Explanation:

• Correct Option: (d) 
• All statements are correct Supplementary Notes Bioremediation Bioremediation techniques are destruction techniques to stimulate the growth of microorganisms, using the contaminants as a food and energy source.
• These techniques have been successfully used to remediate soils/sludge & groundwater contaminated by petroleum hydrocarbons, solvents, pesticides, wood preservatives, and other organic chemicals.
• Oxygen, water & nutrients are added, and the temperature and pH are controlled.
• The rate at which microorganisms degrade the contaminants is in fl uenced by: the speci fi c contaminants present, their concentrations, the oxygen supply, moisture, temperature, pH, nutrient supply, bio-augmentation, and co-metabolism.
• Micro-organisms can be adapted to degrade speci fi c contaminants or enhance the process.
• In situ bioremediation Bioventing: supply of air and nutrients through wells to contaminated soil to stimulate the growth of indigenous bacteria.
• It is used for simple hydrocarbons and can be used where the contamination is deep under the surface.
• Biosparging: Injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by naturally occurring bacteria.
• Bio augmentation: Microorganisms are imported to a contaminated site to enhance the degradation process.
• Bioleaching: It is the extraction of metals from their ores through the use of living organisms.
• This is much cleaner than the traditional heap leaching using cyanide.
• Ex-situ bioremediation Bioreactors: These are large vessels where the contaminated material can be monitored and conditions for bioremediation can be controlled.
• Biological organisms typically have conditions where they operate best.
• In bioreactors we can control the mixing rate, temperature, pH, and nutrient levels to suit the organisms breaking down our contaminants.
•   Land farming: It involves spreading contaminated soil into a lined bed (to prevent leaching) and periodically applying nutrients and mixing the soil to boost biological activity.
• Bio piling: It places the contaminated soil into piles that are well aerated and nutrients are added to speed up bioremediation.
• In all cases, the contaminant levels are monitored to verify that bioremediation is taking place and steps are taken to ensure that contaminated material stays out of contact with the environment.