**7. Potential valorisations of produced biomass**

Since Fourier-transform infrared spectroscopy (FTIR) represents a rapid, simple, and reproducible method to identify the different compositions in the different biomass [26], it was employed to firstly examine the quality of algae samples in this study. FTIR spectroscopy revealed different proximate biochemical composition (lipids, carbohydrates, phosphates, and proteins) of indoor and outdoor cultivated algae (**Figure 5A**). In comparison, *Klebsormidium* biomass had more lipid, protein, and phospholipid, but *Spirogyra* contained more carbohydrates (**Figure 5B**). For the co-culture, the biochemical profile was a bit consistent among three batches, and the proportion of those biochemicals seemed to between the levels of inoculums. In the principal component analysis (PCA) analysis (**Figure 5C**), it seemed that the *Klebsormidium* could take over *Spirogyra* during consecutive pilot tests. This result was coincident with the microscopy observation. This is probably because that *Spirogyra* prefers growing in warm temperature [28].

FTIR results were further validated by the following analytical analysis. About 50% of *Klebsormidium* biomass was protein, but *Spirogyra* biomass was only 21% (**Figure 6**). However, *Spirogyra* had more starch (7% of DW) than *Klebsormidium* (3.3%). In the outdoor pilot test, the protein content of co-culture was increased gradually from 1st to 3rd batch with 20–30% of DW. However, the starch content became less from 5–4%. Like the PCA analysis, this result also suggested that the proportion of *Klebsormidium* in the co-culture increased. The lipid content was detected below 8% of DW with a small variation across different samples. Despite microalgae could increase lipid content in a condition of nutrient starvation [6], this is not applicable to the biological response of experimental filamentous algae in the outdoor pilot tests. Maybe it is why that filamentous algae are not compelling to the research attention as did on most of microalgae for typical algae economy values (e.g. biofuel and omega-3 oil). Moreover, with the notable protein content, the potential impact on anaerobic digestion (AD) process shall be investigated if the biomass is used for AD biogas production.

Another consideration is the ash content in the produced biomass. It was high in the first two WWT batches (26.6% –23.3%), lower in 3rd batch (13.8%). However,

**Figure 5.**

*FTIR analysis of microalgae biomass. (A) FTIR spectra with characteristic bands noted (note: The moisture condition was similar between different algae samples (3400–3200 cm<sup>1</sup> ). As the variation between 3000 and 2500 cm<sup>1</sup> was not correlated to the changes in biochemical composition [27], the major differences between 1800 and 800 cm<sup>1</sup> were used for assessment.), (B) peak height of characteristic bands, and (C) scores plot of principal component analysis (PCA).*

they were all more than the content in the indoor inoculums of *Klebsormidium* (6.4%) and *Spirogyra* (9.4%). Since the ash content is almost associated with the minerals content in biomass [29], those higher values of ash content in the pilot test also can

*A New Insight of Phycoremdiation Study: Using Filamentous Algae for the Treatment… DOI: http://dx.doi.org/10.5772/intechopen.104253*

**Figure 6.** *Proximate biochemical analyses of microalgae biomass from indoor monocultures and outdoor co-cultures on wastewater.*

evidence that filamentous algae removed certain amounts of mineral chemicals and heavy metals along with the treatment of tertiary wastewater in this case study. Regardless of heavy metals and/or other hazardous substances accumulated in the biomass, high ash content will also affect the algae inclusion level for food and feed utilization [30] and increase problems in combustion for energy conversion [31].

Given these concerns, there is still a great potential to utilize the produced biomass for biofertilizer, soil ameliorator, or new material development. For example, the heavy metals content in the produced biomass was below the maximum limit for permissible content in the organic fertilizers, according to the Norwegian regulations on organic fertilizers (FOR-2003-2007-04-951). There is no doubt that a comprehensive evaluation will be needed prior to this viable application, such as to match the restrictions of hygiene conditions, pesticides, and requirements for soil mixtures, as well as public perception. Apparently, it is going to be an inclusive question to evaluate the potential usage of produced biomass from this case study. However, it is undeniable that this represents a new value creation, as an authentic solution to facilitate the green transition of WWTP. Therefore, this case study provides a new paradigm for WWTPs to integrate the management of tertiary wastewater with emerging circular economy requirement.
