## 3 Results and Discussion
### Sequential Batch Photobioreactor Experimentation with Duckweed and microalgae
#### 3.3.4 Effect on Biomass Production and the Proximate Chemical Composition of Microalgae  
Figure 8 shows the results from a two-way multivariate ANOVA (MANOVA) of main effects MEDIUM (i.e., treated raw whey, TRW%) and ALGA, and their interaction (MEDIUM-ALGA) on growth kinetic parameters and concentrations of the elemental biochemical compounds in the PBR-2 cultures after a 7-day cultivation period, coinciding with the entry of the cultures into the stationary phase. Regarding growth, the analysis revealed a significant main effect of the MEDIUM factor on the combined \(\mu_{max}\), \(P_{B}\), and \(Y_{B}\), Wilk's Lambda = 0.000, F (14, 12) = 1102.7, \(p<0.001\) (Figure 8A,D,G). Subsequent multivariate tests showed that MEDIUM significantly influenced the three growth kinetic parameters: \(\mu_{max}\) (F = 88.2, \(p<0.001\)), \(P_{B}\) (F = 726.1, \(p<0.001\)), and \(Y_{B}\) (F = 726.1, \(p<0.001\)). The mean maximum values were obtained at RW-20%. This observation confirms the importance of adjusting the RW% level to effectively modulate microalgal growth. Similarly, there was a significant main effect of the ALGA factor on the combined \(\mu_{max}\), \(P_{B}\), and \(Y_{B}\), Wilk's Lambda = 0.001, F (7, 6) = 1087.7, \(p<0.001\) (Figure 8B,E,H), affecting the three parameters: \(\mu_{max}\) (F = 41.3, \(p<0.001\)), \(P_{B}\) (F = 364.6, \(p<0.001\)), and \(Y_{B}\) (F = 364.6, \(p<0.001\)). There was an effect of the interaction of factors (Figure 8C,F,I). As evident from Figure 8A-I, both strains demonstrated the ability to produce biomass from RW (10% to 30%) treated with duckweed on the PBR scale. _Chlorella_ sp. consistently outperformed _Scenedesmus_ sp. with 4.79%, 20.95%, and 20.95% higher \(\mu_{max}\), \(Y_{B}\), and \(P_{B}\) (\(p<0.05\)), respectively. This suggests that _Chlorella_ sp. may be more efficient in converting the available nutrients in TRW% into biomass. Similarly, the higher \(\mu_{max}\) of _Chlorella_ sp. indicates its superior ability to thrive in the TRW% medium. This faster growth rate can be beneficial in the context of bioremediation, where the aim is to rapidly remove pollutants. As far as we know, there are no studies reporting the sequential cultivation of duckweed and microalgae to take advantage of the nutrients contained in raw dairy wastewater. Table 2 summarizes results reported in previous literature on other treatments of dairy wastewater using microalgae. The results of the study presented here show higher biomass productivity. Despite the variations in conditions and treatment types between the studies, the comparison in Table 2 consistently showed the superior ability of _Chlorella_ and _Scenedesmus_ to thrive in culture mediums based on dairy wastewater. Figure 8: Evaluation from a two-way multivariate ANOVA (MANOVA) of main effects MEDIUM (i.e., treated raw whey, TRW%) and ALGA, and their interaction (MEDIUM–ALGA) on the following dependent variables: (i) growth kinetic parameters; mean \(\mu_{max}\) (**A–C**), \(P_{B}\) (**D–F**), and \(Y_{B}\) (**G–I**); (ii) proximate chemical composition; carbohydrates (**J–L**), lipids (**M–O**), proteins (**P–R**), total chlorophylls (**S–U**), and carotenoids (**V–X**). Every MEDIUM (**C,F,I**) and ALGA group (**B,E,H**) gathers  
all the results obtained for the two microalgae, _Chloella_ sp. MC18 (CH) or _Scenedesmus_ sp. MJ23-R (SC), and for the three MEDIUM levels, TRW-10%, TRW-20%, or TRW-30%, respectively. Bars around points represent 95.0% confidence intervals. Overlapping bars indicate no significant difference. The findings suggest that microalgae benefit from duckweed-treated raw whey in several ways. Duckweed acts as a natural filter, removing excess nutrients and creating a more suitable medium for microalgae growth. This balanced nutritional profile supports healthier conditions, leading to improved growth rates and biomass yield. Additionally, the use of treated raw whey reduces the need for costly synthetic nutrient supplements, making the cultivation process more cost-effective.