There are different factors which affect the ability of microorganisms to bioremediate heavy metals such as total metal ion concentration, soil structure, moisture content, temprature, pH, solubility of heavy metals in water any many more. Some of the factors affecting microbial bioremediation are discussed below.
Factors affecting microbial bioremediation
1: pH
Different microbes prefer different pH to survive in an environment. At low pH, heavy metals form free ionic species which would saturate the heavy metal’s binding site. Optimum pH range which favours the bioremediation is 6.5 to 8.5. Furthermore, pH of an environment also effects the structure of pollutant.
2: Essential nutrients for Microbial Bioremediation
Microbes require important nutrients such as carbon, nitrogen and phosphorous in an adequate amount for bioremediation. Therefore it is necessary to maintain C:P:N ration to enhance the bioremediation rate. These nutrients can be added to improve the microbial activities.
3: Moisture Content
Moisture is also an important factor which affects heavy metal’s solubility in water. When moisture content is high, rate of microbial degradation is low as this creates anaerobic condition which ultimately leads to death of aerobic microorganisms. Similarly, at low moisture content, survival rate of microbes might also be low. Therefore, an optimum amount of moisture is required for biodegradation process.
4: Temprature
At low temprature, heavy metals degradation by microbes becomes slow as only psychrophiles can survive at this temprature. Also decrease in metabolic activities occurs due to sub-zero water which freezed the microbial transport channel. So, the most of bioremediation processes occurs at high temprature as the solubility of heavy metals increase at this temprature, which ultimately increase their rate of availability and microbial biodegradation as well.
5: Chemical Structure
Chemical structure also has impact on rate of microbial degradation. Heavy metals having simple chemical structure and low concentration are easier to be degraded by microbes than ones having complex composition. For example, cyclohexane are difficult to bioremediate than lighter polyhydrocarbons and unbranched alkanes.
6: Soil Parameters
Soil parameters like soil region, moisture-holding capacity, texture, and particle size influence microbial biodegradation rate. Top layer soils have a higher microbe population due to oxygen and organic matter availability. Well-drained soil supports oxygen availability and microbes. Salinity affects hydrocarbonoclastic activity and exposes soil microbes to stress. Increased saline concentration negatively impacts metabolic activities, transportation, and heavy metal solubility. Therefore, well-drained soil is optimal for increased microbial biodegradation.
The success of bioremediation processes is influenced by the type and population of microbes, their molecular nature, gene and enzyme induction, metabolite production, growth efficiency, and survival rate. Additionally, the ionization of cell wall’s chemical moieties and microbial cell wall configuration also impact biodegradation rates.
Role of microbial enzymes in bioremediation
Microbial enzymes are effective in removing pollutants, particularly heavy metals, from the environment through mechanisms like elimination, oxidation, ring-opening, and reduction. However, factors like temperature, contact time, concentration, and pH affect their potency. Enzyme bioremediation is expensive, time-consuming, and unsustainable due to its instability and difficulty in identifying multiple enzyme sources.
Other bioremediation metabolites produced by microbes
Microbes produce metabolites like organic acids, biosurfactants, and polymeric substances, which are used in bioremediation. Organic acids enhance metal bioavailability, while polymeric substances enhance phytostabilization. Biosurfactants help solubilize, mobilize, and increase hydrophobic substrate bioavailability.
Conclusion:
So it is concluded that there are several factors ranging from pH, temprature, moisture, nutrients chemical structures to different soil parameters. These factors have huge impact on microbial bioremediation. And the region, where all these factors exist in an optimum range, highly favours the microbial bioremediation. Regulatory bodies should monitor potential risks associated with microbes in specific environments. More awareness on microbial degradation is needed to help policymakers and the public use this method, as many people may not be aware of it.