11.2 Microalgae for Wastewater Treatment

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nitrogen and phosphorus can be further used as low-cost fertilizer or as animal feed.

Microalgae-based biofertilizers have the same efficiency as the chemical fertilizers

[11]. Moreover, using microalgae-based biofertilizer resulted in lower phosphorus

concentration in water runoff as organic phosphorus is slowly mineralized by

microalgae and then liberated at a rate almost equal to that of the phosphorus

uptake by plants. It was also observed that this type of biofertilizer does not have

negative effects on the soil microbiome and biological activity. Microalgae used for

biofertilizers include Chlorella sp., Acutodesmus sp., Nostoc muscorum, Anabaena

variabilis, Tolypothrix tenuis, and Aulosira fertissima. Cultivation of microalgae in

wastewater also results in the capture of CO2, one of the most abundant green-

house gases. It also yields biomass convertible into biodiesel, biochemicals having

pharmaceutical applications and other value-added products.

Chlorella and Scenedesmus are the most common microalgae used for wastewa-

ter treatment due to their ease of isolation, propagation, and efficient removal of

nutrients. Investigations have been carried out to test the efficiency of microalgae

in remediating wastewater [12]. It may have various effects on the characteristics of

wastewater as:

11.2.1

Biological Oxygen Demand (BOD)

BOD indicates the amount of biologically degradable organic pollutants in the

water bodies. It is the amount of oxygen used by microorganisms to completely

disintegrate organic molecules to CO2 and water. BOD depletes dissolved oxygen in

the water leading to the dead of fishes and anaerobiosis, hence, its reduction is the

primary objective of wastewater treatment. Microalgae utilize the CO2 released as a

carbon source for photosynthesis, using carbonic anhydrase. BOD values vary with

the concentration of organic pollutants. The BOD of pristine waters lies below 1,

2–8 mg/l for moderately polluted waters and 20 mg/l for treated municipal sewage

[13]. Studies have shown Scenedesmus sp. reduced BOD of a fertilizer wastewater

plant in Vietnam by 83.7% [1], while species of Neochloris, Chlorella, and Chloro-

coccum reduced BOD of river polluted with pharmaceuticals effluents by 91%, 84%,

and 83%, respectively [4]. C. vulgaris reduced BOD of domestic wastewater by 68.4%

[14]. Another study showed that a consortium of microalgae removed 82% of BOD

in an untreated sewage wastewater [10].

11.2.2

Chemical Oxygen Demand (COD)

COD is an indicator of the amount of total organic carbon in the water, denoting

both the amount of biologically active and inactive organic matter in water. The

COD varies with water bodies, wherein the surface water normally ranges from 5 to

20 mg/l [15]. A study showed that COD of domestic wastewater from IIT Kharagpur

campus, India was reduced by 95.9% using Scenedesmus sp. [2]. COD of primary

septic tank effluent from Environmental Sciences and Engineering Department

(NUST), Pakistan, was reduced by 84.86% and 95% by Chlorella sp. and Scenedesmus

sp., respectively [12]. Further studies showed that the COD removal efficiency