68 ÇEVRE TEKNOLOJİLERİ/ENVIRONMENmL TECHNOLOGIES 4. Nanofiltration and Reverse Osmosis Plants Experimental nanofiltration and reverse osmosis plants are usual and already described (Figure 2). A heat exchanger (C) was installed in the feed line 1 to maintain a constant temperature T measured by a thermometer. The value of permeate fluxes were adjusted at 20°c, to avoid variations in viscosity linked to temperature changes. A feed pump (B) ensures !he circulation of the fluid and controls the velocity in the nanofiltration module (D) with the valve (F). Retentate feed 3 is recycled to the feed tank (A). The pressure is controlled by gradually closing the valve (E) and the transmembrane pressure TMP is defined as the mean value of upstream (P1) and downstream (P2) pressures (MGS10/3-63, Serv'instrumentation, lrigny, France). The difference (P1-P 2) is called pressure drop (DP). lf it is necessary, pure water is introduced with a pump (F) in the tank (G) to perform the diafiltration step. Two draining lines (5) are used to collect the retentate at the end of each experiment. The flow rate and the permeate flux were measured. Moreover a conductivity and pH electrodes are placed in the feed tank (A) and in the permeate line 6 to measure continuously conductivity and pH during each experiment. G A Tank o Membrase valve takes place as long as the conductivity in the tank is lower than the value required (90% of the electrolyte in the permeate side). Then, the hydrolysed reactive dyes and the additives of dyeing retained are concentrated in !he retentate side by nanofiltration. t if !he effluent has a strong concentration in hydrolysed reactive dyes (deep shade), the nanofiltration only includes two steps : diafiltration to recover electrolyte and a concentration step. in case the reverse osmosis is carried out on the permeate of the nanofiltration which it in fact a diluted bring, we get a pure brine available for a new dyeing, fresh water to be used during diafiltration or during !he dyeing process. 5. Analysis The main analytical characteristics for suitable re-use were determined: pH conductivity, total hardness, chlorides and colour. We have collected samples of permeate and retentate during experiments. Chlorides were analysed by different methods: conductimetry, potentiometry, spectrophotometry and certified by an independent and external laboratory which is the SEM (Societe des Eaux de Marseille). RESULTS 1. Pre-filtration We have prefiltered around ten cubic meters of industrial effluents through the filter calibrated for to fulfill all requirements already described (Figure 3). AII the fibres were stopped without any reduction of the drainage flow. 2. Carbonate Neutralisation The problem is to check if we can used !he usual control methods when we have coloured and concentrated mixtures. For !his reason, we reconstituted synthetic solutions containing a constant quantity of carbonates and a variable quantity of sodium chloride. The results are compiled in Table 1. Sodium 5 Retantene chloride concentration doesn't have an influence on the 6 ! Permeate I H hydrochloric acid volume to add to neutralize carbonates. Figııre 2. Naııofılıration and reverse osıııosis planı. We verified !hat the pH ofa solution in contact with air rise what is due to dissolved CO2 (Table 2) and we eliminated this According with the type of effluents the nanofiltration is carried problem by addition of fine air bubbles which accelerated the out in different ways : t if the effluent has a very low concentration of hydrolysed reactive dyes (pale shade and/or high rate of fixation), the nanofiltration consists ofa single concentration step. in this permeate, which will be recycled has !he same salt concentration as the starting effluent. t if the effluent has a low concentration in hydrolysed reactive dyes (medium shade), the nanofiltration includes three steps : pre-concentration, diafiltration and concentration. After !he conventionnal nanofiltration, the flow decreases and becomes very low. Then !he so-called diafiltration ENERJi DÜNYASI EKiM 2006 Figııre 3. Pre-filter used (Pall-Exekia).
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