Process water from a Swedish thermomechanical pulp mill was purified by consecutive treatment by microfiltration, ultrafiltration and nanofiltration. In the present study the nanofiltration step was studied. The flux and retention of four nanofiltration membranes were compared. The NF99HF membrane (Alfa Laval, Lund, Sweden), had significantly higher flux and higher retention of lignin and charged compounds (measured as conductivity) compared to the others. The flux was 220 l/m2 h and the retention of calcium ions was 99% at 20 bar transmembrane pressure and a temperature of 50°C. At the same conditions, the conductivity (measured at 20°C) was decreased from 1 500 µS/cm in the feed solution to 150 µS/cm in the nanofiltration permeate.
The influence of pH and surfactants during treatment of E-stage effluent was studied. Three tubular ultrafiltration membranes were used in the experiment. The flux of the three membranes was at its highest level at the normal, high pH, of the effluent. In this experiment the densest membrane showed the greatest flux decrease, while the most ouen membrane was either unaffected bv variations in ph or experienced a more moderate decrease. The flux after treatment with a nonionic surfactant could be restored by cleaning with a commercial cleaning agent, but it was not possible to restore the initial flux when a cationic surfactant had been added to the effluent. The role of cleaning during membrane treatment is also discussed.
SammanfattningBakgrund: Intensivvardssjukskoterskan ingar tillsammans med en narkoslakare i en Mobil Intensivvardsgrupp (MIG). Om en patient pa en vardavdelning pavisar forsamring i vitala parametr ...
Extn. of lignin from kraft black liquor is one method of lowering the large energy surplus in pulp mills. The lignin can be used as a bio-fuel to replace fossil fuels in heat or power generation, and the lignin-depleted black liquor can be reused in the cooking operation. As kraft black liquor lignin has a fairly high mol. wt., ultrafiltration can be used to selectively fractionate lignin from cooking chems. However, ultrafiltration of kraft black liquor calls for membranes that can withstand high temps. at high pH, i.e. ceramic membranes. In this investigation the performance of a ceramic membrane manufd. by Orelis, France, with a cut-off of 15 kDa was studied. The temps. employed during the expts. were 75 and 90°C and no adjustment of the pH was made. The influence of transmembrane pressure, temp., cross-flow velocity and vol. redn. on flux and retention of lignin and inorg. compds. (cooking chems. and multivalent, non-process elements) was studied. A correlation was found between the av. flux and retention during concn. The highest av. flux attained during concn. to 90% vol. redn. was 160 L/m2 h with a lignin retention of 35%. The retention of cooking chems. was found to be insignificant, while multivalent inorg. compds. were found to be retained to a high degree. (Less)
Effluent from alkali extraction of chlorinated pulp was treated with ultrafiltration (UF). Three different ultrafiltration (UF) membranes were tested. The permeate from one of the UF membranes was further treated with reverse osmosis (RO). Titration curves for the permeates from the different UF and R0 membranes were determined. The concentration of charged compounds was calculated from the titration data and compared with the COD and AOX of the permeates. The retention of COD and AOX was between 50 and 90% for the UF membranes, whereas the retention of carboxylic acid groups was considerably lower, 15-45%. During the R0 treatment the retention of all compounds was found to be very high. For the densest R0 membrane the retention of AOX and compounds with carboxylic acid groups was higher than 99%. The retention of COD was 96%. (Less)
When applying membrane processes on industrial scale in the food industry both the fouling and the subsequent cleaning of the membranes are key but often underestimated factors. This presentation will focus on the impact of pre-treatment, operation conditions and module design on fouling and cleaning.After reviewing the current state-of-the-art of membrane fouling and cleaning in the food industry, the presentation will focus on an application study related to a membrane unit integrated in the purification of starch-based sweeteners such as glucose after liquification and saccharification. Conventionally, retrograded starch, proteins and fats are removed in this purification step which is often referred to as “demudding” by using a rotary vacuum filter supported by filter aids such as kieselguhr or perlite. Alternatively, a membrane-based hybrid process consisting of a decanter combined with an ultrafiltration unit has been developed. The focus of this study will be on the control and optimisation of the fouling and cleaning of the ultrafiltration membrane unit to achieve a stable and sustainable membrane performance. Overall, the goal of this presentation is to demonstrate how appropriate measures can reduce the impact of fouling and cleaning on membrane processes and thus improve their long-term sustainability in the food industry. (Less)
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