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Important Topics in Sanitary
Engineering
By
Husam Al-Najar
Environmental Engineering Department-The Islamic University of Gaza
http://site.iugaza.edu.ps/halnajar/courses/
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What is the job description of the Sanitary engineer?
The sanitary engineer job became essential with the rapid increase of cities and
other rural population concentrations.
Sanitary Engineering Fields
Watersupply
-Collection systems
-Treatment
-Reuse (and/or) disposal
- Storm water
collection
- Storm water reuse
(and/or) disposal
- Storm watertreatment (if needed)
-Water collection
-Ground water
-Surface water
-Water treatment
-Water Distribution
Waste waterManagement Storm waterManagementSolid wasteManagement
- Collection systems
- Treatment
methods
- Reuse (and/or)
disposal
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WASTE WATER COLLECTION SYSTEM
Sewer: Sewers are under ground pipes or conduits which carry sewageto points of disposal.
Sewage: The Liquid waste from a community is called sewage.
Sewage is classified into domestic and non-domestic sewage.
The non domestic sewage is classified into industrial, commercial,institutional and any other sewage that is not domestic.
Sewerage: The entire system used for collection, treatment anddisposal of Liquid waste. This includes pipes, manholes, and allstructures used for the above mentioned purposes.
IMPORTANT DIFINITIONS
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What Types of collection systems?
Separate system
Sanitary system
Combined system
Both sanitary & storm water
1. Used for domestic and industrial wastes inaddition to inflow and infiltration. Storm
water is not considered.
2. It is preferred for the following:
The size of pipes is much smaller than thecombined system sewers. This gives the
advantage of good hydraulics in the pipe
(the pipe is Designed to have a minimum
velocity to prevent sedimentation of sand)
Separation of wastewater from storm water
minimize the total quantity of sewage which
has the following advantages :
1. Smaller pumping stations are needed.2. Smaller and more efficient treatment plants
are needed.
3. Overflow of combined sewers in the storm
events produces pollution to environmentwhich is not the case in separate sewer.
Only unavoidable Storm water inters the system
which protects the system from theaccumulation of sand in the sewers in thenon- aved areas.
It is used for both storm water and wastewater.It is preferred for the following cases:
For areas of long rainy seasons.
For areas where it is difficult to construct two
pipelines in the streets crowded with otherservices (electricity, telephone, gas, etc...).
Its not preferred for areas of short rainy season,
and for areas poorly paved which leads to the
accumulation of sand in the system.
Combined system is 40% lower in cost than
separate system.
Storm water
Generally, most of the countriesrecently preferring separate
systems.
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What type of studies are needed for the design of sewagecollection systems?
1. Contour maps, and longitudinal profiles.2. Geotechnical investigation( type of soil).3. Hydrological investigation( water table).4. Metrological data( rain,.).5. Detailed map of the area showing streets, buildings, levels of
buildings entrance etc6. Detailed cross section for the streets showing the undergroundservice (water pipes, electricity cables, gas pipes, telephone,..).
7. Water supply and consumption study.8. Identification of industrial, commercial institutional and domestic
areas.
9. Identification of collection points of sewage and possible locations ofpumping stations and point of final collection.
10. Population forecast studies.11. Expected Development of the area (Master planning).
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Design of W.W. Collection System
Design criteria:
Data needed::Estimation of the design flow Qdes
Average daily water consumption per capita for domestic areas (L/c/d), (Qavg).
Average daily water consumption per capita for institution ( school, offices,.etc. ), (Qavg).
Average daily water consumption for commercial and industrial areas.
Infiltration, inflow:
Qinfil is taken as [24-95 m3/day/km] or [0.5 m3/day/diamter (cm)], take the
bigger value of the two.
Qinflo is taken as 0.2-30 [m3/ha/day]. ( hectare = 10,000 m2 )
Qdes = Qmax + QI/I ( if found) QI/I = Qinfil + Qinflo
Qmax = [0.80* Qavg] * P ( 0.8 > 80% return from water supply).
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- P : peak factor for domestic wastewater can be calculatedfrom one of the following formulas :
PfP 4
14
1 , ( P: population in thousands)
Or167.0
5
Pf
P
The minimum domestic wastewater flow (Qmin) is necessary to checkfor the minimum velocity in the sanitary sewers, it is estimated from
the following formula:
WavgQPQ
*6
1
2.0min
A typical value ofWavg
3
1min
Note:[Qavg]w= 0.8 Qavg, which isthe average domestic wastewaterproduction , while Qavgis theaverage water consumption.
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Materials used for pipes:Sewers are made from:1- Concrete2- Reinforced concrete3- Vitrified clay
4- Asbestos cement5- Cast iron (lined with cement).6- Ductile iron (lined with cement).7- Steel (lined with cement).8- PVC, UPVC9- GRB (fiber glass).
Factors effecting the selection of materials:1- Chemical characteristics of wastewater and degree ofresistance to acid, base, solvents,2- Resistance to scour and flow (friction coefficient).3- External forces and internal pressures.
4- Soil conditions.5- Type of backfill6- Useful life7- Strength and water tightness of joints and effectivecontrol of infiltration and inflow.8- Availability in diameter, length, and ease of installation.9- Cast of construction and maintenance.
How to select the Pipes Materials?
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How to measure the Strength of pipes:The crushing strength of sewer pipes is determined by the three-edge bearing test. The pipe
is stressed until failure occurs. Table (3) gives the minimum crushing strength for claypipes.
Strength requirements for reinforced concrete pipes are given in table 4, for this table the
crushing force correspond to 0.25mm crack. The values in the table are pre mm diameter,thats why they are called D-Loads (KN/m.mm)
The pipe strength in supporting loads dependson the method of pipe bedding :- Class (D) bedding support the three bearing load only.- Class(C) support (1.5) the three edge load (1.5 = Load factor)
- Class (B) bedding has a load factor of 1.9.
- Class (A) bedding has a load factor of 2.3 to 3.4.- Other pipe material has similar tables to estimate their strength
The three- edge bearing test
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The Objectives of storm water drainage
To prevent erosion in hillside areas (paved roads and terracing are needed)
To prevent land-slides
To improve the hygienic conditions with regard to the conveyance of wastewater
To limit inconvenience to people and traffic
To limit damage to unpaved roads
Prevent damage to housing, in case the elevation of ground floor is below streetlevel.
Collection for reuse purposes, Agriculture use, domestic use and recharge the aquifer
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What type of Information are needed for the design of storm waterdrainage system
1. Metrological and hydrological data
Rainfall intensity
Storm duration and occurrence
2. Topographical data
Boundaries of the catchments areas
Point of collection
3. Classification of catchments areas
Industrial, domestic, ..
Build up areas (run-off coefficient)
4. Soil investigations
Permeability (run-off coefficient)
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Methods of Run-off Computation
Rational method
Q = C i AWhere;
(Q = is the run-off in (m3/hr
C = is the Run-off coefficient
i =is the average rainfall intensity in (m/hr)
A =is the drainage area in (m2)
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Runoff Coefficient (C)
CoefficientDevelopment
0.9Pavement,
Road/Parking
0.7Commercial /
Public lots
0.6Residential
Communities
0.3Parks /
UnimprovedAreas
0.2Irrigation Areas
0.05Natural Zones
Only a part of the precipitation upon a catchments area will appear in theform of direct runoff.
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To prevent groundwater pollution
To prevent sea shore
To prevent soil
To prevent marine life
Protection of public health
To reuse the treated effluent
For agriculture
For groundwater recharge
For industrial recycle
Why do we need to treat wastewater ?
Solving social problems caused by the accumulation of wastewater
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Wastewater treatment methods
Chemical
Sedimentation GasTransfer
FiltrationFlocculation FlotationMixingScreening
BiologicalPhysical
Aerobic Anaerobic
Precipitation Adsorption Disinfection
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Biological waste water treatment
Classification of biological Waste water methods
Aerobic and anaerobicSuspended and attached treatment
Aerobic: biological treatment is a process inwhich the pollutants in the waste water(organic matter) are stabilized bymicroorganisms in the presence ofmolecular oxygen
Anaerobic: biological treatment is a process
in which the pollutants in the waste water(organic matter) are stabilized bymicroorganisms in the absence of molecularoxygen
Suspended growth process is a biological w.w.tin which microorganisms are maintained insuspension while converting organic matter togases and cell tissue (Activated sludge).
Attached growth is a biological w.w.t in whichmicroorganisms responsible for the conversion
of organic matter to gases and cell tissue areattached to some innert material such as rocks,sand, or plastic (Trickling filter).
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Many treatment systems based on suspended microorganisms have been
developed and still used till now.
Some of these systems are aerobic and other are anaerobic.
Some of the most commonly used systems are:
Conventional activated sludge system
Oxidation ditches
Sequential batch reactor (SBR)
Aerated lagoons
Waste stabilization ponds
Up flow anaerobic sludge blanket (UASB)
Suspended growth
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"Examples of Attached growth system:
Many types of this system has been developed:
Trickling filters( biological tower ). Rotating biological contactors( RBC ). Packed bed reactors Fluidized bed biofilm reactors.
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Parameter
(mg/l)
Wastewater characteristics
North
area
Gaza Rafah
BOD 728 667 777
COD 1385 1306 1399
SS 663 617 540
Wastewater characteristics in Gaza Strip (PWA,2003)
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The existing treatment systems in the Gaza Strip
Anaerobic Lagoons
Aerated lagoons
Trickling filters
Maturation Ponds
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1998
Existing WWTP
proposed WWTP
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Potential areas for Wastewater reuse
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Parameter Palestinian Standards
Irrigation Recharge
BOD (mg/l) 20-60 20
TSS (mg/l) 30-90 30
TDS (mg/l) 1500 1500
EC (ms/cm) - -T-N (mg/l) 45 100
Na (mg/l) 200 230
Cl (mg/l) 500 600
SAR 9 -
B (mg/l) 0.7 1
F. Coliform (MPN/100ml) 200-1000 200-1000
Nematodes (ovum/l)