is known about the factors (natural and/or anthropogenic) that control the groundwater chemistry and, hence the quality and source of fluoride contamination as well as its distribution.

Due to the permanent risk as well as the lack of known effective treatment for fluorosis and other related health hazards, defluoridation of fluoride-contaminated groundwater sources intended for drinking is a necessity, to avoid the ingestion of excess fluoride as a preventive measure. Several defuoridation technologies have been developed in many places around the world, some of which are described as “Best Available Technologies” (BATs). The current methods, however, mostly have some limitations which generally make their use unsustainable and/or unacceptable under most conditions, particularly in remote areas in developing countries. This include for instance:

(i) the Nalgonda technique, which is popular in some Asian countries but is known to have limited efficiency (up to about 70 %), requires careful dosing of chemicals and close monitoring to ensure effective fluoride removal, hence demanding labour, skills and time that are usually problematic under rural conditions in developing countries;

(ii) the contact precipitation process, which is still under study, and moreover the reaction mechanism for the defluoriidation process is thought only to be feasible with use of bone charcoal as a catalyst. Bone charcoal is however not culturally acceptable in some societies due to local taboos and beliefs;

(iii) adsorption using activated alumina as adsorbent media, which is known to be expensive especially for developing countries,

(iv) adsorption with bone charcoal as adsorbent media, which is not acceptable in many places as earlier mentioned, and,

(v) reverse osmosis (RO), which has high capital and operational cost, require specialized equipment, skilled labour and a continuous supply of energy.

Due to the negative health impacts of excess fluoride in drinking water, however, the search for an appropriate technology for its removal from contaminated-groundwater still remains very critical. Among the available fluoride removal techniques, the adsorption process is generally considered as one of the most appropriate, particularly for small community water source defluoridaton. This is due to its many advantages including flexibility and simplicity of design, relative ease of operation, and cost- effectiveness as well as its applicability and efficiency for contaminant removal even at low concentrations. The appropriateness of the adsorption technology, however, largely depends on availability of a suitable adsorbent.Several adsorbent materials have been developed and tested, mostly in the laboratory, for the treatment of fluoride-contaminated water including: manganese-oxide coated alumina, bone charcoal, fired clay chips, fly ash, calcite, sodium exchanged montimorillonite-Na+, ceramic adsorbent, laterite, unmodified pumice, bauxite, zeolites, fluorspar, iron-oxide coated sand, calcite, activated quartz and activated carbon. While some of these adsorbent materials have shown certain degrees of fluoride adsorption capacity, the applicability of most is limited either due to: lack of socio-cultural acceptance, non regenereable nature, and therefore may not be cost-effective, high cost and/or effectiveness only under extreme pH conditions. This may require pH adjustment and consequently additional capital, operation and maintenance cost, and could limit feasibility of such a fluoride removal technology in remote rural areas of developing countries. Some of the studied defluoridation materials are also available in the form of fine particles or powders, with the potential of clogging and/or low hydraulic conductivities when applied in fixed bed adsorption systems. The search for appropriate alternative fluoride adsorbents therefore remains of interest.

The overall goal of the study was therefore twofold: (i) to study the groundwater chemistry in the Northern region of Ghana with focus on the occurrence, genesis and distribution of fluoride-contaminated waters in the eastern corridor of the region (which is the most fluoritic part), and (ii) to contribute to the search for an appropriate and sustainable fluoride removal technology for the treatment of fluoride-contaminated groundwater for drinking water production in developing countries.

In order to accomplish the first component of the research goal, the climate, geology, mineralogy and hydrogeology of the study area was reviewed in a desk study. Three hundred and fifty seven (357) groundwater samples taken from boreholes drilled in the study area, were analyzed for the chemical data using standard methods. Univariate statistical analysis, Pearson’s correlation and principal component analysis (PCA) of the chemical data, using the SPSS statistical software package, as well as Piper graphical classification using the GW chart software, and thermodynamic calculations with PHREEQC, were used as complementary approaches to gain an insight into the groundwater chemical composition, and to understand the dominant mechanisms influencing the occurrence of high-fluoride waters in the area. The geo-referenced groundwater chemical data were further analyzed using ArcGIS software to determine the spatial distribution of fluoride in groundwater at the sampled points of the study area. Inverse distance weighting interpolation (IDW) (using ArcGIS), was also used to examine the fluoride distribution in the study area and to help predict the fluoride levels at non-sampled points as well.

*Read the full report: Fluoride Removal from Groundwater by Adsorption Technology. The occurrence, adsorbent synthesis, regeneration and disposal.

Submitted in fulfillment of the requirements of the Board for Doctorates of Delft University of Technology and of the Academic Board of the UNESCO-IHE Institute for Water Education for the Degree of DOCTOR. Netherlands.