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A comparison between water exchange and settling tank as a method for suspended solids management in intensive biofloc technology systems: effects on shrimp (Litopenaeus vannamei) performance, water quality and water use Abstract Biofloc systems rely on microbial processes in the water column to recycle animal waste products, reducing the need for water exchange. These increases biofloc concentration in the water and some form of removal is needed. An experiment was carried out to evaluate two management practices to control biofloc in Litopenaeus vannamei culture. Six tanks (48 m 3 ) were divided into two treatments: water exchange and solid settler. Shrimp were stocked at 164 shrimp m À2 and with 0.67 g of weight. After 61 days, shrimp under solid settler treatment demonstrated mean weight of 12.7 AE 0.5 g with survival of 73.8 AE 1.4%, and those under water exchange had a final weight of 10.1 AE 0.2 g and survival rate of 57.8 AE 11.1%. Total suspended solids did not differ between the treatments: 326.8 AE 24.9 mg L À1 for water exchange and 310.9 AE 25.3 mg L À1 for solid settlers. Settleable solids and productivity/respiration ratio was higher (P < 0.05) in water exchange treatment, indicating differences in physical and biological characteristics of bioflocs. Solids removal method influenced the water use, in which 1150 AE 249 L of water was necessary to produce one kilogram of shrimp using water exchange strategy, and 631 AE 25 L kg À1 with the use of settlers. Our results indicate that continuous operation of settlers can reduce variability in solids characteristics and water quality variables such as ammonia. Both strategies are efficient in controlling biofloc concentrations of the water; however, settlers can reduce water use and improve shrimp production.

This experiment evaluated the effect of salinity on growth performance of different lettuce cultivars (Lactuca sativa) in an aquaponics system with biofloc technology. The device contained two independent systems with two different salinities: 0 ppt and 3 ppt. Juvenile tilapia (Oreochromis niloticus) 6.1 kg m-3 and three varieties of lettuce: red leaf and smooth and crisp 20 plants m-2 were stored in the floating system. All fish performance parameters showed no statistical differences, except for the hepatosomatic index, higher in 3 ppt (4.35%) versus (3.07%) in 0 ppt (P<0.05). In general, the productivity of lettuce cultivars was superior in fresh water (1.21 kg m-2) compared to brackish water (0.8 kg m-2) (P<0.05). In most phyto-technical parameters evaluated, the purple variety had better performance than the smooth and crisped varieties. In relation to plant quality index (IQP), purple variety in brackish water had the best score, presenting leafs with higher integrity and intense coloration. The results demonstrated that it is possible to integrate the production of red leaf variety in aquaponics systems with the technology of bioflocs in low salinity.

-The design and performance of a radial anaerobic/aerobic immobilized biomass (RAAIB) reactor operating to remove organic matter, solids and nitrogen from sewage are discussed. The bench-scale RAAIB was divided into five concentric chambers. The second and fourth chambers were packed with polyurethane foam matrices. The performance of the reactor in removing organic matter and producing nitrified effluent was good, and its configuration favored the transfer of oxygen to the liquid mass due to its characteristics and the fixed polyurethane foam bed arrangement in concentric chambers. Partial denitrification of the liquid also took place in the RAAIB. The reactor achieved an organic matter removal efficiency of 84%, expressed as chemical oxygen demand (COD), and a total Kjeldahl nitrogen (TKN) removal efficiency of 96%. Average COD, nitrite and nitrate values for the final effluent were 54 mg.L , respectively.