Lab- and pilot-scale photo-biofilter performance with algal–bacterial beads in a recirculation aquaculture system for rearing rainbow trout

Abstract

AbstractIndustrial aquaculture has proliferated due to increased world demand for fish and seafood. Aerobic bacterial biofilters typically perform the nitrogen abatement of wastewater. Recirculation aquaculture systems (RAS) require nitrifying microorganisms developed in the biofilter. Despite the advantages of these biofilters, there are disadvantages, such as the time needed to mature, decrease in oxygen concentration, accumulation of organic matter and difficulty of backflushing, among others. On the other hand, microalgae effectively eliminate nutrients-pollutants, consuming inorganic carbon, nitrogen, and phosphorus and balancing soluble oxygen, conditions not attributable to nitrifying biofilters. The current study used a photo-biofilter to determine the depuration capacity of an immobilized co-culture of microalga Tetradesmus dimorphus and nitrifying bacteria isolated from a Salmon RAS. Bacteria frorm genera Flavobacterium, Microbacterium, Raoultella, Sphingobacterium, and Pseudomonas were identified. Biofilters were tested in sequential batch (lab-scale; 2.85 L) and continuous mode (pilot-plant scale; 120 L) attached to a RAS system for rearing rainbow trout. The algal–bacterial community structure was studied using 16S rRNA gene sequencing. Results showed that at typical loading rates, the algal–bacterial community could simultaneously remove ammonium, total ammonium nitrogen (TAN), nitrate and phosphate. Moreover, the system evaluated removed TAN daily, at an average of 1.18 kg per m3 of beads. Graphical Abstract