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

Abstract

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°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.

Received December 19, 2012; accepted May 15, 2013

ACKNOWLEDGMENTS

We are grateful to all members of the Recirculating Aquaculture Engineering and Technology Laboratory for technical advice and helpful discussions. This study was funded by the National Natural Science Foundation of China (31202033).