<P> In the event of biostimulation, adding nutrients that are limited to make the environment more suitable for bioremediation, nutrients such as nitrogen, phosphorus, oxygen, and carbon may be added to the system to improve effectiveness of the treatment . </P> <P> Many biological processes are sensitive to pH and function most efficiently in near neutral conditions . Low pH can interfere with pH homeostasis or increase the solubility of toxic metals . Microorganisms can expend cellular energy to maintain homeostasis or cytoplasmic conditions may change in response to external changes in pH . Some anaerobes have adapted to low pH conditions through alterations in carbon and electron flow, cellular morphology, membrane structure, and protein synthesis . </P> <P> Bioremediation can be used to completely mineralize organic pollutants, to partially transform the pollutants, or alter their mobility . Heavy metals and radionuclides are elements that cannot be biodegraded, but can be bio-transformed to less mobile forms . In some cases, microbes do not fully mineralize the pollutant, potentially producing a more toxic compound . For example, under anaerobic conditions, the reductive dehalogenation of TCE may produce dichloroethylene (DCE) and vinyl chloride (VC), which are suspected or known carcinogens . However, the microorganism Dehalococcoides can further reduce DCE and VC to the non-toxic product ethene . Additional research is required to develop methods to ensure that the products from biodegradation are less persistent and less toxic than the original contaminant . Thus, the metabolic and chemical pathways of the microorganisms of interest must be known . In addition, knowing these pathways will help develop new technologies that can deal with sites that have uneven distributions of a mixture of contaminants . </P> <P> Also, for biodegradation to occur, there must be a microbial population with the metabolic capacity to degrade the pollutant, an environment with the right growing conditions for the microbes, and the right amount of nutrients and contaminants . The biological processes used by these microbes are highly specific, therefore, many environmental factors must be taken into account and regulated as well . Thus, bioremediation processes must be specifically made in accordance to the conditions at the contaminated site . Also, because many factors are interdependent, small - scale tests are usually performed before carrying out the procedure at the contaminated site . However, it can be difficult to extrapolate the results from the small - scale test studies into big field operations . In many cases, bioremediation takes more time than other alternatives such as land filling and incineration . </P>

The bioleaching processe(s) used by the industries for the large scale operation is/are