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Bioremediation for Sustainable Environmental Cleanup

Various reports exhibited that active as well as inactive fungal cells, play an essential role in the

adsorption of inorganic metal ions (Srivastava and Thakur 2006, Tiwari et al. 2013, Igiri et al. 2018).

Lakkireddy and Kües (2017) reported that Coprinopsis atramentaria could accumulate 94.7% of

800 mg L⁻¹ of Pb²⁺. As a result, it is being identified as a good heavy metal ion accumulator for

mycoremediation. Some of the fungal biomasses viz. Aspergillus niger, Rhizopus oryzae, Penicillium

chrysogenum and Saccharomyces cerevisiae are also effective in converting the most hazardous

oxidation state of heavy metal to less toxic/non-toxic oxidation state of heavy metals (Park et al.

2005). Inoculum of Arbuscular Mycorrhizal Fungi (AMF) is found to enhance the Pb remediation

efficiency of Japanese clover (Kummerowia striata (Thunb.)) and barnyard grass (Echinochloa

crus-galli L.) (Chen et al. 2005). Fungi like Aspergillus sp. and Coprinopsis sp. are largely used

as biosorbents for eliminating toxic metals with great potential for metal absorption and recovery

(Akar et al. 2005, Dursun et al. 2003).

Biosurfactants produced by fungi also play a major role in cleaning heavy metals from

contaminated soil. Luna et al. (2016) reported that anionic biosurfactant from Candida sphaerica

has 79% removal efficiency for Pb from heavy metal contaminated soil. The biosurfactant was

found to be effective in removing the exchangeable, oxide, carbonate and organic fractions of heavy

metals by forming complexes with metal ions.

Yeast biosurfactants are also found to be effective in cleaning heavy metals and petroleum

derivatives from contaminated soils by reducing soil permeability. The crude biosurfactant

significantly reduced the concentration of Pb and other heavy metals from the test sample of soil.

Biosurfactants being amphoteric in nature, not only help in eliminating heavy metals but can also

be applied to remove hydrophobic organic compounds. They reduce the interfacial tension and

solubilize hydrocarbons in the aqueous phase or capture the oil droplets within their micelles. On

the other hand, anionic nature biosurfactants capture the metal ions through electrostatic interactions

or complexation (Rufino et al. 2011). In recent years, biosurfactants have received a lot of interest

for their biodegradable nature, low toxicity and diversity. Several yeast strains such as S. cerevisiae,

Rhodotorula pilimanae, Hansenula polymorpha, Yarrowia lipolytica and Rhodotorula mucilage

have been utilized to convert more toxic forms of heavy metals to non-toxic ones (Ksheminska

et al. 2008, Chatterjee et al. 2012).

Phycoremediation is an important aspect that deals with removing or degrading heavy metals

from contaminated sites with the help of algal biomasses. Features that make dead algae biomass

an ideal candidate for the removal of heavy metals include the presence of sulfate and carboxylic

acid functional groups on the cell wall that facilitate metal adsorption and large surface area/volume

ratios. In comparison to other microbial biosorbents, algae are autotrophic, require little nutrients and

produce large amounts of biomass. Heavy metal removal has been achieved using these biosorbents

with a high sorption capacity. Algal biomass bioremediates the heavy metal contaminated effluent

either through adsorption or by integrating inside the cells (Abbas et al. 2014, Chabukdhara et al.

2017, He and Chen 2014).

When compared to other microbial biosorbents, algal biomasses had biosorption effectiveness

of 15.3–84.6%. Ion exchange techniques are used to accomplish this (Mustapha and Halimoon

2015). For successful heavy metals cleanup from the polluted area, algal biomass has been

immobilized using various chemical pretreatments, which lead to the formation of stable cellular

aggregates with appropriate size, efficient mechanical strength, rigidity, porosity and increased

biomass concentration (Laxman and More 2002). Red marine algae Jania ruben L. was found to be

effectively bioadsorb Pb, which was further confirmed by thermal analysis (Hanbali et al. 2014).

Various reports are available in literature regarding the use of algal biomasses in the decontamination

of toxic metals. Goher et al. (2016) reported that dead cells of Chlorella vulgaris could be used for

the removal of copper (Cu²⁺), cadmium (Cd²⁺) and lead (Pb²⁺) ions from an aqueous solution under

several conditions of biosorbent dosage, pH and contact time. The biomass of C. vulgaris removed

cadmium (Cd²⁺), copper (Cu²⁺), and lead (Pb²⁺) at the rate of 95.5, 97.7 and 99.4%, respectively,

constituting a combined solution of 50 mg dm⁻³ of each metal ion. Thus applying appropriate