Seaweed Pressing

December 12, 2010

Pressing News #78 describes our failure in 1997 to dewater seaweed with a screw press.  Off and on since then we have worked with seaweed, always with about the same poor results.

Processors who work with seaweed work with red, brown, green, and black varieties. These have come to Vincent from the Philippines, the Canadian Maritimes, Chile and Ireland. The products manufactured from seaweed are food additives (carrageenan), alginate (a gum), pharmaceuticals, and agricultural fertilizer.

Seaweed, a range multicellular alga, has moisture contents of 79% to 82% when harvested fresh. Processing generally requires that the seaweed first be dried to 18% moisture content. Mechanical removal of the moisture (as with a screw press) has the obvious thermal advantage over using a rotary drum dryer.

Recently we ran tests on brown seaweed from Nova Scotia. This material was sent to us by Eurocan Bio-Marine. It had been diluted to 11% solids in a grinding process. First we ran our sample through a Fiber Filter in an effort to remove the water that had been added. The results were disappointing, but they did show promise: the solids were increased to 13%.

This material with 13% solids was fed into a CP-4 laboratory press. As with our previous efforts, nothing was achieved. The seaweed cake came out still at 13% solids.

Next we injected steam through the resistor teeth of the press. Temperatures of 165° F were achieved at the inlet; 155° F at the cake discharge; and 145° F press cake temperature. The solids content of the press cake increased to 16%.

Our next effort was to wash the 13% solids material with 70% isopropyl alcohol. The seaweed was mixed with a 1:1 ratio of alcohol. It was not practical to go through a three stage counterflow wash system. So the mixture of ground seaweed with an equal proportion of alcohol was run through the press. During this testing we continued the steam injection. The result was press cake with 25% solids content.

This is the best we have ever done with seaweed. And it is probable that even better results are feasible. We have experience that indicates that an alcohol counterflow wash system may allow a higher solids content to be achieved. We look forward to another round of testing.

Issue 228