## 2 Wastewater Treatment by Microalgae
### Industrial Wastewater
#### 2.3.3 Microalgae Treatment of Industrial Wastewater
NO\({}_{3}\)-N (nitrate-nitrogen), NO\({}_{2}\)-N (nitrite-nitrogen), NH\({}_{4}\)-N (ammonium-nitrogen), H\({}_{2}\)PO\({}_{4}\) (dihydro phosphate), HPO\({}_{4}\) (hydrogen phosphate), HMs (Heavy metals), CCM (carbon concentrating mechanism), RBP (ribulose biphosphate), R5P (ribulose 5 phosphate), G3P (glyceraldehyde 3 phosphate), BPG (bisphosphoglycerate), 3 PG (3 phosphoglycerate), F1,6-DP (fructose 1,6-bispnbnbate), F6-P (fructose 6 phosphate), Glu\({}_{6}\)-P (glucose 6 phosphate), Glu1-P (glucose 1 phosphate), MEP (methylerythntol phosphate) and TAGs (triacyl glycerols). chemical oxygen demand [121]. In contrast, [PERSON] et al. immobilized _Nannochloropsis_ sp. in the form of beads using sodium alginate to assess the treatment of palm oil mill wastewater diluted 10 times in comparison with free cell culture [130]. Other authors immobilized _Nannochloropsis_ sp. and found that it achieved the best biomass of 1.27 g L\({}^{-1}\) and could remove 71% of the chemical oxygen demand (COD) from palm oil mill effluent, compared to culture with free-cells of _Nannochloropsis_ sp. which showed 0.37 g L\({}^{-1}\) for biomass production and 48% of the COD removal efficiency [130]. This sodium alginate immobilization technique did not interrupt the development of _Nannochloropsis_ sp., but rather optimized it by facilitating the passage of nutrients from palm oil mill effluent through the membrane pores of beads, allowing the authors to conclude that this technique is viable for palm oil mill wastewater treatment [130]. Recently, [92] used raw and diluted olive mill wastewater after treatment by anaerobic digestion followed by ultrafiltration to cultivate _Scendesmus_ sp., which had the highest biomass productivity (0.15 g L\({}^{-1}\) d\({}^{-1}\)) in 25% of the ultra-filtrated anaerobic liquid digestate of the olive mill with a nitrate removal efficiency of 98%. Additionally, _Arthospira platensis_ has been utilized to remediate cassava processing effluent [101]. The authors cultivated _Arthospira platensis_ for eight days in an SKM culture medium with modest changes (NaCl: 8 g L\({}^{-1}\), NaHCO\({}_{3}\): 5 g L\({}^{-1}\), Ca(H\({}_{2}\)PO\({}_{4}\))\({}_{2}\)-H\({}_{2}\)O: 0.01 g L\({}^{-1}\), urea: 0.1 g L\({}^{-1}\)) and with a daily addition of a volume of cassava processing effluent as a source of nutrients (0-2 mL L\({}^{-1}\) of culture) [101]. The findings demonstrated that when 1.5 mL d\({}^{-1}\) L\({}^{-1}\) of cassava wastewater was added to the culture, _Arthrospira platensis_ could successfully remove nitrogen (88.4%) and phosphate (43.4%) [101]. Over 99% of ammonium, nitrites and nitrates may be reduced by adding up to 2.0 mL d\({}^{-1}\) L\({}^{-1}\) of cassava processing effluent [101]. The authors of [103] examined the reduction of the chemical oxygen demand of cassava wastewater (COD: 1570.00 mg L\({}^{-1}\)) and the biosynthesis of lipids by the microalgae _Desmodesmus armatus_ in both heterotrophic and mixotrophic growing modes. After 14 days of culture, they discovered that _Desmodesmus armatus_ can biosynthesize 21.91% of lipids and remove 92% of the COD in the mixotrophic mode, as opposed to 74% of the COD and 20.86% of lipids in the heterotrophic mode [103]. Other food-processing wastewaters such as winery, potato and instant coffee wastewaters, have also shown their ability to be treated by microalgae [119; 125; 126]. The authors of [119] used a continuous flow photobioreactor with a membrane column to co-culture _Chlorella vulgaris_ and _Arthrospira platensis_ for 15 days, using winery wastewater (119.3 g L\({}^{-1}\) COD) as the culture medium. This co-culture technique allowed the removal of 75% of the chemical demand from the industrial winery wastewater for a retention time of 2 days, producing a lipid yield of 278 mg \({}^{-1}\) and a biomass of 3.61 g L\({}^{-1}\)[119]. In a lab test, five species of _Scenedesmus_ and three species of _Desmodesmus_ were examined to find the potential of microalgae for potato wastewater remediation with a high pigment content [126].