Effects of tree harvesting time and tannin cold/hot-water extraction procedures on the performance of spruce tannin biocoagulant for water treatment

This study investigated the effect of seasonal variation (i.e. winter and summer) on tannin extracts from spruce bark as biocoagulants for water treatment applications. Tannins were extracted through three different water extraction procedures: cold-water extraction (21 degrees C), cold-water plus hot-water extraction (85 degrees C) and direct hotwater extraction (85 degrees C). 1H nuclear magnetic resonance spectra showed that the cold-water plus hot-water extractions possessed the highest proportion of phenols. Electrospray ionization-mass spectrometry indicated that a preliminary cold-water extraction sufficiently reduced the non-phenolic constituents (monosaccharides and sugars) from the winter bark in the cold-water plus hot-water extraction but not from the summer bark. The synthesis of tannin-based coagulants was performed through the Mannich reaction using formaldehyde and ethanolamine. Coagulants with the highest charge densities (3.379 +/- 0.012 meq/g) were produced with tannin extracts obtained from the winter bark cold-water plus hot-water extractions. Water treatment experiments with the coagulants from the winter and summer bark cold-water plus hot-water extractions demonstrated that they were effective for particle settling. The study proved that the tree harvesting season and extraction procedure play a critical role in obtaining high-quality spruce tannin for the synthesization of tannin-based biocoagulants that provide better coagulative performance.