- The Filtration Society - http://www.filtsoc.org -

Volume 13, Issue 2

SEPARATION CHALLENGES FOR BIOTECHNOLOGY – SMART IS ONE ANSWER
Karsten Keller (pages 92-98)

Downstream process costs in biotechnology are responsible for up to 80% of the total process costs due to the challenging separation tasks. The valuable products are embedded in a complex mixture and the product concentration is very low. Traditional chemical engineering approaches are lacking economical solutions. New processes need to be discovered to overcome these separation challenges. SMART is a systematic approach to find better separation solutions for the industry.

Selective separation technology
Manage the product properties
Advanced mechanical separation technology
Reorganize the separation forces
Treatment with enzymes

This paper provides examples of how SMART is changing the way of separation in biotechnology. SMART examples include membrane technology, magnetic separation, enzyme treatment and additional approaches. Some SMART examples are in the early research stage, while others are close to implementation.

DETERMINATION OF THE MODIFIED FOULING INDEX (MFI) AND COMPRESSIBILITY OF THE CAKE-LAYER ON A MEMBRANE DURING ULTRAFILTRATION FOR OILY WASTEWATER TREATMENT
Irena Petrinić, Arnela Murić and Morten Lykkegaard Christensen (pages 99-102)

Oily wastewater is one of the major pollutants that occur in many industrial fields and it is very harmful to the environment, especially aquatic life. All conventional methods for the treatment of oily wastewater, such as dissolved air flotation (DAF), coalescence and adsorption have their advantages, but none is effective enough. Therefore, membrane technology appears to be a promising method which offers many possibilities regarding membrane materials, process configuration and operational parameters (high pressures, temperature, crossflow etc.). However, the main problem in membrane filtration is fouling. In this study the Membrane Filtration Index (MFI) was extended to improve the precision of MFI for oily wastewater. A tubular module with a PES membrane was used in a crossflow ultrafiltration mode. In order to examine the correlation between the measured cake resistance and rejection of different feed components (COD, TSS, Fe, etc.), laboratory analyses were performed. It was found that formed cakes were compressible and the values of cake resistances were almost the same for different parameters even if rejection values increased.

UNDERSTANDING THE ROLE OF THE TWO CALCIUM POOLS ON CENTRIFUGAL DEWATERABILITY OF SLUDGE TO AVOID STICKINESS PROBLEMS IN CENTRIFUGE-DRYERS
Bart Peeters, Raf Dewil, Luc Vernimmen and Ilse Y. Smets (pages 103-112)

The purification of wastewater with activated sludge generates huge amounts of excess sludge, which is most often incinerated after mechanical dewatering and drying. During the dewatering-drying process, i.e. to within a certain range of dry solids content, the sludge passes through a sticky phase. Its sticky consistency causes the sludge to cling to the dryer walls, causing operational downtime. Hence, it is of utmost importance to control the dry solids content of the sludge at the end of the mechanical dewatering step (i.e. before it enters the drying step) to avoid the sticky issues.

Ca2+ ions play a crucial role in the bioflocculation process and, hence, in sludge dewatering, by means of (i) the exchangeable Ca2+ and (ii) the enmeshed CaCO3 solids in the flocs. It is demonstrated that both Ca2+ pools improve the cake dryness obtained after centrifugal compaction. More specifically, in the case when exchangeable Ca2+ is present in the sludge, in this way stabilizing the floc structure, the cake dryness increases by about 2% DS. An increase of the sludge CaCO3 fraction from 30% to 70% raises the cake dryness by 10% DS.

At the Monsanto Antwerp WWTP, Belgium, for sludge characterized by too good a natural dewatering capacity due to the presence of both Ca2+ pools (and, in particular, due to the incorporation of the CaCO3 solids in the sludge), the traditional addition of clay mineral as a skeleton builder is reduced in the sludge feed to the centrifuge-dryer apparatus. In this way the cake dryness after the centrifuge is controlled which avoids the stickiness phenomena in the dryer operation.

INVESTIGATING SKIN FORMATION DURING THE FILTRATION OF MICRO-CRYSTALLINE CELLULOSE
Tuve Mattsson, Maria Sedin and Hans Theliander (pages 112-119)

Separating solids from liquids through filtration is an important unit operation employed in a wide range of industrial sectors. It is vital that accurate and applicable models are employed when designing industrial sized filters. Comprehensive models are readily available for materials that form incompressible cakes, whereas those for compressible cakes are lacking. Materials that form compressible filter cakes may also form a dense initial cake close to the filter medium, i.e. a ‘skin’. In this study the local filtration properties of a model material, TiO2, and micro-crystalline cellulose (MCC), are measured to investigate skin formation in a compressible filter cake. Indications of the formation of a skin in the filtration experiments using MCC could be observed; local pressure measurements were found to be useful in the investigation of its formation. Both the choice of the filter medium and the electrostatic interactions affected the skin formation. The tendency for skin to form was reduced at a lower pH, this lower pH corresponding to less charged particles and filter media.

FILTRATION OF FIBRE/PARTICLE MIXTURES
Steve Tarleton, Kuhan Chellappah and Richard Wakeman (pages 120-126)

New data are reported for the filtration of binary fibre/titania (rutile) mixtures. The combined use of the Kozeny-Carman equation and Darcy’s law is discussed in relation to the filtration of these mixtures. Upon study this approach is shown to have its limitations, particularly when significant aggregation takes place between the two solids species. The difficulties in overcoming these limitations from a fundamental basis are highlighted and a semi-empirical model is presented and discussed. This model is shown to better represent the specific resistance trend with solids composition for a range of binary mixture filtration data.