How to purify water from heavy metals?

Heavy metals are elements of the periodic table of Mendeleev that have metallic properties and a large molecular weight.

Here we will tell you about the harm these substances can cause to a person, in which regions of Ukraine certain pollutants are common, and describe their characteristic impact on human health. And finally, we will introduce you to reverse osmosis technology, which will prevent dangerous ions from entering water and food.

What water is contaminated?

It is important to understand that most heavy metal salts enter the environment as a result of human activity - mainly from emissions from mining and processing enterprises, as well as thermal power plants. In other words, this is anthropogenic pollution.

The largest source of pollution is wastewater, which is discharged into surface water bodies with insufficient treatment. Another source of heavy metals is flue gases that settle on the ground and are washed off into water sources. And one more, perhaps the most serious type of pollution is the water generated by flooding mine workings, in which case even groundwater is contaminated.

It is worth noting that the maximum risk of poisoning from heavy metal salts increases when water is used without further treatment from surface water bodies and wells. In cases where groundwater is contaminated, consumption of water from wells is also not recommended. This primarily applies to industrial regions of Eastern Ukraine.

Manganese in the water

Note that due to the subtleties of translation from Ukrainian to Russian, manganese is often called manganese. We start with this metal because, after iron, which we discussed in a separate article, it is the most common contaminant of well water.

Signs of manganese in your water are black, gray, dark brown deposits on pipes and plumbing. The taste of such water is usually viscous, yellowish in color. Hands can darken with prolonged contact, and nail plates can turn black. At high concentrations of this mineral, black sediment may appear in the water.

The picture shows the difference in plaque formed by water with a high content of iron alone and that which additionally contains manganese.

Manganese belongs to the third group of toxicants, that is, it is moderately dangerous, and while the most unpleasant consequences of drinking “iron water” are regular constipation, it is more complicated. Despite the fact that it is involved in the processes of fermentation, hematopoiesis, and bone formation, an excess of this mineral can negatively affect a person's health. The main consequences of regular consumption of water with a high manganese content are problems of the central nervous system, which are manifested by drowsiness, weakness, and sometimes even long-term depressive disorders. Studies have also confirmed that its excess can negatively affect the gastrointestinal tract, kidneys, and bone tissue. The latter is critical for children, as there is a musculoskeletal disease called manganese rickets.

The main sources of manganese in surface waters are leaching processes of iron-manganese ores and other manganese-containing minerals. As for its natural content in well water, it is caused by the decomposition of living organisms.

Lead in water

The standard for lead in drinking water in Ukraine is 0.01 mg/l, which is in line with international standards. A dangerous dose is already 1 mg/l, and lead is classified as a toxic substance in the 2nd group.

Lead in surface waters in Ukraine is widespread almost everywhere. The degree of contamination depends on the development of industry and traffic on highways. For example, in large cities and villages located near highways, surface water often exceeds the MPC, which means that drinking water from wells or springs is usually risky. It is worth noting that lead in small concentrations gives water a pleasant sweetish taste.

Among the impactful effects are damage to the nervous and hematopoietic, cardiovascular and excretory systems, and impaired sexual function in women and men. There are also studies that confirm the carcinogenic effects of lead. It is worth noting that it is most toxic to young children, as they absorb up to 40% of it, while adults absorb no more than 10%.

Lead has a dangerous effect on the nervous system, and its consequences, again, primarily affect children. Lead encephalopathy is accompanied by epileptic seizures, headaches, etc. Depending on the degree of poisoning, the symptoms may vary and manifest themselves with different intensity. In children, lead poisoning can lead to a decrease in mental development, as well as problems with hearing and visual reactions.

Another common consequence is anemia, which is typical for children and is similar to classic iron deficiency. Kidney dysfunction (reversible and irreversible nephropathy) is common.
The effect on the cardiovascular system and gastrointestinal tract is significantly less than on the central nervous system, but it is also noted in the development of bradycardia and a number of nonspecific reactions, respectively.

The main sources of lead in water and the environment are:

• non-ferrous (98%) and ferrous metallurgy (2%) - these are the processes of obtaining the metal itself, alloys, and processing of raw materials;
• machine building, fuel industry and energy - pollution is caused by the use of leaded gasoline, which leads to the release of toxins into the atmosphere and their subsequent entry into water bodies. In many developed countries, such gasoline is practically not used, while in Ukraine its use is limited, but not prohibited;
• chemical industry - production of pigments. Nowadays, the production of such paints is minimized;
• transportation companies - the same use of gasoline;
• household waste - this point is very important, people throw organic waste and batteries into common containers. Returning household and car batteries for recycling or proper disposal can have a significant positive impact on the environment.

Mercury in water

Everyone knows what mercury balls from a broken thermometer look like, in fact, they are generally considered a major health hazard, but let's talk about soluble mercury compounds. These are inorganic compounds that are formed in the process of burning coal at power plants, utilizing industrial waste, and producing batteries. Thus, mercury compounds are released into the atmosphere and then into water.

The second group of toxic substances formed by bacteria in water bodies and the ocean is organic mercury compounds.One of the most common is methylmercury. It is found in fish and shellfish that are harmful to eat.In Ukraine, there are no systemic critical levels of mercury in the water.

An example of industrial mercury pollution is the Mykytivka deposit in Horlivka.Since 2014, due to the de facto occupation, the mine has been in a state of “dry mothballing,” in 2016, the equipment began to be sold for scrap, and in 2018, the pumping equipment was shut down, which led to flooding. The level of contamination of surface and groundwater in the area makes it unfit for drinking.

Another example is the territory of the Radical plant in Kyiv, which is not yet fully treated and poses certain threats.But this factor can be disregarded in the issue of drinking water contamination, as water from the centralized water supply system in Kyiv is not exposed to mercury. Also, a non-critical increase in mercury levels can be observed in cities with coal-fired thermal power plants.

Cadmium in water

This is a heavy metal that has serious side effects. In drinking water, the MPC for cadmium is 0.001 mg/dm³, and all cadmium compounds are toxic, belonging to the second class of toxicity. Its action is based on the ability to bind sulfur-containing acids and enzymes, resulting in nephro- and hepatotoxicity.The consequences of acute poisoning can be an increase in blood pressure, renal and pulmonary failure, and cardiovascular pathologies.

It is worth noting that cadmium is a carcinogen and can accumulate in the human body.Unlike the previously mentioned mercury, it is unable to penetrate the brain, so it has no neurotoxicity.
The most serious water polluters with cadmium are enterprises of the mining and metallurgical complex of Ukraine.They are concentrated near Kryvyi Rih, Mariupol, Kamianske, and Nikopol. Both surface and groundwater are contaminated in the areas close to the production facilities, so the safest source is tap water, which is treated if possible.

Zinc in water

Zinc is a trace element that is involved in small amounts in enzyme metabolism, as well as in the formation of steroid hormones, insulin, etc. If the content is high, it can cause specific diseases.

Water may contain soluble zinc compounds, often sulfates and chlorides.In case of intoxication with zinc salts, changes occur in the kidneys, and in case of a critical overdose, jaundice may occur. It is worth noting that prolonged exposure causes a decrease in the calcium content in the blood and bones, thus disrupting phosphorus metabolism and developing osteoporosis.It also has carcinogenic properties and can cause infertility in case of systemic exposure.

The main sources of phosphorus in water are metallurgical and machine-building enterprises, with a significant contribution from the chemical and pharmaceutical, woodworking, and textile industries.

In Ukraine, surface water pollution by zinc is typical for cities with developed metallurgical and machine-building industries: Kryvyi Rih, Mariupol and others.

Nickel and cobalt in water

Nickel is an important trace element, excessive amounts of which lead to increased excitability of the central nervous system, anemia, and allergic reactions. Nickel can affect the structure of DNA and increases the risk of tumors. As for cobalt, its effects are similar and can also cause heart disease.

In Ukraine, nickel and cobalt deposits are located in Kirovohrad and Mykolaiv regions. The only enrichment facility is the Pobuzhsky Ferronickel Plant near Kropyvnytskyi. As for the production of nickel-plated products, they are mainly located in Poltava, Dnipro, and Kirovohrad regions. Nickel has also been found to be above the MPC in the Yavoriv Reservoir in Lviv Oblast, which used to be a sulfur quarry. 
There are other localized increases in the level of these toxicants.

Arsenic in water 

It should be noted that Arsenic is often called Arsenic due to the peculiarities of translation from Russian into Ukrainian. Arsenic was one of the most popular poisons in the Middle Ages. Even very low levels of arsenic salts in drinking water are dangerous for humans. It has a toxic effect on all systems of the human body and can lead to death.

Sources of natural arsenic contamination include some natural minerals, but more often it is introduced into water by anthropogenic means. Sources include non-ferrous metallurgy enterprises, steel mills, and coal-fired thermal power plants.

Pesticides with a small content of arsenic are also actively used, and their washout leads to contamination of groundwater and, consequently, water bodies.

High levels of arsenic in surface water are observed in the Tisza River basin in western Ukraine.

How to purify water from heavy metals?

An example of industrial mercury pollution is the Mykytivka deposit in Horlivka.Since 2014, due to the de facto occupation, the mine has been in a state of “dry mothballing,” in 2016, the equipment began to be sold for scrap, and in 2018, the pumping equipment was shut down, which led to flooding.

Ion exchange reduces the content of heavy metals and hardness, and is often used at centralized water treatment plants. Read more about ion exchange technology here.

To remove manganese and iron, specific catalytic materials are also used to convert them into an insoluble form and retain the resulting particles.