Abstract
Effluent from a fish tank with Nile tilapia (Oreochromis niloticus) was treated in a system of two parallel fixed-bed anaerobic reactors followed by a suspended stirred, anoxic reactor for solids, organic matter and nitrogen removal. Microbial community structure was compared between the reactors and an enriched anammox culture originated from anaerobic sludge by using the PCR (Polymerase Chain Reaction) and DGGE (Denaturing Gradient Gel Electrophoresis) techniques. DGGE analysis revealed three large microbial clusters, namely, the biomass in the inoculum, the biomass growing in the reactors, and the enriched anammox culture. The similarity between the microbial community recovered from the anaerobic reactors and the anammox community was considered low (32.7%), suggesting differentiation of the bacterial community as a function of the selection of specific anammox groups. The last step in the anoxic reactor had worsened the effluent quality. The potential of organic matter and ammonia removal in a single anaerobic reactor was demonstrated.
Highlights
Fish production is carried out in intensive and semi-intensive systems by small producers
The enriched anammox culture originated from a parallel study, with the objective of obtaining anammox bacteria, which had the biomass of an anaerobic baffled reactor sludge (ABRS) as inoculum, and was selected in a sequential batch reactor after 210 d fed with autotrophic medium according to Dapena-Mora et al (2006)
The mean values of temperature, pH, Dissolved oxygen (DO), turbidity, color and electrical conductivity (EC) of the fish tank water were in accordance with the recommended values for the fish species used (Makori et al, 2017)
Summary
Fish production is carried out in intensive and semi-intensive systems by small producers. Anaerobic denitrifying bacteria reduce nitrate and nitrite to nitrogen gas (Khin and Annachhatre, 2004) These reactions are widely known and have been successfully applied in most wastewater treatment systems (Egli et al, 2001). This process has some limitations when the objective is to treat effluents containing high concentrations of nitrogen and low concentration of carbon (low C / N ratio) since there are difficulties in the transfer of large amounts of oxygen necessary for nitrification and the need for a large amount of biodegradable organic matter in the denitrification phase (Xing and Clark, 2012). We evaluated the performance of an anaerobic and anoxic mixed biomass for the treatment of fish waste effluent in anaerobic reactors, and an agitated anoxic reactor for removing organic matter, ammonia, nitrite and nitrate by partial nitrification and the anammox process
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