i.Solid-phase treatment

*Trace Metals in the Environment - New Approaches and Recent Advances*

like type of soils, pH, temperature, oxygen and nutrients.

**3.2 Biotic or biological factors**

**3.3 Abiotic or environmental factors**

terrestrial and aquatic systems [8].

**4. Bioremediation technique**

above factors are control degradation kinetics [5, 7].

composition [5, 6].

the activity of bacteria, fungi, algae and plants. Enzymatic metabolic pathways of microorganisms facilitate the progress of biochemical reactions that help in degradation of the pollutant. Microorganisms are act on the pollutants only when they have contact to the compounds which help them to generate energy and nutrients to multiply cells. The effectiveness of bioremediation depends on many factors; including, the chemical nature and concentration of pollutants, the physicochemical characteristics of the environment, and their accessibility to existing microorganisms [4]. The factors are mainly microbial population for degrading the pollutants, the accessibility of contaminants to the microbial population and environment factors

Biotic factors are helpful for the degradation of organic compounds by microorganisms with insufficient carbon sources, antagonistic interactions among microorganisms or the protozoa and bacteriophages. The rate of contaminant degradation is frequently dependent on the concentration of the contaminant and the amount of catalyst present in biochemical reaction. The major biological factors are included enzyme activity, interaction (competition, succession, and predation), mutation, horizontal gene transfer, its growth for biomass production, population size and its

The interaction of environmental contaminants with metabolic activity, physicochemical properties of the microorganisms targeted during the process. The successful interaction between the microbes and pollutant depends on the environmental situations. Microbial growth and activity are depended on temperature, pH, moisture, soil structure, water solubility, nutrients, site conditions, oxygen content and redox potential, deficiency of resources and physico-chemical bioavailability of pollutants, concentration, chemical structure, type, solubility and toxicity. This

Biodegradation of pollutant can occur under range of pH (6.5–8.5) is generally optimal for biodegradation in most aquatic and terrestrial environment. Moisture affects the metabolism of contaminant because it depends on the kind and amount of soluble constituents that are accessible as well as the pH and osmotic pressure of

Superficially, bioremediation techniques can be carried out ex-situ and in-situ site of application (**Figure 1**). Pollutant nature, depth and amount of pollution, type of environment, location, cost, and environmental policies are the selection standards that are considered for selecting any bioremediation technique. Performance based on oxygen and nutrient concentrations, temperature, pH, and other abiotic factors that determine the success of bioremediation processes [9, 10]. **Ex-situ bioremediation techniques** involve digging pollutants from polluted sites and successively transporting them to another site for treatment. Ex-situ bioremediation techniques are regularly considered based on the depth of pollution, type of pollutant, degree of pollution, cost of treatment and geographical location of the polluted site. Performance standards also regulate the choice of ex-situ bioremedia-

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tion techniques.

Solid-phase bioremediation is an ex-situ technology in which the contaminated soil is excavated and placed into piles. It is also includes organic waste like leaves, animal manures and agriculture wastes, domestic, industrial wastes and municipal wastes. Bacterial growth is moved through pipes that are distributed throughout the piles. Air pulling through the pipes is necessary for ventilation and microbial respiration. Solid-phase system required huge amount of space and cleanups require more time to complete as compared to slurry-phase processes. Solid-phase treatment processes include biopiles, windrows, land farming, composting, etc. [11].

ii.Slurry-phase bioremediation

Slurry-phase bioremediation is a relative more rapid process compared to the other treatment processes. Contaminated soil is combined with water, nutrient and oxygen in the bioreactor to create the optimum environment for the microorganisms to degrade the contaminants which are present in soil. This processing involves the separation of stones and rubbles from the contaminated soil. The added water concentration depends on the concentration of pollutants, the biodegradation process rate and the physicochemical properties of the soil. After completion of this process the soil is removed and dried up by using vacuum filters, pressure filters and centrifuges. The subsequent procedure is soil disposition and advance treatment of the resultant fluids.
