## 3 Results and Discussion
### Tolerance of Duckweed to Raw Whey (RW) Wastewater
Although pasteurization effectively reduces the bacterial load, it does not necessarily eliminate all  
Figure 2: Evaluation from the two-way ANOVA of the effect of (**A**) proportion of RW in the culture medium, (**B**) initial wet biomass surface density (DEN) of _Lemma minor_, and (**C**) interaction between RW%-density on the mean total (\(a+b\)) chlorophyll content (\(Chl_{\text{total}}\)) of _Lemma minor_ (if the factors do not interact, the lines on the plot should be approximately parallel; if they are not, then the effect of one factor depends on the level of the other). Every RW% (**A**) and surface density (**B**) gathers all the results obtained for the surface density three, five RW% levels, and HSH control (CTRLL), respectively. Bars around points represent the standard error of 95.0% confidence intervals. Overlapping bars indicate no significant difference. (**D**) Photograph showing part of the _L. minor_ flask cultures carried out in the cultivation system used. microorganisms, including LAB [38]. Some LAB may survive pasteurization, but their numbers should be significantly reduced, making them less likely to cause spoilage or other issues. The presence of live LAB after pasteurization depends on various factors such as the initial bacterial load, the effectiveness of the pasteurization process, and post-pasteurization handling and storage conditions. Although pasteurization is effective at reducing the microbial load, including LAB, to safe levels, there may be certain strains that exhibit varying degrees of resistance to heat. Factors such as specific strains of LAB, its genetic makeup, and environmental conditions can influence its heat resistance. In fact, the high value of BOD\({}_{5}\) measured for RW (see Table 1) suggests the presence of LAB (a sterile organic wastewater typically has a low initial BOD\({}_{5}\) value, often close to zero, because it lacks active microbial populations that would contribute to organic matter decomposition). Hence, it is plausible that heat-resistant LAB continues to convert lactose into lactic acid during duckweed cultivation, potentially allowing the duckweed to assimilate this lactic acid. This hypothesis is consistent with the observed drop in culture pH below 5 within the initial three days of culture in both flask and PBR-1 cultures (Supplementary Material), suggesting LAB's acidifying activity through lactic acid excretion into the medium [37]. Given these considerations, it is plausible that the conversion of lactose to lactic acid observed in this study could be partially attributed to the residual LAB present in the pasteurized RW. However, this remains a hypothesis since the presence and activity of LAB--or other microorganisms capable of metabolizing lactose--have not been definitively confirmed. Further studies, including genetic sequencing, would be necessary to validate this mechanism and to explore the potential involvement of other microbial species in the process. Extracellular and intracellular proteolytic and lipolytic activities of LAB are extensively documented [37; 39]. Proteolytic enzymes can break down high-molecular-weight and complex proteins into peptides and amino acids, along with generating aromatic compounds such as aldehydes, alcohols, ketones, esters, or among others. Given that triacylglycericyerides constitute a significant portion of the lipids present in whey, lipolytic enzymes play a crucial role in hydrolyzing triglycerides to produce free fatty acids, glycerol, and intermediate products such as mono- and diglycerides. These metabolites, whether released into the medium by LAB or formed through extracellular proteolytic and lipolytic transformations, hold potential for assimilation by duckweed or microalgae. Furthermore, duckweed and microalgae cultures in RW-based media could leverage the antibacterial properties of lactic acid and bacteriocin peptides, which are released into the culture medium as by-products of LAB metabolism [37; 39].