## 4 Economic Analysis of Microalgae Wastewater Treatment Technologies
### Economic Assessment of microalgae-Based Wastewater Treatment  
The feasibility of wastewater treatment by microalgae toward a biorefinery system is influenced by a number of variables, including upstream and downstream processing, environmental effects and commercial analysis [5]. Assessment of the economic analysis can be examined by LCA and TEA, which are life cycle assessments and techno economic assessments, respectively [162]. Generally, LCA uses \"cradle-to-grave\" system boundaries that take into account every step of the treatment process to quantify the mass and energy exchanges between the treatment system and the overall environment. However, the TEA is often fixed to the treatment stage using \"cradle-to-gate\" system limitations, eliminating the waste treatment [163]. The five phases of TEA are generally the process design, mass and energy balance, cost projections, profitability and sensitivity analysis [163]. Therefore, a complete schematic design of the entire treatment process is essential to properly estimate the cost of the microalgae-based wastewater treatment process in a biorefinery system. The design process is the mean problem that limit both LCA and TEA analysis, thus, it is clear that there is huge research gap from lab-scale to pilot or large-scale, which limits the implementation of microalgae-based wastewater treatments in a biorefinery system. According to earlier research, regular open ponds or even sophisticated high-rate algal ponds (HRAP) are the most effective approach for growing microalgae in wastewater [164]. The environmental effect of HRAP systems for wastewater treatment has been evaluated through research using the life cycle assessment approach. They showed that, when compared to traditional systems (such as activated sludge systems), HRAPs might potentially aid to minimize environmental impacts and costs linked with wastewater treatment [165; 166; 167; 168]. [PERSON] et al. [168] evaluated the sustainability of HRAP systems for municipal wastewater treatments by microalgae compared to sewage sludge systems. According to their findings, modern HRAP technology is more energy-efficient than an activated sludge-based sequencing batch reactor, requiring just 22% of their electricity demand [168]. Furthermore, HRAP is more cost-effective (0.18 \(\mathrm{\upmu}\)m\({}^{-3}\)) compared to activated sludge (0.26 \(\mathrm{\upmu}\)m\({}^{-3}\)) and more ecologically friendly, with reduced global warming (146.27.10\({}^{3}\) kg CO\({}_{2}\) equivalent m\({}^{-3}\)) and eutrophication potentials (126.14 vs. 158.01.10\({}^{6}\) kg PO\({}_{4}\) equivalent m\({}^{-3}\)), but the net environmental benefit of an activated sludge-based sequencing batch reactor was slightly larger than HRAPs because of the removal rate of nutrients [168]. Recently, [PERSON] et al. [169] compared co-pyrolyzing sewage sludge and wastewater-grown microalgae for biofuel production using LCA, global warming, energy recovery, and economic analysis in five scenarios while varying the mixture of sewage sludge and microalgae. They found that the 1:1 mixture produced the largest net profit (9% higher than sewage sludge). However, the environmental effect of the 1:1, 1:2 and 2:1 scenarios was lower than that of sewage sludge alone. For energy consumption, due to the high moisture content of the feedstock, they revealed that drying was the most energy-intensive operation, accounting for 69-88% of total used energy [169]. In another study, [PERSON] [170] investigated the possible ecological effects of microalgae systems for wastewater treatment and bioproduct extraction. In this regard, a life cycle evaluation of two systems treating urban wastewater and food-processing wastewater with the recovery of bioproducts and bioenergy was performed. Furthermore, both solutions were compared to an existing method employing a typical growth medium for microalgae cultivation, in order to demonstrate the potential benefits of using wastewater against traditional cultivation methodologies [170].