## 2 Wastewater Treatment by Microalgae
### Domestic Wastewater
#### 2.1.3 Microalgae Treatment of Domestic Wastewater
vulgaris_ had the highest lipid content (15.11%) when municipal wastewater was supplemented with 5 g L\({}^{-1}\) of glycerol compared to wastewater without glycerol (7.72%). In the same way, _N. oculata_ had a high lipid content (8.91%) with 2 g L\({}^{-1}\) of glycerol compared to the culture without glycerol (4.59%) [34]. Similar to this finding, [40] demonstrated that combining a municipal wastewater with glycerol for boosting the mixotrophic culture of _C. vulgaris_ Wu-G22 was a viable option for integrating wastewater treatment with energy production from algal biomass. They found that this microalga had the highest removals for COD, TN and PO\({}_{4}\)-P from 6195.6 mg L\({}^{-1}\) to 448.47 mg L\({}^{-1}\), from 46.78 mg L\({}^{-1}\) to 3.39 mg L\({}^{-1}\) and from 9.79 mg L\({}^{-1}\) to 0.75 mg L\({}^{-1}\), respectively, when domestic wastewater was supplemented with 50 mM of glycerol [40]. In addition, _C. vulgaris_ Wu-G22 produced a high lipid content of 15.7% and produced contents of other compounds such as carbohydrates and proteins by about 7.3% and 70%, respectively [40]. A recent study used sodium acetate (NaAc) to enhance the removal efficiency of nutrients from municipal wastewater [27]. _S. obliquus_ cultivated in the municipal wastewater grew faster and accumulated more lipids than those cultivated in the BG11 synthetic medium, indicating that the domestic wastewater might be used to replace the synthetic medium for microalgae growth [27]. Furthermore, introducing exogenous NaAc to mixotrophic cultivation significantly increased the algal growth and lipid synthesis [27]. The growth of _Scenedesmus obliquus_ was 2.40 times greater (from 0.2 mg L\({}^{-1}\) to 0.48 mg L\({}^{-1}\)) with the addition of 1 g L\({}^{-1}\) of sodium acetate than that in the municipal wastewater without supplement. Furthermore, this concentration enhanced the microalga removals of nitrogen and phosphorus by 1.75 (from 46.85% to 82.2%) and 2.23 times (from 34.18% to 76.35%), respectively, accompanied with a high lipid productivity of 22.08 mg L\({}^{-1}\) d\({}^{-1}\)[27]. The dilution approach was investigated as a strategy for improving _Scenedesmus_ sp. nutrient recovery and biomass. The author of [41] investigated the impact of different dilutions of fresh leachate (5%, 10%, 15%, 20% and 25%) using treated municipal wastewater on the growth and nutrient recovery potential of _Scenedesmus_ sp. They found the highest removal efficiencies of 100%, 94% and 96% in 15% of fresh leachate for nitrite, ammonium, and phosphorus removals, respectively. [PERSON] et al. research [42] on _Acutodesmus obliquus_ revealed that poultry litter extract (2 g) diluted in municipal wastewater (100 mL) has the potential to be utilized as a nutrient and water source for this species. _A. obliquus_ produced the most biomass (1.90 g/L) and had the greatest NO\({}_{3}\)-N, NH\({}_{4}\)-N and PO\({}_{4}\)-P removal rates (79.51%, 81.82%, and 80.52%, respectively). Furthermore, raw poultry litter extract had a slightly greater COD recovery efficiency of 50.80% when compared to poultry litter diluted in municipal wastewater (40.47%), which might be attributed to the proliferation of heterotrophic microorganisms/bacteria in the raw poultry litter extract [42]. Figure 2: Cont. S. obliquaus ([PERSON] et al, 2021) S. obliquaus ([PERSON] et al, 2021) S. obliquaus ([PERSON] et al, 2021) S. abudantas ([PERSON] et al, 2015) P. tricormutation ([PERSON] et al, 2019) N. osculating ([PERSON] et al, 2022) M. reisseri ([PERSON] et al, 2011) M. reisseri ([PERSON] et al, 2017) M. reisseri ([PERSON] et al, 2017) M. reisseri ([PERSON] et al, 2017) M. reisseri ([PERSON] et al, 2017) Isocrphysi sp. ([PERSON] et al, 2021) Isocrphysi sp. ([PERSON] et al, 2021) \(H\). plivivallis ([PERSON] et al, 2014) H. plivallis ([PERSON] et al, 2013) C. \(z\). \(\alpha\). \(\beta\). \(\gamma\).