Macronutrients of Brown and Green Water Types of BFT Systems May Behave Differently During Recirculation in Saline Aquaponics

Abstract

Biofloc technology (BFT) systems are sustainable for aquaculture due to the growth of microorganisms in the culture medium that can uptake toxic nitrogen compounds, which generates "in situ" microbial protein that can be eaten, decreasing feed costs. BFT brown (formed with no direct natural light and bacterial dominance) and green (exposed to direct natural light, algal system) waters can be potentially used for aquaponics of commercial halophytes. This study evaluated changes in physical-chemical parameters and macronutrient concentrations of brown and green saline waters of BFT systems, with marine shrimp (Litopenaeus vannamei) breeding stock, subjected to a one-week recirculation cycle in saline aquaponics with halophytes (Salicornia neei, Apium graveolens and Paspalum vaginatum). For 30 days in the summer of 2019, clarified brown and green waters of BFT systems of L. vannamei were used for aquaponic cultivation of these three halophytes. Water samples were collected before and after one week of water recirculation in the aquaponic systems. Halophytes grow well with both water types. The brown water had a higher phosphate concentration and its nitrate content reduced 3-fold in magnitude after one week of recirculation. The green water had higher average concentrations of nitrate, potassium, calcium, magnesium and sulfate compared to the brown water, and its nitrate and nitrite contents significantly increased after one week of recirculation. The remediation of dissolved macronutrients using aquaponics can be ineffective for green water types, mainly due to the death and decay of photoautotrophic microorganisms during the water recirculation process inside aquaponic structures.