Elsevier

Chemosphere

Volume 229, August 2019, Pages 142-159
Chemosphere

Review
Removal of heavy metals from water sources in the developing world using low-cost materials: A review

https://doi.org/10.1016/j.chemosphere.2019.04.198Get rights and content

Highlights

  • Removal of heavy metals on adsorption was reviewed in water sources.

  • Low-cost materials were reviewed in the developing world.

  • Various adsorption mechanisms for heavy metals were discussed.

Abstract

Heavy metal contamination is a growing concern in the developing world. Inadequate water and wastewater treatment, coupled with increased industrial activity, have led to increased heavy metal contamination in rivers, lakes, and other water sources in developing countries. However, common methods for removing heavy metals from water sources, including membrane filtration, activated carbon adsorption, and electrocoagulation, are not feasible for developing countries. As a result, a significant amount of research has been conducted on low-cost adsorbents to evaluate their ability to remove heavy metals. In this review article, we summarize the current state of research on the removal of heavy metals with an emphasis on low-cost adsorbents that are feasible in the context of the developing world. This review evaluates the use of adsorbents from four major categories: agricultural waste; naturally-occurring soil and mineral deposits; aquatic and terrestrial biomass; and other locally-available waste materials. Along with a summary of the use of these adsorbents in the removal of heavy metals, this article provides a summary of the influence of various water-quality parameters on heavy metals and these adsorbents. The proposed adsorption mechanisms for heavy metal removal are also discussed.

Introduction

Freshwater is a basic requirement for humans and wildlife. The availability of clean drinking water is critical for maintaining a healthy life. However, while global water demand increases annually, various forms of pollution have compromised potential water sources (UN-Water, 2018). Moreover, researchers have found that the impacts of climate change, such as higher temperatures and changes to the water cycle, will also exacerbate these water issues and potentially result in increased flooding, more severe droughts, and enhanced toxicity of chemical contaminants in the environment (Milly et al., 2002, Noyes et al., 2009, Xi et al., 2017). Polluted water sources can be harmful to humans due to potential exposure to pathogens or toxic chemicals via irrigation of plants with contaminated water, the consumption of toxins in aquatic organisms, or the use of contaminated surface water for recreational purposes (e.g., swimming) (Schwarzenbach et al., 2010). However, for the majority of individuals living in the developing world, human health is most commonly affected by the direct consumption of contaminated water.

In developing countries, the impact of increased pollution is particularly problematic because these populations do not have the resources to effectively treat contaminated water or access to clean drinking water systems that can supply water to their homes. The World Health Organization (WHO) estimates that 844 million people do not have a basic drinking water source and that 230 million people spend more than 30 min/d collecting water from an improved water source, which may include piped water, boreholes, protected wells and springs, rainwater, and packaged/delivered water (WHO, 2017a, WHO, 2017b). The inability for people in developing countries to have consistent access to an improved drinking water source increases the likelihood of water-related diseases. According to WHO estimates, approximately 1.6 million people die every year from preventable water-related diseases, such as diarrhea, and 90% of these deaths are children under 5 years of age (Pandit and Kumar, 2015). In the developing world, drinking water contamination due to microbial agents (e.g., bacteria and viruses) represents the greatest threat to human health. However, the proliferation of heavy metals in drinking water sources is also a growing concern. Table 1 provides the characteristics of common heavy metals found in the developing world.

In recent years, industrial and urban activities have increased throughout the developing world, which has subsequently contributed to increased heavy metal pollution. The release of contaminated wastewater from various industries, including coal-fired power plants (Demirak et al., 2006) and mining (Archundia et al., 2017), along with waste recycling and solid waste disposal activities (Herat and Agamuthu, 2012, Olafisoye et al., 2013, Perkins et al., 2014, Wu et al., 2015), represents a major source of pollution, while emissions from vehicles and other urban activities also contribute to it (Pandey and Pandey, 2009, Prasse et al., 2012). According to the United Nations, an estimated 80% of all industrial and municipal wastewater in the developing world is released to the environment without any prior treatment (UN-Water, 2018). Moreover, additional contributions to water pollution include polluted urban stormwater runoff, agricultural runoff, and rainwater transport into potential drinking water sources (Kambole, 2003, Lye, 2009). Heavy metals are of particular concern due to their toxic and carcinogenic nature, along with their documented harmful effects to human health (Chakraborty et al., 2013, Gleason et al., 2016, Jarup, 2003, Schwartzbord et al., 2013). Heavy metal pollution is also a concern because many of the drinking water treatment techniques used in the developing world, including chlorination, boiling, and solar disinfection, are ineffective at removing heavy metals (De Kwaadsteniet et al., 2013).

When considering the impact of heavy metals in the developing world, numerous review papers have investigated the prevalence of heavy metals in drinking water sources in several developing countries (Chowdhury et al., 2016, Emmanuel et al., 2009, Rahman et al., 2009, Rossiter et al., 2010), along with the human health hazards associated with heavy metal contamination (Amadia et al., 2017, Holecy and Mousavi, 2012, Jarup, 2003, Odongo et al., 2016). Many researchers have conducted detailed studies on the heavy metal contamination of water sources in specific developing countries, including China (Cao et al., 2015, Li et al., 2014, Qu et al., 2012, Xu et al., 2017, Zou et al., 2015), India (Awasthi et al., 2016a, Awasthi et al., 2016b, Pandey and Pandey, 2009, Ramasamy et al., 2017, Sridhar et al., 2017), Bangladesh (Gleason et al., 2016, Islam et al., 2015b, Linderholm et al., 2011, Nahar et al., 2014, Wang et al., 2016), Ethiopia (Prasse et al., 2012, Yohannes et al., 2013), Pakistan (Bhowmik et al., 2015, Nawab et al., 2016, Nawab et al., 2017, Rasheed et al., 2017, Rehman et al., 2008), and various other developing countries (Archundia et al., 2017, Belabed et al., 2017, Nweke and Sanders, 2009, Tarras-Wahlberg and Nguyen, 2008). Moreover, due to the well-documented impacts of heavy metals to human health, a significant amount of research has been conducted on methods of removing heavy metals from drinking water sources, as well as municipal wastewater, industrial wastewater, and other water sources. Many recent review articles highlight treatment methods and technologies that achieve high removal efficiencies for heavy metals and are currently being explored for use in many developed countries, such as membrane filtration (Kim et al., 2018), electrocoagulation (Al-Qodah and Al-Shannag, 2017, Bazrafshan et al., 2015), microbial remediation (Ayangbenro and Babalola, 2017, Li and Tao, 2015), activated carbon adsorption (Li et al., 2018a, Renu et al., 2017), carbon nanotechnology (Peng et al., 2017, Sherlala et al., 2018, Xu et al., 2018), and various modified adsorbents (Jiang et al., 2018, Sajida et al., 2018, Zare et al., 2018). However, these technologies are not feasible or cost-effective in the context of the developing world. To treat water in the developing world, proposed technologies must be easy to obtain, constructed by local workers with limited education, and have low operating and maintenance costs.

Therefore, in this review paper, we focus on the use of low-cost, often locally-available, materials that do not require additional energy input or modifications to remove heavy metals from water sources. While providing an exhaustive review of the studies conducted in the developing world regarding heavy metal removal is challenging, the objective of this review paper is to examine the major categories of materials that would be most readily available and utilized in the context of the developing world. The materials investigated in this review are divided into four broad categories: agricultural waste, which includes various types of residual waste from nuts (e.g., peanut, cashew, pistachio, etc.), along with fruit and vegetable waste materials (e.g., rice straw, corn, orange, banana peels, lemons, beets, grapefruit, etc.); naturally-occurring soil and mineral deposits; aquatic and terrestrial biomass (e.g., seaweeds, water hyacinth, trees, etc.); and other waste materials that are commonly found in developing countries (e.g., tea waste, local seashells, industrial by-products, etc.). We examined the removal of various heavy metals using these materials and surveyed the proposed removal mechanisms associated with these materials. To date, few review papers have surveyed the use of low-cost materials for the removal of heavy metals from water. The most recent review was published over approximately a decade ago (Babel and Kurniawan, 2003, Kurniawan et al., 2006).

Section snippets

Effect of water quality characteristics on heavy metal removal

When investigating the removal of heavy metals, it is important to evaluate the behavior of the heavy metals, along with the characteristics of the adsorbent, under varying water quality conditions. Among the most important water quality parameters related to heavy metal removal are pH, temperature, the presence of natural organic matter (NOM), and ionic strength. While heavy metal contamination is most often associated with industrial wastewater, in the developing world, heavy metals have been

Agricultural waste

The use of agricultural waste to remove heavy metals has been widely investigated by researchers in both developed and developing countries. When considering the removal of heavy metals in the context of a developing country, agricultural waste often represents a source of abundant, effective adsorbents to implement into water treatment processes. For example, dairy manure compost is a unique material that has been shown to effectively remove heavy metals by achieving maximum adsorption

Proposed mechanisms for heavy metal removal

When examining the ability of these low-cost adsorbents to remove heavy metals in the context of the developing world, adsorption has received the most attention as a removal method. With interactions between heavy metals and various materials, adsorption typically occurs in two different ways: surface adsorption and interstitial adsorption. During surface adsorption, heavy metal ions migrate by diffusion from the aqueous solution to the surface of the adsorbent, which contains an opposite

Conclusions

In the developing world, increased water scarcity and pollution contribute to a significant lack of access to clean drinking water. While various forms of water pollution exist, heavy metal contamination in drinking water sources is a growing concern. Moreover, developing countries do not have access to common water treatment methods that would remove heavy metals. As a result, a significant amount of research has been conducted to investigate the use of low-cost adsorbents to remove heavy

Acknowledgements

This research was supported by the Korea Ministry of Environment (The SEM projects; 2018002470005, South Korea). This study was also supported by the University of South Carolina ASPIRE program.

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