## 2 Wastewater Treatment by Microalgae
### Agricultural Wastewater
#### 2.2.3 Microalgae Treatment of Agricultural Wastewater
In this research, they used _Chlamydomonas_ sp. JSC4 cells as an attached culture and assessed the effect of different parameters such as the volume of the swine wastewater and the concentration of Cu(II) on the productivity of the biofilm and removal efficiencies [61]. They reported that the swine wastewater had the best productivity levels (49.70 g\({}^{-1}\) m\({}^{-2}\) d\({}^{-1}\)) at an initial composition of 600 mg L\({}^{-1}\) of total nitrate and 0.23 mg L\({}^{-1}\) of Cu(II), but when the concentration of Cu(II) was increased to 15 mg L\({}^{-1}\), the productivity of the biofilm was decreased to 37.73 g m\({}^{-2}\) d\({}^{-1}\) with a TN removal of 85.79%, TP removal of 96.56% and Cu(II) removal of 93.70% [61]. Tetraselmis sp. ([PERSON] et al, 2021) S. obliquaus SXND-02 ([PERSON] et al, 2021) H. pluvialis ([PERSON] et al, 2022) H. pluvialis ([PERSON] et al, 2022) Duraliella FACHB-558 ([PERSON] et al, 2019) C. vulgaris ([PERSON] et al, 2019) Chlorella sp. HL ([PERSON] et al, 2019) C. sorkiniana SVMBIOEN2 ([PERSON] et al, 2021) C. sorkiniana AK-1 ([PERSON] et al, 2020) C. pyrenoidosa ([PERSON] et al, 2020) C. pyrenoidosa ([PERSON] et al, 2020) Chlamydomonas sp. JSC4 ([PERSON] et al, 2018) B. braunii ([PERSON] et al, 2018) A. maxima ([PERSON] et al, 2019) S. obliquaus SXND-02 ([PERSON] et al, 2021) H. pluvialis ([PERSON] et al, 2022) H. pluvialis ([PERSON] et al, 2022) H. pluvialis ([PERSON] et al, 2022) Duraliella FACHB-558 ([PERSON] et al, 2019) H. pluvialis ([PERSON] et al, 2022) Duraliella  
The microcalga _Desmodesmus_ sp. PW1 was used to treat piggery wastewater [83]. The results showed that this isolated strain from piggery wastewater had two important potentials, the first was the ability to reduce the pollutants in piggery wastewater, and the second was to self-flocculate in it and overcome the harvesting problem [80]. It can remove about 90% of total nitrogen and about 70% of total phosphorus from piggery wastewater with an initial composition of 296.7 mg L\({}^{-1}\) of TN and 28.6 mg L\({}^{-1}\) of TP under 25 \({}^{\circ}\)C and 4000 lx [83]. In addition, as this strain can self-flocculate more than 90% in 2.5 h of sedimentation, it could be a promising candidate for biomass and biodiesel production (1.76 g L\({}^{-1}\) and 7.2%, respectively) [83]. To improve the efficiency of piggery wastewater treatment, [84] used the digestion technique before microalgae treatment, and they used a marine microalgal specie rather than the genus _Chlorella_ and _Scenedensmus_, which have been widely used in the literature [84]. In the same investigation, they used the CO\({}_{2}\) produced by the digester to feed the microalgae culture bioreactor during its operation [84]. Under these conditions (CO\({}_{2}\) from digester (94.7%) and pH 7.5), _Tetraselmis suecia_ had the highest production of biomass, lipids and carbohydrates, which were 59.8, 25 and 6.5 mg L\({}^{-1}\) d\({}^{-1}\), respectively, with TN and TP removals of 96 and 72%, respectively [84]. Microalgae have also demonstrated their ability to remediate aquaculture effluents [64; 78]. [PERSON] et al. [64] reported that _Chlorella sorokiniana_ MB-1-M12 was the best candidate to treat shrimp culture wastewater because of its biomass and lutein productivities (1.9 mg L\({}^{-1}\) d\({}^{-1}\) and 5.55 mg L\({}^{-1}\) d\({}^{-1}\), respectively) in 75% of shrimp culture effluent. Another recent study used the immobilization method to treat aquaculture wastewater [78]. In this research, they immobilized _Tetraselmis_ sp., a marine microcalga, using alginate beads in aquaculture wastewater [78]. _Tetraselmis_ sp. beads removed about 0.08 mg L\({}^{-1}\), 0.10 mg L\({}^{-1}\) and 0.17 mg L\({}^{-1}\) from the initial concentration of the total ammonium (7.7 mg L\({}^{-1}\)), nitrite (3.1 mg L\({}^{-1}\)) and phosphorus (2 mg L\({}^{-1}\)) after two days, which corresponds to the following removal efficiencies of 98.9%, 97.7% and 91.1%, respectively [78].