## 2 Wastewater Treatment by Microalgae
### Domestic Wastewater  
#### 2.1.1 Physicochemical Properties  
Domestic effluent is defined as water that has been used by a population and contains all the materials that have been added to it throughout its usage [9]. It is generally classified into two types (Figure 1): black-water and grey-water, and is mostly made up of discharge from domestic and home activities [10]. In some part of the world, this type of wastewateris disposed into drainage systems, lakes and rivers without any previous treatment, posing challenges to the enhancement of the community's living conditions, because untreated wastewater has a significant negative impact on the environment and human health [9; 11]. Black-water may consist of urine, flash water, fecal matter, toilet paper and others water, such as water from cleaning activities [10], and grey-water is wastewater that comes from kitchen sinks, laundromats and showers, or any other domestic activity other than toilet waste [11]. Kitchen wastewater is a type of wastewater that includes a lot of ammonium due to food protein degradation, and its excessive thickness supplements a terrible odor signal that must be treated. The treatment of kitchen wastewater by microalgae has been explored and it appeared that the collected kitchen wastewater had a high organic content due to the existence of oil, grease and food products and was acidic, with chemical oxygen demand (COD) levels ranging from 800 mg L\({}^{-1}\) to 1400 mg L\({}^{-1}\), compared to raw sewage wastewater which has COD levels ranging from 250 mg L\({}^{-1}\) to 800 mg L\({}^{-1}\)[12]. To solve this problem and make the kitchen wastewater acceptable for microalgae development, it should be diluted by about 1:1 with water [12].  
The composition of different domestic wastewaters, which have been used in the literature for microalgae culture, is given in Table 1. As described in this table, sewage effluent has a pH of 6.6 to 8.81, a chemical oxygen demand (COD) of 97 mg L\({}^{-1}\) to 1100 mg L\({}^{-1}\), a total nitrate content (TN) of 0.22 mg L\({}^{-1}\) to 265 mg L\({}^{-1}\), a total phosphate concentration (TP) of 0.6 mg L\({}^{-1}\) to 170 mg L\({}^{-1}\) and other constituents such as chloride and potassium. Kitchen wastewater has a COD content of 560 mg L\({}^{-1}\), whereas toilet wastewater has a COD value of 506.8 mg L\({}^{-1}\), with TN and TP levels of 203.6 mg L\({}^{-1}\) and 22.3 mg L\({}^{-1}\), respectively. As a reason, using domestic wastewater for microalgae growth is a suitable choice for both wastewater treatment and the generation of biodiesel and other chemicals from the produced biomass.  
Figure 1: Domestic wastewater types.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Type**} & **Chloride** & **Na** & **F** & **Fe** & **Cu** & **Zn** & **Mg** & **Ca** & **K** & **Pb** & **Turbidity** & **References** \\  & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **NTU** & \\ \hline  & - & - & - & - & - & - & - & - & - & - & [27] \\  & - & - & - & - & - & - & - & - & - & - & [28] \\  & - & - & - & - & - & - & - & - & - & - & 140-160 & [29] \\  & - & - & - & - & 0.098 & 0.0321 & 0.0218 & - & 52.2 & 12.16 & 0.1707 & - [31] \\ Kitchen & 92.08 & 130 & - & - & - & - & - & 180 & 148 & - & - [12] \\  & - & - & - & - & - & 8.6 & 23.8 & 98.2 & - & - & [33] \\ \hline  & & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \\ \end{tabular}
\end{table}
Table 1: _Cont._