Effects of Temperature on Inorganic Nitrogen Dynamics in Sequencing Batch Reactors using Biofloc Technology to Treat Aquaculture Sludge

As a new aquaculture technology, biofloc technology (BFT) makes it possible to minimize water exchange and convert the nitrogen in aquacultural waste into biofloc, which can be a natural fish food within the culture system. In the current study, biofloc bacteria were employed to treat sludge from a recirculating aquaculture system under four different temperatures (15, 20, 25, and 30 degrees C) in three sequencing batch reactors (SBRs) per temperature. Ammonium reduction was seen on days 19, 17, 13, and 17 for the 15, 20, 25, and 30 degrees C groups, respectively, indicating that the biofloc bacteria started to convert ammonium to microbial biomass on that day. The nitrite concentration remained below 6.5mg/L for each group except the 30 degrees C group, in which the value reached 13.88mg/L. The nitrate concentration remained below 4.5mg/L for each group. An ammonia nitrogen removal study revealed that all SBRs could remove a total ammonia nitrogen (TAN) concentration of 10mg/L in 6h without increasing the nitrite and nitrate concentrations; the 25 degrees C group needed only 3h to remove the TAN. The protein content of the biofloc at the end of the study was 27.81 1.99% (mean +/- SD) for the 15 degrees C group, 28.6 +/- 3.14% for the 20 degrees C group, 36.80 +/- 3.31% for the 25 degrees C group, and 35.06 +/- 3.94% for the 30 degrees C group, indicating that the bacteria could be harvested as biological protein for feeding the cultured species.