Table of Contents:
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.
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 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.
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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.