Sanitary Engineering1

8/2/2019 Sanitary Engineering1

1/24

Important Topics in Sanitary

Engineering

By

Husam Al-Najar

Environmental Engineering Department-The Islamic University of Gaza

http://site.iugaza.edu.ps/halnajar/courses/


2/24

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


3/24

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


4/24

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.


5/24

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).


6/24

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).


7/24

- 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

QQ

3

1min

Note:[Qavg]w= 0.8 Qavg, which isthe average domestic wastewaterproduction , while Qavgis theaverage water consumption.


8/24


9/24

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?


10/24

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


11/24

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


12/24

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)


13/24

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)


14/24

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.


15/24

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


16/24

Wastewater treatment methods

Chemical

Sedimentation GasTransfer

FiltrationFlocculation FlotationMixingScreening

BiologicalPhysical

Aerobic Anaerobic

Precipitation Adsorption Disinfection


17/24

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).


18/24

18

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


19/24

"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.


20/24

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)


21/24

The existing treatment systems in the Gaza Strip

Anaerobic Lagoons

Aerated lagoons

Trickling filters

Maturation Ponds


22/24

1998

Existing WWTP

proposed WWTP


23/24

Potential areas for Wastewater reuse


24/24

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)

Documents

Sanitary Engineering1