Acidifying remediation and microbial bioremediation decrease ammoniacal nitrogen, orthophosphates, and total suspended solids levels in intensive Nile tilapia farming under biofloc conditions

Abstract

In biofloc technology (BFT) systems, the formation of bioflocs and accumulation of suspended solids are constant, which can cause impairments in water quality parameters and negatively impact the growth performance of farmed animals. We herein investigated two integrated solutions for intensive farming of Nile tilapia under BFT conditions. In this study, EUROGUARD® SOFT F60 (60% formic acid and 40% lignosulfonic acid) was used as the acidifying remediator, while ADD LIFE PRO BACIL ACQUA based on a mixture of Bacillus spp. was used as the microbial bioremediator. First, assays were conducted for in vitro inhibition tests of acidifying remediator against seven different strains of pathogenic bacteria. A dose-response test was performed for both acdifying bioremediator and microbial bioremediator. Then, an in vivo assay was conducted over four weeks. In 12 BFT units with a capacity of 250 L each, one group received the acidifying remediator at a concentration of 2.5 part per million (ppm), while another group received the bioremediator Bacillus spp. at a concentration of 0.10 g m−3 directly in tank water. A control group without aditives was also established, all in quadruplicate. The culture environment was evaluated daily by measuring dissolved oxygen, temperature, floc volume and weekly by measuring total ammonia nitrogen (TAN), ammoniacal nitrogen (N−NH3), nitrite (N-NO2), nitrate (N-NO3), alkalinity (CaCO3), orthophosphate (PO43−), electrical conductivity (μS−1), potential of hydrogen (pH) and total suspended solids (TSS). At the end of the period, in the in vivo assay, the bacterial community in the BFT, hematological parameters, and zootechnical performance of the tilapia were evaluated. In in vitro inhibition tests, the acidifying remediator inhibited the growth of all pathogenic bacteria evaluated. All concentrations reduced the count of filamentous bacteria, and the pH values were dose-dependent. Both in vivo treatments altered bacterial communities. Both treatment groups had lower concentrations of N-NH3, N-NO2 and N-NO3. PO43− content was lower in the acidifying remediator group. CaCO3 was higher in the treatment groups, while TSS was higher in the control group. Both remediation strategies were efficient in removing nitrogenous chemical compounds. However, the acidifying remediator concomitantly reduced N-NH3, N-NO2− and PO43− levels, becoming a powerful ally in the reduction of aquaculture effluents, as well as in the reduction of potentially pathogenic bacteria in tilapia culture.