Here are the solutions to the examples in Section 9.10 of the document: Example 1: A VIP latrine is designed to serve a family of 6 people. The solid accumulation rate is taken as 0.06 m3/person/year. Calculate the effective pit volume required if the design life of the pit is 5 years. Solution: Given: Number of people (P) = 6 Solid accumulation rate (C) = 0.06 m3/person/year Design life (N) = 5 years Effective pit volume (V) = C x P x N = 0.06 x 6 x 5 = 1.8 m3 Example 2:

1. ON-SITE HUMAN WASTE MANAGEMENT
Technological Options
SHOWAIB AHMED CHOWDHURY
Lecturer
Department of Building Engineering & Construction Management
Rajshahi University of Engineering & Technology(RUET)
BECM 4103 : Basic Environmental Engineering

2. Introduction
There exists a wide range of alternative sanitation technologies that are low cost,
easily maintainable and can be chosen to suit different hydrological, socio-
economic and cultural conditions, such as
 Simple Pit Latrine;
 Ventilated Improved Pit (VIP) Latrines;
 Single-pit VIP Latrines;
 Alternating Twin-pit VIP Latrines;
 Reed Odorless Earth Closet (ROEC);
 Compost Latrines : Continuous Compost Latrines; Batch Compost Latrines;
 Pour-Flush sanitation technologies: Direct Pit Pour-Flush Latrines, Off-set Pit
Flush Latrines; Alternating Twin Off- set Pour-flush Latrines;
 AQUA PRIVIES and SEPTIC TANK.
 Communal Sanitation System.

3. Simple Pit Latrines
 Most common and simplest form of excreta disposal in many
developing countries.
 The cheapest system possible and the system most appropriate for
individual householders responsible for their own sanitation.
 A pit latrine consists of amanually dug or bored hole into the ground, an
appropriate set or squatting slab,and a superstructure erected over it. The
pit is simply ahole in the ground into which excreta fall.
 Urine and other liquids soak into the ground and solid materials are
retained and decomposed in the pit.
 Simple pit latrines (often called “home made” latrines) as the family
members can construct them.

4. OI;POI;
Simple Pit Latrines

5. Simple Pit Latrines
With slight modifications in design and with very little intervention,
conventional pit latrines can be improved to be hygienic.
 When excreta falldirectly into apit underneath the user,it is called adirect
pitlatrine.
 When excreta pass through ashort pipe or achannel to apit afew metres
away,it is called an offsetpitlatrine.It maybe called apartlyoffsetpitlatrines
when part of the pit is under the shelter and part is outside, where a
removable cover allows the contents to be taken out.
 The most appropriate types of pit latrine, however, depends on the local
situation, particularly on the type of materials used for analcleansing,
including the levelof the underground and the traditions and the choice of
the users.

6. General design considerations for pit latrines
 The pit should be as large as possible(should not be more than 1.5m wide)
 Soils with low permeability (below 2.5 mm/hour) are unsuitable for pit
latrines as the liquid portion is unable to infiltrate into the soil.
 Pits in unstable soils must be fully lined, otherwise there is risk that the pit
will collapse and the superstructure will fall into it. (concrete rings, bricks,
cement stabilized soil blocks, masonry, perforated oil drums, etc.
 Safe distance between the latrine pit and a source of drinking water e.g.,
tube-well, should be provided (a distance of at least 10 m)

7. Design of Pit Latrines
Effective Pit Volume: The effective pit volume depends on the solids accumulation rate,
the number of users and the desired lifeof pit. The effective volume canbe calculated as:
V= C X P X N ,where
V= effectivevolume of the pit in m³ C= solid accumulation rate in m³ /person/year
P= number of person who will be using the latrine
N= design life in years.
• The total pit size for apit latrine not exceeding 4.0 m in depth can be determined by V =
1.33 x C x P x N
The factor of 1.33 is incorporated to ensure a clear space above the remains of the excreta
atthe end of the design period. The factor will allow 75% of the pit to be fullatthe end of
this period.

8. Design of Pit Latrines
Solidsaccumulationrate,C: excreta deposited into the pit havetwo essential
components( liquid fraction of excreta (mainly urine) and the faecal solids in
excreta) are digested anaerobically to produce gases & soluble compounds, etc.
 In dry pits (not extended below the groundwater table), solids accumulation
rates vary between 0.30 and 0.06m³/person/year,and in wet pits between 0.02
and 0.04 m³ /person/year.
 For design purposes, solid accumulation rates may be taken as 0.04 and 0.06 m³
/person/year in wet and dry pits respectively.

9. Advantages and Disadvantages
Themainadvantagesof asimplepit latrine are:
 Leastcostly
 Easilyconstructed and maintained
 Structurallysafeandthereforefreefrom risk ofchildrenfallinginto it, and thus lessfrightening
for children.
 Preventshookworm transmission;and
 Offers abettersolution thanopen defecationandunhygienichanging latrines.
Themostseriousdisadvantagesofasimplepitlatrine are:
 Flieslaytheireggsinfaeceswithinpoorly buildlatrines.Increaseinthefly populationincreases
spreadofdiseases causedbythefaecalpathogensthey carry.
 Improper liningofpitsmayleadto collapseofthe superstructure

10. Ventilated Improved Pit (VIP) Latrines
 Ventilated improved pit latrines commonly known as VIP latrines are an
improvement to overcome the disadvantages of the simple pit latrines.
 Fly and mosquito nuisance and unpleasant odors, are effectively
minimized by the action of avent pipe, flyscreen and asquatting cover in
the VIP latrines.
 VIP latrine pits receive excreta in the same fashion as those of the simple
pit latrines, by direct deposition through a squat hole or apedestalseat.
 The liquid part infiltrates into the surrounding soil and the faecalsolids
are digested anaerobically,gradually accumulating and eventually
requiring emptying the pit for further use.

11. Ventilated Improved Pit (VIP) Latrines

12. Elements of VIP Latrines
• The basis elements of aVIP latrines are:
• The pit
• Acoverslab
• Asuperstructure for privacy and protection from rain and sun
• The vent pipe and the fly screen which keep the latrine free from the
mosquitoes, and unpleasant odors.
The principal mechanism of ventilation in VIP latrines is the action of wind
blowing across the top of the vent pipe. The wind creates a strong circulation
of air through the superstructure, down through the squat hole, across the pit,
and up and out of the vent pipe.

13. Types of VIP Latrines
• Single-pitVIPLatrines:consist of one pit,a ventpipeand asuperstructure andare suitablewhere
mechanicalemptyingis possible when the pitis full.
• Alternate twin-pit VIP Latrines: have two separate pits with their own vent pipe, and the
superstructure is located centrally over the off-set pits. The slab covering the pits has two squat
holes, one over each pit.

14. Design Consideration ForVIPLatrines
 Design life: for single-pit VIP latrines, the design life should be as long as possible; at
least10years is desirables. For alternatingtwin-pit VIP latrines thedesignlifeshould be
1-3 years.
 Dimensions:usually the pitcross- sectional areashould not bemore than2m²inorder
to avoid cover slabs with large spans. VIP latrines serving one household commonly
haveadiameterof 1-1.5 m.
 Vent Pipe: a wide variety of materials are used for VENT pipes such as polyvinyl
chloride (PVC), unplasticized PVC (uPVC), bricks, etc. For flat roof, top of the vent
should be at least 500 mm higher than the roof, and in case of sloping roofs the vent
pipe should be 500 mm above the highest point of the roof. PVC (150mm did); Brick
(230mm square);Others (230mmdiameter).
 Fly screen specification: the purpose of fly screen is to prevent passage of flies and
mosquitoes;themesh aperture must not belarger than 1.2mmX1.5mm

15. Design Consideration ForVIPLatrines
Relocation and Emptying Of Pits
Soakaway
A VIP LATRINE with adjacentsoakaway increases the pitlife.Thelatrinepit is completely
sealedwith cement mortared brickwork anda PVC pipeof 75mm dia which leadsto the
adjacentsoakaway is attachedataheightof about 2.25m above the pit base.
The soakaway has diameterof 1.5mandadepth of 2m.It is linedwith unmortared bricks to
adepth of 1.4m. At this depth areinforced concrete cover slabis placedon the bricks and
the remainingspaceabove itis backfilled.

16. Advantages and Disadvantages
The major advantages of VIP latrine technology are as follows:
Controls odor and insects;
Minimum health risk;
Low cost;
Easy construction and maintenance;
Minimum water requirements;
Twin-pitVIP latrine system offers along-term solution.
The main disadvantages of a VIP option may be as follows:
Potential for groundwater pollution.
Lack of space for relocating the pit in densely populated areas.
Difficulty of constructions in rocky and high water table areas.

17. Mathematical Problem
Section 9.10
Example 1, 2