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A composting toilet is installed at Camp Atterbury, Ind. between training ranges 18 and 19.

A composting toilet is installed at Camp Atterbury, Ind. between training ranges 18 and 19. (Photo by U.S. Army Corps of Engineers)

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Posted 7/5/2013

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Under the Installation Technology Transition Program, a commercially available composting toilet was installed and evaluated at Camp Atterbury, Ind., as part of efforts to identify inefficient water usage and assess conservation technologies. The U.S. Army Engineer Research and Development Center conducted the demonstration in cooperation with Camp Atterbury’s Environmental Division.

Army training offers both challenges and opportunities for water conservation, both in technology implementation and in reaching a broad cross-section of Soldiers for water awareness education. Training populations come from many regions that vary in water availability and thus sensitivity to issues of water scarcity. In addition, Soldiers in training are often preparing for deployment to austere environments where water conservation is critical to the Army mission.

One opportunity to implement water-saving technologies is in latrine operation. For remote training areas, latrines incur major costs, both for treatment and, for flush toilets, water consumption. Whether it is hauling tankers of water to supply trailer-based flush toilets or the requirement to pump porta-potties on a regular maintenance schedule, maintaining toilets in the training environment is expensive.

Composting toilet technology offers an alternative to conventional latrines. Composting toilets use aerobic decomposition to treat excreta, with bacterial action in presence of oxygen breaking down the organic material and destroying pathogens. The cost effectiveness of replacing either flush toilets or porta-potties with composting toilets depends on the operation and maintenance costs of the existing units. Training sites are ideal locations for this retrofit due to the long distances traveled to maintain sanitation facilities.

Currently Camp Atterbury pays about $935,000/year for maintenance of 550 porta-potties, regardless of the units’ usage rates. This amounts to $1,700/year in maintenance cost for each porta-pottie. It is likely that most are not being used at the maximum capacity of 30 uses per day. Monthly maintenance for a single composting toilet is $3,000/year based on the maximum 60 uses per day. If it is assumed that many porta -potties are used 15 times/day, then one composting toilet serviced monthly could replace four underused porta-potties. The installed cost per unit for one composting toilet is $25,000. The life cycle of the unit is 20 years. In this scenario, the simple payback, including monthly maintenance, is 6.57 years.

On the surface, the composting toilet may seem costly. However, as the number of composting toilets at a particular site increases, the maintenance cost per unit decreases. The most expensive part of maintaining a composting toilet is the maintenance contractor’s drive to the post. Once on post, the cost to maintain each additional unit is low. Especially for locations with variable or low use, composting toilets can offer an effective alternative to porta-potties.

The following table shows the economics of several example scenarios for using composting toilets. It assumes that maintenance for porta-potties is constant at $1,700/each for the cantonment and $2,200/each for a remote site, and that one composting toilet replaces four porta-potties. It also assumes that maintenance for the first composting toilet costs $250/month for the cantonment and $350/month for the remote site, and that each additional composting toilet adds $50/month to the maintenance cost. Economies of scale can also be realized when installing composting toilets.

Location of

Composting Toilets

Number of Units

Unit Cost

Installation Cost

Maintenance Cost (old/new)

Simple Payback

Cantonment

2

40000

8000

13600/3600

4.8 years

Cantonment

4

80000

16000

27200/4800

4.2 years

Cantonment

8

160000

28000

54400/7200

3.9 years

Remote Site

2

40000

9000

17600/5400

4 years

Remote Site

4

80000

18000

35200/6600

3.4 years

 

Site selection is a key factor that affects the performance and economics of composting toilets. Installation staff should strategically locate composting toilets to achieve the maximum of 60 uses per day.

The Camp Atterbury demonstration showed that it is possible to save money over the longer term by installing composting toilets at remote training sites. The Army has become dependent on porta-potties as a means for dealing with human waste on training ranges and contingency bases. However, there is a high cost for the convenience and in the potential to damage local environments if the removed waste is not deposited at treatment facilities, which is the case at some contingency bases. Large amounts of human waste can also overload sewage treatment plants, particularly those located on post.

While the demonstration at this site did not consider flush toilets—and therefore water savings were not realized with this retrofit—other sites do truck water into remote areas to service flush toilet trailers. Composting toilets should be explored at these sites as both hauling and pumping maintenance are likely to be high-cost items. In regions where water scarcity is a concern, this technology will help conserve water for more critical life support uses.

POC:  Elisabeth Jenicek, 217-373-7238, elisabeth.m.jenicek@usace.army.mil