The term "macerator" is one of the most misused terms in boating. The applicable definition of the word "macerate" (also spelled "mascerate" in the Queen's English) from Webster's New Collegiate Dictionary is as follows, "to cause to become soft or separated into constituent elements by or as if steeping in fluid; broadly: steep, soak ~ vi: to soften and wear away esp. as a result of being wetted or steeped." No it isn't Greek.
The key phrase is "to become soft." Macerators beat up (grind, shred, chop up) the sewage and paper, reducing it in size and texture, basically into a slurry, to make it easier to pump through a hose or pipe, and for another reason that will be mentioned below.
How does this apply on a boat? There are three distinctly different applications:
1) A macerator that is built into an electric marine toilet. This is, again, to grind up and reduce the size and texture of the sewage that has been deposited into the head, making it easier to pump it off to a holding tank, treatment system, or overboard. Note that manual toilets, electrified manual toilets, and vacuum toilets do not have macerators built into them. Only electric toilets that have rotating blades or cutters of some sort, have macerators built into them.
2) A macerator that is built into an onboard sewage treatment system. The purpose, again, is to grind up and reduce the size of the sewage that has been pumped into it by a marine toilet. The specific purpose is to reduce the particle size, so that the disinfectant being used by the treatment system can penetrate all the way into the center of each individual particle, to kill all the bacteria contained in the sewage. If maceration were not being done inside the treatment unit, there would be an excellent chance that when it emptied back out into the water, the sewage would not be fully treated, because the disinfectant wouldn't have penetrated all the way to the center of the particles, and it could still contain harmful bacteria, viruses, and the like.
3) Macerator pumps. Macerator pumps are the most common application where the term "macerator" is used. But the correct term is "macerator pump," not simply "macerator." The term is very commonly misused, and this is where much of the confusion comes from. A macerator pump is a macerator (cutter/shredder/grinder) combined with a positive displacement pump. The purpose of a macerator pump is to pump out a sewage holding tank when at sea, beyond any territorial limits. The macerator portion of the pump reduces the size and texture of the material being pumped out of the tank, so that it is less prone to clog in the hoses or pipes. Otherwise it is merely a positive displacement pump, nothing more. Macerator pumps have some sort of rotating blade or other shredder immediately in front of a rotating rubber impeller. This grinds up the sewage, then the rotating impeller pumps it out of the tank. Again, only pumps that have some sort of rotating cutter system have macerators built into them. Common brands of macerator pumps are ITT Jabsco, Sherwood, Johnson, and Raritan. The SeaLand "T" series pump, which is also used to pump out holding tanks does not have a rotating cutter, and thus, it is not a macerator pump. It is simply a positive displacement pump that can handle solids as well as liquids.
