Fluoride Removal from Groundwater by Adsorption Technology

Abdulai Salifu

• Publisher: CRC Press
• Year: 2017
• Print ISBN: 9781138373204
• eBook ISBN: 9781351199971
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

In the Eastern corridor of Northern region of Ghana, presence of high fluoride concentration in the groundwater has made many drilled boreholes unusable for drinking. Little is, however, known about the factors contributing to the occurrence of high fluoride in this part of Ghana and it's spatial distribution. Treatment of the fluoride-contaminated groundwater by adsorption is also hampered by the lack of suitable adsorbents that are locally available.

Based on principal component analysis, and saturation indices calculations, this thesis highlights that, the predominant mechanisms controlling the fluoride enrichment probably include calcite precipitation and Na/Ca exchange processes, both of which deplete Ca from the groundwater, and promote the dissolution of fluorite. The mechanisms also include F-/OH- anion exchange processes, as well as evapotranspiration processes which concentrate the fluoride ions, hence increasing its concentration in the groundwater. Spatial mapping showed that the high fluoride groundwaters occur predominantly in the Saboba, Cheriponi and Yendi districts.

The thesis further highlights that, modifying the surface of indigenous materials by an aluminium coating process, is a very promising approach to develop a suitable fluoride adsorbent. Aluminum oxide coated media reduced fluoride in water from 5. 0 ± 0.2 mg/L to ? 1.5 mg/L (which is the WHO health based guideline for fluoride), in both batch and continuous flow column experiments in the laboratory. Kinetic and isotherm studies, thermodynamic calculations, as well as analytical results from Fourier Transform Infrared Spectroscopy and Raman spectroscopy, suggest the mechanism of fluoride adsorption onto aluminium oxide coated media involved both physisorption and chemisorption processes.

Field testing in a fluoritic community in Northern Ghana showed that the adsorbent is also capable of treating fluoride-contaminated groundwater in field conditions, suggesting it is a promising defluoridation adsorbent. The adsorbent also showed good regenerability potential that would allow re-use, which could make it practically and economically viable. Additional research is, however, required to further increase the fluoride adsorption capacity of developed adsorbent.

1
General introduction

1.1 Background

Significant progress was made during the Millennium Development Goal (MDG) period (1990 — 2015), towards the achievement of the global target for safe drinking water, which was met in 2010, much ahead of the MDG deadline of 2015 (UNICEF and WHO, 2015). In spite of the good achievement and, with 91% of the global population now having access to improve drinking water, it was also observed that some developing/least developed regions including Southern and Central Asia, North Africa, Oceania and sub- Saharan Africa were unable to meet the drinking water target. Moreover, huge disparities with regards to the global access to safe drinking water were also observed, including inequalities such as the gap between the urban population (who are better served) and the rural population, the gender burden of water collection and the gap between the richest and the poorest and most venerable segments of society, who lack access to improved water services. It was observed that 8 out of 10 people (i.e 80%) who still lack access to safe drinking sources are rural dwellers (UNICEF and WHO, 2015).

As early as 2015, it was estimated that 663 million people worldwide still use unsafe drinking water sources, mostly in the least developed countries/regions including sub-Saharan Africa and Southern Asia, a vast majority of who are mostly poor and also live in rural areas.

At the start of this study (2009), the population across the developing world without safe water sources was estimated at 884 million (UNICEF, 2009; MacDonalds, 2009), and even though a lot was achieved by the end of the MDGs deadline (2015), it is clear that a great deal still require to be done.

Access to safe drinking water is not only fundamental to human development and well- being, but is also recognized as a human right (UN General Assembly, 2010; UNICEF & WHO, 2015). The provision of safe potable water is considered critical and pivotal to the achievements of overall development, including adequate nutrition, education, gender equality and especially eradication of poverty in less developed countries (Pollard et al., 1994; UNICEF and WHO, 2015).

One of the main problem concerning the provision of safe drinking water in developing countries is often associated with the poor quality of the water source and the need for treatment. There are many problems associated with water treatment in developing countries. These include:

• high investment as well as operation and maintenance cost,
• complexity of some processes that require the use of special equipment, electrical energy and skilled personnel which are mostly not available in rural areas (Dysart, 2008).
• environmental concerns with regards to disposal generated waste (Boddu et al., 2008).

Due to economic constraints, the development of low-cost and appropriate water treatment technologies is deemed very necessary (Pollard et al., 1994).

1.2 Groundwater, fluoride contamination, the benefits and pathophysiology

Groundwater sources are generally known to be of good microbiological and chemical quality and mostly require minimal or no prior treatment for use as safe drinking water sources. Hence its use for water supply is associated with low capital as well as low operation and maintenance cost. It is therefore the most attractive source for drinking water supply in the often scattered rural communities in developing countries (Buamah et al., 2008; MacDonald and Davies, 2000; Gyau-Boakye and Dapaah-Siakwan, 1999). Problems can, however, occasionally arise with the chemistry of groundwater, due to elevated concentrations of some elements, which can have negative health impacts on the user (MacDonald, 2009). Provision of safe drinking water from groundwater in such situations therefore require some level of treatment. Fluoride is one of the water quality parameters of concern that contaminates groundwater resources in many parts of the world and renders it not potable for human consumption due to adverse health effects.

Fluoride is known to have both beneficial and detrimental effects on health, depending on the dose and duration of exposure (Mjengera and Mkongo, 2009; WHO, 2011; Madhnure et al., 2007; Ma et al., 2007; Biswsa et al. 2007; Fawell et al. 2006; Nagendra, 2003). For instance the unique ability of the chemical to inhibit, and even reverse negative health effects with regards to the tooth has been' well observed (Whitford, 1996). Ingestion of optimum concentrations of fluoride (about 0.5 — 1.5 mg/L) in drinking water can prevent the incidence of dental caries, particularly in children up to age 8. It prevents the tooth decay by inhibiting the production of acid by decay-causing bacteria. These orally present bacteria (most prominently, streptococcus mutans and streptococcus sobrinus, and lactobacilli), consume food debris or sugar (sucrose) on the tooth surface (from the food we eat) for their own source of energy, and in the process convert them to lactic acid through a glycolytic process known as fermentation. These organisms are capable of producing high levels of lactic acid and when in contact with the tooth, can cause the dissolution/breakdown of minerals from the enamel (a highly mineralized cellular tissue), which plays a very important role in protecting the teeth from decay. When the tooth enamel loses its mineral content (i.e demineralization of mostly hydroxyapatite and calcium phosphate), it becomes weak and vulnerable to decay. Thus inhibition of the action of the decay-causing bacteria (by fluoride) from creating the required acidic environment around the enamel, beneficially helps to prevent the chemical processes (i.e mineral dissolution/breakdown) leading to tooth decay. Moreover, fluoride is also known to be a re-mineralization agent which can enhance the replacement of lost minerals from enamels that has been attacked, and thus reverse the formation of dental caries. Fluoride can bind to hydroxyapatite crystals in the tooth enamel and the incorporated fluorine makes the enamel stronger and more resistant to demineralization, hence resistance to decay (Whirtford, 1996).

Intake of excess fluoride (beyond 1.5 mg/L) for long periods can, however, result in negative human health effects. Fluoride has several mechanism of toxicity (Firempong et al., 2013; Shin, 2016; Whirtford, 1996). When it enters into the human body, mainly through the intake of water and to some extent food and dental products, about 75 — 90% is adsorbed (Harder, 2008; Shomer, 2004; Fawell et al., 2006). Ingested fluoride ions initially acts on the gastrointestinal musoca to form hydrofluoric acid (HF) in the stomach by combining with hydrogen ions under the acidic condition in the stomach. The formation of hydrofluoric acid leads to nausea, diarrhoea, vomiting, gastricintestinal irritation and abnominal pains. About 40% of the ingested fluoride is adsorbed from the stomach as HF. Fluoride not adsorbed in the stomach is adsorbed in the instestine. Once absorbed into the blood stream, fluoride readily distributes throughout the body and tend to accumulate in calcium rich areas such as bone and teeth (dentin and enamel) (Fawell et al., 2006; Firempong et al., 2013; Shin, 2016; Gessner et al., 1994). At moderately high levels (1.5 — 4 mg/L) of ingestion, it leads to dental fluorosis, particularly in children. According to Whirtford (1996), even though the mechanisms underlying the development of dental fluorosis are not well understood, there is evidence that the processes probably involve effects on the ameloblasts, which deposit tooth enamel. Ameloblast are cells present during tooth development (in childhood), and secretes the ana...

Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Acknowledgments
• Summary
• Table of Contents
• List of Figures
• List of Tables
• 1 General introduction
• 2 Fluoride occurrence in groundwater in the Northern region of Ghana
• 3 Drinking water defluoridation using aluminium (hydr) oxide coated pumice: Synthesis, equilibrium, kinetics and mechanism
• 4 Laboratory-scale column filter studies for fluoride removal with aluminum (hydr) oxide coated pumice, regeneration and disposal
• 5 Fluoride removal from drinking water using granular aluminum-coated bauxite as adsorbent: Optimization of synthesis process conditions and equilibrium study
• 6 Aluminol (Al-OH) fuctionalized wood charcoal for treatment of fluoride-contaminated groundwater: Effect of wood source, particle size, surface acidity-basicity and field assessment
• 7 General Conclusions
• Samenvatting