intro to wwtp

8/13/2019 Intro to WWTP

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Wastewater Quality

Wide variations in the quality of wastewaters are quite common. Beside the

nature of the manufacturing process, the variations are also beingcontributed by the rate of hydraulic flow, which can affect the concentration

of the untreated effluent to be discharged.

An industrial WWTP is required to handle varying inputs, but is expected to

give an output of effluent fit for discharge to the environment at all times.

This is possible to achieve in a well designed, operated and maintained

plant.



Effective Wastewater Treatment Operation

In order to be able to bring about effective treatment of the effluent, it is

necessary to know more about:

• Characteristics of wastewater to be treated

• Requirement of treated wastewater quality

• Types of treatment alternatives available

• Techniques of wastewater sampling and analysis

These are the additions to the preventive and corrective maintenance of the

treatment machinery, knowledge of repairs to and replacement of various parts of equipment, record keeping, report preparation, aspects of safety in

treatment plants.



WWTP Aims

Ultimate aims for the WWTP operation is to remove the unwanted

constitutions in the wastewater to a level where they can be safelydischarged into the environment.

Malaysian Standard for industrial effluent discharged is listed in EQA 1974.



General Description of EQA

Regulations and Orders under EQA:

- Control of Agro based Water pollution

- Control of Municipal and Industrial Waste water pollution

- Control of Industrial Emissions

- Control of Motor Vehicle Emissions- Control of Toxic and Hazardous Wastes

- Integration of Environment and Development

- Control of Substances That Deplete the Ozone Layer



Control of Municipal and Industrial Waste water pollutionControl of Municipal and Industrial Waste water pollution

• Environmental Quality (Sewage and Industrial Effluents): Regulations 1979

• Environment Quality (Prohibition on the used of control substance in soap,synthetic detergent and other cleaning agent): Order 1995

• Control the discharged of wastewater from domestic (sewage) and

industrial premises



WWTP Design

Suitable combination of various available unit operations and unit processes

constitutes a flow scheme. It is to be noted that WWTP is like an assembly line in

a factory, where the various steps in purification are arranged in such a sequence

that the quality of output of one step is acceptable in the next step.

Explanation and illustration

Unit of operations include screening, sedimentation, filtration, adsorption, heating,drying, incineration, i.e. those steps involving physical forces.

Unit of processes include chemical and biological agents which bring about

purification and include pH correction, coagulation, aerobic and anaerobic

treatment.



Integrated Wastewater Treatment OperationIntegrated Wastewater Treatment Operation

• Generally, the coarsest material is removed first such as floating objects by

screenings.

• Inorganic grit particles are removed next.; Thereafter, the organic material is

handled. The larger organic particles which are big enough to settle by themselves

are removed in settling tanks and enter the sludge phase.

• A part of the finer organic particles may also settle in these settling (or

sedimentation) tanks.

• Further, settling of very fine particles needs the addition of chemicals.

• Finally the dissolved organic can be treated in biological processes (i.e. activated

sludge or trickling filter).



Sewage Treatment Plant (STP)Sewage Treatment Plant (STP)

P u m p

h o u s e

P r i m a

r y C l a

f i e r

A e r a t

i o n P o

n d

S l u d

g e T h

i c k e n i

n g

D i s i n f

e c t i o n

P u m p H

o u s e a n d

F i l t r a t

i o n

S l u d g e P

r o c e s s i n g



Conveyance System: CollectionConveyance System: Collection

SystemSystem



Preliminary Treatment:Preliminary Treatment:

ScreeningScreening



Conveyance System:Conveyance System:Pumping SystemPumping System



Primary Treatment System: SettlingPrimary Treatment System: Settling

Tank Tank



Secondary Treatment: AerationSecondary Treatment: Aeration

Tank Tank



Secondary Treatment: Clarifier Secondary Treatment: Clarifier



Secondary Treatment: SolidSecondary Treatment: Solid

ThickeningThickening



Tertiary Treatment: DisinfectionTertiary Treatment: Disinfection

ChlorinationChlorination



Tertiary Treatment: DisinfectionTertiary Treatment: Disinfection

UltravioletUltraviolet



Tertiary Treatment:Tertiary Treatment:

FiltrationFiltration



Solid Processing: AnaerobicSolid Processing: Anaerobic

DigestionDigestion



Sludge DewateringSludge Dewatering



BiosolidBiosolid RecyclingRecycling



WWTP House KeepingWWTP House Keeping

In a WWTP, it is always necessary to check the volume and quality of raw

and treated wastewater and also to keep A FAITHFUL RECORD OF THERESULTS OF THESE ANALYSES.

In addition, close watch over the quality and quantity of chemical added for

treatment is required to ensure economy. It may be even necessary to

conduct treatability studies in the plant laboratory to decide if anymodifications are required to the existing treatment processes.



CharacterisationCharacterisation of Wastewater of Wastewater

The characterisation involves determination of physical, chemical and

biological characteristics of the samples of wastewater using laboratorytechniques such as gravimetry, colorimetry and titrimetry.

Knowledge of the characteristics help the plant operators to provide the

information on:

• the strength of the raw and treated wastewater

• the efficiency of the plant operation as a whole and each of the treatment

processes

• the nature of treatment required in the case of the given wastewater to meet thequality standard



Introduction to Wastewater Constituents and its GenerationIntroduction to Wastewater Constituents and its Generation

Industrial activity results in the generation of a number of pollutants which

can be broadly grouped as•O2 demanding substances

• Suspended solids

• Nutrients• Disease producing organisms

• Salts

• Toxic metals

• Toxic organic chemical

• Heat



Categories of Water PollutantsCategories of Water Pollutants

Pollutants can be classified into several groups.:

The first are the nutrients, i.e. dissolved inorganics i.e. nitrate, and phosphate.

A second group included heavy metals, such as chromium, lead, and arsenic.

The third and largest group is the organics substances, which included pesticide,

industrial by-products, and solvents. Organic substances can be divided into twosubclasses based on solubility or lipid partitioning. These are hydrophobic

compounds, which dissolve in lipids (fats), and hydrophilic compounds, which

dissolve in water.



Categories of Water Pollutants IICategories of Water Pollutants II

Other than chemical characteristic, water pollutant also can be categorised based

on the physical analysis which include the temperature, colour, solids contents, pH, dissolved oxygen.



Wastewater from RefineryWastewater from Refinery

The process-intensive petrochemical industry has demanding environmentalmanagement challenges to protect water, soil and atmosphere of the refinery

pollution.

Petroleum refineries use relatively large volumes of water, especially forcooling systems. In fact, wastewater from the petrochemical industry usuallycontains hazardous chemicals, as hydrocarbons, phenol or ammoniacalnitrogen among others.



General Description



General Issues in Refinery Plant

- Cooling system produced 3.5-5 m3 of wastewater generated per ton of crude

- Polluted wastewater contains

BOD 150-250 mg/l COD 300-600 mg/l

phenol 20-200 mg/l

oil 100-300 mg/l (desalter water)

oil 5000 mg/l in tank bottom

benzene 1-100 mg/l

heavy metals 0.1-100 mg/l

- Solid waste and sludge

- VOC emissions- Others emissions



General Issues in Refinery Plant 2

• Salts in the feedstock (corrosion and fouling problems) and aromatics

(source of VOC)• Aromatics, oil, grease and organic removal

• Phenol and ammoniacal nitrogen removal with a biological treatment

• The organic and inorganic contaminants from refinery wastewater

• Oily water separation

• Oily rain water

• Process water

• Petroleum refineries and heavy metals



Oxygen demanding substancesOxygen demanding substances

Basically, O2 demanding substances originated from organic matters. Thesematter can be measured by four ways :

a. Theoretical Oxygen Demand (ThOD)

b. Biochemical Oxygen Demand (BOD)

c. Chemical Oxygen Demand (COD)

d. Total organic carbon analyser (TOC)



Theoretical Oxygen Demand (Theoretical Oxygen Demand (ThODThOD))

ThOD is the amount of oxygen to oxidise a known compound completely to CO2 andH2O.

It can also be used to calculate the amount of oxygen required to oxidise the ammonia present in the water of wastewater, which is known as Nitrogenous Oxygen Demand

(NOD) which is not able to be determined by BOD analysis.

Example 1

Acetic acid (CH3COOH); molecular weight = 60 g/mol

CH3COOH + Y O2 2CO2 + 2H2O

complete oxidation requires Y O2 which is equal to 260 g acetic acid requires 64 g O2

if 1000 mg/L acetic acid, then the oxygenrequirement will be

60g CH3COOH = 1000 mg CH3COOH

64g O2 Y O2Y = 1000mg x 64g / 60g = 1067 mg O2



Biochemical Oxygen Demand (BOD)Biochemical Oxygen Demand (BOD)

BOD measurement is the most widely used parameter of organic pollutant applied to bothwastewater and surface water. This determination involves the measurement of thedissolved oxygen used by microorganism in the biochemical oxidation of organic matter.

Calculation: BODt = DOi – DOf x dilution factor

Example

Time Dissolved O2

T0 25 mgl-1

T1 22 mgl-1

T2 19 mgl-1

T3 18 mgl-1

T4 16 mgl-1

T5 15 mgl-1

BOD5 = (T0 - T5) x dilution factor

BOD5 = 25 - 15 = 20 mgl-1 x 10 = 200 mg.l-1



BOD AnalysisBOD Analysis

δTt/δt = - k.t

integration ( from 0 to t) δTt/t = - δt.k

ln Tt - l n T0 = - k.t

ln [Tt / To ] = - k.t Tt = T0 . exp - k.t

BOD5 = T0 - T5

= T0 - T0 . exp - k.5

= T0 ( 1- exp - k.5 )

T0 = BOD5 / ( 1- exp - k.5 )



BOD Analysis 2BOD Analysis 2

Example (Dilution 100 times)

DO measurement (mg/L)

Day Sample 1 Sample 2

0 18.0 20.0

1 12.0 15.0

2 9.5 13.0

3 6.0 10.0

4 5.0 8.0

5 4.0 6.0

Both samples give BOD5 = 140 mg.l-1

The differences is based on the degradation rate which can be determined based on thegraph plot.



BOD Degradation Rate (BOD Degradation Rate (k k ))

Determination of coefficient k can be obtained based on

ln [Tt / To ] = - k.t

Convert the equation as a linearequation:

y = mx + c; where

y = ln [Ti/T0]

k = m

x = time

Dissolved Oxygen Depletion

0

5

10

15

20

25

0 1 2 3 4 5 6

Time (d)

O x y g e n C o n c ( m g / L ) Sample 1

Sample 2

Thus another set of data is required for the linearation of the equation. This set of data can be

used for the plot of Ln [Ti/To] against time where the cut off value point is ZERO.

O A l i 2BOD A l i 2



BOD Analysis 2BOD Analysis 2

Linear Equation for BOD analysis

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 6

Time (d)

L n [ T i / T o ]

Sample 1

Sample 2

Linearisation of BOD curveLn [Ti/T0]


0 0 0

1 0.36 0.22

2 0.51 0.363 0.92 0.62

4 1.1 0.91

5 1.21 1.21

k 1 = 0.26

k 2 = 0.23

Sample 1 has higher

degradation rate

more biodegradable

Oxygen ConsumptionOxygen Consumption



Oxygen ConsumptionOxygen Consumption

Sometimes the amount of O2 consumption plays important roles.

Dissolved Oxygen Consumption

0

2

4

6

8

10

12

1416

0 1 2 3 4 5 6

Time (d)

O x y g e n C o n c ( m g / L )

Sample 1

Sample 2

DO consumption


0 0 0

1 6 52 8.5 7

3 12 10

4 13 12

5 14 14

It can be used to determine ultimate

BOD which indicate the final fate of

the organic constituent in the

wastewater

BOD ultimateBOD ultimate



BOD ultimateBOD ultimate

Determination of BOD ultimate can be done based on the BOD rate (k ) whichhas been previously determined.

lnln [ [ T T t t / T / T oo ] = ] = -- k.tk.t T T t t = T = T oo expexp--kt kt

Oxygen consumption

Y t = T o - T i

Y t = T o – (T oexp-kt ) T o (1-exp-kt )

T o = Y t / (1-exp-kt)

Based on BOD5

T o for both samples Sample 1: 140 / (1-exp-0.26 x 5) = 192 mg/L

Sample 2: 140 / (1-exp-0.23 x 5) = 205 mg/L

Application



Chemical Oxygen Demand (COD)Chemical Oxygen Demand (COD)

COD is the test that measure the oxygen requirement to oxidise the organicmatter by a strong oxidising agent in an acidic medium. Its able to determineorganics which both biodegradable and non biodegradable. Some inorganicmatter may interfere with the measurement such as chlorine.

6Cl- + Cr 2O72- + 14H+ 3Cl2 + 2Cr 3+ + 7H2O

A few "preservative" reagents can be used to eliminate interference.Hg2+ + 2Cl- HgCl2

Measurement is based on the unreacted Cr 2O72- , thus high salinity or

conductivity sample interfere with COD analysis.

COD analysis can be used after correlation with sources of organic matter has been established.



COD analysisCOD analysis

For many type of wastes, COD is correlated to BOD. This can be useful to

estimate the BOD measurement in the next analysis. COD takes 3 hours for

the result, while BOD takes 5 days for the result, which is going to be too late

if the discharge is already entering the external system. Once the correlation

has been established, COD measurement can be used to good advantage fortreatment-plant control and operation.

Ratio of BOD:COD analysis indicates biodegradable content for the organic

constituent. Example BOD:COD < 0.7; chemical processes are required ratherthan solely depending on biological processes.



COD analysis 2COD analysis 2

Many costly mistakes in wastewater plant design and operational strategies

can be traced to a lack of knowledge and measurement data on these COD

constituents, by both plant designers and operations staff.

The common use of BOD5 as the only carbonaceous load plant parameter

monitored, has further acerbated the situation - although BOD5 has been

known within the industry for many years as an inferior parameter forcharacterizing the biological processes within a wastewater plant.




The four primary carbon components of influent wastewater above, play a

fundamental role in activated sludge plant design and operation. These are

commonly referred to as:

a. Biodegradable COD (BCOD) components:

• Readily Biodegradable COD (RBCOD), and

• Slowly Biodegradable COD (SBCOD)

b. Unbiodegradable COD (UCOD) components:

• Unbiodegradable Soluble COD (USCOD), and

• Unbiodegradable Particulate COD (UPCOD).

Relationship between COD and BODRelationship between COD and BOD



pp

9001100

680930

500700

450750

550800

240500

730950

8501000

BOD ultimateCOD

Correlation Between BOD ultimate and COD

y = 1.13x - 336.19

R2 = 0.97

0

200

400

600

800

1000

0 200 400 600 800 1000 1200

COD

B O D u l t i m a t e

BODultimate = 1.13 COD – 337

Correlation andCorrelation and LinearisationLinearisation of COD and BODof COD and BOD



Using MS – Excel:• Plot scattered data for BOD

vs COD

• Add trend line with specificcommand to linear line

• Add equation andcorrelation values

COD l i 3COD l i 3




http://www.scitrav.com/wwater/sasspro/fraccalc.asp (Scientific Traveller)

http://www.scitrav.com/wwater/sasspro/fraccalc.asp (Science Traveller)



Sampling TechniquesSampling Techniques

Characterisation is greatly affected by the sampling techniques, and follwed by prompt

conveyance of the samples to the laboratory and preservation of the samples, if required.

Correct sampling techniques yields a sample which is truly representative of the nature of

the wastewater. If the flow of wastewater comes to the sampling point in batches, one grab

sample during the flow period may suffice. But if the flow in known to be fluctuated in

quantity and quality, collecting small samples at regular time intervals and mixing them

will be more representative of the actual condition than one grab samples. Mixing up thegrab samples is known as composite samples.

Sampling can be done manually or with the help of autosampler. When sampling program

extends over a long time, it is necessary to preserve either by storing or using suitable

preservatives.



Wastewater flow fluctuationWastewater flow fluctuation

Every industrial WWTP is designed to handle a certain volume of wastewater per

unit time.

The hydraulic loading varies with time; magnitude of this variation depends on:

•diversity of products manufactured

•process operations contributing to waste

•batch or continuous operation

Difficulties caused by the fluctuation are overcome by providing equalisation

tanks which ensure a more uniform wastewater to the downstream treatment unit

in terms of quality and flowrate.



Flow measurementFlow measurement

Flow measurement at a treatment plant can be done by:

•Use of stopwatch and bucket

•Area velocity method

•Use of overflow weirs

•Use of Parshall flume

Each method has its own limitations.

Area velocity method

http://e/Type%202%20web/files%20and%20forms/Miscellaneous/Flowrate.ppt









Area velocity method

Flow can be measured without a hydraulic structure such as a

weir or flume. In the area velocity method, the mean velocity of

the flow is calculated at a cross-section, and this value is

multiplied by the flow area. Flow rate Q is determined according

to the continuity equation:

Q = V x A

The area velocity method is used when it is not practical to use a weir or flume, andfor temporary flow measurements.

The velocity measurement is made using a variety of technologies, including:

Doppler Transit time Electromagnetic Radar

http://www.marsh-mcbirney.com/Articles/yoder-open_channel_flow-3.htm

Overflow weirs



Overflow weirs

Weirs are structures consisting of an obstruction such as a dam or bulkhead

placed across the open channel with a specially shaped opening or notch. The

weir results an increase in the water level, or head, which is measured

upstream of the structure. The flow rate over a weir is a function of the headon the weir.

http://www.engineeringtoolbox.com/49_592.html

O fl W i 2



Over-flow Weirs 2

Common weir constructions are the rectangular weir, the triangular or v-

notch weir, and the broad-crested weir. Weirs are called sharp-crested if their

crests are constructed of thin metal plates, and broad-crested if they are made

of wide timber or concrete.

Water level-discharge relationships can be applied and meet accuracy

requirements for sharp-crested weirs if the installation is designed and

installed consistent with established ASTM and ISO standards .




V or Rectangular Notch

The basic principle is that discharge is directly related to the water depth above the crotch

(bottom) of the V; this distance is called head (h). The V-notch design causes small changes

in discharge to have a large change in depth allowing more accurate head measurement than

with a rectangular weir.

http://www.engineeringtoolbox.com/49_524qframed.html

http://www.dwaf.gov.za/HydroMpumalanga/structure_types.htm

VV-- Notch Equation Notch Equation



qq

V-notch weir equations have become somewhat standardized. ISO (1980) and ASTM (1993)

all suggest using the Kindsvater-Shen equation, which is presented below from USBR (1997)

for Q in m3

s and heights in m units. All of the references show similar curves for C and k vs.angle, but none of them provide equations for the curves.

C i T bl f V N h (90 C)



Conversion Table for V Notch (90oC)

68.0300

57.3280

47.6260

38.9240

31.3220

24.7200

18.9180

14.1160

10.2140

6.911204.36100

2.4980

1.2160

0.44140Flow (l/s)Head (mm)

http://www.fao.org/docrep/T0848E/t08

48e-09.htm

Rectangular Weirs



The flow rate measurement in a rectangular weir is based on the Bernoulli

Equation principles and can be expressed as:

where

Q = flow rate

h = head on the weir

b = width of the weir

g = gravity

C d = discharge constant for the weir - must be determined

C d must be determined by analysis and calibration tests. For standard weirs - C d - is well

defined or constant for measuring within specified head ranges.

3

2

232 h g C Q d .=




Parshall FlumesA Parshall flume is a specially shaped structure which

can be installed in a channel to measure the water flow

rate. The flume was developed and calibrated by Ralph

Parshall at Colorado State University early in this

century and has been used extensively. AlthoughParshall flumes are difficult devices to set and build,

they are an accepted and widely used measuring device.

where:

ha = measuring head (m)

Q = discharge (m3/s)

C and n for each size are given

http://waterknowledge.colostate.edu/parshall.htm



Flow rateFlow rate

Unit of measurement of flowrate which is often used is meter cubic per second

(m3.s-1) or also known as cumec.

Example

A rectangular channel 3 m wide contains water 2m deep and flowing at a velocity

of 1.5 m/s. What is the flow rate in cumec?

Q = V.A: 1.5m/s x 3m x 2m = 9 cumec.



Selection of formulaSelection of formula

Most problems involving mathematics in WWTP can be solved by selecting the

proper formula, inserting the known information and calculating the unknown.

Example: Hydraulic Retention Time (HRT) in the processing tank. Q = 6,360

m3/d and the dimension for volume (V) = 18m x 9m x 2.4m (388.8 m3).

HRT = V/Q 388.8 / 6360 = 0.061 d = 1.47 hours



Selection of formula: Mass Loading RateSelection of formula: Mass Loading Rate

Most of the regulation include the emission standard, but not on the

environmental standard. Environmental standard consider the mass loading rate.

Example:

Plant A emits discharge BOD5 at 100 mg.l-1 with Q: 0.1 cumec

Plant B emits discharge BOD5 at 10 mg.l-1 with Q: 1 cumec

Which plant pollutes more?



Mass Loading Rate (Answer)Mass Loading Rate (Answer)

MLR = Q x Concentration (mass/time)

Q = m3.s-1 (60 s.min-1 x 60 min.h-1 x 24 h.day-1)

= 86400 m3/d

Concentration = mg.L-1 = g.m-3

Unit for MLR = m3.d-1 x g.m-3 = g.d-1

Plant A: (0.1 x 86 400 x 100) g.d-1 = 864 kg.d-1

Plant B: (1.0 x 86 400 x 10) g.d-1 = 864 kg.d-1

intro to wwtp

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