Composting toilets: A green approach to dealing with voyaging wasteOct 5, 2009
What goes in, must come out. That basic problem has haunted marine plumbing designers and boat owners since the beginning of seafaring. In the age of sail, answering the call of nature meant hanging one's nether regions off the head of the boat near the bowsprit &mdash hence the term "using the head." That was a simple way to get rid of the unpleasant business, and the technology was easy to use, quick to repair, and self cleaning.
I'm not sure the same can be said for many contemporary below-decks heads installed on the latest boats. Instead, boat owners are typically faced with various primitive toilets &mdash most not in any serious way different than those used by sailors for the last 100 years or so &mdash attached to equally primitive plumbing arrangements that endeavor to route the effluent through a maze of tubes and valves to a tank. We then sail around with an ever-growing load of noxious sludge in the often vain hope of finding a working pumpout station before something overflows, jams, or leaks. Further valves, hoses, and fittings allow us to (hopefully) pump out the effluent at either an approved pumpout station or into the ocean when offshore. Needless to say, this process generates some powerful odors, tricky procedures, and repair techniques that frequently end in tragic comedy.
Can't there be a better way? For some of us, the answer has been to reverse the clock and go back to some of the earliest sewage technology used prior to the invention of boats: composting. The marine composting process is very simple. If sewage spends enough time drying out, natural bacteria, heat, and other processes eventually aerobically biodegrade the potentially disease-causing (and stinky) material to the point that you are left with something that not only looks and smells like garden soil, but is equally as innocuous. This is a much faster process than is found in the typical anaerobic liquid sewage system. Natural degradation and drying will eventually achieve the goal, but composting toilets use various technologies to speed the process.
There are two basic ways composting heads work. Some units endeavor to keep the solids as dry as possible by separating the liquids from the solids into two separate tanks. Other units allow the two materials to mix, but provide greater drying capacity or allow the liquids to be drained off later. Both types utilize enhanced air flow via fans and ventilators, and various types of stirring devices to further enhance the process, and when greater power is available, various heating devices are used.
Advantages for the mariner are many. First, the units generally do not require any through-hull fittings, eliminating potential sinking problems. On top of this great advantage, many marine units come as self-contained modules, eliminating a lot of difficult, expensive and precise installation. Obviously, this latter feature can be a disadvantage in that the larger the capacity, the bigger the space in the head that will be taken up. However, it is also possible on some smaller units to purchase and carry additional holding bins that can be filled and then stored until an appropriate dump site is reached. On the urine separating units, there will be a need to store and get rid of liquids periodically, which might mean the use of a more traditional (but simple and small) holding tank, or a removable container that can be carried ashore or emptied over the side when offshore.
One of the things that will be much appreciated by those with experience using traditional marine plumbing is that, in general, composting technology is extremely simple. There are no pumps to rebuild, hoses to clear, through-hulls to maintain, electronic controls to replace, etc. Most everything is mechanical, simple, and can be repaired or jury rigged with typical hand tools and spare parts most boats carry. This is a great advantage when one is voyaging to areas where marine parts may be hard to get.
Most marine units utilize a small fan and a ventilation tube to keep air flowing through the composting material. This vent will suck air in from the head cabin and push it out of the boat, and we have found that tends to make composting toilets the most odor-free marine solution. Our most direct experience is with the Air Head unit we have on our 38-foot boat. The Air Head vent is powered by a small computer-type fan that burns so little power we just leave it running year round, boosted by the various solar panels we have that keep our batteries up. It is great to arrive after being away for a few weeks with the boat all closed up only to have a nice smelling and ventilated cabin, all without the use of strong chemicals or odor masking deodorants.
On the Air Head there is a small trap door that is opened manually by the user once you sit down. The solids drop down the hatch, and the door is closed. The rather ingenious design of the bowl directs liquids into a separate container at the front of the unit (men should always be seated). The detachable liquids jug (with a screw on cap for safe carrying) can easily be taken ashore for disposal in a marina toilet or other proper location. It is suggested that some peat moss be added to the composting mix periodically to add organic material and make an airier mix to promote drying &mdash we add a cup every day or so. It is easy to carry enough for a season or longer, and it can be found at any gardening supply store. Toilet paper can be simply thrown right in, which acts in a similar way to the peat moss, but it also adds considerable bulk resulting in an earlier fill up of the holding container. If you do put toilet paper in the toilet, use the thinner single sheet type &mdash no need to use special marine-type toilet paper.
Emptying the solids
One great advantage is the ability to go long periods between trips to a sewage dock. Occasional or weekend users of the Air Head might be able to go a month or two without emptying the solids &mdash the longer you wait, the better the composting. We simply bag it up and put it into a dumpster. However, it is possible to overwhelm the natural pace of composting if you have more people onboard using the toilet. Nothing bad happens, but it is less pleasant to empty things if the composting process hasn't had sufficient time and the material isn't fully dried.
Another slight problem we have encountered is that without water being pumped through the head, the bowl can get a bit dirty and begin to smell. We keep a small spray bottle of white vinegar handy and give the head bowl a wipe periodically, which solves the problem. The vinegar also acts to clear the urine ducting areas which can get clogged with crystals. Strong chemical cleaners should be avoided as they might kill off the good bacteria necessary for the composting process.
An air duct leads from the head to a deck fitting. The vent fan on the Air Head is mounted right below the deck vent, and we have found that no matter how good your deck fitting, a bit of water can come in during heavy weather. Water has shorted out our fan several times, but an appropriate computer fan is easy to locate wherever computer parts are available. We connected our vent line to a solar-powered deck vent for added air flow when the sun shines. A spare fan is a must on a voyaging boat, as without it, not only does the composting process slow way down, but smells can back vent into the boat. We've got ours wired into the same circuit as the emergency bilge pump so that we don't turn off the fan when shutting down the power.
Composting may not be for everyone. Inevitably, even when things are working perfectly, you have to get a bit more up closewith the results. Traditional marine plumbing works on the out of sight, out of mind philosophy. However, when things go wrong there's no comparison. The composting head is easy to fix and is much less unpleasant to do so. n
John J. Kettlewell is the author of Intracoastal Waterway Chartbook: Norfolk, Virginia to Miami, Florida, now in its fifth edition.