Nitrogen reclamation from aquaculture wastewater as potential fish feed additives via bacterial and algal-bacterial granular sludge systems

In this study, the potentials of aerobic granular sludge (AGS) and algal-bacterial granular sludge (ABGS) systems for the recovery of nitrogen from aquaculture wastewater as protein-rich fish feed additive were assessed. During 88 days' cultivation, the average chemical oxygen demand (COD), total phosphorus (TP) and total inorganic nitrogen (TIN) removal efficiencies were determined to be 96.7 %, 75.7 %, and 73.2 % in the AGS system, 96.8 %, 82.5 %, and 76.6 % in the ABGS system, respectively. The net biomass yield of ABGS was 24.0 % higher than that of AGS. About 11.3 % and 14.1 % of the TIN in wastewater were recovered as organic nitrogen in AGS and ABGS, respectively. The two granules had a similarly high content of total proteins (52 %, dry matter based), both containing 9 essential amino acids for fish and 7 non-essential amino acids, these features enabled them to serve as a low-cost substitute for conventional protein-rich additives in the fish diets.