The 155.8 gal (589.77 liters) of urine produced by one person in a year is a significant load for any composting toilet system to manage, so dealing with it separately offers some advantages. Draining it for immediate use is the most direct solution. Consider the following for one person:

• To evaporate one gallon would require a minimum of 9000 BTUs (2.6 KwH) of energy (enthalpy of about 1044 BTU/lb or 87°F). However, so much is lost in the transfer of heat, you would likely require more BTUs of fuel.
• To store it would require at least two 55-gal (208.20-l) drums.
• To soak up one year’s worth of urine into a moist carbonaceous form, so that it will compost (minimum 50 percent moisture by weight) will require at least 980 lb (441 kg) of an absorbent, such as bone-dry sawdust. That might require a lot of material. For example, sawdust has a density of 12 pounds (5.4 kg) per cu ft, so you might need 82.5 cu ft (2.3 cu meters) of dry sawdust to soak up 115.7 gal (437.97 l) of urine.

If you plan to use urine for fertilizer, it needs to be oxidized to a plant-available nitrate state first or diluted and mixed into well-aerated soil, where the aerobic microbes will complete the oxidation (nitrification) process.

• To utilize effectively the nutrients in urine:
• Drain urine combined with graywater directly into an aerobic soil system. Drain urine from the urinal or urine-diversion toilet, combine it with graywater, and use it on site; no storage necessary.

Note: Urine is high in nitrogen. Graywater is high in carbon from soaps, detergents, and hair conditioners and low in nitrogen. Combine the two, and you have a better effluent to use in a planted system. However, both contain a lot of sodium, so be sure to use salt-tolerant plants. Collect the urine for later use. Drain the urinals or urine-diversion toilet to storage tanks that can be carried or pumped to the point of use; for example, an orchard. Then the urine should be diluted. For one part urine, dilute it with eight parts fresh water, because the urea and salt in urine is too concentrated for most plants. The diluted urine should be sprinkled on the soil, not on the plants. The soil microbes will oxidize the nitrogen-containing compounds to a form that the plants can best utilize.

• The bacteria mostly responsible for converting urea into a nitrate are Nitrobacter and Nitrosomonas. These nitrifying bacteria need carbon for their protoplasm, cell walls, and enzymes that convert organic nitrogen molecules to nitrates. For a more specific inoculate, you can grow a Nitrobacter-Nitrosomonas culture by mixing urine and sugar, letting it process aerobically, and adding this to the urine barrel or composter