Using Microbes To Eat Up Pollution

When we consider pollution and solutions to combat its effects, many of us likely think of problems like littering and solutions like recycling. While these are not insignificant topics in the discussion of pollution, in reality, the problem is much more complicated. Pollution is a global problem that comes from industrial to agricultural and domestic to military sources, and contaminates air, soil, and water, making it a widespread, deep-rooted problem that threatens the health of both ecosystems and our bodies. An emerging solution to this problem is bioremediation, a method of cleaning air, soil, and water by using microorganisms and plants to remove pollutants or break them down into less toxic or hazardous forms.One of the most prominent uses of bioremediation is in sewage treatment. In the first stage of sewage treatment, known as primary sewage treatment, solids are mechanically filtered out of wastewater. This is followed by secondary sewage treatment, in which air is introduced to aeration tanks holding wastewater, leading to increased growth of aerobic bacteria and other microbes. These microbes digest the organic material—material containing carbon—in the wastewater into ammonia gas, carbon dioxide, water, glucose, alcohol, and nitrate, and detoxify inorganic material. The products of their digestion are heavy and sink to the bottom of the tanks, and when they are removed from the wastewater, they are known as sludge, or biosolids. The sludge can be incinerated, applied to soil to increase its fertility, or disposed of in landfill. Sludge can also be further processed by anaerobic bacteria, which convert the remaining organic matter into biogas, a mixture of carbon dioxide and methane, further reducing the volume of organic matter and pathogens within the wastewater. Biogas can also be captured for combustion so that it can be used for electricity and heat.

In addition to breaking down organic matter in wastewater, bioremediation can also be effective at processing other types of organic matter, including hydrocarbons, which is especially important in cleaning oil spills. In order to use bioremediation to deal with oil spills, sulfate or nitrate fertilizers are added to the affected area, stimulating bacterial decomposition of the oil. The amount of hydrocarbons can be significantly reduced through oxidation that occurs between the layers of water and oil when oxygen is present and is performed by fungi, green algae, and bacteria. Within a year, this can lead to almost 80 percent of hydrocarbons being removed.

Bioremediation can even be used to manage nuclear waste. Nuclear waste is largely produced from spent fuel in nuclear reactors that generate energy—what remains after the fuel in the reactor can’t effectively be used to produce energy anymore. It is radioactive, meaning that it produces radiation, which can damage human tissue and cause cancer, and it also produces substances such as ionic mercury and toluene, which are toxic. Deinococcus radiodurans, a bacterial species, has the greatest radioresistance, or ability to withstand radiation, of any known organism, and due to genetic engineering, it is able to digest ionic mercury and toluene. Nuclear waste is highly hazardous and is one of the biggest problems caused by nuclear energy, so bioremediation is crucial in preventing further harm from it.

Bioremediation that uses plants rather than microbes is called phytoremediation, which is often used to stabilize or remove pollutants from the soil, and is additionally beneficial as it can prevent pollution from spreading via water or wind and is relatively inexpensive. There are several types of phytoremediation, including phytostabilization, phytoextraction, phytovolatilization, and phytodegradation. The method that is selected varies based on the particular situation, as does the type of plant chosen. The type of plant is chosen based on the accumulation factor, which is the ratio of the amount of pollution the plant can take up to the amount of pollution in the soil. A low accumulation factor means that plants only take up pollution into their roots, while a high accumulation factor indicates that pollution is taken into the plants above the roots. In phytostabilization, a layer of plants with low accumulation factors is grown to last for a long period of time. The plants stabilize organic or metal pollutants in the soil by taking them up through their roots and holding them there, without transporting them further, which prevents them from being introduced to the food chain. Alternatively, in phytoextraction, plants with high accumulation factors take up pollutants such as nickel, arsenic, and cadmium. The plants are then removed from the soil and disposed of, which can be done through multiple methods, including incineration, decomposition by microbes, and compression in a landfill. In phytovolatilization, plants remove pollutants from the soil and convert them into gases that they release into the air, while in phytodegradation, they convert pollutants into less toxic or non-toxic forms. 

Bioremediation is a tool that is necessary in managing pollution, and it will likely be a key feature of future efforts to reduce it. Its applications are abundant and versatile, and may be even more so in the future, as microbiologists are currently researching topics such as using microbes to sequester carbon dioxide in the atmosphere, build a sustainable economy, and manage microplastics. However, bioremediation alone is not enough to effectively manage the problem—we need to stop producing so many pollutants in the first place, which will require major societal changes in production and consumption, from the structural level through actions such as shifting toward cleaner and more efficient energy usage and using fewer toxic or otherwise harmful chemicals in industry and agriculture, to the personal level by reducing the amount we consume. For individuals, reducing the amount of pollution we produce can take the forms of decreasing our food waste, using less water, and cutting down on single-use plastics, as well as speaking out to advocate for changes at the structural level. Progress in the fight against pollution will include both a reduction in the amount of pollution we produce and bioremediation to clean it up, and although there is still much work to be done in both areas, it is also both utterly necessary and possible to do it.