The Sewerage System In Malaysia Construction Essay

Sewerage systems are one of the most important infrastructures in construction of residential, industrial or commercial project as it determines the quality of life enjoyed by a community. It consists of a network of underground sewer pipes, pump stations, sewage treatment plants and sludge treatment facilities. This system usually operates based on by gravity due to the slope of the pipe which reduces the high cost required for pumping.

Sewers are further classified into a few categories, which depend on the type of wastewater that each of it carries. For example, storm sewers are designed to carry stormwater from roofs, paved areas, pavements and roads; industrial sewers are designed to carry wastewater generate from the industry; sanitary sewers are designed to carry the waste water from cooking and washing and the wastes from toilets. There is another type of sewer which is known as combined sewers. These types of sewers are designed to carry stormwater, industrial wastes, and domestic sewage. In Malaysia, many towns and cities use the separate sewer system. The wastewater is transported in separate pipes from storm sewers, industrial sewers and sanitary sewers. This system will not experience CSOs (Combine Sewer Overflows) which usually happen to combined sewer. The flooding will cause by stormwater only.

Sewerage system is very important as it helps people to transport the wastes or sewage away from their places. Therefore, the system must be functioning well because improper functioning system will lead to pollution and contamination of various aspects of our surrounding which affect human life and health. Hence, regular maintenance must be done to the existing sewerage system and appropriate design must be applied to the new sewerage systems to ensure the sewerage systems are in good condition.

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The efficiency of the sewerage system is affected by the flow of the wastewater. In designing a sewerage system, the type and size of the pipe to be used must be able to accommodate the peak flow. The peak flow is based on the population equivalent which is a direct measurement of the population in an area. When designing the sewerage, there is a standard and criteria that should be followed. The standard code of practice for sewerage design in Malaysia (MS 1228:1991) was adopted from British Standard; BS 8005:1987. However, British Standard may not be as applicable to Malaysia due to the season and climate factor which have direct effect on the peak flow. This is the main reason of doing this research to find out whether the standard is suitable to be used in Malaysia.

Problem Statement

Any sewerage system will be designed to carry a certain amount of sewage based on the population equivalent (PE). In sewerage design, the per capita flow and the peak flow rate (Qpeak) are important parameters. Based on British Standard, the per capita flow is 225L/day/person and the peak flow factor, K is 4.7. However, a previous study indicated lower per capita flow and peak flow factor in the sewerage system in Malaysia although no conclusive results were obtained (Dayalan, 2007). A lower peak flow factor will result in smaller pipes which will incur lower cost. Therefore, further research is needed to study the suitability of current design criteria for sewerage system located in tropical climates.

1.3Research Objectives

The objectives of the study are:

To obtain flow data from pre-determined sewer tributary area.

To evaluate the parameter in the peak flow factor equation for medium scale sewerage catchment system.

To determine the relationship between population of an area to the peak flow of sewerage system.

1.4 Scope of Research

To collect relevant information of sewerage design from selected literatures.

To find out relevant formula provided in selected codes for sewerage design.

To study the peak flow factor in sewer line that serve the PE value of 1000-10000.

To measure flow characteristics by using flow meter with build-in sensor in manholes at Tropicana Indah.

To compare the results obtained with the formula in the standard code.

To make recommendation on the feasibility of the code formula to tropical climate.

CHAPTER 2: LITERATURE REVIEW

2.1 Sewerage System in Malaysia

The sewerage system is designed to collect wastewater or foul sewage generated from residential, industrial and commercial areas through sewer pipes and discharges it to the treatment plants or facilities to ensure the sewage is released to the natural water bodies in an appropriate condition and quality (Geoffrey, 2004). In Malaysia, sewerage systems range from simple toilet with little or no treatment provided to modern sewage treatment plants that treat the sewage to the desired quality accordance to environment standard. There are two main types of sewerage system in Malaysia. A premise sewerage system is either connected to a public sewage treatment plant or an individual septic tank. Indah Water Konsortium (IWK) is responsible to provide service and maintenance to public sewage treatment plants and all the underground pipes and also provide desludging services to individual septic tanks (Abd Aziz, 2006).

IWK decided to divide the underground pipe into two sections, public pipe and private pipe (Figure 2.1) to make sure that all underground pipes operate without any problem. Public pipe is under the responsibility of IWK and the private pipe is under individual responsibility. An individual have to pay for the IWK services when the private pipe need for servicing. (Abd Aziz, 2006).

http://www.usj23.com/planet_free/sewage_system/Sewage%20System.jpg

Figure 2.1 Flow of wastewater from private pipe to public pipe (USJ 23 Residence

2.2 Transportation of Wastewater

Wastewater is usually transported through sewer pipes that are connected to the sewer mains by clay, cast-iron, or polyvinyl chloride (PVC) pipes that range from 80-100mm diameter. The large sewer mains can be located about 1.8m deep or more than that along the centerline of a street or pathway. The small and large sewer pipes are made by different material, in which the smaller sewer pipes are made of clay, concrete, or asbestos cement, and the large sewer pipes are made of reinforced concrete construction. The flow of wastewater is different from water-supply system. The water supply is transported to each house by the application of pressure. However, the wastewater from each house is flows through sewer pipes by gravity. Therefore, the sewer pipe must laid on slope surface to allow the wastewater to flow at a velocity of at least 0.8m/s and not more than 4m/s. (MS1228:1991). If the wastewater flows at velocity lower than 0.8m/s, the solid material tends to settle in the pipe which will lead to blockage. Storm-water mains have similar structure as sanitary sewers but they have a much larger diameter than sanitary sewers. In certain places, the urban sewer mains are connected to interceptor sewers, which can then join to form a trunk line. The trunk line will then discharge the wastewater into the wastewater-treatment plant. This transportation process is shown in Figure 2.2. As the interceptors and trunk lines will carry the wastewater discharge from sewer main, they are usually made of brick or reinforced concrete which can carry more load than the other pipe. Sometimes, they are large enough for a truck to pass through them. (Norhan Abd Rahman et.al, 2007)

http://techalive.mtu.edu/meec/module21/images/CombinedSewer.jpg

Figure 2.2 Transportation of Wastewater (Michigan Environmental Education Curriculum,

Wastewater Treatment)

2.3 Concept & Theory

In designing a sewerage pipe network, the pump stations and sewage treatment plants are required to carry and pump volumetric flow rate. The flow rates are usually measured in cubic meter per second (m3/s) and need to be calculated for both existing land use and for expected future development. There are two parameters that are used to calculate expected flow rates. One of the parameters is per capita flow. This per capita flow of 225L/person/day is an average daily flow, which means a person will produce 225 liters of sewage in a day. Another design parameter named “population equivalent” (PE) of a catchment can also be used to calculate the flow rate. PE is not a measure of population. However, it is used to measure the estimated number of people that use the sewage facilities. In residential areas, the PE is a direct measurement of the population in an area which is calculated as five per dwelling. The PE has a different method of measurement in commercial area. It is calculated from the floor area and this PE value is considered to be proportional to the number of people using a premise during the day which does not reflect the population living in an area.

2.4 Quantity for Wastewater

2.4.1 Tributary Area

Tributary area is an area from where the wastewater is being transported to a particular sewer section. The types of activities in that area determine the quantity of wastewater being collected by a particular section. A survey has to be done when there is no information available on existing areas in order to determine the number and classification of persons and the types of industries. (Guyer, 2010)

Table 2.1 shows the method of calculating the PE.

Table 2.1 Equivalent Population, PE (MS1228:1991)

No.

Type of Premises/Establishment

Population Equivalent (recommended)

1

Residential

5 per unit

2

Commercial:

(include entertainment/recreational centres, restaurants, cafeteria, theatres)

3 per 100m gross area

3

School/Educational Institutions:

– Day schools/institutions

0.2 per student

– Full residential

1 per student

– Partial residential

0.2 per student for non-residential student and 1 per student for residential student

4

Hospitals

4 per bed

5

Hotels (with dining and laundry facilities)

4 per room

6

Factories (excluding process wastes)

0.3 per staff

7

Market (Wet Type)

3 per stall

8

Petrol kiosks/Service stations

18 per service bay

9

Bus terminal

4 per bus bay

2.4.2 Sanitary/Domestic Wastes

2.4.2.1 Contributing Population

In designing the flow, the population to be used depends on the location of the sewer. The design population in a residential area is based on the number of houses served. However, the design population for an industrial area is the maximum number of staff ever employed. The design population for sewers that serve both residential and industrial areas include residents and non-residents. Designing of these sewers denote that no person should be counted more than once. Allowances should be made for future population changes caused by master planning projections and facility personnel requirements. (Guyer, 2010)

2.4.2.2 Average Daily Flow

The average daily flow is counted by multiplying the population equivalent from resident and non-resident with the appropriate per capita flow and adding the two flows generated from both resident and non-resident. The average daily flow shows the total volume of waste generated over a 24-hour period. It cannot be used for wastes that were generated over shorter periods of 8, 10, 12 hours, etc. Therefore, it can only be used for designing sewers that generate wastewater over a 24-hour period (e.g. residential area). In Malaysia, the average daily flow for residential area is usually taken as 225L/person/day. In industrial areas, the average daily flow is taken as 115L/person/day as non-resident personnel and employees is working for 8-hour shifts. These quantities are usually used in designing wastewater treatment facilities. However, they are also used for sizing interceptors, trunk sewers and pumping stations serving large portions of the installation. (Guyer, 2010)

2.4.2.3 Average Hourly Flow Rate

Average hourly flow rate is used for designing sewers that serve small areas of the installation (e.g. industrial area), where most of the wastewater is generated by non-residents or other short term occupants. The average hourly flow rate is counted based on the actual period of waste generation. For example, 1000 non-residents with an average daily flow of 115L/person/day would generate 115,000 liters in 8 hours which is equivalent to an average hourly flow rate of 14,375 L/h or 345,000 L/d. However, the average daily flow would still be 115,000 L/d. Therefore, the sewer must be designed hydraulically to carry 115,000 liters of waste in 8 hours instead of 24 hours (Guyer, 2010). If the sewer is designed to carry a waste of 115,000 liters in 24 hours, then the sewer pipe will not be able to transport the wastes as the actual volume of wastes generated is more than the design waste. This will lead to the blockage of sewer pipes and overflow in the toilet.

2.5 Design Wastewater Flow

The design flow of wastewater must be determined for any section of a proposed sewer. The design flow is not only based on sanitary sewage; industrial flows, inflow and infiltration must also be taken into account. The following shows the equation to determine the peak flow factor and the factor to be considered in sewerage design.

2.5.1 Design Equations

The peak flow required to design sewers, pumping station and treatment facilities are calculated by the following equation:

Peak flow factor = 4.7 x p-0.11

p – Estimated equivalent population, in thousand.

The sewers are designed based on peak flow to ensure that the sewer pipes would be able to accommodate the wastewater generated at any time.

2.5.2 Factors Affecting Sewer Design

In designing sewers, there are a few factors as stated in MS1228:1991 that must be taken into consideration:

Economy in the design

The sewers should be kept as short as possible and avoid unproductive lengths.

Shallow rider sewers can be laid under highways having expensive foundations and surfaces to receive the local house connection, and to connect the riders at convenient points into the main sewers.

Location of sewers

The sewers should be placed within streets or right-of-way to ease the maintenance work.

If topography dictates, the sewer is to be located within private properties, and provide adequate access for maintenance purposes.

Location or the position of other existing or proposed service lines, building foundation, etc for maintenance purposes.

A minimum at 3 m horizontal and 1m vertical separation from the water main should be provided to avoid the sewage from entering the water main.

The impact of sewer construction and subsequent maintenance activities towards road users.

Hydraulic Design

The sewers should be laid at such gradients to produce adequate velocities to convey the solid matter. The gradient should produce a minimum velocity of not less than 0.8 m/s and a maximum velocity of not more than 4.0 m/s to avoid scouring of sewer by erosion action of suspended solid.

Structural Design

The depth of sewers must be adequate to accommodate the sewage from existing and future properties. The minimum depth should be 1.2 m.

The minimum size of the sewer should be 200 mm in diameter in order to convey raw sewage.

Straight alignment and uniform gradient between consecutive manholes should be laid for sewers of 600 mm or less in internal diameter while curves can be laid for sewers of larger than 600 mm internal diameter.

Flexible type and watertight joints should be provided between sewers, sewer manhole or other appurtenance structure to avoid infiltration and breakage due to differential settlement.

The foundation should be able to maintain the pipe in proper alignment and carry the weight of soil above the sewer and any other superimposed load.

Service Connection

The diameter of the connection must be adequate enough to prevent blockage problems.

The sewer must have a minimum gradient of 2%.

The minimum size of the connection should be 150 mm.

Tee junction should be used to connect service connection to the main sewer.

2.5.2.1 Gravity Sewer Design

Sewers are designed to convey the wastewater flows as required. Generally, it is not recommended to design the sewers for full flow, even at peak rates as the chances for problem arising are high. The flows that cover above 90% to 95% of full depths are considered unstable which may lead to sudden loss of carrying capacity with surcharging at manholes as shown in Figure 2.2 (Guyer, 2010). Surcharging means that the pipe that is designed to flow full or partly full, is now transporting the flow under pressure. When the flow exceeds the design capacity, there will be surcharge in the manholes (David and John, 2011). Besides that, large trunk and interceptor sewers laid on flat slopes experience less fluctuation in flow. If it is designed to flow full, the sewers may lack sufficient air space above the liquid for proper ventilation. Ventilation in sewer is important in preventing the buildup of explosive, corrosive or odorous gases, and for reducing the formation of hydrogen sulfide. Thus, the depth of design flow for trunk and interceptor sewers should not exceed 90% of full depth; laterals and main sewers, 80%; and building connections, 70%. Regardless of flow and depth, the minimum sizes of sewer pipes to be used are 150 mm for service connections and 200 mm for all other sewer types. The sewer pipes for service connections are usually smaller than 150 mm as they only convey liquids with little or no solids (e.g. condensate lines). A condensate line of more than 100 mm is recommended for most situations. Same design criteria as sanitary sewers can be applied to industrial application except pipe material that is resistant to the waste are to be specified. (Guyer, 2010)

Figure 2.2 (a) Part-full pipe flow without surcharge

(b) Pipe flow with surcharge (David and John, 2011)

2.6 Pipe Materials for Gravity Sewer

There are many types of material which can be used for sewerage construction. However, the type of materials that we choose must depend on its life expectancy, previous local experience, roughness coefficient, structural strength and local availability. Table 2.2 shows the common materials that are suitable for sanitary sewers. Sewer pipes made by different material have different diameters and lengths.

Table 2.2 Pipe Materials for Gravity Sewer

Types of Pipe Material

Length (m)

Diameter (mm)

Pipe Joints

Vitrified clay pipe (VCP)

0.6 – 1.0

100 – 300

Flexible

Reinforced concrete pipe

< 375mm diameter

1.83

150 – 3000

Spigot & socket type with rubber rings

> 375mm diameter

3.05

Fabricated steel with sulphates resistance cement lining

9

100 – 1500

< 750mm diameter

Spigot & socket, flange and mechanical

> 750mm diameter

Welded joints

Cast iron

3.66

Vary

Flange and spigot & socket type

Asbestos cement pipe

4

100 – 600

Plastic pipe

6

110 – 630

Spigot end and socket type with rubber seals, jointing by flanges, welding and solvent cementing

Other material

CHAPTER 3: RESEARCH METHODOLOGY

3.1 Introduction

In this research, a field work will be conducted to get the information that will be used to reach the objectives of this research.

3.2 Preliminary Works

This is the initial works that has to be done before conducting the field work at site. It includes information gathering on the topic of sewerage design and self-study on similar and related topics in order to learn more.

3.2.1 Information Gathering

A series of books, articles and online information has to be studied to obtain information on the topic of sewerage design. Sources for sewerage design mostly come from abroad. However, the information on the method to evaluate the design criteria is obtained from related research by a local university.

3.2.2 Standard Code of Practice for Design and Installation of Sewerage Systems

(MS1228:1991)

With the reference to this code book, the design criteria and the factors to be considered for sewerage design is obtained. The equations to calculate the peak flow which depend on the population equivalent are all available in this standard code of practice.

3.3 Site Work

A site has been identified for the field work data collection. The location of this site is in Tropicana Indah. Approval is still pending from IWK for access to their manholes.

3.3.1 Flow Characteristics Measurement

The flow characteristic of a section of sewerage pipe systems can be measured by using a flow meter. This flow meter is provided with sensor which will automatically record the flow, velocity and water height at a specific time interval, which in this case is 5 minutes. Once the measurement is completed, the data from the flow meter will be linked to a computer that has Flowlink4 software. This software would aid the plotting of graphs for the 3 parameters (flow, velocity and height) as well as transfer of data to other software. From the data, the maximum and minimum hourly flow rate can be obtained. The average flow rate can be used to calculate per capita flow.

Flow per capita = Average daily flow (m3/day) / Total population equivalent (PE)

= m3/day/person

The evaluation of peak factor and per capita flow for sewerage can also be done through the data obtained from field experiment. The equations that are used for sewerage design are as follow:

a. Peak flow factor = 4.7 Ã- p-0.11

b. Average daily flow = Flow per capita Ã- PE

= m3/day

c. Peak domestic flow = Peak flow factor Ã- Average daily flow

= 4.7 Ã- p-0.11 Ã- Flow per capita Ã- PE

= m3/day

From MS 1228:1991, the ‘p’ value is an estimated PE in thousands and the average flow per capita is 225 L/day/person.