4.1. Criteria for Bioremediation Strategies

There are critical factors that should be considered when evaluating the use of bioremediation for site clean up. These factors are described below under separate headings.

4.1.1. Magnitude, toxicity and mobility of contaminants

The proper investigation and characterization for contaminanted sites have to be done as follows:

•Horizontal and vertical extent of contamination

•Nature of contaminants at the site

•The likely mobility of contaminants in the future

4.1.2. Geophysical, geochemical and biological characteristics of the contaminated site

Soil structure contains different textures ranging from low to high contents of sand, silt and clay. A granular and well-structured soil can facilitate effective delivery of air, water and nutrients to the microorganisms for in situ bioremediation.

Moisture content (water) is the primary factor in determining the dielectric constant of soil and other mediums. Soil moisture content generally ranges from 25 to 28 %.

pH (power of hydrogen) ranges from 5.5–8.0, which is the optimum range for the growth of microbes and to destroy the contaminants.

Temperature ranges from 15–45 ^oC. Temperature affects biochemical reaction rates and the rates are double for each 10 ^oC rise in temperature.

Oxygen is mainly used for the initial breakdown of the hydrocarbon in the contaminated sites. The amount of available oxygen will determine whether the bioremediation is carried out under aerobic or anaerobic condition.

Microbial diversity exists in the contaminated site such as Pseudomonas, Aeromonas, Flavobacteria, Chlorobacteria, Corynebacteria, Acinetobacter, Mycobacteria, Streptomyces, Bacilli, Arthrobacter, Aeromonas, Cyanobacteria, and etc.

Macrobenthos diversity is consortium of aquatic plants such as Eichornia crassipes, Salvinia molesta, Ceratophyllum demersum and is consortium of aquatic animals such as Anodonta woodiana and Limnodrilus hoffmeisteri which have high potential to degradation of turbidity, biochemical oxygen demand, chemical oxygen demand, ammonia, nitrite and nitrate in domestic wastewater.

4.1.3. Proximity of human and environmental receptors

Whether or not the bioremediation is suitable for cleaning the environment for a site is dependent on whether the rate and extent of contaminant degradation is sufficient to maintain low risks to human or environmental receptors.

4.1.4. Degradability of contaminants

The biological degradation of a compound is generally high if the compound occurs naturally in the environment such as petroleum hydrocarbons. In contrast, synthetic compounds with a high molecular weight (complex ring structures and halogen substituents) degrade more slowly than simpler straight chain hydrocarbons.

4.1.5. Planned site use

In order to decide whether bioremediation is a suitable cleanup method for a site depends on whether the rate and extent of contaminant degradation is sufficient to reduce risks to acceptable levels.

4.1.6. Ability to properly monitor

The environmental factors include chemical and physical characteristics that influence the bioavailability of contaminants, the availability of other nutrients, the activity of biological processes (temperature and pH, for example), and characteristics of the contaminants with respect to how they interact with the site’s geochemical and geological characteristics.

4.1.7. Research and technical aspects

Although there are a number of contaminants that are biodegradable, including petroleum hydrocarbons, alcohols and solvents, many widely used industrial chemicals such as polychlorinated biphenyls (PCBs), pesticides, coal tars, chlorinated solvents, and polynuclear aromatic hydrocarbons are not degraded so readily. So, more intensive research is needed, but funding for this kind of basic research is diminishing. Unlike the conventional treatment technologies, bioremediation technique must be tailored specifically to each polluted site. Each waste site has unique characteristics, and thus requires individual attention. As yet, official criteria for evaluating the success or failure of particular strategy have not been established.

4.1.8. Human resources

Because bioremediation is a new technology, there is a lack of trained human resources in this field. A successful bioremediation program requires a multidisciplinary approach, integrating fields such as microbiology, engineering, geology, hydrogeology, soil science and project management. Universities do not offer qualifications in bioremediation engineering and such combined expertize can be acquired only through experience and training on the job.

4.1.9. Degradability of contaminants

Unlike other industries, bioremediation does not result in the production of high value-added products. Thus, venture capital has been slow to invest in the technology and, as a consequence, commercial activity in research and development has lagged far behind other industrial sectors. As bioremediation is considered innovative technology, clients and regulatory agencies often scrutinize bioremediation more closely than conventional technologies. Consequently, tighter restrictions and performance standards are frequently imposed on bioremediation than on other remediation technologies. This can ultimately lead to a greater risk from a liability standpoint if the bioremediation program does not accomplish the predetermined goals.