Wood Ash Absorbs Odors Best

Wood shops, lumber yards, and garden stores offer suitable ‘mulch.’

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The media serves several purposes in a desiccating toilet. It provides visual cover, draws moisture away from the solids (good wicking and coating are more important than absorption, since sustained drying is the goal), and to provide some amount of air filtration (fuzzy fibers and organic nature help). If you compost the remains, bulking and biodegradability are further requirements.

Compact storage is a double-edged sword. On one hand, a compressed absorbent like coconut coir saves considerable storage space, but ready-to-use products like millwork shavings avoid the messy expansion process.

Folks can be opinionated on this topic and lots of things work. We tried a few for a week each.

SO PHRESH ASPEN PET BEDDING

Reasonably compact, easy to use, and superior wicking and odor filtration are advantages. The light color means it does not camouflage waste as well, and we seemed to need a little more for good coverage.

Bottom line: Recommended.

MILLWORK SAWDUST AND SHAVINGS

Nearly indistinguishable from the aspen bedding, this is probably the same stuff without the sawdust removed. Perhaps the small amount of saw dust fines help with coating without inhibiting wicking. Available for free from many millwork shops. It can be compressed about by ramming it into a sturdy container with your fist.

Bottom line: Best Choice if you can identify a source.

SO PHRESH CEDAR PET BEDDING

The cedar aroma does not help, wicking is mediocre, and it does not compost well.

Bottom line: No.

COCONUT COIR

Advantages include dark color, compact storage (comes in bricks that expand 6:1), economy, and established reputation. Downsides include mediocre odor filtration and the mess and effort involved in expanding the bricks. Odor control was average.

To expand coconut coir bricks for use, place a 1- to 3-pound brick in a 1-gallon resealable bag with 1/3–cup/ pound coir water overnight. Crumble, shake, and allow to rest for another hour.

Bottom line: Recommended by its popularity, but we’d only use it if storage was a problem and we couldn’t get aspen.

KAY TEE CLEAN AND COZY

Made from recycled paper, it is very absorbent and the odor control was acceptable, but the clumpy texture meant we needed to use more to get acceptable coverage.

Bottom line: Based on our experience, there are better choices

MIRACLE GROW PEAT MOSS

Easiest to use and least effective. The odor control was sub-par and it also required the most storage space because it is not compacted.

Bottom line: Not recommended.

WOOD ASH

Extensively studied for third world and off-grid applications, the high pH of ash provides both a surface bio-stat and enhances dehydration, resulting in the best odor control of any product tested. It is also potentially the messiest (handle carefully), but there is no question, if you have a wood burner on the boat or cabin, this is the way to go. Excellent for composting; ash is high in phosphorous and increases the pH, a benefit, since compost often goes sour.

Bottom line: Best Choice for odor elimination and dehydration.

There are also some additives that can be helpful:

DIATOMACEOUS EARTH (DE)

Well known for its ability to kill bugs, and recommended by the US Department of Agriculture for livestock lots, DE functions by dehydrating the bugs. A small addition will help control breeding of flies and moths. You’ll only need it if you go more than a week before emptying. About 2 cups/cubic foot of media (1/4-cup/gallon).

Bottom line: Recommended if you find flies or moths to be a problem. Once a bug infestation occurs, the most effective treatment is a cleanout and light spray with insecticide. DE is for prevention only.

SWEET PDZ HORSE STALL REFRESHER

Basically a lot like a high-end claybased litter that is mixed in with shredded wood bedding to improve its tolerance for urine spills. Not a bad idea if some of the urine is getting in the bucket, and only $10 for 25 pounds at Tractor Supply.

Bottom line: We did not test this, but it was recommended by a reader.

TIDY CAT CLUMPING LITTER

Used straight up, it is heavy and not very good at wicking away moisture. However, when used sparingly in combination with a lighter bedding, the zeolite clay is effective at adsorbing urine odors in a manner very similar to how activated carbon adsorbs bad tastes in drinking water. That is why it remains the standard for littler boxes. However, since we are separating the urine, we only need a little to help with the occasional spill. It won’t interfere with composting if you use just a little.

Bottom line: Using more absorbent is probably a better answer.

SWIMMING POOL CHLORINE TABS OR POWDER

Not an additive that you add to the mix, sodium dichloroisocyanurate controls odor while suspended inside the bucket. It also can be used to purify drinking water (see PS July 2015 “Keeping Water Clean and Fresh”). C-Head tells us that sodium hypochlorite pool powder works just as well. Place an ounce or two in a small cup, strainer, or mesh pouch, suspended just inside of the lip of the bucket.

Reacting with humidity in the air, the powder or tab slowly releases a trickle of chlorine into the air, which oxidizes any odors. It will not penetrate into the waste or stop biological activity; the amount is far too small. We suspect it also prevents bug infestations; we’ve never had one while using it. One ounce lasts 3-6 months, depending on humidity. Do not add the chemical directly to the media or the bucket.

Bottom line: Recommended. With this treatment, with the more effective absorbents we couldn’t smell anything other than the slightest trace of bleach, even when we put our nose right to toilet the opening.

CONCLUSION

Experiment. There are many combinations that have not been tried.

VALUE GUIDE: ABSORBANTS FOR SOLID WASTE

MANUFACTURER TYPE/BRAND NAME MOISTURE CONTENT (WEIGHT) ODOR RANKING (1-5, 1 IS BEST) EXPANSION RATIO PRICE PER BAG COST $ / CUBIC FOOT COST PER 2 CUP USE 
ONE-PART VARNISHES 
VIAGROW Coconut Coir 0.24 Very good $16.70 $24.49 41 cents 
SO PHRESH Aspen bedding 0.1 Very good $10.87 $5.44 9 cents 
KAYTEE Clean and Cozy 0.16 Good $12.99 $22.55 38 cents 
MIRACLE GROW Peat Moss 0.28 Fair $4.97 $18.59 31 cents 
GENERIC CHIPS Chips and Dust 0.12 Excellent Free -- -- 
GENERIC SAWDUST Shavings and sawdust 0.14 Fair Free -- -- 
GENERIC ASH Wood Ash 0.05 Excellent Free -- -- 
ADDITIVES 
GENERIC ADDITIVE DE Did not test $9.50 $38 1 cent 
TIDYCAT ADDITIVE Cat Litter Did not test $16 $8.56 > 1 cent 
GENERIC ADDITIVE Lime Did not test $4 $6.66 > 1 cent 
Darrell Nicholson is Director of Belvoir Media Group's marine division and the editor of Practical Sailor. A lifelong thalassophile, he grew up sailing everything from El Toro dinghies to classic Morgans on Miami's Biscayne Bay. In the early 90s, he left a newspaper job to sail an old gaff-rigged ketch across the Pacific and has been writing about boats and the sea ever since. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida.

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