Why Do We Need a Sewer System? . Each time we flush the toilet or wash sth down the sink's drain,we create sewage (also known in polite society as wastewater). One question that many people might ask is, "Why not simply dump this wastewater onto the ground outside the house, or into a nearby stre
1. DOMESTIC SEWAGE TREATMENT(septic tank and soak pit)
TRILOK CHAND GUPTA
VIJAY PAL OLA
2. Why Do We Need a Sewer System?
Each time we flush the toilet or wash sth down the sink's drain,we create sewage (also known in polite society as wastewater).
One question that many people might ask is, "Why not simply dump this wastewater onto the ground outside the house, or into a nearby stream?" There are three main things about wastewater that make it sth you don't want to release into the environment:-
3. It stinks. If you release wastewater directly into the environment, things get very smelly very fast.
It contains harmful bacteria. Which causes health hazard.
It contains suspended solids and chemicals that affect the environment.
4. SEPTIC TANK INTRODUCTION
ADVANTAGES AND DISADVANTAGES
DISPOSAL OF EFFLUENT
5. INTRODUCTION In rural areas where houses are spaced so far apart that a sewer system would be too expensive to install, people install their own, private sewage treatment plants. These are called septic tanks.
6. A septic tank is a key component of the septic system or sewer system.
In North America approximately 25% of the population relies on septic tanks; this can include suburbs and small towns as well as rural areas
Septic tanks are generally installed by isolated communities like schools, hospitals & institutions.
Septic tank may be defined as primary sedimentation tank.
Having capacity to remove 60 to 70% dissolved matter.
8. CONSTRUCTION DETAILS Tank is designed to prevent directs currents between the tank inlet and outlet.
T-pipes or baffles at inlet & outlet with submerged ends to stop currents and retaining the scum.
Manhole covers are provided in top slab to permit inspection & maintenance.
10. Top of tank is covered with RCC slab.
Sometimes stairs steps are also provided.
Provide vent pipe to escape foul gases.
Side sump-well with portable pump.
Two Compartment Septic Tank.
11. DESIGN CONSIDERATIONS CAPACITY OF SEPTIC TANK:-capable of storing sewage flow during detention period &extra volume of sludge for .5 to 3 yrs.
INLET AND OUTLET TEES
DETENTION PERIOD:- 12 to 36 hrs (adopted 24hrs)
LENGTH TO WIDTH RATIO:- Length is 2 to3 times of width.
12. Sewage enter through the Inlet.
There are three layers
Anything that floats rises to the top and forms a layer known as the scum layer.
Anything heavier than water sinks to form the sludge layer.
In the middle is a fairly clear water layer. This body of water contains bacteria and chemicals like nitrogen and phosphorous that act as fertilizers, but it is largely free of solids.
The water in the tank is not pure water, it is called gray water because it still contains organic materials that need to be filtered out.
As more water enters from influent the water level inside the septic tank rises and gray water will exit through effluent.
16. CLEANING “Prevention is better than cure”
Regular septic tank cleaning is the only way to prevent septic tank systems from clogging and well.
Pumping is only way of cleaning.
Frequency of cleaning depends on volume of solids, amount of indigestible solids and the ambient temperature.
17. So there is no “rule of thumb” because period of cleaning very from few months to so many yrs.
Generally this very from 6months to 4-5 yrs.
Sludge from tank disposed after drying.
18. Installation tips According to vastu the location of the septic tank should be such north west corner under any condition.
Do not construct the septic tank higher than the plinth level of the building. The best bet would be to construct it at ground level.
The septic tank should be at least 2 feet away from the wall or plinth.
19. POTENTIAL PROBLEMS Oils and grease are difficult to degrade can cause the inlet drains to block.
Flushing non-biodegradable items (cigarette butts & cotton buds) clog a septic tank.
Chemicals (pesticides, herbicides)and inorganic materials(paints or solvents)damage the working of a septic tank.
Roots from trees may clog and rupture them.
Excessive water entering the system will overload it and cause it to fail.
Septic tanks by themselves are ineffective at removing nitrogen compounds that can potentially cause algal blooms in receiving waters
All toilet paper are not suitable to dispose in septic tank(some toilet paper was specifically marked as suitable for use in septic systems and some was not).
21. ENVIRONMENTAL ISSUES Organic materials +Nutrients CH4 + CO2 +NH3 +Biomass
Sulfates, under the anaerobic conditions of septic tanks, are reduced to hydrogen sulfide (H2S), a pungent and toxic gas.
Nitrates and organic nitrogen compounds are reduced to ammonia.
Because of the anaerobic conditions, fermentation processes take place, which ultimately generate carbon dioxide and methane. Methane, a potent greenhouse gas.
Waste water also contain phosphate and phosphate can be the limiting nutrient for plant growth in many ecosystems.
22. ADVANTAGES Ease in construction.
No maintenance problem(except periodical cleaning).
Excellently functioning ST can considerably reduce suspended solids &BOD from sewage.
Due to digestion reduction in volume is about 60% &reduction in weight is about 30%.
It is suitable for isolated community.
23. It is a completely passive system.
Small area required.
Low initial & operation cost.
Effluent from ST is disposed without much trouble.
24. DISADVANTAGES If ST is not properly functioning, effluent will be very foul &dark.
Leakage of gases from top cover of ST may caused bed smells &environmental pollution.
Periodical cleaning, removal and disposal of sludge remains a tedious problem.
25. DISPOSAL OF EFFLUENT Ways of disposal of effluent are:-
Treated in trickling filters
26. SOAK PIT TANK INTRODUCTION
ADVANTAGES & DISADAVANTAGES
The water in the septic tank is not pure, it is called grey water because it still contains organic materials that need to be filtered out.
29. INTRODUCTION A Soak Pit is a covered, porous-walled chamber that allows water to slowly soak into the ground. Pre-settled effluent from septic tank is discharged to the underground chamber from where it infiltrates into the surrounding soil.
A layer of sand and fine gravel is spread across the bottom to help disperse the flow.
Depth should be between 1.5 and 4m deep, but never less than 1.5m above the ground water table.
The Soak Pit is filled with coarse rocks and gravel.
The rocks and gravel will prevent the walls from collapsing, but will still provide adequate space for the wastewater.
33. WORKING As wastewater percolates through the soil from the soak pit , small particles are filtered out by the soil matrix and organics are digested by micro-organism.
Soak pit are best suited to soils with good absorptive properties; clay, hard packed or rocky soils are not appropriate.
34. ADEQUACY A Soak Pit does not provide adequate treatment for raw wastewater and the pit will clog quickly.
A Soak Pit should be used for discharging pre settled black water or grey water .
35. Soak pits are appropriate for rural and suburban settlements.
They depend on soil with a sufficient absorptive capacity. They are not appropriate for areas that are prone to flooding or have high groundwater tables.
36. HEALTH ASPECTS The technology is located underground and thus, humans and animals should have no contact with the effluent.
The Soak Pit is located a safe distance from a drinking water source (ideally 30m).
The Soak Pit is odourless and not visible.
37. MAINTENANCE the effluent should be clarified or filtered well to prevent excessive build up of solids.
The Soak Pit should be kept away from high-traffic areas.
Particles and biomass will clog the pit so need to be cleaned or moved.
For future access a removable lid should be used to seal the pit.
38. ADVANTAGES Can be built and repaired with locally available materials.
Small land area required.
Can be built and maintained with locally available materials.
Simple technique for all users.
39. DISADVANTAGES Pretreatment is required to prevent clogging, although eventual clogging is inevitable.
Negatively affects soil and groundwater properties.
40. Sub-surface irrigation
41. introductio Effluent is delivered directly to the infiltrative surface of the soil using specially manufactured polyethylene tubing with built-in turbulent flow emitters.
Subsurface irrigation is a highly-efficient watering technique.
It reduces outdoor water use by 30 to 40 percent.
42. design It consist a masonry chamber (Distribution box) where the effluent of septic tank uniformly distributed an underground network.
Emitter lines placed on 2 foot centers with a 2 foot emitter spacing such that each emitter supplies a 4 sq. ft area.
These lines are placed at depths of 6-10 inches below the surface.
Absorption trench 30 to 90cm wide filled with gravel(15cm thick) layer and well graded aggregate(15cm thick layer).
Septic tank effluent is allowed to enter into a masonry chamber (distribution chamber).
from where it is uniformly distributed an underground network of open jointed pipe ,into absorption trench called dispersion trenches .
The suspended organic matter present in the effluent will be absorbed in the absorption trenches.
The clearer water seeping down to the water-table may come up to the plant roots throughly capillarity ,thus fulfilling their irrigation water demands.
45. advantages Health risks are minimized.
The system is easily automated.
Consumption of nitrates by the plant material is increased.
The systems are durable and have a long life.
Disposal of water by means of evapotranspiration by the plants is maximized.
Emitter clogging:-This clogging is usually the result of insufficient water filtration, lateral flushing and/or chemical injection.
Soil structural effects
Guide- Dr. Urmila Brighu, MNIT Jaipur
Sewage Disposal & Air Pollution Eng. BY S.K.Garg