Environmental EngineeringEnvironmental EngineeringEnvironmental EngineeringEnvironmental Engineering----IIIIIIII

General overview of plant components

Clarifier

Raw Wastewater Influent

PRIMARY

SECONDARY

Preliminary Residuals

(i.e., grit, rags, etc.)AAAA

PRELIMINARY

Clarifier

Secondary Sludge

Primary Sludge

DISINFECTION

Biological

Treatment

System

SECONDARY

Clean Wastewater Effluent

Discharge to Receiving Waters

BBBB

CCCC

Wastewater

Treatment

Residuals

Biosolids

Processing

and Disposal

(e.g., attached-grwoth

Suspended-Growth,

Constructed Wetland, etc.)

Clarifier

Usually to Landfill

� Used To remove the suspended solids & the dissolved organic load from the WW by using microbial populations.

� The microorganisms are responsible forfor◦ degradation of the organic matter

� Nutritional RequirementsNutritional RequirementsNutritional RequirementsNutritional Requirements: On the basis of chemical form of carbon required, microorganisms are classified as◦ Autotrophic: Autotrophic: Autotrophic: Autotrophic: organisms that use CO or ◦ Autotrophic: Autotrophic: Autotrophic: Autotrophic: organisms that use CO2 or HCO3

- as their sole source of carbon.

◦ Heterotrophic: Heterotrophic: Heterotrophic: Heterotrophic: organisms that use carbon from organic compounds.

�Energy RequirementsEnergy RequirementsEnergy RequirementsEnergy Requirements: : : : � On the basis of energy source required, microorganisms are classified as◦ PhototrophsPhototrophsPhototrophsPhototrophs: : : : organisms that use light as their energy source.

ChemotrophsChemotrophsChemotrophsChemotrophs: : : : organisms that employ

their energy source.

◦ ChemotrophsChemotrophsChemotrophsChemotrophs: : : : organisms that employ oxidation-reduction reactions to provide energy.

�Temperature Range: � On the basis of temperature range within which they can proliferate, microorganisms are classified as◦ PsychrophilicPsychrophilicPsychrophilicPsychrophilic: : : : organisms whose growth is optimum within 15 to 30°C.

◦ MesophilicMesophilicMesophilicMesophilic: : : : organisms whose growth is

optimum within 15 to 30°C.

◦ MesophilicMesophilicMesophilicMesophilic: : : : organisms whose growth is optimum within 30 to 45°C.

◦ ThermophilicThermophilicThermophilicThermophilic: : : : organisms whose growth is optimum within 45 to 70°C.

� Oxygen RequirementsOxygen RequirementsOxygen RequirementsOxygen Requirements::::

� On the basis of oxygen requirement microorganisms are classified as◦ Aerobes:Aerobes:Aerobes:Aerobes: organisms that use molecular oxygen (usually DO) for their metabolism.

◦ Anaerobes:Anaerobes:Anaerobes:Anaerobes: organisms that use some molecule other than molecular oxygen for molecule other than molecular oxygen for their metabolism

◦ Facultative organisms Facultative organisms Facultative organisms Facultative organisms : : : : organisms that can use either molecular oxygen or some other chemical compound for their metabolism.

� If the micro-organisms are suspended in the WW during biological operation then process is known as suspended growth processes

Examples :- Activated Sludge process, Examples :- Activated Sludge process, Aerated lagoons

�Recycling of settled biomass i.e. sludge is required.

� Process in which the micro-organisms that are attached to a surface over which they grow is known as attached growth processes

Examples:Examples:Examples:Examples:---- trickling filterExamples:Examples:Examples:Examples:---- trickling filterRotating biological contactors (RBC)

� The biomass attached to media (ex. rock, plastic, wood)

� Recycling of settled biomass i.e. sludge is not required, but recycling of sewage may be done.

� These consists of both attached growth as well as suspended growth processes.

� Examples: Examples: Examples: Examples: ----TF and ASPTF and ASPTF and ASPTF and ASP

ASP and TFASP and TFASP and TFASP and TF

Faccultative lagoonsFaccultative lagoonsFaccultative lagoonsFaccultative lagoonsFaccultative lagoonsFaccultative lagoonsFaccultative lagoonsFaccultative lagoons

Trickling filter process

Trickling filter process

� As wastewater trickles through the media layer a film is formed around the media, called slime layer or Biofilm

� Depth of aerobic zone within slime layer, formed on media is 0.1 to 0.2 mm.

The remaining part of film is � The remaining part of film is anaerobic.

� As wastewater flows over the film, the organic matter is rapidly metabolised while colloidal organics are adsorbed onto the surface.

� Since food concentration at the outer edge is more, therefore microorganisms at outer level are in rapid growth phase.

� As microorganisms grow thickness of biofilm increases.

Diffused oxygen is consumed before

biofilm increases.

� Diffused oxygen is consumed before it penetrates the slime layer.

� Therefore anaerobic zone is established at the media surface.

� When microorganisms enter into death phase they loose their ability to hold the surface, and gets detached from the surface

� The phenomena of scouring of slime layer is known as roughing or roughing or roughing or roughing or unloading of filterunloading of filterunloading of filterunloading of filterlayer is known as roughing or roughing or roughing or roughing or unloading of filterunloading of filterunloading of filterunloading of filter

Types of Filters

Trickling filters are classified based on the organic and hydraulic loading applied to the unit.

Low rate trickling filter or standard Low rate trickling filter or standard Low rate trickling filter or standard Low rate trickling filter or standard 1.1.1.1. Low rate trickling filter or standard Low rate trickling filter or standard Low rate trickling filter or standard Low rate trickling filter or standard raterateraterate

2.2.2.2. High rate trickling filterHigh rate trickling filterHigh rate trickling filterHigh rate trickling filter

S.NoS.NoS.NoS.No....Design Design Design Design Feature Feature Feature Feature

Low Rate Low Rate Low Rate Low Rate Filter Filter Filter Filter

High Rate Filter High Rate Filter High Rate Filter High Rate Filter

1.1.1.1.Hydraulic Hydraulic Hydraulic Hydraulic loading, loading, loading, loading, mmmm3333/m/m/m/m2222.d .d .d .d

1 1 1 1 ---- 4444 10 10 10 10 ---- 30 30 30 30

2.2.2.2.Organic Organic Organic Organic

loading,kgloading,kgloading,kgloading,kg0.08 0.08 0.08 0.08 ----0.320.320.320.32

0.5 0.5 0.5 0.5 ---- 1.0 1.0 1.0 1.0 2.2.2.2. loading,kgloading,kgloading,kgloading,kgBOD / mBOD / mBOD / mBOD / m3333.d .d .d .d

0.320.320.320.320.5 0.5 0.5 0.5 ---- 1.0 1.0 1.0 1.0

3.3.3.3. Depth, m. Depth, m. Depth, m. Depth, m. 1.8 1.8 1.8 1.8 ---- 3.03.03.03.0 1.3 1.3 1.3 1.3 –––– 1.81.81.81.8

4.4.4.4.Recirculation Recirculation Recirculation Recirculation

ratio ratio ratio ratio 0000

0.5 0.5 0.5 0.5 ---- 3.0 (domestic 3.0 (domestic 3.0 (domestic 3.0 (domestic wastewater) wastewater) wastewater) wastewater) up to up to up to up to

8 for strong 8 for strong 8 for strong 8 for strong industrial industrial industrial industrial

wastewater.wastewater.wastewater.wastewater.

rotating distributor arms

Packing media

Wastewater

media

Underdrain

◦TF consists of mainly following parts/components:

� A rotating arm A rotating arm A rotating arm A rotating arm that sprays wastewater over a filter medium.

�Filter mediumFilter mediumFilter mediumFilter medium: rocks, plastic, or other material.

◦Under drainage system: Under drainage system: Under drainage system: Under drainage system: The water is

other material.

◦Under drainage system: Under drainage system: Under drainage system: Under drainage system: The water is collected at the bottom of the filter for further treatment.

� Filter media should have

- High specific surface area

- High percent void space

- Resistance to abrasion or disintegration during placementduring placement

- Insolubility in sewage or wastewater and

- Resistance to spalling or flaking

� Should be round or cubical in shape

� Size 25 to 75 mm

PropertyPropertyPropertyProperty Desired valueDesired valueDesired valueDesired value

1. Crushing strength

Not less than 100 N/mm2strength N/mm2

2. Hardness Not less than 12

3. Percent wear Not more than 4

4. Specific gravity Not less than 2.6

� Crushed rock

◦ Durable & insoluble

◦ Locally available

◦ But, reduce the void spaces for passage of air

◦ Less surface area per volume for biological growthbiological growth

� Plastic media ◦ Random packing media

◦ Modular packing media

Cross-flowTubular

Pall rings

� Concentration of organics in sewage decreases as the waste passes the media depth.

� Thus effectiveness of the filter decreases as the depth increases.decreases as the depth increases.

� Hence depth of filter should be restricted

� For slow rate depth in the range of 1.8 to 3.0 m is provided.

� Depth of media is 1.8 to 2.4m

� Perforated blocks are used. Can be made of precast concrete or vitrified clay.

� Drains shall be designed for partial flow condition (Less than 50% of flow).

� Velocity of flow should not be less than 0.75 m/s at peak instantaneous Velocity of flow should not be less than 0.75 m/s at peak instantaneous flows.

� At design flows velocity should be 0.6 to 0.9 m/s.

� Function is twofold to circulate the air and

� It collects sewage from all under drains and conveys it to next unit.

Velocity shall not be less than 0.6

drains and conveys it to next unit.

� Velocity shall not be less than 0.6 m/s.

� Slope is provided so that sewage can be carried under gravity

� Floor should be strong enough to support media.

� RCC slab of 10 to 15 cm thick is usually provided to carry load of usually provided to carry load of entire media.

� Usually 1 % slope is provided.

� Fully plastered stone or brick masonry walls

� Walls are made honeycombed to circulate the air.circulate the air.

� Some times ventilation duct is provided

� Natural ventilation takes place because of difference in temperature of air and sewage.

� Air circulation takes place when temperature difference is 60C.temperature difference is 60C.

� When temperature difference falls below 1.90C then there will be no air circulation.

� Some times forced ventilation is also provided

� The function of rotary distributor is to spread the sewage uniformly over the media top surface.

� Rate of rotation may be 2 rpm for small distributors and 1/3 to ½ for large distributors and 1/3 to ½ for large distributor.

� Clearance between pipe and media should be 15 t o25 cm.

DesignDesignDesignDesignDesignDesignDesignDesign

1.1.1.1. Hydraulic LoadingHydraulic LoadingHydraulic LoadingHydraulic Loading

It is ratio of discharge or flow rate to the surface area

Units Units Units Units –––– million lit/ha/day

2. Organic Loading2. Organic Loading2. Organic Loading2. Organic Loading

It is ratio of BOD load to volume of filter

2. Organic Loading2. Organic Loading2. Organic Loading2. Organic Loading

It is ratio of BOD load to volume of filter media.

Organic loading = (Q x BOD5)/V

Therefore , V = BODV = BODV = BODV = BOD5555 x Q/ Organic loadingx Q/ Organic loadingx Q/ Organic loadingx Q/ Organic loading

UnitsUnitsUnitsUnits---- Kg or gm. of BOD/ m3 of volume/d

BOD removal efficiency of HRTF is 90%

1. Effluent obtained from SRTF is highly nitrified and stabilised.

2. It produces desired quality of effluent under varying weather conditions.

3. They can remove 80% of solids and 80% of solids and 80% of solids and 80% of solids and 3. They can remove 80% of solids and 80% of solids and 80% of solids and 80% of solids and 75 to 80% of BOD75 to 80% of BOD75 to 80% of BOD75 to 80% of BOD

4. Working is simple and cheap and does not require any supervision.

5.They are self cleansing.

6. As it contains less mechanical equipments , wear and tear is small.

7. Electrical power requirement is less.less.

8. Moisture content of sludge coming out of TF is very high

1. High head loss.

2. The cost of construction is high

3. Large area is required3. Large area is required

4. PST is must before SRTF (It can remove 30 to 40% of BOD load).

5. Odour and fly nuisance.

1. Trickling filter is _________________ type of process

2. Detaching of the biofilm from media is known as ________________.

Dissolved organic load can be

is known as ________________.

3. Dissolved organic load can be removed by using ___________________ treatment.

4. Unloading of trickling filter starts when microorganism enter in _____________ phase.

5. Hydraulic loading rate for low rate TF is _______ m3/m2/d. (0.5 to 2/1 to 4/ 2 to 5/ 5 to 8)

6. Organic loading rate for high rate TF is _______ gm of BOD /m3/d. (100-400/400-600/ 500 – 1000/ 1000- 2000)

Q1. Give classification of microorganisms.

Q2. Draw neat sketch of Trickling filter.

Q3. Draw sketch of trickling filter and explain it w. r. t. explain it w. r. t.

i. Filter media

ii. Under drainage system and

iii. Distributor

Q4. Explain ‘biological process in trickling filter’ with neat diagram.

Q5. Explain working of trickling filter with neat sketch.(8 marks, May2011, May 2009).

Q6. Write short notes

i. Types of trickling filter (6 marks, may2009)