The principles involved in the planning and designing of waste disposal system are not materially different in high altitudes and/or sub-zero temperature regions but require suitable modifications to meet the high altitude and low temperature requirements. The modifications required in the designing and satisfactory functioning of waste disposal system in these regions are discussed.
Temperatures and Pressure Condition and their Effects in High Altitude and/or Sub-Zero Temperature Regions:
The essential conditions obtained in these regions are low temperature, that is, below 4°C and/or low barometric pressures, that is, below 0.86 kg (f)/cm2.
ADVERTISEMENTS:
The effect of such low temperatures and pressures in these regions are indicated below:
Effect of Low Temperatures:
(a) Physical:
Water is at its maximum density at 4°C. At 0°C it solidifies and turns into ice having expanded approximately one-twelfth of its volume. The viscosity of water and liquids increases with falling temperatures thus affecting the settling velocities of particles carried in suspension. The kinematic viscosities and density of water at low temperature ranges of 0° to 10°C are given in Table 24.1.
(b) Chemical:
ADVERTISEMENTS:
In general most chemicals react much slower at temperatures near freezing than they do at normal temperatures. Consequently longer reaction times are required for satisfactory performance in the treatment units where chemicals are used.
(c) Biological:
Low temperatures retard biological activity. Thus treatment processes such as septic tanks, trickling filters, etc., which depend on biological activities of micro-organisms are considerably affected.
Effect of Low Barometric Pressures:
ADVERTISEMENTS:
Normal barometric pressures met at high altitudes in regions around Srinagar (Kashmir-Leh area) are given in Table 24.2. Low barometric pressures limit pump suction head. A rate of decrease of 1.15 m in the allowable suction head should be made for every 1000 m elevation above MSL.
Further the efficiency of pumping set also reduces with increase in altitude. An allowance at the rate of fall of overall efficiency upto 2% in the case of electric prime movers and upto 4% in the case of other types of prime movers for every 300 m altitude should be made.
A special care needed to be taken in the operation of the pumps being that, where the ambient temperature conditions so warrant, provisions should be made to ensure that pumps are drained immediately after shutting down to prevent damage to plant due to freezing.
Waste Disposal Systems:
In high altitude regions the biological and chemical reductions of organic material proceeds slowly under low temperature conditions consequently the waste disposal systems are affected. In sub-zero temperature regions it is usually not practicable to install water carriage systems of waste disposal, and hence in these regions the waste disposal systems which do not involve the use of water are adopted. However, in some regions if practicable water carriage systems may also be adopted for the disposal of wastes.
The various waste disposal systems which may be adopted in the high altitude regions and the necessary precautions to be taken in their operation are indicated below:
1. Box and Can System:
In this system the night soil is collected in a box or can and from the box or can the night soil is disposed of by burial in isolated spots far from habitation or by incineration where feasible. The box or can should be fitted with tight fitting lids for use when it is carried for emptying. Further adequate arrangements should be made for the cleaning and disinfection of the box or can after it is emptied of its contents.
2. Trench or Pit Latrines:
Trench or pit latrines may be used where soil and sub-soil conditions favour their use. Whenever these are used they should not be closer than 18 m from any source of drinking water such as well, to mitigate the bacterial pollution of water.
3. Chemical Toilets:
Chemical toilet essentially consists of small cylindrical tank with a water closet seat for the use of about 8 to 10 persons. A ventilation pipe is fitted to the seat. A strong solution of caustic soda is used as a disinfectant. It kills bacteria, liquefies the solids and thus checks the decomposition of organic matter.
The tank is provided with a drain plug from which liquid runs to a soak pit at the time of disposal. For the successful functioning of chemical toilets, they should preferably be installed in heated rooms or enclosures.
4. Bio-Digesters:
In the sub-zero temperature regions the night soil and other wastes do not undergo decomposition and thus may remain the same way without decay even after years. In such regions a device called bio-digester may be used which is an apparatus to decompose human waste. Such devices have been successfully installed in our country by Army engineers in very high altitude regions of Siachen glacier in Kashmir.
An entire brigade of the Army is positioned along and even beyond the 67 km long glacier on the Soltoro Ridge, where there is not even enough place to build a toilet. So in this sub-zero temperature region soldiers defecate in the open and then bury the night soil in snow.
This is actually causing severe problem of organic pollution along the glacier and consequently disturbing the ecological balance of the mountains which can become very dangerous. In order to clean up the glacier, at least of human waste, and thus preserve the ecological balance of the mountains, bio-digesters have been installed along the glacier.
5. Water Carriage Waste Disposal Systems:
Water carriage waste disposal systems may be adopted where practicable. These should be constructed in such a manner that maximum heat is retained by insulation, if necessary. Lavatories and bath-rooms should be kept heated to avoid freezing of water inside traps and flushing cisterns. The various water carriage waste disposal systems which may be adopted.
Sewerage systems (or Sewer System). In this system a network of sewers along with necessary appurtenances is provided.
The necessary considerations in this system are as indicated below:
(i) Under normal circumstances, sewers should be laid below the frost line.
(ii) The trenches for sewers should be loosely filled with earth after laying sewers since loose soil is a better insulator than compacted soil. Consequently, sewers laid under traffic ways and other places where soil compaction may be expected are required to be given adequate insulation.
(iii) Where feasible, sewer should be so located that the trench line is not in shadow when the sun is shining.
(iv) Concrete, cast iron and stoneware pipes conduct heat relatively rapidly and hence these should be adequately insulated.
(v) Manholes should be made of air-tight construction so as to prevent the cold air from outside gaining access inside and freezing the contents.
(vi) Where utilidor is used for water distribution, the sewers may also be placed in the same utilidor for protection against low temperature. But in this arrangement great care should be taken to prevent water mains becoming contaminated on this account. Where this is adopted, the bottom of the water pipe at all points should be at least 30 cm above the top of the sewer line at its higher point.
6. Septic Tanks:
Septic tanks can function only when it can be ensured that the contents inside these do not freeze during low temperature. For this purpose the septic tanks should be located well below the frost line. The location of the manhole openings should be marked by staves.
Fencing around the septic tanks should be provided for discouraging traffic over it. As the rate of biological activity is reduced by 50% for every 10°C fall in temperature, the capacity of the septic tanks should be increased by 100% for operation at 10°C over that for operation at 20°C.
7. Seepage Pits (or Soak Pits):
Seepage pits can be provided when the soil and sub-soil conditions are favourable for water absorption. Frozen soil extending to a great depth would preclude the use of such disposal devices due to lower water absorption capacity. The discharge of the effluent should be made below the frost line.
Sewage Treatment Plants:
For satisfactory functioning of sewage treatment plants in high altitude regions modifications are needed in the design of sedimentation, chemical and biological processes as indicated below:
Settling Tanks:
Settling process is greatly slowed down by the increased viscosity of water at low temperatures. Thus settling tanks operated at near freezing temperature should provide surface loading rates nearly half that for operation at 20°C. Where possible, settling tanks may be covered for increasing the efficiency.
Chemical Reactions:
As indicated earlier almost all chemicals react much slower at temperatures near freezing than they do at normal temperatures. As such longer reacting times should be provided in the design of the treatment units where chemicals are used.
Biological Processes:
The biological activity is considerably retarded at low temperatures. The rate of biological activity is reduced by 50% for every 10°C fall in temperature, and hence the capacity of the treatment units involving biological processes should be increased by 100% for operation at 10°Cover that for operation at 20°C.
Pumping Installations:
Pumps and pumping machinery should be housed inside well-insulated chambers. Where necessary, arrangements should be made for heating the inside of pump houses. Pump houses, as far as possible, should be built directly above the intake structures.
Economic Factors Involved at High Altitude Regions:
The various economic factors involved in providing waste disposal systems in high altitude regions are as indicated below:
1. The cost of transportation of materials to high altitudes is enormous. Consequently preference should be given to the use of materials of lighter weight to facilitate easy haulage.
2. Meagre manpower resources for use in construction and operation of sanitary engineering works in high altitude areas should be recognized.
3. Labour cost go up considerably due to decreased human output in high altitude regions on account of low oxygen content in the atmosphere.
4. Adequate spares should be maintained to meet emergencies as non-availability of materials and equipment, difficult accessibility of the areas and modifications required for severe weather conditions add to the cost of facilities at high altitudes.