11.1 Introduction

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production under stress. Different species of microalgae adapt with changing mode

of nutrition. Based on their metabolic process microalgae may be divided into:

Autotrophs: Autotrophic microalgae C. vulgaris, Coenochloris pyrenoidosa, and

Scenedesmus sp. can produce hydrocarbons, proteins, lipids, adenosine triphos-

phate (ATP), oxygen, and 3-phosphoglycerate, by photosynthesis, using light and

CO2, which are utilized for their growth.

Heterotrophs: Heterotrophic microalgae rely on organic carbon-like glycerol and

carbon for their energy and cannot utilize atmospheric CO2 and light. They can

convert sugar molecules into biomass-like lipids [3].

Mixotrophs: Mixotrophic microalgae have the metabolic ability of both autotrophic

and heterotrophic growth. They can propagate under low light intensity and prof-

its from the aspects of both type of metabolism.

Photoheterotrophs: The source of energy include light and organic carbon. In the

absence of light, they use organic carbons as the main source of energy, making

them favorable for wastewater treatment overcoming light dependency, which is

an important disadvantage of large-scale photobioreactors.

11.1.2

Composition of Wastewater

The composition of wastewater depends on the sources and is an intricate assort-

ment of organic and inorganic compounds. Most organic constituents of sewage

are in the form of carbohydrates, lipids, polypeptide, and volatile acids. The inor-

ganic components include high concentrations of calcium, chlorine, potassium,

magnesium, sodium, sulfur, phosphate, and heavy metals. The organic water

contaminants can be macro (organic acids, carbohydrates, melanins) or micro

(xenobiotics-antibiotics, pesticides, and recalcitrant chemicals) pollutants which

are highly toxic to the ecosystem. Domestic wastewater has a high concentration

of organic macro and micropollutants with increasing discharge of low-molecular

hazardous pollutants, including phthalates, polychlorobiphenyls (PCBs), polycyclic

aromatic hydrocarbons (PAHs), bisphenol A originating from pharmaceuticals,

which can be excreted in its original or metabolized form. Study has shown that

high concentration of these molecules is also present in urban wastewater, sewage

from hospitals, groundwater, and drinking water [4]. Total nitrogen (TN) and total

phosphorus (TP) have been reported to be 10–60 mg/l in municipal wastewater [5].

Wastewater from agricultural fields has high concentrations of nitrogen and

phosphorus derived from manure compared to municipal wastewater. Agricultural

and agro-based industries release high volumes of organic contaminants, inorganic

nutrients, pathogens, antibiotics, and pesticides [6], which may not contain a high

concentration of heavy metals and hazardous pollutants. The amount of TN varies

from dairy (185 mg/l) to swine wastewater (3213 mg/l), whereas TP content ranges

from 30 mg/l in dairy wastewater to 987 mg/l in swine piggery wastewater [7]. The

TN and TP have been reported to be more than 1000 mg/l in agricultural wastewater

to 500–600 mg/l in farms [5].