SEWERAGE AND URBAN DRAINAGE

MIDTERM REVIEW

WASTEWATER ENGINEERING

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Mirror image of water supply utilities

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collect, send, treat, dispose

Wastewater systems _______,__ ________,__ _________,__ and ________ of water supply.

ENVIRONMENTAL ENGINEER

Responsible to supply safe water, to effectively remove the waste from the dwellings and preserve the quality of all natural water bodies.

SANITARY ENGINEER

Has an important role in reducing the damage, by way of suggesting and implementing suitable methods of treatment before their disposal into the natural water sources.

SEWAGE

Spent/used water.

Domestic, Industrial, Infiltration/ Inflow, and Storm water

Classification of Sewage

DOMESTIC SEWAGE

Sanitary sewage: liquid waste coming from residential areas.

RESIDENTIAL DISTRICT

The largest flow come from single family houses and has about 60-90% of domestic water-withdrawal rate.

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COMMERCIAL DISTRICT

Estimates for commercial wastewater flows range from 7.5 to 14 cu. m per hectare/day.

INDUSTRIAL SEWAGE

Discharge from industries (manufacturing/chemical process)

7\.5 to 14 cu. m/ha-d

Typical design value in estimating the flows in light industrial development

MEDIUM INDUSTRIAL DEVELOPMENT

Typical design value of 14 to 28 cu. m/ha-d in estimating the flow of industrial sewage

INFILTRATION

Water entering a sewer system, does not include inflow.

INFILTRATION

Examples of this is groundwater that seeps into the sanitary sewer through cracks/joints.

INFLOW

Water discharged into a sewer system.

INFLOW

Examples of these are rainwater that enters a sewer system through holes in utility access hole covers, catch basins, or improper plumbing connection

STEADY INFLOW

Not distinguishable from infiltration when hydraulic measurements are taken in the sewer.

STEADY INFLOW

Includes water from basement and footing drains.

DIRECT INFLOW

Type of inflow that cause an almost immediate increase in wastewater flows.

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DIRECT INFLOW

Sources includes roof downspouts, basement yard, and area drains, drainage.

STEADY INFLOW AND DIRECT INFLOW

The two types of inflow.

STORM WATER

Runoff from rainfall and snow melt

STORM WATER

Resulting mixture of sewage and storm water are critical to the receiving bodies of water.

STORM WATER

Drainage from streets, pavement, open areas, and rooftops during storms.

SEWERAGE

An infrastructure that conveys sewage or surface runoff.

SEWERAGE

Encompasses components such as receiving drains, maintenance holes, pumping station, storm overflow, screening chambers.

SEWERAGE

Describes the system of pipes, pumping station, and appurtenances.

SEWERAGE

Collection and transport part of wastewater engineering

INTEGRATED SEWERAGE SYSTEM

The Philippines currently practices the conventional septic tank system, what would be practiced due to possible scarcity of clean groundwater/ aquifer resources?

SANITARY SEWER AND STORM SEWER

Types of Sewer System according to type of sewage

SANITARY SEWER

Transport domestic and industrial waste by gravity flow to treatment facilities.

STORM SEWER

Surface water enters a storm drainage through inlets located in street gutter/ depressed areas.

SEPARATED SYSTEM, PARTIALLY SEPARATED SEWERAGE SYSTEM, COMBINED SEWERAGE SYSTEM

Types of sewer system according to system.

SEPARATED SYSTEM

Sanitary sewage and storm water are carried separately in two sets of sewers.

SEPARATED SYSTEM

Sewage is conveyed to wastewater treatment plant (WWTP)

SEPARATED SYSTEM

Storm water is discharged to rivers without treatment.

SEPARATED SYSTEM

Suitable when separate outlet for storm water is available and topography is such that storm water can be disposed of in natural drains.

SEPARATED SYSTEM

System with one for collection and conveyance, one for storm water.

SEPARATED SYSTEM

This system is for:

* Flat topography
* Treating of sanitary sewage only, and storm water is not treated.
* Not high magnitude of frequency and intensity of storms.
* Rock cutting requirements of sewer laying.
* Not enough financial position to have large, combined sewers

SEPARATED SYSTEM

Load on treatment plant is less (only sewage is carried on plant).

SEPARATED SYSTEM

Size of sewer is small, thus, economical.

SEPARATED SYSTEM

CONS

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* Difficult to clean due to size
* Self-cleansing velocity is not obtained.
* Storm sewers operates in rainy season only.
* Maintenance cost is high
* Sewage sewers are provided below storm sewer causing greater depth and pumping at WWTP

PARTIALLY SEPARATED SYSTEM

System compromised between separated and combined system taking advantages of both.

PARTIALLY SEPARATED SYSTEM

Sewage and storm water of building are carried by one set of sewers while storm water from roads, street, pavements are carried by other system of sewer usually open drains.

PARTIALLY SEPARATED SYSTEM

PROS

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* Combines good feature of both systems
* Silting is avoided due to entry of storm water
* Storm water from houses is easily disposed off
* Sewers are of reasonable size

COMBINED SEWERAGE SYSTEM

Sewage and storm water are carried combine in only one set of sewers to the WWTP before disposal

COMBINED SEWERAGE SYSTEM

This system is for:

* Systems needed when pumping is required.
* High population density
* Systems with existing storm sewer
* Evenly distributed rainfall during the whole year.

COMBINED SEWERAGE SYSTEM

Advantage of this system includes:

* Easy cleaning because of large diameter
* Reasonable maintenance cost
* Strength of sewage is reduced due to dilution of sewage by storm water
* System only requires only one set of sewers thus economical.

COMBINED SEWERAGE SYSTEM

Disadvantages of this system includes:

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* Sewer may overflow in storm season; sewer may damage causing health risks
* Get silted and becomes foul in dry days
* Load on treatment plant is more because of storm water
* Storm water gets polluted unnecessarily
* System become uneconomical when pumping is needed.

SUSPENDED, COLLOIDAL, OR DISSOLVED

Different types of impurities in wastewater may be ________,__ ________, or__ ___________ in nature.

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FACTORS OF RELATIVE IMPORTANCE OF COMPONENTS

1. Location
2. Diet of the population
3. Presence of industrial and trade effluents
4. Type of collection system
5. Condition of the collection system

DOMESTIC WASTEWATER

Generated primarily from residential properties; includes contribution from institution and recreational facilities.

WASTEWATER

Main liquid waste of community.

FLOW QUANTITY

The defining variable is water consumption, linked to human behavior and habits.

1. Climate
2. Demography
3. Socio-economic factors
4. Development type

FACTORS AFFECTING MAGNITUDE OF PER CAPITA WATER DEMAND

Water closet flushing, personal washing, food/ drink preparation

Three main areas in homes where water is used.

EFFLUENT

Often result from the following:


1. Sanitary (washing, drinking, personal hygiene)
2. Processing
3. Cleaning
4. Cooling

WASTEWATER

Contains a complex mixture of natural organic and inorganic material present in various forms.

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POLLUTANT SOURCES

The following are ____________:


1. Human Excreta
2. Toilet
3. Food
4. Washing/ Laundry
5. Industry

* Availability of palatable and potable water
* Removal, treatment, and disposal of all the waste produced.
* Improved sanitation of overall environment.

WHY IS THERE A NEED FOR SEWERAGE SYSTEM?

DRY WASTE

Waste generated from all sorts of activity namely residential, commercial, and industrial which are dry in nature.

REFUSE

If nature of waste is mostly inorganic, and partly organic it is called _______________.

GARBAGE

Mostly organic waste

0\.1 to 0.2 kg/ capita

Quantity of refuse and garbage per capita

Collection, Conveyance, and Disposal

Three main aspects of Sanitary Engineering

COLLECTION

Includes collection of wastewaters by plumbing system.

CONVEYANCE

Transport through an under-group pipe

DISPOSAL

At the outskirts, water is treated to make it harmless and then disposed off.

CONSERVANCY SYSTEM AND WATER CARRIAGE SYSTEM

Two methods of Sanitation

CONSERVANCY SYSTEMS

Also known as Dry System

CONSERVANCY SYSTEM

Different type of wastes is collected separately and transported manually.

CONSERVANCY SYSTEM

Method of sanitation where waste is disposed-off by composting methods.

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WATER CARRIAGE SYSTEM

Waste from water closets is collected by flushing with water, this water is used to transport waste to treatment works by a system of pipes.

WATER CARRIAGE SYSTEM

Hygienic, but costly; Waste strength is reduced by dilution and waste becomes amenable for treatment.

1. PERPENDICULAR
2. INTERCEPTER
3. ZONE PATTERN (*Zone wise)*
4.  FAN PATTERN
5. RADIAL PATTERN

Five patterns of sewerage layouts

PERPENDICULAR

If storm water drains are laid through shortest route to the existing surface water courses.

INTERCEPTER

Collect the sewage from all the main sewers and transport it either to a treatment plant or natural water course at a downstream point.

ZONE PATTERN

Entire area is divided into zones of different elevations. Sewerage system is provided for each zone separately and separate interceptors are laid to collect the flow.

FAN PATTERN

Flow is collected from outward to inward, to a central trunk sewer.

RADIAL PATTERN

Wastewater is collected from heart of the city to outside periphery by two or three trunk-sewers. Laid radially to the area to be serve; suitable when the city is developed in two or more directions in an elongated patter from the heart of the city.

QUANTITY OF SANITARY SEWAGE

Expressed as liter per day (l/d) or cubic meter per second ( cm­­3­/s)

DRY WEATHER FLOW (DW)

The flow of only sanitary sewage in the absence of storms in dry season.

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DRY WEATHER FLOW (DWF)

Defined as population x per capita rate of sewage contributed per day

Residential Areas (Detached Houses)

Population density of 100-250 person/ ha.

Multistorey Apartment

Population density of 500-1000 persons/ha.

Mercantile Areas

Population density of 30-70 persons/ha.

Industrial Areas

Population density of 15-30 persons/ha.

1. POPULATION
2. TYPE OF AREA
3. RATE OF WATER SUPPLY
4. GROUND WATER INFILTRATION

Dry Weather Flow depends on:

QUANTITY OF STORM WATER

A portion of rainfall that falls on the ground is lost as evaporation and percolation. The remaining flows over the ground surface as storm water.

1. Health of inhabitants
2. Traffic Safety
3. Safety of structures
4. Aesthetic reasons

Reasons to remove storm water

1. Intensity and duration of rainfall
2. Time of concentration
3. Impervious factor
4. Catchment area

Quantity of Storm water depends on:

SEWER APPURTENANCES

Various accessories on the sewerage system necessary for the efficient operation.

MANHOLES

Openings of either circular or rectangular in shape constructed on the alignment of a sewer line to enable a person to enter the sewer for inspection, cleaning, and flushing.

MANHOLES

Objectives of this is to:

* Permit inspection, cleaning, and maintenance
* Allow joining of sewer, changing directions, or both.
* Serves as ventilators, by provisions of perforated covers.
* Facilitate the laying of sewer lines in convenient length.

1. At all junctions of two or more sewers
2. Whenever diameter sewer changes
3. Whenever direction of sewer lines changes
4. When sewers of different elevations join.

Where are manholes to be located?

45 meters

Spacing interval of manholes with diameter up to 300 mm

75 meters

Spacing interval of manholes with diameter of 301-500

90 meters

Spacing interval of manholes with diameter of 501-900 mm

Beyond 900 mm

Any spacing interval depending upon local conditions are applicaple to manholes with diameters _________.

DESIGN PRINCIPLES

The following are __________________ of a manhole:

* Stable, and must be capable of withstanding loads coming over it.
* Capable of allowing sewage to flow smoothly from incoming sewer to outgoing sewer without blocking.
* Cross-section of sewer within the manhole must be U shaped.
* Channel is of semi-circular shape up to half the diameter of sewer; remaining upper half of the wall are vertical.
* Benching is provided on either side
* If sewer joins 2 main-sewer at 90 deg., should be curved, downstream.
* Maximum distance between two consecutive manholes should not be greater than 30 m for small sewers, 100 m for large sewer.