Bioremediation

Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi in mycoremediation, and plants in phytoremediation), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings.

[1] The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment.

[1] In comparison to conventional physicochemical treatment methods bioremediation may offer advantages as it aims to be sustainable, eco-friendly, cheap, and scalable.

Research on bioremediation is heavily focused on stimulating the process by inoculation of a polluted site with organisms or supplying nutrients to promote their growth.

[8] In both these approaches, additional nutrients, vitamins, minerals, and pH buffers are added to enhance the growth and metabolism of the microorganisms.

Some examples of bioremediation related technologies are phytoremediation, bioventing, bioattenuation, biosparging, composting (biopiles and windrows), and landfarming.

Other remediation techniques include thermal desorption, vitrification, air stripping, bioleaching, rhizofiltration, and soil washing.

[7] Microorganisms can degrade a wide variety of hydrocarbons, including components of gasoline, kerosene, diesel, and jet fuel.

Under ideal aerobic conditions, the biodegradation rates of the low- to moderate-weight aliphatic, alicyclic, and aromatic compounds can be very high.

[7] This results in higher contaminated volatile compounds due to their high molecular weight and an increased difficulty to remove from the environment.

The choice of substrate and the method of injection depend on the contaminant type and distribution in the aquifer, hydrogeology, and remediation objectives.

Substrate can be added using conventional well installations, by direct-push technology, or by excavation and backfill such as permeable reactive barriers (PRB) or biowalls.

[21] Slow-release products composed of edible oils or solid substrates tend to stay in place for an extended treatment period.

The VFAs, including acetate, lactate, propionate and butyrate, provide carbon and energy for bacterial metabolism.

[25] Biopiles, similar to bioventing, are used to remove petroleum pollutants by introducing aerobic hydrocarbons to contaminated soils.

[26] Windrow systems are similar to compost techniques where soil is periodically turned in order to enhance aeration.

[30] This process is an above land application and contaminated soils are required to be shallow in order for microbial activity to be stimulated.

[33] Heavy metals from these factors are predominantly present in water sources due to runoff where it is uptake by marine fauna and flora.

The mobility of certain metals including chromium (Cr) and uranium (U) varies depending on the oxidation state of the material.

These microorganisms over time have developed metabolic networks that can utilize hydrocarbons such as oil and petroleum as a source of carbon and energy.

[44] Microbial bioremediation is a very effective modern technique for restoring natural systems by removing toxins from the environment.

[47][48] Harming all manners of organic life with long term health issues such as cancer, rashes, blindness, paralysis, and mental illness.

As well as causing central nervous system issues in smaller mammals such as seizures, dizziness, and even death.

As well as being a reusable technique that strengthens through further use by limiting the migration space of these cells to target specific areas and not fully consume their cleansing abilities.

Despite encouraging results, Actinobacteria has only been used in controlled lab settings and will need further development in finding the cost effectiveness and scalability of use.

[53] For example, under anaerobic conditions, the reductive dehalogenation of TCE may produce dichloroethylene (DCE) and vinyl chloride (VC), which are suspected or known carcinogens.

[51] In addition, knowing these pathways will help develop new technologies that can deal with sites that have uneven distributions of a mixture of contaminants.

Microorganisms containing nitrile hydratases (NHase) degraded harmful acrylonitrile compounds into non-polluting substances.

[62] There are concerns surrounding release and containment of genetically modified organisms into the environment due to the potential of horizontal gene transfer.

Visual representation showing in-situ bioremediation. This process involves the addition of oxygen, nutrients, or microbes into contaminated soil to remove toxic pollutants. [ 9 ] Contamination includes buried waste and underground pipe leakage that infiltrate ground water systems. [ 10 ] The addition of oxygen removes the pollutants by producing carbon dioxide and water. [ 6 ]
An example of biostimulation at the Snake River Plain Aquifer in Idaho. This process involves the addition of whey powder to promote the utilization of naturally present bacteria. Whey powder acts as a substrate to aid in the growth of bacteria. [ 14 ] At this site, microorganisms break down the carcinogenic compound trichloroethylene (TCE), which is a process seen in previous studies. [ 14 ]
The former Shell Haven Refinery in Standford-le-Hope which underwent bioremediation to minimize the oil contaminated site. Bioremediation techniques, such as windrows, were used to promote oxygen transfer. [ 27 ] The refinery has excavated approximately 115,000 m 3 of contaminated soil. [ 27 ]