A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Natural Resources Management, School of Environment, Resources and Development

Thesis (Ph.D.) - Asian Institute of Technology, 2019

Aquaculture effluent is a major concern due to the negative impacts on the aquatic environment. This study aims to determine the effects of seaweed density, salinity, and aeration on the uptake ofN02-, N03-, NH3, and P043- by Caulerpa lentillifera from Poecilia latipinna (Sailfin Molly) effluent using spectrophotometry and regression analysis. Laboratory experiments were conducted to measure nutrient uptake at five different seaweed density levels (10 g L-', 20 g L- 1, 30 g L-1, 40 g L-1 and 50 g L-1), three salinity levels (20 ppt, 30 ppt and 40 ppt) with and without aeration. Quadratic regression analysis revealed significant and nonlinear effects of seaweed density on uptake ofN02-, N03- and P043--, where the maximum uptake was predicted to occur at the seaweed density of 31.58 g L-1, 33.25 g L-1 and 20.03 g L-1, respectively. As the effect was found to be linear, NH3 was assumed that the maximum uptake occurred at 50.00 g L-1{u2022} The effect of salinity on uptake ofN02-, N03-, NH3 and P043- was significant and nonlinear where the maximum uptake was predicted to occur at the salinity levels of29.09 ppt, 30.68 ppt, 29.53 ppt, and 29.48 ppt, respectively. The result on the effects of aeration was mixed but somewhat indicated a positive effect on nutrient uptake within the 24 h time period. Our findings can be used to inform aquaculture producers to apply optimum levels for removing the excessive nutrients (N02-, N03-, NH3, and P043y by Caulerpa lentillifera from aquaculture effluent while achieving long-term sustainable aquaculture production. Based on the laboratory experiment results, the second part of the study was conducted to investigate the effectiveness of the use of Caulerpa lentillifera for nutrient removal from fish (Poecilia latipinna ) culture effluent by conducting an on-station experiment and measurements before the actual implementation. In this study, there were 15 circulations and effluent from fish culture unit was circulated though seaweed culture unit in each three days. Multiple linear regression analysis revealed that the application of the bioremediation system led to significant reduction in nutrient concentrations in one day, and further in the following two days. On average over the 15 circulations, the first one day of application decreased the concentrations ofN02-, N03-, NH3, and P043- by 0.247, 81.6,0.682, and 0.352 mg/L, respectively. The C:N ratio of seaweed was lower at the end of the 60-day application period than at the beginning, providing evidence of the nutrient uptake by seaweed. Moreover, concentration of heavy metal in Caulerpa lentillifera reduced sugnificantly as well. The initial concentration of Cd and Pb was 0.033 + 0.001 and 0.183 ± 0.02 mg (kg ww}", respectively, while the final concentration was 0.032 ± 0.001 and 0.138 ± 0.004 mg (kg ww}", respectively. Hence, based on the European Union (EU) standard, seaweed grown in the integrated system was safe for human consumption. The initial and final As concentrations were 0.597 + 0.03 and 0.434 + 0.02 mg (kg dwf', indicating that both had safe levels for human consumption according to the quality criteria by France and the Joint FAO WHO Expert Committee (JFWEC). The results of our experiment imply that recirculating aquaculture systems utilizing Caulerpa lentillifera for biofiltration has potential for enhancing water use efficiency through the integrating offish and seaweed production.