Mimosa me Tannin-Based Coagulants in Decolouration Processes
The structure of synthetic organic dyes permits their easy modification as well as their application in various industries. However, the effluents from dyeing are quite persistent molecules and difficult to degrade. Obtaining environmental friendly, cost effective and reliable products for water purification is, therefore, required. This includes those effective in the removal of mutagenic, carcinogenic and toxic dye particles. In this study, Mimosa Me tannin (wood extract) was modified to introduce cationic charges. In several colored waters systems the tannins produced could successfully remove different dyes in jar tests.
The bio-coagulants were produced via Mannich reaction starting from tannin powder, using dimethylamine hydrochloride and formaldehyde at 80 °C for 1h. This resulted in obtained product with shear viscosity of 37 cPs. The modified tannin was tested in model colored waters, in order to evaluate the capacity of color removal, which was monitored, over time, by UV-spectroscopy. Good decolouration results with bio-coagulants can be obtain by introducing other elements to the process such as bentonite, polyamines, polyaluminium chloride (PAC), cationic flocculants based on acrylamide and dimethylaminoethy acrylate as well as anionic, high molecular weight copolymers of acrylamide and acrylic acid. The acidification of the water can also be useful as a pre-treatment. Due to the different characteristics and properties of each dye, several procedures must be tested. The most efficient way of treatment is summarized in the Table I.The objectives were to remove the colour and have the remaining water as close to potable as possible. The best results yield an extinction coefficient, measured at 340 nm, of 0.03-0.04, down from 1.24. The performance of color removal was evaluated over time, after 10, 30, 60 and 180 minutes as well as after 24 hours. It was also not surprising that from 3 to 24 hours of settling the color removal increased up to three times, the highest value being up to 99%.
This study reviews several procedures for effluent decolouration and emphasizes the use of modified tannin as an alternative option for colored wastewater treatment from several industries. The natural origin of these coagulants and biodegradability of produced sludge are favourable as potential wastewater treatment agents.