Workshop on Sewage Treatment Plant Designat

Gujarat Jalseva Training Institute 28 Aug, 2018

Designing Sewage Treatment Plant

Prepared by:

Urv Patel, M.Eng. (Env)

SWA Environmental Consultants & Engineers, Ahmedabad

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1. History of sewage treatment

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Drainage (Treatment by dilution) - Indus Valley 2500-3000 BCE

1. History of sewage treatment –Activated Sludge Process

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Lawrence Research Lab, Massachusetts where Arden & Lockett discovered the Activated Sludge Process in 1914

1854 Cholera Epidemic of London

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1854 Cholera Epidemic of London

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• John Snow (15 March 1813 – 16 June 1858[1]) was an English physician and a leader in the adoption of anesthesia and medical hygiene. He is considered one of the fathers of modern epidemiology, in part because of his work in tracing the source of a cholera outbreak in Soho, London, in 1854. His findings inspired fundamental changes in the water and waste systems of London, which led to similar changes in other cities, and a significant improvement in general public health around the world.

• John Snow was one of the first physicians to study and calculate dosages for the use of ether and chloroform as surgical anaesthetics, allowing patients to undergo surgical and obstetric procedures without the distress and pain they would otherwise experience.

• He personally administered chloroform to Queen Victoria when she gave birth to the last two of her nine children, Leopold in 1853 and Beatricein 1857,[11] leading to wider public acceptance of obstetric anaesthesia

Source- The Ghost Map by Steven Johnson and Wikipedia

1850 Cholera Epidemic of London

• In 1854 it was discovered that a cholera epidemic spread through water. The outbreak seemed less severe in areas where sand filters were installed.

• British scientist John Snow found that the direct cause of the outbreak was water pump contamination by sewage water.

• He applied chlorine to purify the water, and this paved the way for water disinfection.

• Since the water in the pump had tasted and smelled normal, the conclusion was finally drawn that good taste and smell alone do not guarantee safe drinking water.

• This discovery led to governments starting to install municipal water filters (sand filters and chlorination), and hence the first government regulation of public water.

Read more: https://www.lenntech.com/history-water-treatment.htm#ixzz5N0cjUBrF

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2. Sewage - CharacterizationMacro-pollutants

• pH

• Chemical Oxygen Demand

• Total Organic Carbon

• Biological Oxygen Demand

• Total Nitrogen

• Nitrates & Nitrites

• Ammonical Nitrogen

• Total Phosphorous

• Coliform Count

• Bio-Assay

Micro-pollutants

• Endocrine Disrupting Hormones- Estrogen etc.

• Pharmaceuticals

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2. Sewage - Characterization

Chemical Oxygen Demand – The amount of oxygen consumed to digest all organic matter present in wastewater. Unit mg/l

Biological Oxygen Demand – The amount of oxygen consumed to digest all organic matter by bacterial activity in 5 days and at 20 C temperature. Unit mg/l

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2.1 National Discharge standards

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Refer the following links for more detailed standards:1. STP Workshop\Dischagre

Standards CPCB_MOEF.pdf2. STP Workshop\Dischagre

Standards CPCB_MOEF_Latest.pdf

3. www.moef.co.in

2.2 Implications of each water quality parameters

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Parameter Implications on receiving body

pH Acidity & Basicity

BOD or COD Oxygen Uptake / Demand and ultimately Dissolved Oxygen

Nitrogen/ Phosphorous Nutrient supply through which Eutrophication takes place and ultimately the DO levels

Total Coliform Pathogenicity / Disease causing potential

Total Suspended Solids Turbidity (Can also contribute to the BOD through the biodegradable part of TSS )

3. Typical process flow diagram of a Sewage Treatment Plant

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Source: Google Images

4. Unit operation and their target parametersUnit Operation Target parameter

Screen –Fine/Coarse

Filter debris >4-6 mm for protecting the plant pumps and other machinery from wear and tear

Grit Chamber Grit removal for protecting the plant pumps and othermachinery from wear and tear

Primary Clarifier Remove Total Suspended Solid and some COD

Aeration tank COD/BOD/Ammonical Nitorgen removal

Secondary Clarifier Remove Biological Sludge and recycle

Chlorine Contact Tank

Disinfection

Anaerobic Digester Digestion of waste sludge and solids reduction13

4.1 Fine Screens

• Removes Particles >4-6 mm

• Protects Plant Machinery form wear and tear

• Principle of operation is Mechanical Screening

• Typically installed in a channel

• Design Parameters : STP Workshop\1. Fine Screen Design Parameters.pdf

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4.1 Fine Screens

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Source: CPHEEO manual for STP design

4.1 Fine Screens - Types

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Rotary Drum Screen

5. Grit Chamber

• Removes Grit

• Protects Plant Machinery form wear and tear

• Principle of operation is Gravity Settling

• Design Parameters : STP Workshop\Manual on Sewerage and Sewage Treatment (CPHEEO)\Part A Engineering\Chapter 5.pdf

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5.1 Grit Chamber

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Source: Metcalf & Eddy

5. Primary Sedimentation: Gravity Settling

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Source: Google Images, Monroe Environmental

Terminal Settling velocity

Design parameter:• Surface Overflow Rate

in cum/sqm-day• Weir Loading rate in

cum/m-day• Side water Depth • Retention time

5. Primary Sedimentation: Surface Overflow rate

Surface Overflow Rate (SOR) =

Flowrate (cum/day) / Cross Sectional area of Clarifier

(sqm)In more simpler terms it is

the vertical up flow velocity in the clarifier

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5. Primary Sedimentation: Lamella Clarifier

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Design parameter:• Surface Overflow Rate in cum/sqm-

day• Weir Loading rate in cum/m-day• Side water depth • Plate spacing • Plate inclination • Velocity through each plate• Retention time

6. Biological Treatment- Activated Sludge Process (CSTR reactor)

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6. Biological Treatment- ASP and Modifications

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6.1 Biological Treatment- Design Equations

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• The design basis for the design and sizing of aeration tank in biological treatment is governed by Michalis- Menten Enzyme Substrate reaction.

• http://elte.prompt.hu/sites/default/files/tananyagok/IntroductionToPracticalBiochemistry/ch09s02.html

6.1 Biological Treatment- Design Equations

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• Firstly, make select SRT and make initial guess for NOx and solve the below equation:

𝑃𝑋,𝑏𝑖𝑜 =𝑄𝑌 𝑆𝑜 − 𝑆

1 − (𝑘𝑑)𝑆𝑅𝑇+𝑄𝑌𝑓𝑑𝑘𝑑(𝑆𝑜−𝑆)𝑆𝑅𝑇

1 − (𝑘𝑑)𝑆𝑅𝑇+

𝑄𝑌𝑛(𝑁𝑂𝑥)

1 − (𝑘𝑑𝑛)𝑆𝑅𝑇

where,

o Px,bio = Rate of biomass generation (kg/day)

o Q= Influent flow rate

o So= Influent bCOD

o S= Effluent bCOD desired

o SRT= Sludge Retention Time selected

o Y= Biomass Yield (Maximum Bacterial Growth Rate / Maximum Substrate Utilization Rate)

o fd= fraction of biomass undergoing endogenous decay

o kd= Endogenous decay coefficient

o NOx= TKN oxidized

6.2 Biological Treatment- Design Equations• Then, solve the below equation to calculate NOx,

𝑁𝑂𝑥 = 𝑇𝐾𝑁 − 𝑁𝑒 − 0.12𝑃𝑋,𝑏𝑖𝑜/𝑄

• If the NOx concentration calculated is not same as the assumed initially then iterate until we reach convergence.

• Then after 𝑃𝑋,𝑏𝑖𝑜is calculated, calculate 𝑃𝑋,𝑉𝑆𝑆 & 𝑃𝑋,𝑇𝑆𝑆 based on equation below:

𝑃𝑋,𝑉𝑆𝑆 = 𝑃𝑋,𝑏𝑖𝑜 + 𝑄(𝑛𝑏𝑉𝑆𝑆)

𝑃𝑋,𝑇𝑆𝑆 = (𝑃𝑋,𝑏𝑖𝑜/0.85) + 𝑄(𝑛𝑏𝑉𝑆𝑆) + 𝑄(𝑇𝑆𝑆𝑜 − 𝑉𝑆𝑆𝑜)

• After calculating Total Solids production, calculate the volume of aeration tank based on a selected MLSS concentration:

𝑋𝑉𝑆𝑆 . 𝑉𝑎𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = (𝑃𝑋,𝑉𝑆𝑆)𝑆𝑅𝑇

•

𝑋𝑇𝑆𝑆 . 𝑉𝑎𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = (𝑃𝑋,𝑇𝑆𝑆)𝑆𝑅𝑇

• Check, the F/M ratio based on the below equation:

𝐹

𝑀=𝑄𝑆𝑜𝑋𝑉

• If the F/M ratio is not within the prescribed limits then change SRT to bring it within the limits.

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6.3 Secondary Sedimentation- Design & Operating parameters

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6.3 Secondary Sedimentation- Design & Operating parameters

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6.3 Secondary Sedimentation- Activated Sludge Floc under microscope

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GOOD FLOC- Activated Sludge Floc

6.4 Activated Sludge Poor Floc- Under Microscope

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Floc with High Flagellates resulting from low F/M ratio

Floc with High Filamentous Bacteria resulting from high F/M ratio

Stalked Ciliates, Amoeba

31Source: http://www.havasuwatersavers.org/wastewater_treatment.php

6.4 Process Control Activated Sludge Process

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7.1 Disinfection- Chlorination • Picked up only after World War-1

once the production of Cl gas was economical

• Involves adding chlorine as a strong oxidizing agent to essentially oxidize the cell wall and cause cell lysis (death)

• Typical dosing 5-7 mg/l can be calculated based on Watson Chicks Law and CT value (Contact time * Concentration)

• Residual Property • Disinfection by-products are

carcinogenic

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7.1 Disinfection- Chlorination (Distribution of Chlorine based on pH)

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7.1 Disinfection- Chlorination

7.1 Disinfection- Chlorination

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Chlorine toners standard size 500 kg and 990 kg

Some design considerations • Very harmful gas when inhaled and can

be fatal if inhaled in certain amount • Safety considerations like neutralization

pit, scrubber, personal protective equipment to be made mandatory while handling Chlorine for plant personnel

7.1 Disinfection- Chlorination

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Chlorine Contact Tank

7.2 Disinfection- Ultraviolet radiation

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• Dosing is measured in mW/cm2

• Does not produce disinfection by-products

• Disadvantage when the water is turbid as the particle can cause a shielding effect

• Low risk of handling compared to chlorine. As not chemical handling is involved

• Need safety equipment when the UV radiation is ON

• Expensive equipment compared to Chlorine

7.2 Disinfection- Ultraviolet radiation

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7.3 Disinfection- Ozonation

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• Dosing is measured in mg/l

• Does not produce disinfection by-products which are carcinogenic

• Low risk of handling compared to chlorine. As no chemical handling is involved

• Need safety equipment when near the ozone generator

• Expensive equipment compared to Chlorine

• High power cost compared to UV and Chlorine

8. Design - Stages 1. Population estimation and forecast 2. Design period 20,30 years or so 3. Determine ideal process based on TYPE OF INFLUENT WATER 4. Process Design based on FLOW and HOURS OF OPERATION 5. Layout based on available land 6. Hydraulic Design based on FSL of receiving sump (U/G) based on head

loss between each unit. Preparing HFD 7. Sizing Electromechanical Equipments and Piping schedule 8. Preparation of General Arrangement Drawing (GAD)9. Structural Design based on GAD, Process Design and HFD10. Other utilities

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8.1. Design – Manual of Reference

• Central Public Health and Environmental Engineering Organization, India

• Water Environment Federation (WEF), MOPs

Other technical references:

• Water quality engineering by Mark Benjamin & Desmond Lawler

• Metcalf & Eddy

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8.2 Process Design- Example 35 MLD

WTP example file.pdf

Learnings on how to size

1. Cascade Aerator

2. Parshall Flume

3. Flash Mixer

4. Clariflocculator

5. Sand Filter

6. Chlorine Contact tank

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8.3 Hydraulic Design- Example 7.5 MLD

STP Workshop\Design\STP design_7.5MLD_Dhandhuka.pdf

STP Workshop\7) HFD.pdf

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8.4 Hydraulic Design- Typical

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8.7 Typical P&ID

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• STP Workshop\8) P&ID.pdf

9. Recent Advances in Activated Sludge Process- SBRs

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9. Recent Advances in Activated Sludge Process- Granular ASP (Nereda)

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9. Recent Advances in Activated Sludge Process- Granular ASP (Nereda)

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https://www.royalhaskoningdhv.com/nereda