Abstract:
This study involved the water quality control in aquaculture system using natural microalgae to remove nitrogen compounds, coupling with the separation of excess microalgal cells and particulate matters by cross-flow filtration process. Optimization experiments for cross-flow filtration were performed using the diatom Chaetoceros gracilis due to its small cell size (6 microns) and could not be removed by simple filtration. It was found that cross-flow filtration could remove diatom cells even its cell size was smaller than pore size of the filter. The best operating condition for C. gracilis removal was at filtrate to concentrate ratio of 50:50. It should also be noted that cross-flow velocity of 0.0007 m/s could maintain high filtrate flux than that of the high velocity of 0.0016 m/s. When applying cross-flow filtration system to White shrimp (Litopenaeus vannamei) tank and Black tiger shrimp (Penaeus monodon) tank, the removal of natural microalgal cells and particulate matters was found to be effective, with 61.6 and 76.6 percent removal in White shrimp and Black tiger shrimp tanks, respectively. The highest value of filtrate to concentrate ratios obtained from White shrimp trials were equal to 45:55 and 25:75 for water velocities at 0.0007 and 0.0016 m/s respectively. While for Black Tiger shrimp tank they were found to be 40:60 and 30:70 for water velocities at 0.0007 and 0.0016 m/s respectively. Nevertheless, nitrite and nitrate in all the systems were found to be accumulated in the tanks, and further treatment was necessary before discharging or recirculating water back to the system.