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The use of biosorbents in water treatment: History
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Subjects: Materials Science, Biomaterials
Contributor: Mothusi Molebatsi

Biological materials used to adsorb pollutants from water 

  • biosorption
  • adsorption
  • materials
  • heavy metals
  • organic pollutants
  • water purification
  • mechanisms
  1. Introduction

The introduction Water is essential to our lives; it plays a pivotal role in maintaining public health, promoting social well-being, and is a critical driver of economic growth [1][2][3]. In Botswana, mining activities, industries, and agricultural processes add problems to the already scarce freshwater resources due to the country’s semi-arid climate. Studies show that wastewater from Gaborone treatment plants is not well treated before discharge, leading to contamination of surface and groundwater sources [4].

Within the Southern African Development Community (SADC) region, industrialization, poor sanitation, and climate change have also caused water scarcity and pollution. A review by the United Nations stated that many African countries struggle with access to clean water, and that the treated wastewater in Africa is mostly discharged untreated due to a lack of sustainable water treatment technologies. Lack of clean water systems is a global problem and creates risks to human health and the environment [5][6]. Addressing the water challenges requires innovative, low-cost, and sustainable solutions such as the use of biosorbents, which is closely aligned with the United Nations Sustainable Development Goals, SDG 6, that focuses on ensuring access to clean water and sanitation for all [7].

Access to clean and safe drinking water is crucial for preventing waterborne diseases (aligns with SDG 3 which aims to promote good health and well-being for people everywhere), reducing child mortality, and ensuring overall community health [8][7]. Water is beneficial to the body as it flushes waste out of the body through perspiration and urination. It transports minerals and oxygen throughout the body and regulates body temperature [9]. Access to clean water is essential for maintaining overall health as it prevents medical conditions by lubricating the joints and regulating the body temperature. It also improves strength and endurance, especially during physical activities [10].

Industries and businesses also require a reliable water supply for their operations. Access to safe water supports agricultural activities, enabling farmers to irrigate their crops and ensure food security. Furthermore, it fosters entrepreneurship by providing a foundation for small-scale businesses, encouraging economic growth at the local level [11].

Therefore, to maintain water safety, the World Health Organization (WHO), the Environmental Protection Agency (EPA), and Bureau of Standards from different countries are statutory bodies that safeguard human life and the environment by removing pollutants from water resources.

  • Types of Pollutants

Pollutants compromise the water quality, making it necessary to purify water to make it safe. They come from various sources like industries, domestic waste, and agriculture (pesticides, fertilizers, and animal waste), effluent discharges, mining activities, pharmaceuticals, tanks, and pipeline leakages [12]. Polluted water may contain organic, radioactive, inorganic substances, emerging, and microbial pollutants [13][14].

Examples of organic pollutants are dyes (for example, methyl red, methyl orange, methylene blue, etc), phenolic compounds, petroleum products, surfactants, pesticides, and pharmaceuticals [15][16]. Inorganics include cations of heavy metals e. g., lead (Pb), mercury (Hg), copper (Cu), cobalt (Co), manganese (Mn), iron (Fe), chromium (Cr), and anions (chlorides (Cl-), fluorides (F-), nitrates (NO3-), phosphates (PO4-), nitrites (NO-), sulfates (SO42-) [14][17][18][19]. The physicochemical parameters, including biochemical oxygen demand (BOD), chemical oxygen demand (COD), pH, total suspended solids (TSS), dissolved oxygen (DO), electrical conductivity (EC), and total dissolved solids (TDS) [20] are critical indicators of water quality.

In many parts of Africa, domestic waste is mostly from faecal waste, which contaminates underground water sources that supply drinking water through wells and boreholes, especially in undeveloped communities. These communities rely on the use of pit latrines where there are no maintained sewage lines, and urban road runoff [21]. Countries such as Uganda, Nigeria, Malawi, Kenya, Ethiopia, Ghana, South Africa, and Zimbabwe face challenges as pit latrines are located close to boreholes, and this leads to elevated concentrations of microbial contaminants, and anions amongst other pollutants, posing a risk of cholera [22][23].

Research was done in South Africa, where the use of pit latrines was not advised in areas where groundwater was used for drinking. This was because the levels of nitrates were above the acceptable limit of 10 ppm, and Escherichia coli (E. coli) counts above 10,000 colony-forming units (E. coli/100 mL) [24]. In Botswana, groundwater pollution was linked to pit latrine usage, especially in villages surrounding the capital city, Gaborone. Villages like Ramotswa and Mochudi wellfields experienced nitrate and bacterial contamination linked to pit latrine seepage. High levels of nitrates were reported in Ramotswa to the point where the Ramotswa wellfield had to be shut down as a source of potable water. Other areas like Molepolole, Serowe, Palapye, Pallaroad, and in the northeast were also affected in a similar way [25].

Polluted water sources can contribute to diseases such as cholera, dysentery, and diarrhea, particularly affecting vulnerable populations, including children, the elderly, and those with compromised immune systems. Table 1 illustrates how various pollutants impact human health and the environment.

 

Table 1: Effects of pollutants on human health

 

Pollutant class

Pollutant

Effects

Organics

Volatile organic compounds, for example, toluene, benzene, vinyl chloride, etc

Exposure can be through ingestion or inhalation and causes chronic illnesses like cancer and reproductive disorders, and affects the central nervous system. Inhalation brings lung problems, and a mild problem associated with ingestion is ulcers [26][27]

Persistent organic pollutants (POPs): Polychlorinated Biphenyls (PCBs), DDT (Dichloro diphenyl trichloroethane),

These can cause stroke, hypertension leading to heart failure, metabolic disease, reduced fetal growth, endocrine disruption (when hormones are interfered with), and cancerous [8]

Pesticides e.g. benzamide found in Fluopyram

They cause skin irritation and allergic reactions [28]
 

Pharmaceuticals like amoxicillin, ciprofloxacin, ibuprofen, diclofenac

Prolonged or even low-level exposure may lead to various organ dysfunctions. May also lead to hormonal imbalances to decreased fertility, as some of them are contraceptives, developmental abnormalities, and even congenital conditions in future generations [29]

Dyes: methylene blue, turmeric, congo red, crystal violet

Dye pollution in water brings allergies, cancer, dermatitis, and skin irritation [30]

Inorganics

Nickel (Ni)

It has harmful effects on human health. These include gastrointestinal complications, headache, anemia, dizziness, allergies, lung, and kidney failure [31]

Total dissolved solids (TDS)

Fluoride, F

Prolonged exposure to high amounts of dissolved salts leads to kidney stones. Fluoride consumption causes dental problems like teeth discoloration and weakening [32]

Arsenic, As

Besides causing cancer, elevated levels of Arsenic are associated with discoloration of the skin, stomach pain, nausea, diarrhea, and vomiting.

Mercury, Hg

Causes neurological disorders and may lead to abortion in expectant women. Methylmercury causes cardiovascular diseases and dementia in elderly people [33].

 

Copper, Cu

Chromium, Cr

Nausea, diarrhea, liver, and kidney damage [34][18]

Cadmium, Cd

Lead, Pb

Excessive amounts of damage to the nervous system and destroy the blood circulation. Irritation of the respiratory system [35][36][37]

Biological pollutants

Viruses, protozoa, and bacteria

These produce harmful toxins and are cholera-causing organisms. Exposure causes liver damage and skin problems [32]. Mild problems are diarrhea, nausea, vomiting, headaches, and dehydration

 

To address water pollution challenges, a wide range of water treatment methods has been developed, such as adsorption, flocculation, photocatalysis, sedimentation, neutralization, and membrane technologies [38][39][40][41]. These methods are simple, fast, and target various pollutants, but often come with high operational costs, limited removal of dissolved pollutants, and environmental impacts [30]. In recent years, biosorption has emerged as an eco-friendly and cost-effective alternative, yielding high pollutant removal efficiencies [42][26]. Biosorption is a process that involves using materials of a biological nature known as biosorbents to remove contaminants from water, making it an attractive option for water treatment in areas with limited access to advanced filtration technologies [41]. Biosorbents, including microbial, agricultural, and modified materials, are extensively used in the removal of heavy metals from industrial effluents, ensuring compliance with environmental regulations [43]. Furthermore, biosorbents are useful in decentralized water purification systems, especially in remote or disaster-stricken areas, providing cost-effective and sustainable water management practices through biosorption [44].

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