**6. Other discoveries in the phycoremediation pilot tests**

Three consecutive pilot batches showed that the pH value increased from 7 to 9 within a day and stabilized at 9 if CO2 was not supplied. At this point, it needs to clarify that the treated wastewater used in this study was collected after the denitrification treatment, and the water thereby could be CO2 saturated. Apparently, the 3rd

batch needed CO2 addition to maintain pH level. Albeit its algae growth was not as good as previous two batches (with the reasons mentioned above), it is believed that the fresh filamentous co-culture can rapidly deplete CO2 in the treated wastewater. With this regard, a large amount of CO2 supplement will be needed for the proposed filamentous co-culture in the process of wastewater purification. As a return, it is foreseen that this can significantly reduce the carbon footprint of WWTPs.

A total of 14 elements were measured in this case study, but only the mercury (Hg) was undetectable (**Table 3**). As a background study, these elements were also analysed on the indoor monocultures (inoculum), to exclude the influence of indoor cultivation medium. The differences between indoor inoculums of *Klebsormidium sp*. and *Spirogyra sp.* showed that they had variable update affinities to these elements. In contrast, the detected discrepancies from the outdoor co-cultures indicated the effectiveness of accumulation/absorption of these chemicals and heavy metals from the wastewater treatment. As discussed above, it was conceived that the biomass produced in pilot test could have less P. Interestingly, the indoor and outdoor biomass contained similar amount of Mg and K, while Ca content was more in the outdoor biomass. As showed in the results, these mineral chemicals in the municipal treated wastewater can be assimilated effectively by the tested co-culture to constitute the produced algae biomass at a level of g kg<sup>1</sup> .

It is worth noticing that there was a substantial accumulation of AI and Fe residues in the outdoor samples (g kg<sup>1</sup> ). Although these two metal ions also existed in the algal cultivation medium, indoor algae samples contained much less than that of outdoor samples. One side, it is verified that there were still certain amounts of AI+ and Fe+ ions in the treated wastewater. It is believed that they were derived from the WWTP's chemical treatment process, as cationic coagulants/flocculants (e.g. ferric chloride,


*# Spirogyra is the mean value of 2 replicates because of an accident with one of the replicates. \* Cd is the result of only one replicate.*

#### **Table 3.**

*Chemical elements analysis in the experimental algae biomass (mean SE).*

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

aluminum chloride, and polymers) are usually used for P precipitation at the secondary treatment process of municipal wastewater. Although there is little information on their scavenge in water, using the filamentous algae can act a new approach to reduce these cationic residues from the municipal tertiary wastewater. Apparently, this can further diminish the environmental burden of the chemical treatment for the WWTP.

Heavy metals are hazardous substances and persistent pollutants in municipal wastewater [4]. Although they are close to undetectable levels at ug L<sup>1</sup> or ng L<sup>1</sup> [20], their appearance is a recalcitrant problem. As indicated in this case study, these trace elements were encapsulated in the algae biomass at a level of mg kg<sup>1</sup> from tons of municipal wastewater. This process is normally accomplished through a robust combination of non-active biosorption and active metabolism-dependent mechanisms [21, 22] because of algae's high binding affinity, abundance of binding sites, and large surface area [23]. Numerous studies in recent years have approved the existence of heavy metals and emerging contaminants in aquatic system and pointed out wastewater discharge as one of the main pollution sources [24, 25]. Therefore, using filamentous algae co-culture can be an effective and pragmatic approach to purify the tertiary wastewater in an environmental-friendly manner.
