||Constructed wetland treatment systems are environmental-friendly and economic technologies for wastewater treatments. The Dapeng Bay National Scenic Area Administration collected the wastewaters from the salty water aquacultural ponds and community households in the adjacent areas and discharged them into salty water type of constructed wetland treatment systems, which is quite rare in Taiwan presently. According to the surveying result of water quality in these constructed wetland treatment systems in previous study, we found that some species of macroalgae Gracilaria, were existed in some units of the wetland systems. Further, we found that the wastewater treatment efficiencies of the constructed wetland systems could be substantially enhanced by the macroalgae. Reviewing some literatures also confirmed that the macroalgae, Gracilaria, can be effectively applied to aquaculture wastewater treatment because it is able to absorb the nutrients and benefits its own growth. Besides, it can reduce the algal bloom caused by excess nutrients.|
In this study, we explored the macroalgae Gracilaria’s role in those saline constructed wetland wastewater treatment systems. In the laboratory scale study, a constructed wetland model tank was designed to culture Gracilaria as a way to explore the situation of wastewater treatment. The experimental results showed that when cultured in the still water system, the macroalgae, Gracilaria, was able to increase both of the levels of dissolved oxygen and pH in wastewater. Moreover, when it was cultured in its biomass density of 10 g/L for 4 days, the removal efficiency of chlorophyll-a concentration could ideally reach to 79.10 ± 7.62 %, while the total nitrogen, and total phosphorus could reach to 47.10 ± 25.93 % and 60.49 ± 45.29 % respectively. However, the reduction of ammonia nitrogen concentration was found rather obvious only one day after culture.
Whereas, when the species of Gracilaria was cultured in the continuous flow system, we found that there were significant difference in the test result of the turbidity, chlorophyll-a, and BOD in the experimental group with addition of Gracilaria. After testing the concentrutions of chlorophyll-a over a long period of time, we found that the chlorophyll-a concentration were markedly increased when Gracilaria was not added. On the contrary, the chlorophyll-a concentration was remained stably when Gracilaria was added. When it comes to the nitrogen removal, we found that the removal efficiency of ammonia nitrogen in the experimental group could reach up to 92.27 ± 3.82 % in average. Other than that, it was found obvious decrease of the ammonia nitrogen concentration on the first day of culture. As to the test of soil’s impact on the phosphorus removal, we found that the removal efficiency in the experimental group was higher than the group without soil. Therefore, the removal efficiency was found obviously higher when there was soil. In the continuous flow system, when the species of Gracilaria was added, the removal efficiency of total nitrogen and total phosphorus in the model tank could reach averagely up to 75.23 ± 2.46 % and 53.96 ± 11.18 %, respectively.
Comparing the experimental results by growth of Gracilaria for water quality with laboratory study and the saline constructed wetland systems in the Dapeng Bay, we found that the removal efficiencies of contaminants and nutrients could be enhanced by Gracilaria.