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Bioremediation for Sustainable Environmental Cleanup

BV SORBEX, a company owned by the pioneer researcher in the field of biosorption, McGill

University and Bohumil Volesky from Canada, has applied the laboratory process of biosorption to

an industrial level (Volesky 2003b).

However, there are some limitations in the application of the biosorption method on an industrial

scale. This limitation is due to less durability and low mechanical resistance of the biomass, which

create problems in the process and other factors, including regeneration of the sorbent and its

subsequent declination. Thus the success of the sorption process depends on the recovery and reuse

of the sorbent. It is further required that the biosorption process be integrated into other microalgae­

based applications, including energy recovery in the form of biofuels like biohydrogen or biodiesel

and value-added biomaterial production to make the overall procedure more economically feasible

and sustainable. Next new directions for integrating various microalgae-based technologies have

been described with a view to make it a competitive metal bioremediation technology with additional

applications to raise its sustainability. Various new opportunities for such combined technologies

and the biorefinery approach for microalgal wastewater treatment and bioremediation are discussed

next.

12.4 Combining Microalgal Technologies as Low-cost and Sustainable

Approach

Schenk et al. (2008) emphasized on exploiting the biological pathways for improving the efficiency

of the bioremediation potential of algae. Wastewaters have been used for biomass production of

microalgae during the bioremediation process and utilized for yielding carotenoids (Kalra et al.

2020). Microalgae can grow about 10% of their total volume during every 2 d. The biomass of

Chlorella vulgaris and Scenedesmus obliquus have the biochemical composition of 30–35% proteins,

6–8% lipids, 39–30% carbohydrates (Bhatia et al. 2017) and are used in pisciculture feeds. The algal

biomass derived from wastewater bioremediation sludge can also be used as a biostimulant for crop

plants (Kalra et al. 2020). The biomass of algae can be processed with the torrefaction process to

produce 72.5 ± 1.7% charcoal yields.

Further, microalgae can successfully hold carbon in the form of gas from the environment.

The heterotrophic algae can also intake carbon in the form of organic carbon from acetate, glycerol

and glucose, whereas autotrophic algae take up inorganic carbon. Carbonates soluble in water act

as a fount of carbon dioxide that enters the algal cell by diffusion at pH 5.0–7.0 (Picardo et al.

2013, Sydney et al. 2014). Bicarbonate is transformed to CO2 within the microalgal cell before

being turned into energy-rich molecules by enzyme ribulose bisphosphate carboxylase/oxygenase

(Gonçalves et al. 2017).

Wastewater contains heavy metals in addition to phosphate, nitrogen and carbon. Microalgal

assisted wastewater treatment is regarded as one of the most effective heavy metals elimination

methods. However, the metal ion bioconcentration capacity is influenced by various factors, such

as temperature, pH, availability of nutrients, cell number, cell size and cell structure (Kosek et al.

2016).

12.4.1 Integrating Biofuel Production and Bioremediation using

Microalgae

To make the overall process of microalga-based bioremediation of metals an economically sustainable

technology, it has been proposed to integrate the process with various other applications. It has

been reported that even the waste biomass of cyanobacteria from biohydrogen rectors can be used

successfully for metal bioremediation (Mona et al. 2011c). The twofold uses of the cyanobacterium

for constant hydrogen production and elimination of some contaminants from textile industry

wastewater by spent algal biomass as an integrated laboratory-scale system were demonstrated by

Kaushik et al. (2011). Waste algal biomass of Nostoc linckia tested at multi-stages (5, 15, 25 d) from

hydrogen-producing photobioreactors when tested for metal bio removal capability show very good