VIP Latrine Design Analysis

  To gain understanding and practice in dealing with sanitation issues in developing regions a design analysis of an Ventilated Improved Pit Latrine. The design analyzed can be found here Design Plans.

  In order to determine if the original design is large enough, the number of people served for various design lives were calculated. Only the rectangular area under the user-interface hole (not the side square with the access door) was included in the pit volume calculations because solids would not fill the area under the access door. Also, a 0.5 m dead space was assumed between the top of the solids and the superstructure. This results in the dimensions of the original being 0.7 m x 1.6 m x 1.1 m and a volume of 1.2 m. A solids accumulation rate for a dry pit of 0.06 m³/person/yr was assumed.

  If the family served was assumed to be 4 people, the design life of 5 years is sufficient. These calculations show the original pit volume is sufficient for a family of 4; however, the shape of the pit is a problem. In order to clean the pit, someone must climb into a 0.8 m x 0.8 m x 1.6 m area and then reach around a corner in order to reach the area where solids accumulate. This would be a cramped and dirty task for any adult. In order to improve the pit, the shape of the pit is changed into a rectangle, where the access door would be above the area where solids accumulate so they can be shoveled or mechanically removed from outside of the pit. The proposed design is 0.8 m wide x 2.8 m long x 1.6 m deep. This depth includes dead space. This volume, 2.5 m³ is still sufficient for the family of 4 for five years, but now is easier to remove the solids. See Appendix 1 for plans of the revised pit layout and superstructure.

 The second revisions are to the materials of construction. While steel corrugated roof is an acceptable material, it may not be easily repaired or replaced by locals in rural South America. It also is more expensive than local materials. It is suggested the roof be changed to a thatch roof made with local materials to make it easier for locals to maintain and replace if necessary.

  It is also suggested the vent pipe material be changed for similar reasons. PVC pipe can become brittle when exposed to high sunlight but stabilized PVC can be expensive and difficult to come by. In order to make the vent easy to maintain and replace it is suggested to be a cement-rendered reed pipe.

  The current design appears to require the use of a door for privacy and the adobe walls and steel roof do not provide for much ventilation. In order to fix both problems, the shape of the superstructure has been revised. A square spiral structure has been designed for the revised superstructure. See figures in Appendix 1 for superstructure plan.

Improved Design Plans

Superstructure Profile

Superstructure Front

Superstructure Plan

Slab Plan

Pit Plan