FSDS - Conference Papers
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WASTEWATER TREATMENT / DISPOSAL
IN DISRUPTED STATES EAST TIMOR (MILITARY & CIVIL)
R.M.C. Patterson, Environmental
Consultant (2001).
ABSTRACT
Urban populations must have basic sanitation and potable water
infrastructures. In disrupted states or during other civil emergencies
such as natural disasters, these infrastructures are usually
made non-operational and are therefore effectively removed.
Disruption of basic hygiene and sanitation, together with an
increased exposure to hazards and reduced resistance to disease
are identified by the U.S. Manual of Naval Preventative medicine
as the three main reasons why disease has always caused greater
personnel loss in military forces than enemy action. Personnel
operating in situations where basic sanitation and water supplies
are failing or non-existent are at greater risk of contracting
a communicable disease than in garrison. Poor sanitation and
water supplies can have a significant impact on the ability
of that military unit or similar organisation to perform its
role. The diseases to which military forces and other non-government
organisations are subjected are largely preventable or controllable.
The aim of this paper is to examine the effectiveness of new
wastewater disposal techniques that were used by the International
Force East Timor (INTERFET) to safely dispose of human waste
in urban areas of DILI and other remote areas such as SUAI on
the boarder with West Timor, that have failed, disrupted or
non-existent infrastructures.
There were a limited number of sewerage waste disposal options
available to INTERFET during the initial deployment to permit
the occupation of the disrupted urban areas. The use of an option
or a combination of options was dependent on factors such as
the size of the force or organisation; the length of time before
basic infrastructure will be operational, environmental factors
such as climate, soil types, high water tables and the tactical
situation. Options included individual cat scrape, shallow trench
latrines (SLT), portable toilets, and water sealed field toilets
connected to field septic tanks (FST). Water sealed toilets
connected to FST requires the use of absorption trenches to
provide the required secondary treatment.
Land based sewage disposal options for urban and high troop
or displaced person concentration areas were considered. These
options fall into two basic categories – centralised systems
and on-site systems. Centralised systems involve the use of
the existing sewage treatment infrastructure to collect the
effluent for treatment and disposal off site in a single large
facility. Treated effluent from the centralised facility is
then preferably directed to a land based system for secondary
treatment and disposal. On-site systems provide both primary
and secondary treatment and disposal within the property boundary
or immediate area. The treatment and disposal processes are
essentially the same.
The fundamental problem of land based secondary treatment is
the ability of the ground to treat and dispose of the large
volumes of primary treated effluent. Historically land based
absorption trenches have had a poor performance record. This
in part is a result site limitations such as non-absorbent soil
types or high water tables that cause the traditional or standard
absorption trenches to fail. This problem has been examined
in detail and over a number of years has resulted in the development
of the Modified Absorption Trench (MAT) systems. These MAT systems
are designed to eliminate site limitations as a factor that
can interfere with the natural physical and biological treatment
processes that occur in ideal soil types. The development of
MAT has enabled ground absorption in soils with poor permeability,
(less than 0.05m/day) or highly permeable soils (greater than
0.6m/day).
MAT have been further developed in Tasmania to also be suitable
in areas with very high seasonal water tables, shallow soils
over rock and high rainfalls that exceed evaporation rates.
There are a number MAT systems operating in commercial and domestic
developments around Tasmania in areas with extreme site limitations
that were previously considered impossible for on-site wastewater
disposal.
The Australian Defence Force was aware of these developments
and the need for effective wastewater treatment and disposal
to ensure INTERFET sustainability in East Timor. The author
who is a member of the Australian Army reserve was transferred
to full time duty and arrived in Dili on 4th October 1999.
The following Case Studies will be discussed in this paper.
1. Wastewater disposal for the Royal Australian Air Force at
Komoro Airfield (Dili), and
2. Wastewater disposal for the Royal New Zealand Air Force (RNZAF)
and Royal New Zealand Army (RNZA) units at Suai near the boarder
with West Timor.
KEYWORDS
FSDS,
MAT (E), INTERFET, Absorption trench, on-site wastewater disposal.
1. INTRODUCTION
The objective of environmental
sanitation is the prevention of the transmission of communicable
disease. This is carried out by controlling the source, the
route and the target. Achievement of the following basic objectives
will significantly reduce disease caused by human sewage:
a. Prevent access of insects and rodents to sanitary facilities
and treatment systems.
b. Prevent transfer of faeces and urine from person to potable
water or food.
c. Prevent disease contamination of surface water or ground
water.
d. Prevent contamination of the soil surface
While on-site wastewater disposal systems are capable of meeting
the above objectives; they have historically been seen as a
temporary measure only until centralized sewage treatment could
be provided.
The basic philosophy for the traditional on-site wastewater
disposal system was that a septic tank system using a standard
absorption trench would make the wastewater go away. This philosophy
was seriously flawed because many soil types are non-absorptive
which restricts the infiltration of the effluent through slow
percolation. In those circumstances many septic systems failed
with trenches filling up and seeping to the surface. Seeping
trenches greatly increased the potential for the spread of disease
and water pollution after rainfall.
Standard trench failure would also result from flooding caused
by seasonally high water tables and shallow bedrock. Rapidly
percolating sand and gravel soil types were also a problem due
the potential of untreated wastewater contamination of ground
water supplies
.
The problem of sewage wastewater disposal was further complicated
by the wide spread failure of centralized sewage treatment systems
that were causing serious pollution of the receiving waters
into which they discharge.
The early 1980’s saw a refocusing of Health and Water Authorities
around the world on to the soil as an efficient natural wastewater
treatment and disposal mechanism. The challenge was to identify
those factors that restricted the use of soil as a treatment
mechanism and develop techniques to defeat those restrictive
factors.
2. ABSORPTION TRENCHES OPTIONS
In Tasmania effective septic tank
effluent disposal is achieved through the use of three basic
designs with site specific modifications being applied as required.
Standard Absorption Trench. (SAT)
The SAT requires the following site conditions;
- Sandy loam to clay loam soil
types
- Minimum 1000mm of soil.
- No soil limitations within 1 metre of the base or sides of
the trench.
- Rainfall is less than or equal to evaporation rates in any
one-month.
SAT systems are not suitable in
rapidly percolating soil types.
Modified Absorption Trench (in ground) MAT (G).
This trench type is used in areas with shallow topsoil or rapidly
permeable soil types.
MAT (G) are suitable in the following site conditions;
- Any soil type except clay
- Minimum 200mm of sand or sandy loam as topsoil.
- No soil limitations within 1 metre of the base or sides of
the trench
- Rainfall is less than or equal to evaporation rates in any
one-month.
In rapidly percolating soil types such as coarse grained sand
and gravel MAT (G) are constructed with a suitable barrier or
clogging mat at the base of the trench.
Modified Absorption Trench (Elevated) MAT (E).
Mat (E) are used in areas with no or shallow soils less than
200mm and/or high seasonal water tables.
MAT (E) are suitable in the following site conditions.
- All soil types including impermeable soils such as clay.
- A soil limitation may occur within 1 metre of the base or
sides of the trench if an impervious barrier is fitted to the
base of the inner core.
- Rainfall may exceed evaporation rates in any month if fitted
with an impervious barrier over the top and sides of the inner
core.
MAT (E) usually require pressure distribution, which enables
the effluent to be evenly distributed along the entire length
of the trench. This avoids the problems of localized overloading
characteristic of some gravity systems. Periodic dosing also
permits aeration at the soil interface between dosing.
MAT (G) and MAT (E) techniques allows the soils natural treatment
mechanisms to operate free from limiting factors. The effective
secondary treatment provided by these systems has enabled reconsideration
of the simple septic tank as a primary treatment option.
3. CASE STUDIES
The problem faced by INTERFET in
both case studies was to provide adequate sanitation to ensure
force sustainability. The two sites selected are remote locations
with site limitations. The use of the basic shallow trench latrine
systems (SLT) can only be considered for short periods of time
during the dry season. The supply and maintenance of portable
toilets was also not a sustainable option.
CASE STUDY 1.
Wastewater disposal for
the Royal Australian Air Force (RAAF) at Komoro Airfield (Dili).
The RAAF required the provision
of permanent toilet facilities for use by airfield ground defenders
who had established strong points to protect the northern and
eastern approaches to the Komoro runway.
The area generally is flat with many low-lying flood prone areas
that were expected to become inundated during the wet season.
There was no power supply and the use of field generators was
not an option due to the tactical situation. Limited equipment
including a backhoe with a front-end loader was available on
a limited basis.
Suitable locations were identified at each site. Each location
was the highest point possible. The site on the northern side
of the runway was on a road shoulder. Primary treatment was
achieved using a three-chambered Field
Septic Disposal System installed at each location. Three
chambered systems are suitable for up to 25 persons and due
to the high digestion rates desludging intervals were expected
to exceed six months.
Two standard WC pans were positioned directly above the first
two chambers. This removed the need for additional plumbing.
Cisterns were also replaced with the FSDS
pour flush funnel that replicates the function of a standard
cistern without the bulk or operating mechanism. To operate
the system4 to 6 litres of water is poured into the flush funnel
connected to the WC. Prior to pouring the water is used for
hand washing. The flushing action evacuates faeces and paper
from the WC and retains the water seal to prevent the access
of insect vectors.
The FSDS has been designed to function
in the same manner as a standard septic tank. FSDS
have been certified as complying with Australian / New Zealand
Standard AS/NZS 1546.1: 1998, On-site domestic wastewater treatment
units, Septic tanks. Solids are removed from the waste stream
and digestion of those solids is facilitated. Unique features
of the system that make them ideal for military or emergency
deployments are its light weight construction (15Kg) for each
chamber, its ability to automatically adjust to seasonally high
water tables and ability to cater very low or very high shock
loads.
Secondary treatment of the wastewater was achieved in 5m MAT
(G) constructed from locally available materials.
Both systems operated without maintenance from November 1999
to March 2000. The transition from INTERFET to the United Nations
Transitional Administration East Timor (UNTAET) and an improved
security situation generally caused a reduction in use of these
facilities. FSDS installations have
a certified life of 15 years and the Komoro Airfield installations
will remain in place for use as required in the future.
CASE STUDY 2.
Wastewater disposal for the Royal
New Zealand Air Force (RNZAF) and Royal New Zealand Army (RNZA)
units at Suai near the boarder with West Timor.
RNZAF and RNZA units also required the provision of permanent
toilet facilities. These facilities were provided in a similar
manner to those discussed in CASE STUDY 1. An additional requirement
was for the collection and on-site treatment of sullage wastewater
generated from shower, laundry and kitchen facilities.
The area generally is flat with many low-lying flood prone areas
that were also expected to become inundated during the wet season.
Power supply was available from field generators 5 HP petrol
pumps were also available. The only available equipment was
the occasional use of a BobCat front-end loader.
The nature of the soil (medium to heavy clays) and the larger
volumes of wastewater that would be generated required the use
of a suitably sized MAT (E) system. The key problem with this
project was the requirement to provide a sullage collection
well adjacent each of the shower, laundry and kitchen facilities
from which the sullage could be pumped to the MAT (E) system.
Suitably sized collection wells have capacities of between 2000
L and 5000 L and need to be located below ground to enable drainage
from floor level. Only plastic prefabricated collection wells
could be transported to SUAI and apart from the expected time
delay of between 4 to 6 weeks, plastic tanks are not suitable
for below ground installation in heavy clay soils with high
water tables. The continual emptying of plastic collection wells
causes significant hydrostatic lifting forces when there is
a high seasonal water table. The provision of suitable anchorage
for plastic collection wells under these conditions is also
difficult.
The collection well problem was solved simply using locally
available materials. A trench 10m long, 1.2m wide and 1.2m deep
was constructed at the rear of each facility. Each trench was
lined with black plastic (double thickness) and covered with
a lightweight roof positioned on a double layer of sandbags.
The lightweight roof was also covered with black plastic (double
thickness) to protect the trench from rainwater infiltration.
The roof black plastic was held in place with 20mm to 40mm of
backfill soil. The construction of the lightweight roof also
prevented access by insects such as mosquitoes that would have
increases the risk Malaria or Dengue Fever. Drainage pipes from
the facilities were connected into these trenches.
The operation of the trench is also simple. Sullage is collected
and pumped as required to the MAT (E) absorption system. The
10m trench has a holding capacity of over 14,000-L, which is
approximately 14 days capacity for 200 persons. During the wet
season when the water table will rise to within 600mm of the
surface the actual storage capacity is reduced by 50% to approximately
7000 L. The reduced capacity is caused by the requirement not
to pump out more sullage than the corresponding water table,
which allows the trench to remain in equilibrium with the water
table. If additional sullage is removed below the level of the
water table the hydrostatic force would caused the plastic lining
on the sides if the trench to fail.
4. LESSONS LEARNT.
The development of MAT (G) and
MAT (E) absorption has revolutionised on-site secondary treatment
of sewage wastewater. This development has permitted the installation
of water sealed toilets connected to FSDS
or basic septic tank system in areas previously thought impossible
due to non-absorbent soil types or other site limitations.
The development of the FSDS for
use in conjunction with MAT (G) or MAT (E) has allowed the use
of water sealed toilets in remote areas. Systems have also been
identified as suitable for NGO use in disrupted states and other
civil emergencies.
The low comparative costs of these on-site sewage wastewater
systems will allow the high levels of sanitation infrastructure
in developed countries to be provided to third world countries.
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