Sustainable tannin-based coagulants synthesized through Mannich reaction using melamine as an amine source for water treatment applications

Effects of Tree Harvesting Time and Tannin Cold-/Hot-Water Extraction Procedures on the Performance of Spruce Tannin Biocoagulant for Water Treatment

“…XPS characterization was performed on the tannin samples to investigate the difference in the chemical compositions and elemental states of the extracts. The XPS wide survey showed that all tannin samples were composed mainly of carbon (C1s ~ 285 eV) and oxygen (O1s ~ 533 eV) peaks, which was in agreement with previous studies [8,10]. Small amounts of inorganics (K, P, Cl, Si, N and Ca) were also detected in most of the tannin samples, and especially the summer batches showed a higher amount of potassium.…”

“…A kaolin/river water mixture was used as the water sample to determine the coagulative effectiveness of the tannin coagulants; the preparation of this mixture has been reported in detail in an earlier publication [8]. The turbidity and conductivity of the water samples were measured with a Hach 2100Q turbidity meter and a Mettler Toledo conductivity meter.…”

“…Many studies on the application of tannin-based coagulants in water treatment applications have established that charge neutralization plays a critical role in the destabilization of colloids and humic substances [8,12,45]. Thus, coagulants with higher charge densities are generally preferred during tannin modification.…”

“…Several studies have alluded to the coagulative efficacy of tanninbased coagulants in effluents with diverse characteristics [5]. Some notable practical applications of tannin biocoagulants in water treatment include the sequestration of heavy metals from surface water [6], decolouration of dye effluents [7], turbidity reduction of industrial process waters [8] and removal of humic substances from peat extraction runoff waters [9]. On the other hand, a significant difference in their coagulative performance due to variation in the chemical composition of tannins from various sources has also been widely reported [10][11][12].…”

“…Spruce is a common tree species in the Nordic countries and accounts for over 30 percent of forest resources in Finland [13]. Several studies have confirmed that hot-water extraction is a viable method for the extraction of spruce tannin [10,[14][15][16], and tannin extracted with hot water from spruce bark has been proven suitable for synthesizing biocoagulants [8,10]. However, the main limitation in the application of spruce bark as a tannin source for tannin-based coagulants is the low tannin yield and the presence of a significant amount of co-extracted impurities such as sugars, minerals and phenolic non-tannin compounds [10,17].…”