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

Abstract

AbstractAs 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°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°C groups, respectively, indicating that the biofloc bacteria started to convert ammonium to microbial biomass on that day. The nitrite concentration remained below 6.5 mg/L for each group except the 30°C group, in which the value reached 13.88 mg/L. The nitrate concentration remained below 4.5 mg/L for each group. An ammonia nitrogen removal study revealed that all SBRs could remove a total ammonia nitrogen (TAN) concentration of 10 mg/L in 6 h without increasing the nitrite and nitrate concentrations; the 25°C group needed only 3 h 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°C group, 28.6 ± 3.14% for the 20°C group, 36.80 ± 3.31% for the 25°C group, and 35.06 ± 3.94% for the 30°C group, indicating that the bacteria could be harvested as biological protein for feeding the cultured species.