Aplicação de um processo de complexação/ultrafiltração para remoção de poluentes do efluente do branqueamento TCF (totally chlorine free)

Abstract

The aim of this work was to investigate the reduction of metals chelates of diethylenetriamine pentaacetic acid (DTPA) from totally chlorine-free (TCF) bleachin geffluent by ultrafiltration-complexation process using polyethylenimine (PEI) and polyvinyl alcohol (PVA). This study was accomplished in two stages: preliminary tests and complemental ones. Preliminary experiments were carried out on batch stirred tank. The parameters, membrane type, the polymeric ligants addition and concentration, contact time (between the polymeric and the effluent), and pH were evaluated. The performance of the membranes and of the polymeric ligants were analyzed in terms of metals removal and COD (Chemical Oxygen Demand) percentage. These experiments were performed as a function of: polymeric ligants poly(ethylenimine) (PEI) and poly(vinyl alchool) (PVA) addition and concentration the contact time (effluent with polymeric ligants) and aqueous pH. The performance of the ipolymeric ligands was evaluated by determining metals removal and Chemical Oxygen Demand (COD). The preliminary tests results have showed that the best removals were reached with the M5 membrane and polymeric PVA. It should be pointed out that polymeric PEI was not applied in this stage. The contact time influenced in a significant way the metals removal, mainly with relationship to the Fe. 54% and 83% of Fe removals were reached for 24 hours and 5 days contact time, respectively, under following conditions (polymeric PEI, pH=4 and M5 membrane). On the other hand, removals of 49% and 68% were reached for 24 hours and 5 days contact time, respectively, using PVA, pH=3 and M5 membrane. The pH has significantly influenced metals removal, and using PEI and M5 membrane, pH range of 4-5, removals of 83% Fe, 46% Mg and 45% Ca were reached. For PVA and in the pH range of 4-6, the removals were of 68%, 39%, 51% for Fe, Mg and Ca, respectively. The polymeric ligants concentration has also significantly influenced the COD and metals removal. Removals of 59% Fe, 48% Mg, 54% Ca and 56% COD were reached using 12 mmol PVA concentration and pH=5. Removal values of 62% Fe, 39% Mg, 45% Ca and 51% COD were obtained working with 12 mmol PEI concentration and pH=4.6. After the preliminary tests parameters determination, complemental tests as a second stage were performed. The complemental tests were accomplished in a tangential flow module. The parameters, temperature, pressure and tangential speed were studied. The influence of these parameters on the metals removal as flux permeate was evaluated in details. The obtained results have showed that pressure and temperature have influenced metals removal in both systems (effluent + PEI and effluent + PVA). However, the tangential speed variation didn't present significant influence on metals removal.In general, the process complexation/ultrafiltration was efficient for metals removal from TCF (Totally Chlorine Free) bleaching effluent. The complexation/ultrafiltration process has increased the effluent final quality, compared to the ultrafiltration simple one.With regard to the permeated flow, the best results were reached working with pressure of 3 bar, speed 0,8 m/s and temperature 50oC for both systems (effluent + PEI and effluent + PVA).