Published: 12:14 AM, 11 October 2026
Tiny Microbes, Big Impact: Bacterial Bioremediation of Tannery Waste
Nazmun Nahar Nipa
Bangladesh's leather industry is one of the country's most important export sectors. Tannery industry has been developed after independence in Dhaka's Hazaribagh. While generating huge revenues for the country, this industry has polluted the environment as well. In the past, the tannery industry has been dumping tons of untreated waste into the Buriganga river every single day. The waste contained highly toxic hexavalent chromium [Cr(VI)], sulfides, ammonia, various organic wastes, and heavy metals that made the river water, sediments, and soil highly contaminated.
The tanneries were ordered to relocate after a writ petition by the Bangladesh Environmental Lawyers Association (BELA) was approved by the High Court and later by the Supreme Court. The tannery industry in Bangladesh was relocated from Hazaribagh to Savar in 2017. While relocating the tannery industry can be considered a major step towards securing the country's environment and health, an important question can be asked; can simply relocating the tannery solve the problems?
While research suggests that it cannot, finding a reliable solution to treat the waste before reusing or disposing of it is a must. One of the possible technologies is bioremediation using microorganisms.
Chromium is one of the most used chemicals in leather processing that can be found in two forms; trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. The latter one is much more dangerous for the environment and human health. As Cr(VI) is water-soluble, it can enter the cells relatively easy inducing production of Reactive Oxygen Species (ROS). ROS can cause DNA damage, protein oxidation, and lipid peroxidation. It has been proved that long exposure to Cr(VI) can result in kidney, liver, and lung damage, respiratory issues, and even cancer.
On the contrary, Cr(III) is significantly less toxic and can be easy removed from the wastewater by precipitation. Thus, one of the main purposes of chromium bioremediation is to convert toxic Cr(VI) into the less toxic Cr(III).
Nature might have a solution to the problem as chromium-resistant bacteria can be harnessed in the bioremediation process. Chromium-resistance bacteria are able to reduce Cr(VI) to Cr(III) by expressing various enzymes such as chromate reductase. This process is referred to as microbial bioremediation.
Microbial bioremediation takes advantage of bacteria's ability to reduce toxic chromium to a less toxic form using their own enzymes through their natural metabolic processes. Some species of bacteria can even remove heavy metals from the solution; this process is known as biosorption. Another mechanism by which bacteria can help is through bioaccumulation, which means accumulating metals inside the cell. Thus, microorganisms can be seen as Earth's attempt to heal itself from the pollution caused by humans.
The application of such bioremediation techniques can be implemented not only in laboratory settings but also on the industrial level. In a bioreactor, a packed bed of bacterial cells can be used for continuous reduction of hexavalent chromium. The reduced Cr(III) can be precipitated as chromium hydroxide [Cr(OH)3] in a settling tank. The settled Cr(III) can be used in various industrial processes again; thus, being an example of recycling. The wastewater can be treated further with Rotating Biological Contactor (RBC) followed by an activated carbon filter.
Chromium-resistant bacteria such as Bacillus spp., and Micrococcus spp., were isolated from tannery waste in Bangladesh. Studies have shown that these bacteria are capable of reducing toxic Cr(VI) to less toxic Cr(III). Thus, bacteria isolated from Bangladesh's own polluted waste can be potential candidates in fighting chromium pollution.
Across the world, new technologies are being explored to combat heavy metal pollution with the help of Environmental Microbiology, Industrial Microbiology, and Biotechnology.
In Bangladesh, universities, research institutes, and industries should join the efforts in harnessing local bacteria in developing bioremediation technologies on the industrial level.
If laboratory findings can be incorporated into the real world, the benefits can go beyond the rivers and water pollution. Fighting the pollution on this level can also help reduce heavy metal pollution of the soil, groundwater, and eventually human health. Thus, in the fight against environmental pollution, tiny microorganisms might be the ones to help.
Nazmun Nahar Nipa is a Master’s thesis
student, Microbiology in
Jahangirnagar University.
