Sewagedisposalunit 8 by K R Thanki

Sewage Disposal

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Sub.: WATER SUPPLY And SANITARY ENGINEERING (3350603)

UNIT -VIII

Prepared By:

K.R.THANKI (BE Civil)

LECTURER CIVIL ENGINEERING DEPARTMENTGOVERNMENT POLY TECHNIC ,

JUNAGADH,GUJARAT-INDIA.

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Characteristics of sewage:

Sewage Charecteristics

Physical Chemical Biological

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Physical • colour• Odour• Temperature • Turbidity


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Characteristics of sewage:Physical Colour :

Fresh domestic sewage has a soap solution or grey colour.

With the time of sewer begins to get black as the decomposition starts.

Colour of septic sewer is more or less black.

Colour of industrial sewage depends on the chemical used.

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Characteristics of sewage:Physical Odour :

Fresh sewage water has slightly soapy or oily odour.

The stale sewage (unpleasant) has offensive odour (strong odour) of hydrogen sulphate and other sulphur compounds.

In the normal temperature when sewage passes through the sewers, the offensive smell will start after 2 hours, which reaches the climates after 6 hours.

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Characteristics of sewage:Physical Temperature :

Generally the temperature of the sewage is slightly higher than the water supply.

When the sewage flows in the close conduits its temperature further rises, resulting in the increase of viscosity and Bacterial activity.

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Characteristics of sewage:Physical Temperature :

Temperature of sewage varies with the season also.

If the temperature of the sewage is below the normal atmospheric temperature, it will indicate the infiltration of ground water , but in case of higher temperature it indicates the addition of industrial sewage.

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Characteristics of sewage:Physical Turbidity :

The turbidity of the sewage directly depends on the quantity of solid matters present in it in suspension state.

When ever suspended matters increase strength of sewage increases.

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Chemical


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The Chemical Characteristics of sewage helps in indicating:

The stage of sewage decomposition.

Its strength, and extent and type of treatment required for making it safe.

Chemical

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Therefore, chemical analysis is carried out, which includes test for determining: Total solids, suspended solids and settleable solids pH value; Chloride content; Nitrogen content; Presence of fats, greases and oils; Sulphides, sulphates and H2S gas; Dissolved oxygen; Chemical oxygen demand(COD); Boi-chemical oxygen demand (BOD)

Chemical

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Total solids, suspended solids and settleable solids

Chemical

Solids present in sewage may be in any of these forms: Suspended / non-filterable solids Dissolved solids Colloidal solids / filterable solids Settleable solids

Further, the solids in sewage comprise of both: Organic solids (45%) Inorganic solids (55%)

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pH value

Chemical

It’s determination is important because efficiency of some of the treatment methods depends upon the availability of suitable pH value.

It can be measured using potentiometer.

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Chloride contentChemical

Chlorides found in sewage is derived from kitchen wastes, urinary discharges, industries.

It can be measured by titrating (calculate the amount of substance in a solution by measuring the volume of a stranded reagent) the waste water(i.e. sewage) with standard silver nitrate solution using potassium chromate as indicator.

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Nitrogen contentChemical

Nitrogen may occur in one of the following forms:

Free ammonia, called ammonia nitrogen; Albuminoid nitrogen, called organic nitrogen; Nitrites and Nitrates

Nitrates and nitrites are measured by colour matching techniques.

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Presence of fats, greases and oils

Chemical

They are derived in sewage from the discharge of animals and vegetable matter, or from the garages, kitchens of hotels and restaurants, etc.

Such matter form scum on top of the sedimentation tanks, clogs the void of filter media and affects the diffusion of oxygen, thus interfering with the normal treatment methods.

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Sulphides, sulphates and H2S gasChemical

They are formed due to the decomposition of various sulphur containing substances in sewage. In aerobic digestion of sewage, the aerobic and faculative bacteria oxidizes sulphur & its compounds to initially form sulphides, which ultimately breakdown to sulphates. In anaerobic digestion, the anaerobic and facultative bacteria reduce the sulphur and its compounds to sulphides, with evolution of H2S along with methane, carbon dioxide.

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Dissolved OxygenChemical

The actual quantity of DO is governed by:

Solubility of oxygen

Temperature

Purity of water

It decreases as temperature increases.

It is also determined by winklers method.

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Chemical oxygen demand(COD)

Chemical

It is the measured amount of oxygen needed to chemically oxidize the organic matter using a strong oxidizing agent like potassium dichromate under acidic condition.

It can be used to measure both biodegradable and non biodegradable organic matter.

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Characteristics of sewage:Chemical

It is defined as the amount of oxygen required by the microorganisms (mostly bacteria) to carry out decomposition of biodegradable organic matter under aerobic conditions.

Boi-chemical oxygen demand (BOD)

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Characteristics of sewage:Chemical

•The BOD test is widely used to determine the pollution strength of domestic and industrial wastes in terms of the oxygen that they will require if discharged into natural watercourses. It is the one of the most important test in stream pollution control activities.


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Chemical

•This test is of prime importance in regulatory work and in studies designed to evaluate the purification capacity of receiving bodies of water.

•It is also useful in design of wastewater treatment plant and also to measure the efficiency of some treatment processes.

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Biological


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Characteristics of sewage:Biological

• Sewer contains large quantity of bacteria which come from excremental matter. (solid waste of animals).

• All the bacteria present in sewage are not harmful, more quantity of harmless bacteria helps to treat the sewage and reduce the cost of treatment plants.

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•All the organisms can be broadly classified as Macroscopic and Microscopic.

•Followings are the main living organisms in sewage:

Bacteria Algae Fungi Protozoa

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• Normally bacteria are harmless to humans they decompose the complex compounds of sewerage and convert it into simple, stable and basic compounds.

• According to Oxygen used they can be classify as,

Aerobic Anaerobic Faculative

Bacteria:

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Aerobic:

Aerobic Bacteria survive by using free oxygen to atmosphere or dissolved oxygen of water.

They produce in water based organic substances.

Bacteria:

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Anaerobic:

Anaerobic Bacteria survive without using free oxygen to atmosphere or dissolved oxygen of water.

They can easily obtain oxygen from Nitrites, Nitrates and Sulphates.

Bacteria:

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Facultative:

Facultative Bacteria survive with or without using free oxygen to atmosphere or dissolved oxygen of water.

Bacteria:

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Characteristics of sewage:BiologicalAlgae:

Algae contains chlorophyl and other additional pigments.

Algae produces oxygen and release carbon dioxide by the process of photoshyntasis.

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Characteristics of sewage:BiologicalFungi:

Fungi is NOT Clorophyl or Pigments (which gives some color).

These are usually colorless and are filamentous having branches.

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Characteristics of sewage:BiologicalFungi:

They have the property of decomposing starches sugar, Cellulose, Fats, Protins, Higher alcohols and Nitrogenous substances.

When they are present in large number they are called mycelium and resemble like a Cat’s tail.

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Characteristics of sewage:BiologicalProtozoa:

These includes all Unicellular animals.

Normally most of Protozoa survive by eating Bacteria.

These are of various types like Amoeba, Flagellates, Free swimming ciliates, etc...

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Amoeba:A single celled organism that is the first to develop in sludge.

If they are predominant the sludge is very young.

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Flagellates :

A large single cell body with a whip like appendage called a flagellum.

Number of flagellates decreasing as the sludge age increased.

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Flagellates :

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Free swimming ciliates :

These are small oval shaped with tiny hairs or also called as cilia.

Cilia move in a wave-like motion to propel them in water and bring in food.

Numbers increase as sludge reaches maturity and achieves its peak settle ability.

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Free swimming ciliates :

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Sampling of Sewage:

Following procedure should be adopted for collecting sample for various laboratory tests:

The samples of sewage are collected at interval of 1hour during the day.

The capacity of the sampling bottles should be 100cc to 150 cc (Cubic centimeters).

The Date, Time and Place of collection of sample should be noted on the bottles.

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Sampling of Sewage:

Grab Sample Composite Sample

Types of samples

Grab Sample

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Sampling of Sewage:

This type of sample is taken at that place where all the particles mixed to gather by the effect of turbulence .

This type of sample is very useful to find out PH, Dissolved Oxygen, etc..

For this sampling method there is no perticular method ; sampling is done by manually.

Grab Sample

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Sampling of Sewage:

When ever the quantity and quality of sewer changes frequently at that places grab samples are not sufficient to analyze the sewage.

At that places a regular samples are taken and mixture of that sample is known as composite sample.

By using this method one can analyze average qualities of sewer.

Composite Sample

Grab Sample

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Sampling of Sewage:

For composite sample a grab samples are taken at every hours.

Composite sample is taken by Automatic sampler during the day.

Composite Sample

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Sampling of Sewage:Sampling Tube:

This tube is useful to collect sewage samples and also it is useful to collect oil , grease etc..

external diameter of this tube is 40 mm.

Length of tube is 1m.

It is madeup of stainless steel or brass.

One bucket is fitted on one end of length 50mm.

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Internal diameter of bucket is 2mm more than outer diameter.

Both sides 6.5mm diameter brass rods are fitted for 100mm sampling space.

Open side sampling tube there is rubber stopper fitted which is removed at the time of sampling.

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Wastewater treatment steps:

Waste water can be treated by:

Artificially

Naturally

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Naturally

Land Treatment

Dilution

Dilution

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Dilution is the disposal of sewage by discharging it into large bodies of water like sea, streams, rivers etc. This method is possible only when the natural water is available in large quantity near the town.

Proper care should be taken while discharging sewage in water so that sewage may not pollute natural water and make it unfit for any other purposes like bathing, drinking, irrigation etc.

Dilution

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CONDITIONS FAVOURING DILUTION

Where sewage is fresh.Where favorable currents exits in a stream.Where sewage is almost free from floating settleable solids.Where through mixing is possible.Where diluting water has high quantities of dissolved oxygen.When the city is situated near river or sea.

Dilution

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SELF-PURIFICAION OF STREAMS

The natural process in which the oxygen of water of streams is consumed by sewage and at the same time it is filled again by the atmosphere is called self-purification of streams.

Dilution

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FACTORS HELPING SELF-PURIFICATION OF STREAMS:-

₪Dilution₪ Sedimentation₪Sun-light₪Oxidation₪Reduction₪Temperature₪Bacteria.

Dilution

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₪DILUTIONwhen sewage is discharged into the stream water , the offensiveness of the organic matter is diminished (reduces in size)by its dispersion through the diluting water .The sewage always remains in aerobic condition & anaerobic conditions never comes because dissolved oxygen always remains present in the water.

Dilution

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₪SEDIMENTATION:The heavier solids with slow current settle in the stream bed & start anaerobic decomposition. An aerobic condition will not develop if dilution is sufficient & scouring tendency of streams during floods will wash the deposits. Settleable solids drop down to the bottom of the stream in the form of sludge deposits. Hence it is purified to some extent.

Dilution

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₪OXYDATION :The oxidation of the organic matter starts as soon as sewage is discharged into the diluting water due to CHEMICAL REACTION GROWTH & ACTIVITY OF OXIDISING ORGANISMS.

Dilution

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₪OXYDATION :When the organic matter meets the water; it starts getting oxidized due to development of oxidizing organisms in water. The process continues till the organic matter has been completely oxidized. The oxygen demand is fully satisfied, the stream becomes pure. Water always contains some dissolved oxygen and it is responsible for oxidation of organic matter.

Dilution

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₪ REDUCTION :when organic matter hydrolyses either chemically or biologically by anaerobic organisms to form gases from the liquids, the process is known as reduction.It also helps for stabilization by oxidation.

Dilution

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₪ SUNLIGHT :It has sterilizing effect on certain bacterias, bleaching powder & photosynthesis by which chlorophyll bearing organisms take energy from sun & convert it into food for other forms of life . Co2 is absorbed & o2 is evolved in the process.

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Wastewater treatment steps:Land Treatment

SUITABILITY OF LAND TREATMENT METHOD OF SEWAGE DISPOSAL:-

₪ The overall rainfall is very low.₪The natural water courses are not available.₪The quantity of sewage is more which pollutes the natural water courses.₪The rivers have very small discharge during summer.

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SUITABILITY OF LAND TREATMENT METHOD OF SEWAGE DISPOSAL:-

₪The water table is very deep and is not likely to be polluted by adopting the land treatment method of disposal.₪The vegetables have good market value as by adopting land treatment, the income also increases.₪The soil is porous as it will allow good areation.

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APPLICATION OF SEWAGE METHODS:

Flooding method

Surface irrigation method

Zig zag method

Lagooning method

Basin method

Sub-soil irrigation method

Ridge and ferrow irrigation method.

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Flooding method

The area to be irrigated is divided into various parts surrounded by dykes. The sewage is filled like small ponds in between the dykes. The depth of dose varies from 3.0 cms. To 5.0 cms. Depending on the irrigation requirements.

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Flooding method

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This method is most suited in sloping area. Here, parallel drains are constructed in the fields. All these drains are connected to a distributaries drain with the help of regulating device so that sewage may flow in the require drain. Here when sewage flows over the fields, its large quantity is absorbed by the field and only excess quantity reaches another drain.

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Zig zag method

In this method the ridges are arranged in a zag-zag method with corresponding furrows by their side.

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Lagooning method

These are used cheaply for sewage disposal. In this method the sewage is allowed to in a natural depression available or artificial constructed tanks.

Detention period is about a month. During this period the sludge is stabilized and dried.

The purified effluent passes way from an outlet placed at the other end. Lagoons should be shallow and must be constructed away from the town.

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Lagooning method

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Basin method

In this method big trees are planted in an isolated manner, basins are formed around each tree. These basins are filled with sewage. This method is suitable for fruit gardens.

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Here sewage is applied at the roofs of plants, through the open jointed agricultural drain-pipes. These pipes are laid about 1.0 m below the ground level. The sewage rises up due to capillary action. Here soil takes less load but this is an economical method.

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In this method , sewage is supplied in furrows between crop rows. Sewage spreads laterally irrigating the area between two furrows. The width of furrow varies from 120-150 cm and the depth from 25-50 cm. The width of the ridge varies from 125-250 cm and length from 10-30 m. The percolated effluent is collected in underground drains flows towards natural drainage for disposal.

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Wastewater treatment steps:• Includes removal of large objects

some solid materials like debris, gravel, sand or liquids like fats, oils and grease from the water.

Primary Treatment

• Includes degradation of biological content of the sewage such as are derived from human waste, food waste, soaps and detergent.

Secondary Treament

• Includes a final treatment to effluent (water) to increase the water quality, before the water is discharged to the natural waterways.

Tertiary Treatment

Artificially

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ScreeningGrit Chamber Primary Sedimentation

Aeration Tank

Secondary Sedimentation

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Sewage Treatment Plant:Primary Treatment

This treatment consists of removal of floating materials .

It also removes heavy settleable inorganic solids.

This treatment reduces BOD about 15 to 30%.

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Sewage Treatment Plant:Primary TreatmentRaw Sewage

Screens(Remove floating materials)

Grit Chambers(Remove Organic and inorganic matters)

Skimming Tank(Remove Oil , Grease, etc..)

To Primary Treatment Plant

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This process is first carried out at a sewage treatment plant, to trap and remove the floating matter , such as dead animals, tree branches, metal containers, plastic containers, etc..

If these matters are not removed, will chock the pipes, or adversely affect the working of sewage pumps.

Screening

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Types of Screens:

Based on Opening size: Coarse screen Medium screen Fine screen

Based on their Shapes: Disc screen Drum screen Band screen Wings screen Cage screen

Screening

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Types of Screens:

Other Types: Racks or Bar- Screens Perforated or Fine screens Cutting screens

Screening

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Types of Screens: Racks or Bar- Screens

Screening

Engineering

Sewagedisposalunit 8 by K R Thanki