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Abstract
The bio-flocculants used in this study were synthesised by the Mannich reaction, which includes three reagents: a substrate (tannin extracts of Acacia, Quebracho, and Castanea), formaldehyde, and an amine derivative (ethanolamine, diethanolamine, ammonium chloride). Nine natural flocculants were prepared by combining extracts and amines; these products were evaluated in three different wastewater samples in two experimental phases. In phase I, five physicochemical parameters were analysed. From the data obtained, a multivariate, completely randomised design (CRD-Manava) was used, with a factorial arrangement and mean plots. In phase II, the three bio-flocculants with the most statistically significant responses and their mixtures were examined, evaluating 14 biological and physicochemical parameters. Statistical analysis was guided in this phase by CRD blocks, finding a significant removal in the physicochemical parameters analysed in the different types of wastewater and obtaining removal rates between 50 and 90%, depending on the parameter. At the end of both phases, the bio-flocculants acacia-ammonium chloride and quebracho-diethanolamine were the most efficient in the removal of turbidity (34-99%), true colour (93-100%) and total solids (12-99%). In addition, the natural flocculants showed low mutagenicity index (MI: 0.33-0.93) compared to aluminium sulphate (MI: 4.87-8.81).
Highlights
Inorganic salts such as aluminium sulphate Al2(SO4)[3] and ferric chloride (FeCl3) have been used for coagulation-flocculation processes in wastewater treatment
Quebracho and Acacia have a high content of condensed tannins; the spectra and bands of these extracts are very similar
At 970 cmÀ1, bands assigned to the asymmetric bending of C-H aromatic interactions are observed; and in the region of 1,283 cmÀ1, there is a peak pertaining to the C-O-C stretch of the C ring of the flavonoids that make up the polymer structure of condensed tannins
Summary
Inorganic salts such as aluminium sulphate Al2(SO4)[3] and ferric chloride (FeCl3) have been used for coagulation-flocculation processes in wastewater treatment. Tannins are water-soluble polyphenolic secondary metabolites of high molecular weight, produced in various plant tissues such as bark, fruits, leaves, and roots depending on the genus considered These compounds were used for leather tanning because of the strong structures generated between leather proteins and tannins (Pizzi ). These metabolites can be divided according to their structure into gallotannins, ellagitannins, complex tannins, and condensed tannins (Khanbabaee & van Ree ); the latter can be used as polymeric additives with inorganic salts or strengthened with cationic regions by the Mannich reaction for direct flocculation (Beltrán et al ) This condensation reaction requires three main components: a compound containing an active hydrogen atom (substrate), formaldehyde, and a primary or secondary amine. These compounds cause aminomethylation of the substrate (Subramaniapillai ) and form a Mannich base
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