3.1. Water Quality Parameter
The water quality parameter during the experiments with four different species as biofilter of hybrid grouper aquaculture wastewater was shown in table 1. Water temperature, salinity, Total Dissolved Solid (TDS), and Total Suspended Solid (TSS) showed no significant difference. Water temperature ranges from 27-29 ºC during the experiment. The overall salinity gradually increased from 14 to 17 ppt, due to the evaporation, also with TDS. The TSS showed the lowest decrease (0.38-0.66 mgL-1) on day 8th from 2.53 ± 0.11 mgL-1 on day-0.
Table 1. Water quality parameter during experiments with four different species as biofilter of hybrid grouper aquaculture wastewater
Treatment
|
Parameter
|
Temp.
(°C)
|
Salinity
(ppt)
|
pH
|
DO
(mgL-1)
|
TSS
(ppm)
|
TDS
|
P0 (Control)
|
27-29
|
14,4-16,4
|
7,2-8,2
|
3,2-9,8
|
0,23-2,53
|
16,43-18,13
|
P1 (U. fasciata)
|
27-29
|
14,3-14,4
|
7,3-8,2
|
3,3-11,6
|
0,20-2,37
|
16,23-18,57
|
P2 (S. ilicifolium)
|
27-29
|
14,4-16,2
|
7,1-8,1
|
2,6-10,5
|
0,32-2,57
|
16,30-18,17
|
P3 (Gelidium sp.)
|
27-29
|
14,5-16,6
|
7,2-7,9
|
2,9-10,1
|
0,17-2,67
|
16,00-18,50
|
P4 (Dictyota sp.)
|
27-29
|
14,5-16,6
|
7,3-8,3
|
3,1-11
|
0,36-2,59
|
16,13-18,43
|
The dissolved oxygen and pH showed significant differences between treatments. The dissolved oxygen in all treatments after day 4th showed decreasing to 3 mgL-1, this was caused by the activity of bacteria to decompose wastewater that needed oxygen. This DO concentration then increased after the 4th day. The highest DO occurred on the 12th day of treatment with U. fasciata until it reached 11.37 mgL-1 that indicating a significant difference from others. After increasing on days 12th and 16th, the DO decreased to an average of 6.1 mgL-1 on day 20th (Fig. 1a.).
3.2 Nutrient Removal
The concentration of ammonia in wastewater with U. fasciata treatment on day 4th was successfully reduced to 0.57 ± 0.04 mgL-1 (63.92%), which was the lowest compared to others. In all treatments, there was an increase in ammonia on the day 16th, and then decreasing on the day 20th until 73.88% (Fig. 2a).
The concentration of nitrate in water in the U. fasciata treatment increased until day 4th, and then consistently decreased until it reached 1.47 ± 0.3 mgL-1, or reduced the nitrate by 79.49% on day 20th. Meanwhile, other treatments showed that the increase in nitrate concentration occurred up to day 8th (Fig. 2b). This increase occurred because, ammonia at that time was still experiencing a change to become ammonium, nitrite, and nitrate which took a certain time because it was influenced by environmental factors, such as temperature, pH, and dissolved oxygen.
Phosphate concentration during treatment showed a consistent decreasing until the 20th day. However, Dictyota sp. showed the fastest decreasing in phosphate concentration on day 12th that reached 0.73 ± 0.09 mgL-1 (81.75%), and the lowest was 0.50 ± 0.06 mgL-1 (87.50%). Meanwhile, U. fasciata, Gelidium sp., and S. illicifolium were able to reduce phosphate concentrations by 83.05%, 75.61%, and 70.27% on the 20th day, respectively (Fig. 2c).
The largest percentage of ammonia reduction in water was shown by the treatment of U. fasciata, followed by S. illicifolium, Gelidium sp. and Dictyota sp. However, the percentage reduction of ammonia in the water showed no significant difference in all the treatments. The highest percentage of nitrate reduction in water was shown in the treatment of U. fasciata that can reduce nitrate 79.53%, although it was not significantly different with S. illicifolium and Gelidium sp.. Furthermore, the largest percentage reduction in phosphate was shown by Dictyota sp. That can reduce phosphate until 87.50%. Eventhough it was not significantly different with U. fasciata (83.05%), however it was significantly different from the control, S. illicifolium, and Dictyota sp (Figure 3.)
3.3. Content of N total and P total in thallus
Figure 4 showed that the percentage of the total P content addition in thallus seaweed tends to be higher than that of total N content. Overall, U. fasciata has the most effective absorption of N and P in wastewater because it has the highest addition of total N and P contents in thallus. Meanwhile, Gelidium sp. has the lowest N and P absorption compared to U. fasciata, Dictyota sp., and S. illicifolium.
3.3 Specific growth rate (SGR)
U. fasciata has the best growth rate at 1.91% day-1, followed by Dictyota sp at 0.36% day-1, and Gelidium sp at 0.25% day-1. While S. illicifolium has the lowest SGR -1.71% day-1 (Figure 5) because some thalli were fragmented, therefore effect on the final weight of seaweed .