Table 1.

Critical factors for microbial bioremediation.

Factors	Remarks	References
Biological factors	Soil microorganisms compete for carbon sources, or bacteriophages and protozoa prey on each other, all of which can affect organic compound degradation. Derivatization rates are influenced by contaminants and catalyst levels. Expressed enzymes can speed up or slow contaminant degradation. Enzymes must also be involved in contaminant metabolism to have an affinity for the contaminant and availability. The major biological factors: interaction (competition, predation, and succession), population size, and composition.	[31,32]
Oxygen	Biodegradation rates can be improved by using organisms that don’t require oxygen. Anaerobic decomposition occurs as most living organisms need oxygen to survive. In most cases, hydrocarbon metabolism can be boosted by the addition of oxygen.	[33]
Moisture content	Microorganisms require a sufficient amount of water to achieve their growth goals. When the soil is too wet, the biodegradation agents don’t work as well.	[34]
Nutrients	Nutrients can influence microbial growth and reproduction, as well as biodegradation rate and effectiveness. Optimizing the bacterial C:N:P ratio can improve biodegradation efficiency, especially when essential nutrients like N and P are supplied. Carbon, phosphorous, and nitrogen are just a few of the nutrients microorganisms need to survive. In low concentrations, hydrocarbon degradation is also limited. Adding nutrients to cold environments can increase microorganisms’ metabolic activity and thus the biodegradation rate. Aquatic biodegradation is limited by nutrient availability. Oil-eating microbes require nutrients to thrive. These essential nutrients are found in small amounts in nature.	[35,36]
Temperature	The most important physical factor influencing microorganism survival and hydrocarbon composition is temperature. In cold climates like the Arctic, natural oil degradation is slow, putting more pressure on microbes to clean up spilled oil. Here, the sub-zero water freezes the microbial transport channels, rendering them unable to perform their metabolic functions.Temperature affects the metabolic turnover of enzymes involved in degradation. Also, each compound’s degradation requires a specific temperature. Temperature affects microbial physiological properties and thus speeds up or slows down bioremediation. Increased microbial activity occurs at higher temperatures. It started to drop suddenly as the temperature increased or decreased, and theneventually stopped.	[37,38]
pH	A compound’s acidity, alkalinity, and basicity affect microbial metabolism and the removal process. Microbial growth can be predicted by the soil’s pH. Even minor pH shifts have a significant impact on metabolic processes.	[39]
Sitecharacterization and selection	Before proposing a bioremediation remedy, it is necessary to conduct adequate remedial investigation work to characterize the extent of the contamination. Site selection procedures include determining the horizontal and vertical extent of contamination, defining parameters and sampling locations, and describing sampling and analysis methods.	[40]
Metal ions	Metals are essential for bacteria and fungi, but excessive amounts inhibit cell metabolism. Degradation rates are influenced by metal compounds on both a direct and indirect basis.	[41]
Microorganisms	High concentrations of some toxic compounds can harm microorganisms and slow decontamination process. Toxicity varies with the toxicant, concentration, and microorganisms exposed.	[42]