3.5. Application of microalgae in wastewater treatment
Results from the previous analysis suggest that the coexistence
of C.vulgaris and bacteria could be important for the elimination of
organic matters from unsterilized wastewater. Although the system
based on stand-alone C.vulgaris can remove NH4
–N more
quickly, the difference between removal rates of both systems
was not significantly large. Furthermore, taking the cost of sterilization
into consideration, the unsterilized system would be favorable
for microalgae-based wastewater treatment applications.
Discussions on this aspect should be based on results from investigations
into unsterilized conditions.
As shown in Table 4, NH4
–N and TP were completely removed
from the effluent of the RN30-RN100 test. DOC concentration
reached a minimum value on day 2 and 3 (Fig. 1(d)). However,
the release of organic matter by C. vulgaris enabled the increase
of DOC concentration on following days. If the treatment process
was controlled within 7 days, DOC concentration could be maintained
at low levels, resulting in the complete removal of nitrogen
and phosphorus. In addition, the reduction of treatment time could
also reduce the scale of treatment structures and treatment costs.
The RN30 test resulted in the best effluent water quality in the
shortest treatment time (7 d), but the average daily removal rate of
TN and TP was only 3.70 and 0.2 mg/(L d) respectively, whereas the
RN175 test attained the optimal removal rate with the highest
treatment efficiency (7.78 mg/L d TN and 0.71 mg/L d TP) and the
highest level of nutrition removal (140 mg/L TN and 12.7 mg/L
TP). The RN175 test also had the highest algal concentration.
During the harvest process it was found that the higher algal cell