| Recirculating Aquaculture Systems (RAS) often produce a substantial quantity of wastewaters contaminated with fish feces and food residues. They must be treated prior to discharge in order to meet regulatory requirements. Thus, the objective of this thesis is to evaluate the feasibility of membrane filtration coupled with chemical precipitation as a pre-treatment to treat RAS wastewater with emphasis on phosphorus removal efficiency. Precipitation experiments were conducted by using standard jar testing apparatus with varying magnesium chloride, alum and lime doses and pH values. Membrane filtration tests were conducted by using crossflow, flat sheet membrane modules operated under both constant transmembrane pressure (TMP) and permeate flux modes, respectively. The effects of TMP, permeate flux and cross-flow velocity on membrane filtration performance were examined for both raw and chemically precipitated wastewater. The results showed that membrane filtration can effectively reduce total phosphorous to less than 0.05 mg/L with an overall removal efficiency of more than 90% for RAS wastewater pre-treated by any of these precipitants. At constant TMP mode, the permeate flux increases slightly with TMP and cross-flow velocity. At the constant permeate flux mode, however, TMP would greatly be increased by increasing permeate flux and decreasing of cross-flow velocity. Finally, chemical precipitation can greatly improve permeate flux and decrease TMP build-up, indicating the occurrence of decreased membrane fouling. |
