Sieving equipment for
marine sediments by Wim Hegeman
Sieving of marine sediments
followed by the determination of contaminants (hydrophobic compounds and trace
metals) in the specific size-fraction has advantages to collect representive
and compartive samples in marine areas. These standardized concentrations can
be used in order to determine pollution in marine sediments.
The sieving system was developed by Wim Hegeman and was succesfully used during 20 years of operation
in the Dutch marine sediments. Here the details of the technical drawings are
presented. The whole system of sieving, collecting the specific size-fraction
and the operations is showned. Specific distances of the drawing are also
given.
The perspex sieving system
is developed in such a way that the sieving nettings can be replaces with ease
therefore this equipment can last for more than two decaces. The sieve-holders
are made of relative thick material and therefore are extremely durabel. The
equipment was tested in the laboratory as on board of a ship.
Nowadays a special made digital film from sampling till analysing is available on digital AVI-film format. The 10 minute film
is around 275 Mbytes (0.275 GB) in size and made by the RIKZ (The Dutch Institute of Coastal and Marine Management). Download it to your computer.
It will take a while but is very instructive to those interested in this subject.
Click to download the AVI-film:
www.waterresearch.nl/sieving/sieving.avi
Method of operation
The system consists of sieving system, (overflow/outflow), vibrating equimpent, collecting centrifuge,
peristaltic pump to pump the resultant water back into the sieving system.
The total sediment sample is
put into the upper sieve, then the lid is closed, centrifuge, vibrating table
and pumping is started. As the water is recyled into the sieving system
approximately 0.5 dm3 water is used.
The size-fraction, for
example the <63µm sediment fraction, was collected from the centrifuge and
is the input for the trace metal and hydrophobic compounds analysis.
All files of the drawings on
this site are on pdf-format.
*Upper lid (top) with inlet
for recycled water.
www.waterresearch.nl/top1.pdf:
www.waterresearch.nl/top1.pdf
www.waterresearch.nl/top2.pdf:
www.waterresearch.nl/top2.pdf
www.waterresearch.nl/top3.pdf:
www.waterresearch.nl/top3.pdf
www.waterresearch.nl/top4.pdf:
www.waterresearch.nl/top4.pdf
*sieving holders (3 times; 1 mm, 63 µm, 20 µm)
www.waterresearch.nl/sieves1.pdf:
www.waterresearch.nl/sieves1.pdf:
www.waterresearch.nl/sieves2.pdf:
www.waterresearch.nl/sieves2.pdf:
www.waterresearch.nl/sieves3.pdf:
www.waterresearch.nl/sieves3.pdf
www.waterresearch.nl/sieves4.pdf:
www.waterresearch.nl/sieves4.pdf
Note that the ring which
gives tension onto the netting has a different shape for the 1 mm sieve because
of the thickness of the 1 mm sieve-netting material.
*Bottom (collecting)
www.waterresearch.nl/bottin1.pdf:
www.waterresearch.nl/bottom1.pdf
As the system was developed
in The Netherlands some dutch language is on the drawings.
Here is the translation from
the dutch to the english language: zeef = sieve; zeven = sieves; zeefhouder=
sieve holder; spanriem=tension belt (tensor; guy-rope); spanblok B= tension
block B; o-ring= O-shaped polymer ring.
The diameter of the sieves is
200 mm (20cm). It is attached with strong belts with blocks and screwed on the
vibrating-tabel. During the sieving process the whole sieving equipment is in
vibration. Mostly an emulsion of water and sediment is on the sieve. The
resultant water with the specific size fraction is removed from the sediment.
In the centrifuge water is separated from the suspended sediment. After a while
the water is transparant while in the beginning the water was muddy.
The system was developed
with a 1 mm sieve (1000 µm), a 63 µm sieve and a 20 µm sieve. The lit and the
bottom completes the system. The lit is where the bands are attached and pushed
the system onto the vibrating table. It can be used with three, two or one
sieve in cascade. If the 63 µm and the 20 µm sieve are used in combination it
is possible that a partial vacuum is developed and that the flow through the
sieves is restircted between these sieves. In order to maintain atmospheric
pressure a small opening with a small tube can be applied into the sieve-holder
wall to compensate the small pressure difference.
Here are some photos of the equipment on board the ship. The sieving is mostly performed in the laboratory but operation is also possibel at sea with calm conditions.
Electronic timer equipment to operate the system (sieve vibrator, centrifuge and pump) automaticly.
It was manufactured by an technical an electronic company in the city of Delft named: Enraf-Nonius ,The
Netherlands department: special products. The price of the tailor-made system
was in year 1987 Euro 2426 (excluded taxes). Enraf-Nonius told me that the time
an effort they put into the sieving equimpent the total price should be Euro
3857. Enraf-Nonis was/is also representend in Solingen, Paris, London, New York
and Copenhagen. The woven sieving netting was supplied by a Swiss company
specialized in polymer sieving netting.
Acknowledgments:
Hans Klamer, Foppe Smedes and laboratory personal of the RIKZ laboratory at Haren, The Netherlands.
[RWS National Institute for Coastal and Marine Management; RWS RIKZ]
A publication on this subject:
Comparison
of Grainsize Correction Procedure for Organic Micropollutants and Heavy Metals
in Marine Sediments. J.C. Klamer, W.J.M. Hegeman and F. Smedes. Hydrobiologia,
208, 213-220, 1990. [PDF]
With the use of the equipment the bottom sediment was of the Dutch coastal North Sea was sampled for several years.
The method is part of the standard monitoring programme for sediment.
Click the report (figure captures are also in English):
Concentraties en Normtoetsing van stoffen in het oppervlakte sediment van het
Nederlandse Continentale Plat (1981 - 2003) Cd, Cu, Zn, Pb, Cr, Hg, Ni en As en organische verbindingen: PCB, PAK, HCB en TBT
Wim J.M. Hegeman en Remi W.P.M. Laane; RIKZ werkdocument 2004.138.
