## 3 Results and Discussion
### Sequential Batch Photobioreactor Experimentation with Duckweed and microalgae
#### 3.3.5 Final RW% Composition after Each Treatment with Duckweed and Microalgae  
Table 3 shows the physicochemical composition of RW (10% and 20%, \(v/v\)) before and after cultivation with duckweed and subsequently after cultivation with each microalgal analyzed. The findings of this study demonstrate the feasibility of the novel sequential culture process with _Lemma minor_ L. MO23 and either _Chlorella_ sp. MC18 or _Scenedesmus_ sp. MJ23-R to produce an effluent that meets environmental regulations for most parameters (see Table 3). This allows the safe discharge of the treated effluent into the environment without causing harm, emphasizing environmental sustainability. However, the final effluents of RW-10% and RW-20% are not in compliance with potassium (K\({}^{+}\)) regulations. This issue can be addressed by reusing the effluent for agricultural irrigation. Additionally, in the final effluent of RW-20%, some parameters--EC, BOD\({}_{5}\), COD, and PO\({}_{4}\)3--are slightly above regulatory limits, but a simple ~50% dilution can solve this problem. Overall, for the referenced states/countries (see Table 3), most of the %TRW media comply with environmental standards, indicating that the sequence of PBR-1 and PBR-2 is feasible for real-world applications. \begin{table} \begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{6}{c}{**Environmental Regulations**} & \multicolumn{2}{c}{**Raw Whey**} & \multicolumn{2}{c}{**Treated Whey (TRW)**} & \multicolumn{2}{c}{**Raw Whey**} & \multicolumn{2}{c}{**Treated Whey (TRW)**} \\ \cline{2-11}  & **Pern** & **Italy** & **Aggenina** & **Brazil** & **Swiss** & & & & **Macorptive** & & & **Macorptive** & & & **Macorptive** \\ \cline{2-11}  & **MAV\({}^{1}\)** & **ILD \({}^{2}\)** & **LRL\({}^{3}\)** & **CSR \({}^{4}\)** & **SUV \({}^{5}\)** & **RW-10\%** & **L.** _minor_ & _Churchla_ & _Soundesems_ & **RW-20\%** & **L.** _minor_ & _Churchla_ & _Soundesems_ \\ \hline pH & 6-9 & 5.5-9.5 & 5-9 & 6-5.8-8.5 & 7.18 & 7.27 & 8.47 & 8.75 & 7.13 & 6.47 & 8.62 & 8.33 \\ \hline Temperature & \textless{}35 & & \textless{}40 & & 24.7 & 27.3 & 22.5 & 21.6 & 24.1 & 27.0 & 21.1 & 21.4 \\ \hline OD at 500 nm & & & & 0.284 & 0.015 & 0.059 & 0.028 & 0.549 & 0.032 & 0.079 & 0.051 \\ \hline EC & & & & 1400 & 1107 & 1203 & 1223 & 1327 & 2000 & 2183 & 2203 & 2290 \\ \hline Turbaily & & \textless{}100 & 25 & 64.86 & 6.85 & 14.27 & 9.62 & 128.55 & 10.67 & 22.16 & 13.58 \\ \hline True color & & & & 35.6 & 75.1 & 95.8 & 99.2 & 62.1 & 43.0 & 122 & 123 \\ \hline TSS & 500 & 50 & & 249 & 10.3 & 12.1 & 9.8 & 358 & 13.8 & 14.9 & 12.7 \\ \hline BODs & 500 & & 125 & \textless{}5 & 3505 & 1146 & 194.6 & 217.9 & 9750 & 3620 & 485 & 1188 \\ \hline COD & 1000 & 160 & 190 & \textless{}5 & 6096.67 & 2039 & 321 & 364 & 14,885 & 4190 & 977 & 2176 \\ \hline OC & 100 & & & 180 & \textless{}5 & \textless{}5 & \textless{}5 & 300 & 4 & \textless{}5.0 & -0.5 \\ \hline NO\({}_{2}\) & 20 & & 30 & 25.4 & 0.051 & \textless{}0.005 & \textless{}0.005 & 60.4 & 0.50 & 0.02 & -0.005 \\ \hline NO\({}_{2}\) & 0.6 & & & 3.13 & 0.011 & ND & 0.007 & 3.33 & 0.067 & nd & nd \\ \hline N-NH\({}_{3}\) & 80 & 25 & \textless{}20 & & 1.95 & 0.973 & \textless{}0.02 & 0.035 & 3.79 & 0.299 & 0.042 & 0.044 \\ \hline TNN & & 15 & & 22.7 & 1.29 & 0.24 & 0.27 & 48.9 & 3.66 & 0.96 & 2.13 \\ \hline PO\({}_{4}\)\({}^{2}\) & 10\({}^{*}\) & 2\({}^{*}\) & \textless{}0.15\({}^{*}\) & & 104 & 54.1 & 10.10 & 1.64 & 238 & 141 & 22.04 & 17.22 \\ \hline SO\({}_{4}\)\({}^{2}\) & & & 200 & 24.4 & 18.8 & 54.7 & 0.03 & 61.4 & 44.9 & 112.4 & 0.16 \\ \hline K\({}^{*}\) & & & 12 & 167.4 & 135.8 & 115.26 & 119.674 & 326.8 & 265.7 & 218 & 209 \\ \hline \end{tabular}   
* MAV: maximum admissible value: HD limits for discharge in surface water; LRL: low regulatory limits, CSR: conditions and standards regulated (CONAMA 400/11-357/05), SUV: standard limit value (World Health Organization). * MVCS [P01]\({}^{2}\) [PERSON] et al. [65]\({}^{3}\) [PERSON] et al. [71]\({}^{1}\)- [PERSON] et al. [72]\({}^{3}\)- [PERSON] et al.