# Microbial Bioremediation and Biodegradation of Petroleum Products--A Mini Review
## 4 Emerging Biodegradation Technologies
### Bioremediation
#### 4.3.1 Agricultural Remediation  
The composition of pollutants, concentration of pollutants and microorganism present, temperature, soil pH, salinity, and nutrient availability are the various factors influencing the success of the bioremediation technique [63]. Generally, microorganisms are present in all sub-surface soil layers, but due to the composition and concentration of pollutants, the microbial biota present may not be effective in treating the contaminated sites, therefore, may need oxygen (for aerobic biodegradation), nutrients (to enhance the growth of microbes) and moisture (to aid microbial activity) [65]. The optimum soil moisture for biodegradation to be effective is within the range of 12-30% weight composition and 40-85% field capacity. pH within 6-8 is optimum for effective bioremediation, but the remediation process may accommodate pH within 4-8.  
Land farming also referred to as land recovery, is a method of remediating above-ground soil that lowers the concentration of crude oil components through the degradation process [65; 66]. Traditionally, land farming involves spreading polluted soils on the ground surface of a treatment site in a thin layer and enhancing aerobic microbial activity inside the soil to accelerate naturally occurring biodegradation mechanisms [66]. This phenomenon is usually used to remediate hydrocarbon-polluted sites, including polyaromatic hydrocarbons. As a result, the two remediation mechanisms involved in the removal of pollutants are biodegradation and volatilization [66]. It decreases the concentration of petroleum hydrocarbon constituents predominantly via bacterial-mediated biodegradation, while volatilization, abiotic, and fungal-mediated processes may also play a role [54]. Therefore, building a suitable land recovery scheme with a waterproof liner minimizes the seeping of pollutants into neighboring areas during the operation [46]. This approach is considered based on the depth of the pollutants below the surface. If a pollutant lies < 1 m below the ground surface, bioremediation can continue without excavation, while pollutants that lie > 1.7 m must be transported to the ground surface to effectively improve bioremediation [67]. At large, excavated contaminated toposils are prudently applied to a fixed layer of support above the ground surface to allow utochthonous microorganisms to aerobically biodegrade the pollutant [68]. Tillage-triggering aeration, nutrient adding (nitrogen, phosphorus, and potassium), and irrigation are the key processes that stimulate autochthonous microorganism activity [57]. This is very efficient when environmental situations are suitable for microbial development and activity. Its application often involves improving certain environmental parameters, including humidity, pH, oxygen, and nutrient availability [69]. Furthermore, because of its structure and pollutant discharge process (volatilization), it is not appropriate for treating soil contaminated with harmful volatiles, particularly in hot (tropical) climatic areas. These and other constraints make land-based bioremediation time-consuming and inefficient when likened to other ex situ bioremediation approaches.