01. sewage and effluent treatment presentation taster

8/3/2019 01. Sewage and Effluent Treatment Presentation Taster

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Waste water engineering:


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Overview: Water Pollution

Wastewater Characteristics

Wastewater Treatment Considerations

Wastewater Treatment Plant Design

Physical, Chemical and Biological

Processes


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Water Pollution

Water is essential for life. Over 97% of water is

present in the oceans but being unfit for human

consumption. Only a limited amount of this is

available for human use. Triggered by enormous

increase in population and shrinking resources per

capita availability of water is decreasing.

Added to the lower availability is the highincidence of pollution of water supplies in the

developing world.


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Sources of water pollution

Point sources: pollutants are discharged from

sewage plants, meat and dairy industries through

pipes at specific points into the discharge waters

(stream, pond, lake or ocean)

Non-point sources: pollutants present in soil are

carried away as run offs by rain water intostreams, rivers or oceans at several points


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Types of water pollution sources

Agricultural wastes- Rain water carries them off as runoffs from fields and animal farms.

Industrial wastes- Waste water discharges from food,

paper, leather, and distillery industries are heavy in terms oforganic load.

Domestic sewage-It is 99% water with 1% solids(drymatter). The solids are made up of 70% organic and 30%inorganic chemicals( grits, salt metal oxides)

Natural sources / run offs- Run offs from virginforests(free of human activities) or those due to

earthquakes or cyclones are not considered as pollution.


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Types of pollutants in water

1. Oxygen demanding pollutants

2. Pathogens

3. Nutrients

4. Salts5. Thermal pollution

6. Heavy metals

7. Pesticides8. Volatile organic compounds

9. Radionuclides

10.Oil pollutants


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Effects of water pollution1.Organic matter causes a decrease in O2 affecting aquatic life.2. Release of nutrients into waters leads to eutrophication and algal

blooms. Shell fish feeding on toxic algae have caused paralytic

shell-fish poisoning.3.Pathogens as pollutants lead to gastroenteritis and dysentery.4.Heavy metals cause nephro toxicity.5. Presence of pesticides,VOC and radio nuclides are harmful; in

drinking water supplies and aquatic life.

6. Pollutants impart colour, off-odour and off-taste to water

rendering it unfit for consumption.


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Sewage treatment-IntroductionWater after use becomes sewage or waste water.Sewage includes all waste waters- from toilets, kitchenand laundry washings, rain water flowing into municipal

drains, industrial wastes from citi drains etc.Municipal wastewater is 99.9 % water , balance made

up of suspended and dissolved solids:Total solids = Total suspended solids + Total dissolved

solids (suspended solids can be removed by filtration,

while total dissolved solids cannot be removed)

In large metropolitan cities this small percentage ofsolids

May account for more than 1000tons of solids per day.


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Overview: WastewaterEngineering

Wastewater Treatment

Wastewateris the water used by a

community Collected and treated prior to discharge

Standards of treatment vary but aregenerally becoming more stringent

Treatment is a process of removal ofsmaller and smaller particles


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Sludge Treatment Sludgesare the product of biological

treatment of wastewater Sludges comprise solids found in

wastewater plus organisms used in thetreatment process

Disposal is a major issueVarious disposal techniques are used but

each has advantages and disadvantages


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Water Disposal and Re-Use

Wastewater treatment generates a Cleaned

Water Stream Cleaned water is often discharged to a

larger body of water for dilution

Alternatively, cleaned water my be re-usedfor irrigation or rarely drinking waterproduction


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Characteristics are normally estimated byempirical methods

Wastewater Flows Flows arise from households, industry,

infiltration and storm flows

Flows are considered in both hydraulic and

process design Levels of treatment may vary for different

flowrates


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Wastewater Flows

There is a variety of methods for

estimating flowrates However there may be great variability in

the factors which affect flowrates fromregion to region

Different multiples of the Dry WeatherFlow will receive each level of treatment


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Wastewater Composition

Key design issues:

Solids: density, particle size, level of VolatileSuspended Solids

Biochemical Oxygen Demand

Temperature

Ammonia

Nutrient levels


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Wastewater Treatment Considerations

Objective: to maintain or improve the

quality of the receiving body of water Treatment stages:

Preliminary

Primary

Secondary

Tertiary


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Primary treatments

Raw sewage

Screening

Grit chamber

Primary settling tank


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Objective of secondary treatment is to further remove BOD

and suspended solids beyond what is achievable by primary

settling tank.Secondary treatment follows three approaches all of which

take advantage of microorganisms to convert organic waste

into stable low energy compounds.Effluent from primary treatment is treated in a) Trickling

filters or Rotating Biological Contactors (RBC) and b)

Activated sludge processSewage untreated can also be directly taken to oxidation

ponds or lagoons for BOD removal.

Secondary treatments


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Tertiary treatment

Primary and secondary treatments do not remove all the biologically

degradable organic matter.

Tertiary treatment is given to remove nitrogen and phosphorus

nutrients from the effluent.To avoid these O2 depletion and eutrophication problems, treatment

plants have to be provided with additional facilities to achieve higher

rates of N2 removal.


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Classification of Methods

Physical

Processes

Chemical

Processes

Biological

Processes

Screening

Sedimentation

Filtration

Precipitation

Chlorination

Aerobic

Anaerobic


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Applicability and Selection of Methods

Different processes are used to treat

wastewater depending on thecontaminants present

Similarly, different processes are used totreat sludges, depending on the objective

of treatment


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Overview: Wastewater TreatmentPlant Design

Flowrate and Mass Loading Wastewater feed is not specified, therefore the

plant must be able to treat whatever thewastewater contains

Plant design will take account of historical flowsand loadings, but must also be able to deal withexpansion

Plant must also be able to deal with a range offlow and load conditions, plus peak upstream flowconditions (eg storms)


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Selection of Design Flowrates Domestic: based on a flow per head.Varies between countries

Industrial: Based on records of dischargeconsents and of metered supplies

Infiltration/Exfiltration: based on a % of

the domestic flow Peaking Factors: Depends on size of

community


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Selection of Design Flowrates

Upstream Flow Equalisation

Plants are not normally designed to treat totalpeak arisings

Instead, hydraulic controls will direct flowsabove plant capabilities to storm system on

larger works


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Selection of Design Flowrates Upstream Flow Equalisation

UK maximum flow to treatment plant is determined byFormula A:

Formula A = PG+E+I+1360P+2E l/d

P=population

G=average daily consumption per head l/h/dE=Industrial & commercial discharges to sewer l/d

I=infiltration l/d


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Selection of Design Flowrates Upstream Flow Equalisation

For larger works with storm tanks, only FullTreatment Flow (FTF) will receive fulltreatment.

FTF=3PG+3E+I

Formula A-FTF will pass to storm tanks


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Selection of Design Mass LoadingsAverage mass loadings for BOD and

Suspended Solids are commonlydetermined by Population Equivalent (PE)

Design mass loadings are more complexand must take account of seasonal, diurnaland industrial load variations


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Manufacturing process: ordinary packaged

drinking water1.Clarification: to remove particles, colloids and contaminant2.Prefiltration : to protect final filter

3.Final Filtration/Sterilization: to remove particles, mould,

algae and protozoa; water sterile filtration to remove bacteria

and other microorganisms

4.Carbonation: to bring CO2 levels in water to original levels

in water. Carbonation. It is used to produce sparkling water.

CO2 injected in water must be free of particles and

microorganisms.5 Filling

01. sewage and effluent treatment presentation taster

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