DOMESTIC SEWAGE TREATMENT(SEPTIC TANK AND SOAK PIT)

Submitted by:- OM PRAKASH RAMKISHOR YADAV TRILOK CHAND

GUPTA VIJAY PAL OLA

Submitted to:- Prof. A.B. GUPTA MNIT, JAIPUR

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:-

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.

SEPTIC TANK INTRODUCTION CONSTUCTION DETAIL DESIGN WORKING CLEANING INSTALLATION TIPS POTENTIAL PROBLEM ENVIROMENT ISSUES ADVANTAGES AND DISADVANTAGES DISPOSAL OF EFFLUENT

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.

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.

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.

Organic materials +Nutrients CH4+ CO2 + NH3+H2S+ Biomass

Anearobic decomposition

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.

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.

Sewage enter through the Inlet. There are three layers1. Anything that floats rises to the top and forms a

layer known as the scum layer.2. Anything heavier than water sinks to form the

sludge layer. 3. 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.

WORKING

Organic matter is digested by bacteria.Digestion of settled sludge is carried out by ANAROBIC DECOMPOSITION also called sludge digestion.Due to decomposition foul gases are produced thus mass of sludge is decreased.BOD of water also decreased .

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.

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.

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.

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.

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).

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.

It is a completely passive system.

Small area required.

Low initial & operation cost.

Effluent from ST is disposed without much trouble.

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.

DISPOSAL OF EFFLUENT Ways of disposal of effluent are:-1. Soak pit.2. Sub-surface irrigation 3. Leaching Cess-pools.4. Treated in trickling filters5. Recycling.

SOAK PIT TANK

INTRODUCTION DESIGN WORKING ADEQUACY HEALTH ASPECTS MAINTENANCEADVANTAGES & DISADAVANTAGES

WHY WE NEED

SOAK PIT TANK ?

REASON

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.

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.

DESIGN

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.

A-masonry ringB-stone or brick aggregateC-brick chamberD-30cm thick outer casing with coarse sandE-effluent from septic tank

WORKINGAs 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.

ADEQUACYA 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 .

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.

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.

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.

ADVANTAGESCan be built and repaired with locally

available materials.Small land area required.Power conservative.Can be built and maintained with locally

available materials.Simple technique for all users.

DISADVANTAGES

Pretreatment is required to prevent clogging, although eventual clogging is inevitable.

Negatively affects soil and groundwater properties.

SUB-SURFACE IRRIGATION

Introduction Design Working Advantages Limitations

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.

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).

Sub-surface Disposal System

WORKING 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.

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.

LIMITATIONS Emitter clogging:-This clogging is usually the

result of insufficient water filtration, lateral flushing and/or chemical injection.

Salt accumulation Mechanical damage Crop establishment Soil structural effects

REFRENCES

Guide- Dr. Urmila Brighu, MNIT Jaipur

Sewage Disposal & Air Pollution Eng. BY S.K.Garg

http//en.wikipedia.org/wiki.com http//home.housestuffworks.com http//septictank.org/wp.com

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