Characterization of a byproduct generated by the treatment of water from a biofloc technology system using a plant tannin-based coagulant

The aim of the present study was to characterize the sludge generated by the treatment of water from a biofloc technology (BFT) system using a tannin-based coagulant. Bromatological, thermogravimetric and microbiolog-ical analyses were performed. Toxicity was investigated using lettuce seeds (Lactuca sativa) and onion roots (Allium cepa). Water samples were obtained from a rearing of Oreochromis niloticus in BFT system. The residue generated by the treatment of water with a tannin-based coagulant was considered in this study. The broma-tological characterization revealed that the sludge had an average of 14.37% crude protein, 50.77% mineral fraction and 0.21% ether extract. Treatment with tannin did not cause an increase in the sludge total phenol content compared to that generated by bioflocs alone. However, the sludge generated by the treatment with tannin-based coagulant caused the complete inhibition of lettuce seed germination and a significant reduction in the mitotic index of onion roots, which may be due to the high dose of tannin-based coagulant applied to promote optimal water treatment conditions to obtain the sludge. In vivo tests are needed to identify the response of animals and indicate the best species for the incorporation of the sludge into the diet.

Automated summary

The present study characterized the sludge generated by the treatment of water from a biofloc technology system using a tannin-based coagulant. The sludge had a certain amount of protein and mineral fraction. The sludge generated by the treatment with tannin-based coagulant showed negative effects on plant germination and root mitotic index.