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Current status and prospects of bioremediation

Recently, emphasis on bioremediation has been increasing in the field of hazardous-waste management such as solid waste, liquid waste, toxic gases, heavy metal, and radioactive waste. However, bioremediation is still an immature technology. Although microbes are the primary stimulant in the bioremediation of contaminated environment and play an essential role in biogeochemical cycles, it is difficult to assess the impact of bioremediation on the ecosystem due to limited understanding of the changes in microbial communities dining bioremediation.

Bioremediation technologies

Bioremediatiou of toxic wastes including solid waste, liquid waste, toxic gases, hearty metal and radioactive waste can be categorized as in situ and ex situ bioremediation. The mam objective of bioremediation is to degrade and transform organic pollutants into a less toxic form. The different strategies of in situ and ex situ bioremediation and phytoremediation technologies which remediate the contaminants from soil, water and air are presented in Table 1. In in situ techniques, the soil and groundwater are remediated in place without excavation, while in ex situ applications it is excavated prior to treatment. Selection of appropriate technology among the different bioremediation strategies to treat contaminants depends upon three basic principles, i.e., biochemistry, bioavailability and the bioactivity (Shukla et al. 2010).

New bioremediation methodologies for waste management

Phycoremediation

Phycoremediation involves algae (micro and macro) for the remediation of contaminants in a water body. At minimal cost, algae remove excess nutrients effectively and fix carbon-dioxide by

Table 1. Technologies available for bioremediation of waste.

Bioremediation

methods

Applications

Advantage

References

Ex situ

Laud farming

Surface application, aerobic process, application of organic materials to natural soils followed by irrigation and tilling.

Cost-effective, Simple and self-heating.

Silva-Castro et al. (2012)

Biopilmg

Above-ground piling of excavated polluted soil, followed by nutrient amendment.

Limited volatilization of low molecular weight pollutants.

Treat large volume of polluted soil m a limited space.

Biopile setup can easily be scaled up to a pilot system.

Dias et al (2015) Chemlal et al. (2013)

Windrow

Periodic turning of polluted soil with addition of water. Uniform distribution of pollutants, and microbial degradative activities.

Higher efficiency towards hydrocarbon removal.

Coulon et al (2010)

Compostmg

Addition of nutrients, watering, tillmg, addition of suitable microflora and bulking agents were considered an alternative option to unprove the bioremediation of oil sludge.

Economical and effective way to treat oil sludge.

Waste stabilization.

Prakash et al. (2015)

Bioreactors (Slurry reactors and Aqueous reactors)

Treat soil or water polluted with volatile organic compounds (YOCs) including benzene, toluene, ethylbenzene and xylenes (BTEX).

Toxic concentrations of contammants.

Excellent control of bioprocess. Increased pollutant bioavailability, and mass transfer parameters. Effective use of moculants and surfactant.

Chikere et al. (2016)

In situ

Biosparging

Used m treatmg aquifers contaminated with petroleum products, especially diesel and kerosene and BTEX contaminated ground water.

Most efficient. Non invasive.

Kao et al. (2008)

Bioventing

Restoring sites polluted with lightly spilled petroleum products. Biodegradability of pollutants.

It can be used in anaerobic condition.

Hoheuer and Ponsin (2014)

Bioauginentatiou

Hazardous waste remediation as well as aerobic waste treatment.

Naturally attenuated process, treats soil and water.

Tale et al. (2015)

Table 1 Contd....

...Table 1 Contd.

Bioremediation

methods

Applications

Advantage

References

Bioslurpmg

Remediating capillary, unsaturated and saturated zones.

Remediate soils contammated with volatile and semi-volatile organic compounds.

Cost-effective.

Kim et al. (2014) Plulp and Atlas (2005)

Phytoremediation

Phytodegradation

Plants and associated microorganisms degrade organic pollutants like petroleum hydrocarbon.

Cost-effective.

Al-Baldavvi et al. (2015)

Phytoextraction

Remove metal pollutants, petroleum, hydrocarbons and radionuclides and accumulate in plants. Remove organics from soil by concentrating them m plant parts.

Used in both soil and ground water. Contammants permanently removed fi'om soil.

Zhuang et al. (2007)

Phytotrausformation

Plant uptake and degradation of orgamc compounds such as xenobiotic substances.

Both economically and environmental friendly.

Al-Baldavvi et al. (2018)

Rhizofiltration

Roots absorb mainly heavy metals such as Zn, Pb, Cd, and As from water and aqueous waste streams.

In situ practice resultuig in no disturbance. Contammants do not have to be translocated into shoots.

Benavides et al. (2018)

Phytostabilization

Plants reduced the bioavailability of heavy metal such as Sb, Cd, Cr, Ni, Pb, and As via precipitation.

Cost-effective. Capable of remediating heavy metal contammated soil without impaumg the soil quality.

Sylvain et al. (2016)

Phytovolatilization

Organic pollutants are absorbed through plant roots and transported through the plant.

The contammant hke Hg may transform mto less toxic form.

Limmer and Burken (2016)

photosynthesis. By algal metabolism, xeuobiotics and heavy metals are detoxified or transformed to less toxic form or volatilized. Numerous recent studies show accumulation and degradation of polycyclic aromatic hydrocarbons and heavy metal by fresh-water algae like Scenedesmus quadricauda, Chlorella vulgaris, Selenastriwi capricornutum, and Scenedesmusplatydiscus. Ajayan et al. (2015) reported that heavy metals such as Cr, Cu, Pb, and Zn were found to be removed very effectively by Scenedesmus quadricauda microalgae with removal rates ranging from 60 percent to 100 percent.

Cyanophyceae, Chlorophyceae, Euglenophyceae, Bacillariophyceae, and Desmidiaceae were used in wastewater treatment plant (WWTP) at Shimoga Town, Karnataka State, India, recorded by Shanthala et al. (2009). The highest Cu, Zn and Co removal of 60, 42.9 and 29.6 percent, respectively, was observed with Oscillatoria quadripunctutata, while highest Pb removal of

34.6 percent was found with Scenedesmus bijuga in sewage wastewater (Ajayan et al. 2011). El-Sheekh et al. (2005) also observed the removal of heavy metals from paper production Verta Company, sewage wastewater and salt and soda company wastewater by mixed culture of Nostoc rnuscorurn and Anabaena subcylindrica microalgae.

Chlorella pyrenoidosa was investigated by Patliak et al. (2015) as pliycoremediatiou of dye removal fr om textile wastewater (TWW) in batch cultures and he observed that alga potentially grows up to 75 percent concentrated textile wastewater and reduces phosphate, nitrate, and BOD by 87 percent, 82 percent, and 63 percent, respectively. Removal of methylene blue dye (MB) was also observed by using dry and wet algal biomass in which diy algal biomass (DAB) was a more efficient biosorbent of MB dye as compared to wet algal biomass (WAB) because of large surface area and high binding affinity for MB dye.

Long term utilization of pesticides creates dangerous effects on human health and environment via biomagnification and eutrophication process. Among all the pesticides, organophosphate pesticides are widely used pesticides in the world and bioremediation is the best method of removing the pesticide that contaminates the land and water. Numerous studies show algae sp. Spirulinaplatensis and Spirogyra were used for the biodegradation of pesticide chloipyrifos and biosorption of heavy metal chromium at various concentrations (Samuel Reinhard et al. 2019). Heavy metals are the most hazardous pollutants such as chromium (Cr) compounds which are highly toxic to plants and retard their growth and development. The utilization of algae to remediate toxicants or pollutants from the contaminated environment is named as phycoremediation. Phycoremediation is a novel technique in bioremediation methods to degrade the pesticide using the algal spp. Zainith et al. (2019) reported that microalgae Scenedesmus rubescens КАСС 2 remove nitrogen, phosphorus, and heavy metals more efficiently from industrial and domestic effluents.

 
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