further information on sludge related applications
...we've bought a Lumifuge 116 and we are now
performing some trials on flocculated sewage sludge.
During these trials, we encountered a few problems leading to following
questions:
*Do you have application notes for flocculated sludge (in english or
german)?
*We are currently using glass vials with 2 ml of sludge. We do see
however that the light intensity in the cleared zone is much more than
100 %. Should we tackle this problem by putting a lower intensity in the
method section ?
*Do we have to homogenize the light at all possible rotational speeds or
is it sufficient to do this at e.g. 1000 rpm ? Do I have to do a
homogenisation with a water filled glass cuvette when using these types
of vials ? Do I have to change something on the pixel settings in the
Menu options.../light homogenisation ?
On the preprint server of chemweb.com the following two articles are assessible:
Investigations on sludge dewatering with the separation analyser LUMiFuge 114
T. Sobisch, D. Lerche, 2000
shifted by elsevier to
Chemistry Preprint Archive, Volume 2002, Issue 10, October 2002, Pages 1-11
http://www.sciencedirect.com/preprintarchive
Pre-selection of Flocculants by the Separation Analyser Lumifuge 114
T. Sobisch, 2002
shifted by elsevier to
Chemistry Preprint Archive, Volume 2002, Issue 4, April 2002, Pages 265-274
http://www.sciencedirect.com/preprintarchive
The first considers general aspects including sludge characterization, the second is a kind of progress report focussing on selection of flocculants for dewatering in decanter centrifuges.
The latest in the series of sludge related publications is the paper that will be presented at the World Filtration Conference - wfc 9 April 18-22 2004 in New Orleans.
# To problems with the glass cells
To study the dewatering behaviour and packing and elasticity of the sludge cake the use of the round glass vials is the only good choice you have at present, however, evaluation of the resulting centrate using these cells is nearly impossible.
Please consider the following,
To trace the kinetics of sludge separation, cake compressional behaviour the precise determination of transmission of the supernatant is not necessary. For evaluation of clarification you should use rectangular cells.
Due to the curvature the cells act as optical lenses, causing an amplification of the incoming light. The magnitude of this effect depends on turbidity insight the sample, quality of the glass tubing and of the very exact position where the vial is hit by the light beam. So you will be unable to ensure reproducible conditions. To improve the situation a little, you might do the homogenization in front of the measurement under the same conditions with the cells filled with water only, however, you should ensure that the position is not altered around the axis of the cells. You then might check the reproducibility of the results (caution!).
In case, the sludge samples have initial total solids below 3 - 4 % wt you might consider increasing the sludge volume above 2 ml (max. 5 ml!) to enhance precision of determination of the volume of the sludge cake. If you are working at the highest centrifugal speed you should be able to trace the phase boundary after 10 to 30 s.
You might determine the volume of the sludge cake from the position of the phase boundary after calibration.
see
How to determine the position of the bottom of the measuring cells and
How to determine volumes (sediment, cream or water layer)
The calibration can be done by filling a set of cells with different amount (mass) of water and do a run in the lumifuge. The position of the meniscus can be traced by the location of a sharp insection of the transmission profiles. From one or two runs you will get a set of data - position - volume. This can be used to fit it by an equation, lets say y = a + bx + bx². Then you will be able to compute all data for the sludge volumes.
Please be aware, that if you take the flocculated sludge samples, in most cases you cannot ensure that the initial total solids content of this sample is identical with that of the reservoir. However, variations in the initial total solids have a marked influence on results measured. For a sample of the same quality but higher solids content the kinetics will seem more hindered and due to a higher excess pressure the samples will compact to a higher density. Therefore, it should be necessary in most cases to determine the total solids content after measurement (drying). We would propose to take parallel samples and do the measurements twice or three times.
The suggestions above are related to the measurement of sludge dewatering, especially in the light of flocculant selection. If your investigations have another focus, eventually, a different approach is needed.
# homogenization
It will be sufficient to do the homogenization at a medium speed. However, if you do this with the filled glass cells, then it should be the same as during the measurement.
Analysis of oil in water (o/w) and water in oil (w/o) emulsions - emulsion type
Chemistry Preprint Archive, Volume 2004, Issue 5, May 2004, Pages 7-18
Einfluß der Tensidzusammensetzung
Using analytical centrifugation determination of O/W or W/O emulsion type is as simple as in other cases when the emulsion starts to separate.
During centrifugation an osmotic pressure is exerted onto the emulsion, forcing the dispersion media out of the space between the droplets. For a detailed theoretical description of this process see for example:
S. Tcholakova, N.D. Denkov, I.B. Ivanov and B. Campbell, Langmuir 18(23) (2002) 8960.
Therefore, you can already trace the emulsion type at the beginning of the separation.
O/W - at the cell bottom you will trace a clearing-up (oil droplets are depleting), at the top layer a zone of a concentrating emulsion appears (low transmission). Release of oil from this emulsion might occur or not (thin upper layer with higher transmission) as a secondary process.
W/O - clearing-up at the upper part of the sample (water droplets are depleting), emulsion is concentrating towards the bottom and so forth.
In summary, you should try to deduce the emulsion type from the first changes that can be noticed because at a later stage secondary processes might occur. Please be cautious and have look at the samples before you place them into the LUMiFuge and after measurement. Experimental errors, like wall effects might cause confusion.
