Luận văn development of a simplified concept for process benchmarking of urban wastewater management

LIST OF FIGURES AND TABLES Figure 1.5 Schematic of trickling filter with rock packing and plastic packing Figure 2.1 Main swps of a beachmarking process Figure 2.2 Extended process model

DRESDEN UNIVERSITY OF TECHNOLOGY VNU UNIVERSITY OF SCIENCE

SUPERVISOR: PROF, DR RER NAT DR H.C PETER WERNER

MSC-ENG PHAN HOANG MAL

Hanoi - 2011

Theoretical Foundations of Lrban Wastewater Management System

11 Characteristics of Urban Wastewater

1.1.1 What ig Urban Wastewater?

1.1.2 Constituents of Wastewater

1.2 Overview of the Urban Wastewater Management System

1.2.1 Components of Urban Wastewater Management System

1.2.2 Types of Wastewater Management System

1.3 Sub-pracesses of Wastewater Management System

13.1 Collection Systems

1.3.2 Wastewater Treatment

1.3.3 Sludge Treatment and Disposal

13.4 lifflnent Disposal and Reuse

1.4 Current situation of Urbun Wastewater Management in Vietnam

1.4.1 The Development of the Urban Drainage System

1.4.2 Current Structure and Operation of Urban Drainage Sysleus

1.4.3 The Organizations of Urban Drainage Services in Vietnam

1.4.4 Kinancial Aspects af Urban Drainage Companies

1.4.5 Logal and Institutional Fuemecworks -

1.4.6 Investment and Management of Usban Drainage System

2.1.2 Types and clements of benclumarking se

2.2 International Benchmarking System in Water Industry

2.2.1 Benchmarking of lage Municipal Wastewaler Treatnent Plants in

Benchmarking in Canada North European Benclunarking Co-operation

2.3 Process Benchmarking in Wastewater Sector

2.3.1 What is Process Benchmarking’

2.3.2 The Objectives of Process Benchmarking

2.3.3 Methodology in Process benchmarking, -

3.3.4 Diftrent Process Bencluuraking Concepla

Performance Indicators of Benchmarking in Wastewater Service

3.1 Basis of Performance Inuicators

3.1.1 Systems of Performance Indicators

3.1.2 The Usage of Performance Ludivaters (PIs)

3.1.3 Performance Indicators A component of ‘Benchmarking

3.2 The System of IWA-PIs for Wastewater Services

4.1 Approach of the Performance Assessment

4.1.1 Classification of various Undertakings

4.1.2 Performance Indicators

4.2 Questionnaire of Wastewater Management System

4-3 Performance Indicators for Wastewater Management System

Performance Indicators Population Equivalent

Wastewater Treatment Plants

LIST OF FIGURES AND TABLES

Figure 1.5 Schematic of trickling filter with rock packing and plastic packing

Figure 2.1 Main swps of a beachmarking process

Figure 2.2 Extended process model for wastewater (reatment plants above 100,000 PE Figure 2.3 Methodology for the development of process performance indicalors

Figure 2.4 NEBC's benchmarking model

Figure 2.5 Procedure of pracess benchmarking

Figure 3.1 Structure of Wastewater Context Information & Performance Indicator

Figure 3.2 Wastewater undertaking context

Tables

Table 1.1 Principal constituents of concern in wastewater treatment

Table 1.2 Important metals in Wastewater Management

Table 1.3 Comparison of ratios of various parameters used to characterize wastewater Table 1.4 Typical wastewater lowrates from urban residential sources in the USA

Table 1.5 Typical wastewater Mowrates from commercial sources in the USA

Table 1.6 Typical composition of untreated domestic wastewater

Table 1.7 Typical wastewater constituent data for various countries

Table 1.8 Mujor biological treatment processes used for wastewater treatment

Table 2.1 Hol

Table 3.1 Relial

approach versus Selective approach in Process benchmarking lity hands of collected data

Table 3.2 ‘The WA Performance Indicators

Lable 4.1 Summary of Performance Indicators for Urbam Wastewater Management

ACKNOWLEDGEMENTS

‘This thesis has been developed in Dresden, Gcrmany with the support of some people

to whom I would like to express my special thanks

I would like to dunk Prof Nguyen Thi Diem Trang - Hanoi University of Scieuce and

Prof Bernd Wilitewski - Institite of Waste Management and Contaminated Site ‘Treatment

(IAA), Dresden University of Technology (TUD) as well as DAAD because of giving me the chance to do my thesis in Germany

I would like to sond ny special thunks to Mec Plu Hoang Mai, GAA-TUD), who gave me this topic, supervised and encouraged me to write my thesis | have learnt some things for my studying from her

Also I would like to thank Dz, Catalin SteGn (AA-TUD) because of his kind help during the time I was in Dresden, Thanks ue also expressed to Mse, Le Thi Hom Ounh (IAA-TUD) who was always willing ta help me as [ need

Especially, I would like to thank my tamily and friends, who always support and

bneourage mec lu Gnish my thesis,

TNTRODUCTION

Wastcwator Managoment is one of the most concems in any urban arca, An cfficicnt management contributes to the wealth of a commumity, never the less a poor management leads to unpredictable hazards related to health, environmental pollution, ote In developed countics, Ue issues of wuler and sunitation ae sulved, Doodings are well controlled, However, the issues of water snpply and ganitation are not solved in developing countries, poor manegement of floodings as well as improper operation and maintenance of sewer systems are vay popule, Therefore, il is un urgent requirement lo improve the system of wastewater management in developing countries Benchmarking is promised to be a solution to this

problem as itis always the useful tool for improvement in management

Benchmarking was first time introduced by Xerox Company in the late 1970s when their poor company Fuji produced the photucopiors wilh betier quality und lower prices Xerox was forced ta critically review their pradnots and production costs by adopting the Japanese philosophy: gaining the best of the bests by leaming, adapting and improving (Purena et al., 2001) That was how benchmarking appeared

In numy countries experiences (Xerox model inypized) Lave been devdloped to adapt

benchmarking procedures in the water context (Parena et al, 2007) Benchmarking has been

conducted in many developed countries such as Australia, Canada, England, Germany ete to assess the performance of water and wastewater service providers, to estimate the quality of services as well as the satisfaction of customers These benchmarking projects have achieved initial success wid ure supposed to sustain, Some systems of performance indicaturs have been developed with the purpose of large scale application such as the rystem International Water Association or Qualserve system, etc In some developing countries such as India, Viettam, ols certain bouchmwking project regarding the isguc of water and sanitation have been

vamied out under the support of lhe World Bank

Aiming at developing a simplified concept for process benchmarking of urban wastewater management which can be applied in developing countries, performance indicators

and quesliounaire prepared for benchmarking it Vietnau, a represenlative of devdoping

6

countries are adapted in this thesis based on the Intemational Water Assaciation (WA) system

of performance indicators for wastewater services There are four chapters in the thesis Chapter I considers the foundation of urban wastewater management in general and the current situation of wastewater management in urhan areas of Vietnam In chapter II fondamentals of benchmarking and process benchmarking for the water industry are discussed

To imeke clear the tool of perfonuance assessment presented in the thesis the performance indicators for wastewater services of [WA as well as the baris of performance indicators are given in chapter II] Chapter IV explains the performance indicators selected for process

benclunarking in waslewater servives of Vietruan; also, the questionnaze at well as the excel

file to collect data from wastewater imdertakings are presented

Benchmarking of wastewater utilities is emerging as an important tool of performance

improvement by regular monitoring and analyses can be the solution to this reality, It ean play

a significant role in the seclor as a tool for inslilutional suengthening, Sustained benchmarking can help utilities in identifying performance gaps and gaining improvements by the sharing of information and best practices, ultimately resulting in better services to people It is expected that benchmarking in wastewater services in developing countries will soon be supported ta

implement

CHAPTERIT Theoretical Foundations of Urban Wastewater Management System

In this chapter the theoretical foundations of urban wastewater management will be considered, including: (1) characteristics of urban wastewater, (2) overview of the urban wastewater management system, (3) sub-processes of wastewater management system and (4)

current situation of urban wastewater management in Vieinam

1.1 Characteristics of Urban Wastewater

1.11 ket ừ Urban Wastewater?

According 6 Tchobanoglous cl al 2003, urban wastewater components may vary depending on type of collection system and may inchide:

1 Domestic (sanitary) wastewater Wastewater discharged trom residential areas, and frou commercial, institulional and similar facilities

2 Indus ial wastewater Wastewater in which industrial wastes predominate

3 Stormwater Runoff resulting from rainfall

4 Infiltration/Inflow Water that enters the collection system through indirect and direct means Infiltration is extraneous water that enters the collection system through Jeaking joinls, cracks and breaks, or porous walls Inflow is stormwater that enters the collection system ftom storm drain connections, roof leaders, foundation and basement drains, or through access port (manhole) covers

1.12 Constituents of Wastewater

The constituents of wastewater can be classified as physical, chemical and biological

Of the constituents listed in table 1.1, suspended solids, biodegradable organics and pathogen organisms the most conceming ones are refered All wastewater treatment facilities are

designed to ranove these eonstiluents completely

There are many kind of solids present in wastewater, varying from coarse to colloidal ones Before any analysis of solids in wastewater the course material should be rameved In

wastewater treatment, the solids can be classified by their size and state (suspended solids &

8

dissolved solids), by their chemical characteristics (volatile & fixed salids) and by settleability (settable suspended solids & non-settable suspended solids) ‘Sperling, 2007)

Table 1.1 Principal constituents of concern in wastewater treatment”

Constituents Reason for Concern

Total suspended solids Sludge deposits and anaerobic conditions

Biodegradable organics Depletion of natural oxygen resources and the

development of septic conditions Dissolved inorganics (e.g total | Inorganic conatitnents added by usage Recycling and

dissolved solids) reuse applications

Heavy mctals Metallic constituents aided by usage, Many melals are

also classified as priority pollutants Nutrients Excessive growth of undesirable aquatic life

eutrophication, nitrate contamimation af drinking water

Pathogens Commnicable diseases

Priority organic pollutants Suspected carcinogenicity, mutagenicity, teratogenicity, or

high weute wxicity Many priority pollulunts resist conventional treatment methods (known as refractory organics)

a: From Crites & ‘lchohanoglous, 1998,

Particle Size Wistribution

The determination of partele size is to understand more about nature of particles composing TSS in wastewater In addition, this analysis is also used to assess the effectiveness

of tealment process (bivlogical treahment, disinfection process, sedimentation, elc)

‘The sonrcer of color in wastewater include infiltration/inflow (humic znhgtances), industrial discharges (e.g, dyes or metallic compounds, etc) and the decomposition of organic

compounds in wastewater

1ransmitiance/ Ábsorptian

Transmittance is the abihfy of a liquid to transmit light of a specified wavelength (ough a known depth of yolution Absorbance ig the loss of radiant energy us light pasy through a fluid (7chohanoglous et al, 2003)

‘The components that affect transmittance include selected inorganic compounds (e.g iron and copper), organic compounds (e.g organic dyes, humic substances, aud conjugated

‘Tho lypical compound that cause bad odor is hydrogen sulfide Oter compounds such

ag indole, skatole and mercaptanes, in anaerobic conditions may canse odors that are much more offensive than that of hydrogen sulfide

Temperature

The measurement of temperature is very important hecanse most wastewater treatment

facilities inchide the biological step, a temperatnre-cependent process The temperature of wastowater depends on season aud location, In culd regions, (he temperature will vary from 7

to 18°C, in warmer regions it will vary fram 13 to 30°C

Temperature is a fatal parameter in water becanse xt affects the chemical reactions, reaction rates and aquatic Life The change in temperature can be a significant factor for the survival of a meang of fish species In addition, higher temperature means lower dissolved oxygen in wator The increase in biochemical reaction rate duc to higher temperature probably leads to the depletion of oxygen in water (Tchohanoglous et al, 1998)

Density, Specific Gravity and Specific Weight

The density of wastewaler, py is defined as its mass per unil volume expressed as g/ or

kg’ (SJ) Density is an important parameter becanse it is needed for the design of some

treatment units such as sedimentation tanks, constructed wetland, etc

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Conductivity

‘The electrical conductivity (LIC) of a liquid is the ability of that liquid to conduct an cleotrical current Because the electricity is transported by ious in solution, the measured value

of RC is used to determine the concentration of total dissolved solids

The electrical conductivity is expressed in SI units az millisiemens per meter (mS/m)

1.1.2.2 Inorganic Chemical Characteristics

The chemical constituents of wastewater can be classified as inorganic and organic In this section, (he inorganic consliluents are considered

pil value

pH is a convenient measure of the acidity/alkalinity of an aqueous solution at a

specified temperature, usually 20°C or 25°C I is typically measured on a continuous scale

from 0 to 14 (richard et al, 2003} ‘Vhe pll is defined as the negative logarithm of the hydrogen-ion concentration:

pH =+g [HỶ]

The suitable range for the existence of most biological hfe is very narrow, typically between pH 5 and 9 If the pH value of wastewalor is below § and grouler thin 9, ilis difficull

for the activity of microorganisms in bialogical treatment Without adjustment of pH most

efiluent fiom domestic wastewater tieatment facilities will alter the pH of receiving water

Nitrite nitrogen iv an unstable form, cusily oxidized lo nitrate form Although present

in wastewater at low concentration nitrite can be very important becanse it is toxic with almost

11

fish and other aqnatic species In wastewater, the concentration of nitrite seldom exceeds

1mgi (fchobanoglaus et al, 1998;

Nitrate nitrogen, the highest oxidized form of nitrogen found in wastewater becomes toxic only under conditions in which it is reduced to nitrite Therefore it is important when effluent fiom wastewater treatment is used as recharge for ground water Nitrate can be a very serious problem because it causes blue baby syndrome or methemeglobinemia in young

infants at a certain concentration Nitrate varies from 2 to 3) mg/l as N in wastewater effluents

(Tchobanoglous et.al, 1998)

Phosphorus

Phosphorus is alsa an essential nutrient to the growth of biological organisms but the assimilation of phozphoms in water bodice eauses the problem of cutrophication In effort to prevent the eutrophication of water bodies, phosphorus in domestic and industrial wastewater and natural runoti'is concemed

Tho usual forms of phosphorus found in aqucous solution are orthophosphate,

polyphosphate and organic phosphate ‘I'he orthaphosphates (eg PO.%, POs, 1sPO4

HPO, and HPO,” complexes) can be absorbed by organisms without any breakdown Polyplosphates convert to orthophosphate by hydrolysis provess but (his proves is noumally

quite slow Organic phosphate can be an important constituent in industrial wastewater and

wastewater sludges ‘Tchabemoglous eral, 1998)

Alkalinity

Alkalinity of'a solution is the ability of acid-nentralizing of that solution

Alkalinity in wastewater results fom the presence of the hydroxides [OH |, carbonates

[COs], and bivarbonales [HCO] of cements such as calcium, magnesium, sodium,

potassinm Of these elements, calcium and magnesium are the most common, Lorates, silicates, phosphates and some similer compounds can cause alkalinity but insignificantly, perhaps in industrial or agricultural wastewater /Trhobanoglous et al, 7998)

Wastewater is normally alkaline; this alkalinity comes fiom water supply, the groundwater and domestic use

For most practical purposes alkalinity can be defined im terms of molar quantities as:

[Alk], mole = [HCOz |+ |CO;"]+ |OH] - |H"]

In ters of equivalents:

Chlorides

The chloride concentration in wastewater is an important parameter with respect to the

reuse of wastewater Chlorides in wastewater result from the usage

Becanse conventional wastewater treatment method does not remove chiloride to any significant extent, the higher than usual concentration of chloride cam be wn indication thal the

water hody is heing used to dispose treated wastewater

Sulfur

The sulfite ion occurs naturally in anost water supplies and as a resull is present in wastewater Sulfur is required in the synthesis of proteins and released during the digestion of proteins Sulfate is rcduecd biologically to sulfide under anaerobic condition, and then sulfide combines with hydrogen to form hydrogen sulfide

Ilydrogen sultide is concemed because of the oxidation to sulfuric acid which is

conosive lo cơnerole sewer pipes Hydrogen sulfide gas secumulaled ut the crown of the pipe

due to the not flowing fall of the sewer pipe can be oxidized biologically to sulfuric avid wilich is corrosive to concrete sewer pipes /Also in digester HS is corrosive to gas piping (Tehobonoglous et al, 2003} Sulfates are reduced ty sulfides in sludge digester cam upsel the

process if the concentration exceeds 200 mg/l (I'chobanoglous et al, 199)

Metals

All living organism require an amount of metallic compounds (ium mice lo rưacro) such as iron, copper, ine for proper growth ‘Though certain amounts of metals are necessary, the elevated concentration of them can be toxic to alll kinds of creatures Therefore, mnelals axe abvays the concer in wastewaler teatment (Telubanvgious et al,, 1998)

‘The sources of metals in wastewater include residential areas, groundwater infiltration, commercial and industrial discharges

The importance of metals are given in table 1.2

Table 1.2 Important metals in wastewater management”

inhibitory effect whether biosolids

on heterotrophic are suituble for Metal Symbol | Macro | Micro? | organisms (mg/l) _land application Arsenic AS 0.05 x

b: often identified az trace elements needed for biological growth

t¡ lal chromium

d: hexavalent chrommum

Gases

Measurements of dissolved gases, such as amunonie, carbon dioxide, hydrogen sulfide,

methane, oxygen ae important in the operation of waslewaler uealment systems eg tu

control the work of anaerobic process,

Henry's law is the busiy to cousider the aetivity of dissolved gas in water Hemry’s law

(More et al, 2008) expresses the relationship between gas pressure and solubility as follow:

Sy=kn*P,

Where: S_ the solubility of the gas in the liqnid [mol‘m*]

P,; the pressure of the gas above the schution (or the partial pressure of the gas ifthe

solution is in contact with amixture of gases) — [Pa]

kee: Henry constant (depends on temperature as well as characteristics of the gas and

the liquid) [Pa mmol]

1.1.2.3 Organic Compounds Characteristics

Purposes of the aualysoy of upgregule orgunic cousliluonts are lo characterize uitrealed

and treated wastewater, to assess the performance of treatment process and to study receiving

waters In this section biochemical oxygen demand (30D), chemical oxygen demand (COD), total organic carbon (TOC), oil and grease and surfactants are discussed

Biochemical Oxygen Demand (BOD)

‘The most used parameter of organic pollution applied to both wastewater and surface water is the 5-day BOD (BOD.) This determination involves the measurement of the dissulved oxygen used by uicroorganins in the biochemical oxidation of organic matter

+, but other

‘Vhe normal incubation time for NOL test iz normally 5 or 7 days at 2

length of time or temperature can be used

Chemical Oxygen Demand (COD)

“The COD test is used iv measure the oxygen equivalent of the organic material in wastewater that can be oxidized chemically by using dichromate in an acid solution” (Fchobanogious et al, 1998}

An udvantage of COD test is dust it can complete in 2.5 hours (compare to 5-day test of

BOD)

Total Organic Carbon (TOC)

The TOC tes! is used to detenuine the total organic carbuu in a sanple The TOC value

of a wastewater sample can be used to assess its pollutional characteristics or sometimes to

relate TOC to BOD and COD TOC test is also in favor because it only takes 5-10 minutes to get the result If a reasonable relationship between TOC and BOD can be established in a

wastewater sample, use of TOC test is recommended

The relatianship of BOD, COD and TOC

There are interrclationships betwoen BOD/COD and BOD/TOC and they are shown in table 1.3 This relationship can be nsed to determine whether a wastewater sample can he treated by biclogical process or not For example, if the BOD/COD ratio of wastewater is 0.5

15

or greater, it can he treated biologically; if this ratio is below about 0.3, the sample needed ta

be treated before any biological process

Table 1.3 Comparison of ratios of various parameters used to characterize wastewater *

D:CBOD / COD (CBOD: Curbonuceous Biological Oxygen Demand — the oxygen demand cxerted by oxidizable carbon in the sample when the nitrification occurs.)

wCBOD / TOC

Oil and Grease

“The lem vil and grease ae commonly used, includes fals, vile, waxes und other related constitnents found in wastewater.” (Ychobanoglous et al, 199%)

The sources of fats and oil contributed to domestic wastewater includes: butter,

margarine, vegetable fats and oils Fats can be found in meats, in cereals, in seeds, in muts and

in certain finits (Tchobanoglaus et al, 2003)

Oil and grease in liquid form may not appesr to be harmful bul as being cooled il becomes solids and eanses many problems It sticks to inner lining of drainage pipes and restrains the flow leading to blockages in sewers These blockages can canse the flooding in sewer and odor problems (Best Management Practice for Catering Outlets, Welsh Water —

Water UK)

Surfactants

Surfactants are orpanic molecnles that are composed of strongly hydrophobic

(insolnble in water) and hydrophilic group (soluble in water)

The presence of surfactants im wastewaler resully from houschold delergents, laundry

industries, and other cleaning operations Surfactants tend fo collect at the air-water interface

and can cause foaming in wastewater treatment facilities or at the surface of discharge

receiving water

1.1.2.4 Biological Characteristics

Biological characteristics of wastewater are in major importance not only becanse of

tho hygienic issues but also the significance of microorganisms in water and wastewater

16

treatment In this section, these following subjects will be discussed: (1) microorganisms found in wastewater, (2) pathogenic organisms related to human diseases, and (3) the use of indicator organisms

Microorganisms found in wastewater

The microorganisms found in wastewater can be classified ax eukaryotes, eubacteria and urchucy Their cell structure, typical size, cuxacterization and representative member ae illustrated in table | (appendix)

Pathogenic Microorganisms

Pathogens found in wastewaler may be discharged by human who are suffering with diseases or who are caiers of a particular disease The pathogenic microorganisms found in wastewater can be classified into three broad categories: bacteria, parasites (protozoa and helminths) and virnses

Protozoa

Because of their significant impact on individuals with compromised unmune systems including very young children, persons with cancer and individuals with AIDS, Cryptosporidian parnan, Cyclospora and Giardia lamblia axe the most conceming protozoan

It is important to uote that these protozoans arc found in wastewater because conventional

disinfection techniques (UV radiation or chlorine) have not proven their inactivation or destruction

and survive normal disinfection procedures though eggs can be removed by common

treatment processes such as sedimentation, filtration (fchobanoglous et al, 1998)

Pin

More than hundred types of enteric viruses capable of producing infection or disease are released in the fecal matter of infected humens Of the most important human enteric viruses, only Norwalk virus and roluvirus which cause diuheal disease have been shown tw

be major waterborne pathogens (Ychohanaglaus et al, 7993)

Use of Indicator Organisms

The Colifonn organism which is numerous and easily tested for is commonly used as

an indicator organism ach person discharges from 100 to 400 billion Coliform bacteria with

other kinds of bacteria per day, Therefore, the presence of Coliform bacteria can be an indication that ather pathogens may be present

Easy and common but the limitation of Coliform test is that it only indicates for the presence of pathogenic bacleria and viruses, ut for waterborne protozoa or pathogenic organisms that may arise from nanknman sources ‘Iherefore the use of new indicator bacteriophages is much more concemed (Tchohanogious et al, 1998)

1.13 Flowrutes and Compovition of Wastewater

The analysis of wastewater dala involves the determination of the owzate aud amass loading variations Hom the standpoint of treatment processes, average flowrates and average BOD and TSS loadings are two of the most concerning parameter in design (Tchobanoglous et

al, 2003}, In this section, flowrates and composition of wastewater will be considered

1.1.3.1 Wastowater Flowratos

The hydrantic design of both collection and treatment facilities is influenced by variations in wastewater flowrates, therefore the flowrate characteristics have to be analyzed carefully

Wastewater flawrates vary during the day, day of the week, season of the year or depend on the sources of discharge to the collection system Short-term variations have diumal patlem which minkuwu Dows uccur during the carly moming, the Girst and ie second pouk flows occur in late morning and early evening respectively Seasonal variations are normally observed in small communities with colloge campuses and in communitics which have

seasonal commercial and industrial activities Industrial variations are difficult to predict and

18

the most troublesome in smaller wastewater treatment plants where the loading capacity is

limited /Ychobanagtous et al., 2003)

The principal sources of domestic wastewater in a conununity are the residential arcas and commercial districts (ata on ranges and typical flawrate values from urban residential

and commercial sources in the United States are illustrated in table 1.4 and 1.4 az followings

Table 1.4 Typical wastewater flowrates from urban residential sources in the USA *

1able 1.5 [ypical wastewater Towrates fram commercial sources in the LSA *

Boarding house Person 95-250 170

(sanitary waste only) 1'mployee 37-130 3

Mobile home park Unit 420-570 530

Motel (without kitchen) Guest 190-290 210

Restaurant

‘The principal factors responsible for variations of loading arc (1) the established habits

of community residents which cause short-term variations, (2) seasonal changes which often cause long-term variations and (3) industrial activities which cause both long and short-tern vaziations

‘Typical data on the composition of raw domestic wastewater found in wastewater collection systems in the USA is presented in table 1.6 It should be noted that there is no

“lypical” wastewater therefore (ie dua in thiz lable is only used us a guide The smounte of

wastewater discharged by individuals in comtries can vary significantly because of

20

differences in culture and socioeconomic conditions Ihe camparison between wastewater discharged by individuals in the USA and other countries is illustrated in table 1.7

Table 1.6 ‘ypical composition of untreated damestic wastewater "

Concentration ©

strength strength strength

Chemical oxygen demand mg/L

‘Votal Coliform No.100ml 105-109 107-102 10109 Fecal Colifum No./100ml 102-102 10-102

Cryptospondum oocysts No./100m1 107-10" 101-101

Giardia lanblia cysts Mo./100u1 10 1-10! 10 !.10ˆ

a: From Tchobanoglous et al., 2003

b: Low strength is based on an approximate wastewater flowrate of 750 L/capitad

Medium strength is based on an approximate wastewater Dowrale of 460 L/capilad

High sucngth is based on an approximate waslowuter Dowrale of 240 Lécapitad

c: Values should be increased by amount of constitnent present in domestic waster supply

Table 1.7 Typical wastewater constituent data for various countries *

Constituent | g/eapitad gícapitad | g/capitad —g/eapitad | g/capitad

a: From Tchabanoglous et al., 2103

1.2 Overview of the Urban Wastewater Management System

1.2.7 Components of Urban Wastewater Management System

Wastewater Management System inclnder three main components: (1) collection, (2)

treatment and (3) disposal or reuse

The first step in any wastewater management system of a community is the collection and conveyance of wastewater from various sơnroes The pipes that collect and transport away wastewater fiom its sources are called sewers and the network of sewers is a collection system (George Tehubanoglous, 1981) Most sowers ure placed underground to prevent interference dne to repair of this aystem (Munna and Jain, 1998) ‘he types of collection systems will he discussed later

Treatnent is an essential step in a waslewaler management system, This step nol only

reduces the amount of pollutants coming into the environment but alsa protects humans from pathogens (Puimia and Jain, 1998) The treatment of wastowater is camicd out by combination of many unit processes The methods of treatment are various, including mechanueal, physical, chemacal, biological methods or the combination of these ones such as physivcheutical mothod ete, The variety of these methods will be consideed in folowing

sections

Afier treatment, water will be disposed ar reused ‘The disposal of treated effluent is related very closely to selfpurification of water bodies Jased on the selected receiving water

or cffluent standard cngincors will decide the degree of treatment and type of plant requixed

‘Vreated wastewater can be discharged into lakes, rivers or the ocean ‘Ihe rense of treated efiuent can be applied for groundwater recharge, itrigation, etc These issues will be referred Tater

7.2.2 Types of Wastewater Management System

"There are two typical types of wastewater management system, including centralized

and decentralized model The former one is the traditional system and applied successfilly in many industrialized counties over decades However, the cost of invesuuent and

implementation of this system is a big problem for any community Decentralized wastewater

systems in which wastewater arc treated ncar the source of generation are getting more concem as a potential alternative of traditional centralized wastewater management system These two wastewater management systems will be discussed as followings

Centralized Wastewater Management

(Source: Wilderer and Schreff, 2000)

Centralized wastewater management is used to describe the system consisting of a collection system that collect all wastewater fiom households, mdustrial zones, small enlerprises, storm walter ruff and convey lo the Leatment plant located very far or outside the city or village boundary (fig 1.1) The treated wastewater which meets the standard will be discharged to the closest receiving water The remaining, part after climinating pollutants from

wastewater (waste shudpe ïn snrnmnary) will also be treated before zny fnther use (Wilderer and Schreff, 2000)

Decentralized Wastewater Management

In contrast with the centralized model, the treatment plants in decentralized system are close to the original sources of waste (fig 1.2) Also, the wastewater is transported by means

of pipes but the length of these sewers is sharter There will he some on-site treatment plants

in which the wastewater and sludge treatment processes are executed The treated wastewater and sludge we dischaged to waler bodies or reused for isrigalion, twilel flushing, ele (Wilderer and Schreff, 2000)

AF sma holt

Figuret.2 Representation of a Decentralized Wastewater Collection and Treatment System

(Source: Wilderer and Schreff, 2000)

Advantages and disadvantages

‘The centralized wastewater management systems have achieved certain success in developed comntries for a long time Sewage and stormwater are collected and transported ont

of the urban area by system of sewers, receive advanced treatment and are controlled before discharge into receiving bodies Waste sludge is tealed, ulikized or disposed in proper way One of achievements of this system is the reliable and efficient management and control of

treatment plants Besides, it is assumed that one large treatment plant is less expensive than

mary sual] plants serving the same urban area, regarding bolh capital and operation costs

(Lettinga et ak, 2001)

Respite of undeniable advantages, centralized systems have many limitations Virst of all, this system requires very long sewer pipes and as a result, the cost for constructing and maintaining the sewers is very high According to the 2005 survey of DWA in 2003, Germany spent about 1.6 billion euro on rehabilitation of sewer system which have the total length of

$15,000 kan and collect wastewater of neatly 82.5 million (Profile af the German water industry 2008} More over, the cullvetion and treatment system is typically designed with the capacity which is proposed to satisfy the upcoming population l3efare getting that point, the capacity is far higher than actually required Consequently, the operation costs are high and the plants work under now-optimal conditions The high cost of construciun leads to lage amount of investment to be spent within a short period, thus the pressure on local economy is

very high (Wilderer and Schreff, 2000} As respective to environmental aspects, water balance

can be affected in a negative way hecanse water is taken from discrete location but treated effluent is discharged into am area distant from origin It is also obvious that the combination

of wastowater and slonmwater from various sources leads to a highly complex of pollutants that fluctuates heavily in composition and concentrations, thus the efficient removal becomes mote difficult to be achieved (Lettinga et al,, 2001)

Decentralized wastewater management systems exist in many parts around the world, mainly in rural areas As compare to centralized management system, the decentralized model has obvious advantages, mcluding: (1) lifting stations and storage tanks to handle combined sewage flow is not needed leading to the reduction in construction az well as operation and maintenance cost, (2) more possibility of water reuse and groundwater recharge becauze it seems to be unfeasible to transport treated wastewater fiom the treatment plant to the place of utilization in case of cenlralized system, (3) failures of single unils will not cause the break down of the whole system (Widderer and Schreff, 2000), (4) more flexible in case of fast population growth becansc the capacity is casily adjusted

The major concems in the decentralized wastewater management system include: (1) effluent quality is low and rarely complied with the water reuse standard, (2) treatment plants are not operated properly, (3) plants ure difficult to control and supervise by water authorities

‘The current methods are primitive (e.g pit latrines) or low technology (e.g one, two or three chamber septic tanks) (Leftinga ef ai, 2001) Normally the owners of the on-site treatment

facilities we responsitle for the proper operation and inainteuutce of their own treatntcul

35

stations Ilowever, the fact is that almost no treatment facility owner has any in-depth

knowledge of processes on which the systems work correctly and efficiently as well as has any motivation to do that (Wilderer and Schreff, 2000)

Decentralized systems can be the solution for wastewater management in part of

industrialized countries and particulaly for developing countries, because of flexibility and simple, However, various problems as refered above necdel to be solved before

implementing this system

1.3 Sub-processes of Wastewater Management System

J Collection Systems

"the fimction of a collection system in the urban wastewater management system is to

collect all wastewater from domestic and non-domestic sources as well as stormwater and

ean will be

convey to Ireatinent plants In this section, typical components of a collection sy:

considered Also, types of sewers are referred

1.3.1.1 Tvpical Components of Collection System

‘Typical components of an urban drainage system include: building drainage, roof drainage and main sewer networks, Building drainage carrics all kinds of wastewater to the

main sewer and roof drainage conveys stormwater to the main sewer In this section the main

components or “hardware” of any drainage system will be discussed (Butler et al, 2004)

Sewers Sewers are components of sewerage thal carry flow from groups uf properties

or larger area to wastewater treatment plants or receiving bodies Sewers can be made of vitrified clay, concrete, cement depending on types of sewers There are three types of

sewers, including: sanitary sewer, stormwater sewer and combined sewer (Butler et al, 2004)

Manholes in sewer zystem, manholes are access points for testing, inspection and blockage clearance Manholoz are usually decp and can be entered if necessary Manholes arc provided at: (1) changes in direction, (2) heads of runs, (3) dunges in gradient, (4) changes in size, (5) major conjunction with ofher sewers ‘The diameter af manhole depends on the size of

sewer and the orientation and number of inlets (Brler et ai, 2004)

Cully inlets, The yurface runoff aulers Ue sewer via inlely called gullies Gully consists of a grating and normally an underlying sump to collect heavy material in the flow

Gully is connected to sewer by a lateral pipe and water scal is incorporated in case of

connecting with the combined sewer The size, number and spacing of gullies will determine

26

the extent of amface ponding of runoff duing siarm evenis (inllies are always placed at low points and typically along the road ‘The simplest approach for the distance of gullies is 5U m

spaciig or per 200 m” of imperions arca (Butler et al, 2004)

Ventilation Venfilation is required in all urban drainage system but particularly in sanitary and combined sewers It is to ensure the aerobic condition within the pipe and to avoid the possibility of toxie and caplusive gas build-up

13.1.2 Types of Sewer

In this section, three lypes of sewer, including sunitany sewors, slonmwaler sewers and combined sewers will be mtrodnced very briefly

a Sanitary sewer

Sanitary sewers are intended lo collect and convey waslewaler fiom households,

institutions and industrial zones to the treatment plants Wastewater is transported by gravity

(gravity sanitary sewer) or pressurc/vacuum (pressure sanitary sewer) (Tchobanoglous, 1982)

Some basic considerations in design of sanitary sewers include: (1) design flows (2) hydraulic design equation, (3) sewer pipes and materials, (4) mmimum and maximum velovitics, (S) nundmuan slopes, (6) allernafive design, (7) sewer appurtenances and (8) sewer ventilation (Ychohanogious, 1982)

by Storm-water sewer

The sterm-waler sewer, as (he name is intended lo collect slorm waler Design of

storm-water sewer is similar to the one of sanitary sewer except some difference ‘he easiest realized difference is that the storm-water scwo is designed to oveiflow periodically For instance, slonn-water sewer designed based on a 10 ycar muinfill Gequeney that means one

storm every 10 year will exceed the capacity of the sewer In contrast, the sanitary sewer

system is designed to prevent the surcharge becanse of high coutents of pollutants If surcharge occurs it will be due to az unexpected break down Anuther easily seen difference is the diameter of the pipe in there two systems ‘The pipe of a sanitary sewer aystem is many times smaller than of a storm-water sewer, therefore only a small amount of excess infiltration can lead to overload (Hammer et al, 2008)

‘Tho procedures used to design the storm-water sewer are similar to that needed for the sanity sewer system, excluding some difTerences in design flow, minimum velocities and

pipe materials and sizes (Y'chohanoglous, 1981)

2

cứ Camihineil š wer

Combined sewer iz a system that collects domestic wastewater, industrial wastewater

and rain water runoff within the same pipe During dry weather, the combined wastowator will

be brought to the treatment plants before discharged into the receiving water ‘The wet weather flow in case of a large ram storm can exceed the capacity of the sewer network and treatment plants, leading to a direcl discharge of some Dow to reciving bodice al a component called

2

The main role ot'a CSO is to take an inflow and divides it into two outtlows in case of

combined sewer overflow (

high flow rates, one lo the treatment planl and ong to the receiving bodies The uonual means

of achieving this is a weir If the surface of the flow passing through CSO ie below the weir, flow continues to the treatment plants only When the surface is above the weir, some of flow passes the weir and the rest flows to treatment plants, Thus, hydraulic design of a CSO requires care to avoid premature overtlow leading ta an unnecessary volume of polluted flow discharged to water bodies ur loo much Dow Jeading surcharging in the sewer system, The

other main role of CS ) ig related to pollution A CSO will he designed to keep as much as

possible the content of fine suspended and dissolved materials in contmmation flow to treatment plants (Butler et al., 2004)

In combined sewer, the design of CSO is the most conceming Basic considerations when considenng this component include: diameter of inflow pipe, control of outflow, weirs,

chamber invert, design relumn period, top waler level and Iaunan access (Butler et al, 2004)

4.3.2 Wastewater Treatment

Typical wastewater treatment consists of preliminary processes, primary scttling to remove Iicavy solids and Moatable materials, and secondary ucatment, uounally biological processes to metabolize and flocculate colloidal and dissolved organics Waste sludge drawn from these units is thickened and processed for ultimate disposal, usually either land application or landfilling, Tertiary treatment is an additional step that fellows primery and secondary treatment when these steps can not comply with the requirement ‘Ihe schematic of

‘unit operations and processes in a wastewator trcatment plant is illustrated in figure 1.3

This section will disenss briefly about the following treatment steps: (I) preliminary and primary treatment, (2) secondary treatment and (3) tertiary treatment Because of the

purpose to give an overview of wastewater treatment, these topics are introduced and

discussed very briefly in following sections

Tit processes processing facilites Wastewater flows

‘Recycle or solids streams

Figure 1.3 Schematic of unit operations and processes in a wastewater treatment plant

(Source: Tchobanoglous et al., 2003)

1.3.2.1 Preliminary and Primary treatment

The purpose of preliminary steps is to remove wastewater constituents such as rags,

sticks, floatables, grit, and grease that may cause maintenance or operation problems to the treatment operations, processes and ancillary systems (Tchobanoglous et al, 2003)

Primary steps can remove a portion of suspended solids and organic matters from wastewater (Tchobanoglous et al., 2003)

Most units in preliminary and primary treatment are physical ones Some of most commonly

used unit operations in preliminary and primary treatment of wastewater include: (1)

screenings, (2) grit removal, (3) flow equalization, (4) sedimentation, (5) flotation

Screenings Screening is typically the first unit operation encountered in a wastewater treatment plant Screenings are classified into three types depending on the size of removal solids: (1) bar racks for coarse screens such as debris, leaves, paper, tree roots, plastic and rags, (2) fine screens for removal of smail particles such as undecomposed fond waste, feces and (3) micro sereens for removal of fine solids, floatable matter and algae (Pchobanogéous et al, 1998; Vehobanoglous et al, 2003)

Grit removal Normally, the location of grit chamber is after the bar racks and before the primary sedimentation tanks (Ramatho, 1983).Grit is composed of sand, gravel, cinders, egg shells, bone chips, or other heavy solid materials (hat have specific gravilies greater Uvan those of organic putrescible solids in wastewater Quantities of grit varied in range of 0.0037-

0.22 3/10? m3, Particles identified as the cause of most problems in downstream trcatment

units are typically 0.2 mm and larger There are three types of grit chamber including: (1} horizontal flow, (2) aerated and (3) vortex type (Tchobanagious er al., 1998)

Flow equalization Flow equalization is used (1) to smooth out individual waslewater stream flaws so that a mixing stream of relatively constant flow rate is fed to treatment plant, (2) to equal variations of BOD concentrations in influents, (3) probably to neutralize the

wastewaler Flow equalization can be applied in different purposes, especially in sinall plants

where experience high peak - to - average flow and organic loading ratios If the peak - to - average flow rate is 2 or less, the use of flow equalization is not economically feasible (Tchohanogions etal, 1998}

Sedimentation Primary sedimentation is responsible to remove readily settleable solids and floating materials, There are two types of sedimentation tanks including rectangular taiks and circular tanks, An efficiently designed and operated tank should remove about 50-70% SS and 25-40% of BODs In small treatment plants, primary sedimentation is nonnally omitted (7chobanoglous, 1979)

Flotation In wastewater treatment, flotation is used principally to remove suspended solids and to concentrate biological sindges The most advantage of flotation compare to sedimentation is thal very small and light particles that sellle very slowly can be removed completely and in shorter time ‘The surface floated particles can be collected by a skimming

operation (Tchabanaglous 1979)

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13 econdary treatment

Biological treatment, the typical secondary level in a municipal wastewater treatment

plant is discussed in this section The following subjects will be considered: (1) introduction of microorganisms in biological treatment, (2) objectives of biological treatment and (3) types of biclogical processes in wastewater treatment

4 Introduction of microorganisms

Microorganisms are the core components of a biological treatment system ‘heir roles

ag well as what they need to fulfill the treatment are following discussions

Role of microorganisms In wastewaler, wicrouganisms convert the culluidal and dissolved carbonaceous organic matter into vations gases and cell tissue Becanse cell tissue has a slightly greater specific density than water it can be removed fiom treated liquid by gravity setiling (Tehobanagious, 7979)

Microorganism's requirement To continue to produce and funetion properly microorganisms nved to have sources of cucrgy Gighl, oxidation) aud carbou (carbon divxide,

organic matter) to synthesize new cell tissue Certain inorganic elements such as nitrogen and

phosphorus and trace elements such ae sulfur, potassium, calcium, magnesium are also vital to cell synthesis (Tehubanoglous, 1979)

‘Treatment processes Based on metabolic function, biological processes used in wastewater treatment can be classified into following gronps: (1) aerobic processes, (2) anoxic processcy, (3) anaorobic piueesses, (4) a combination of the uerobicfmosie or maerobie processes, (5) Facultative processes (Y'chohanoglous et al, 2

BY Objectives of biologteal trectment

In wastewstor treatment, the overall objectives of the biological processes include: (1)

lo transform dissolved und particulate biodegradable constituenls into aecepluble end products, (2) 10 capture and incorporate suspended and non settable colloidal solid into a biological floc

or biofilm, (3) to transform or romove nutrients, such az nitrogen and phosphorus, and (4) in somo œusos Wy romove spucifie Luce organic coustiluenly and eourpounds (Fchubanoglous ef

al, 2004)

e/ Types of Biological processes in wastewater treatment

31

‘The principal biological processes used in wastewater treatment can be classified into two main categories: (1) suspended growth processes and (2) attached growth processes (Fchobanogious et al,, 2003) Typical process applications for suspended and attached growth

biological treatment processes are present in table 1.8

1able 1.8 Major biological treatment processes used for wastewater treatment *

Acrobic processes

Suspended grawth | Activated sludge process(es) Carbonaceous BOD removal, nitrification

Acrated lagoons Carbonaceous BOD removal, nitrification Aerobic digestion Stabilization, carbonaceous BOD removal Attached growth Trickling filters Carbonaceous BOD removal, nitrification

Rotating biological contactors | Carbonaceous BOD removal, nitrification Packed bed reactors Carbonaceous BOD removal, nitrification Hybrid (combined) | Trickling filters! activated sludge | Carhanaccous ROD removal, nitrification suspended and

ailached growth

processes

Anoxic processes

Suspended growth | Suspended growth denitrification | Denitrification

Altached growth Attached growth denitrification Denitrification

Upflow anaerobic sludge blanket

Upflow anaerobic stidge blanket!

attached growth Combined aerobic, anoxtc, and anaerobic processes,

Anaerobic lagoons Single or mulli stage proc

‘various proprietary processes

Single or multi stage processes

with packing for attached growth

a: From Tchnbanoglaus et al., 2003

Carbonaceous BOD removal

Stabilization, solid destruction, pathogen kill

Carbonaceous BOD removal, waste stabilization, denitrification

Carbonaceous BOD removal, especially high strength wastes

Carbonaccans ROD removal

Curbunaceous BOD removal, nitrification, denitrification, and phosphorus removal

Carbonaceous BOD removal, nitrification denitrification, and phosphorus removal

Carbonaceous BOD removal Carbonaceous BOD removal, nitrification

Carbonaceons BOD removal

Carbonaccous ROD remaval, wastc

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Suspended growth pracesses

In suspended growth processes, the microorganisms are maintained in liquid suspension by appropriate mixing methods Many suspended growth processes used for treatment of municipal and industrial wastewater are operated in aerobic conditions However, suspended growth anaerobic reactors are used for high concentration industrial wastewaters and organic shudges

"Lhe most common suspended growth process used for municipal wastewater treatment

is the activated sludge process (see figure 1.4) In the aeration tank of activated sludge proces influent wastewater is aerated and mixed with the snicrobial suspensiun by mechanical equipment ‘he mixed liquor then flows to a clarifier where the microbial suspension is settled and thickened, The scttled biomass, called activated sindge because active microorganisms arc retnmed to the aeration tank to continme the biodegradation af the influent organic matters A portion of thickened solids is removed periodically to avoid the entering of' excess biomass into the system effluent, An important characteristic of the activated sludge process is the

formation of floc particles (sizes of 50-200 um), which can be removed greater than 99

percent by clarifier, leaving a relatively clear liquid as the treated eftiuent

'©ompleiø mức rug tok swoon tan

seetion tank later

Figure 1.4 Schematic of (a) plug flow and (b) complete mix activated sludge process

(Source: Tchobanoglous et al., 2003}

Attached growth processes

In attached growth processes, the microorganisms responsible for biodegradation of organic materials or nutrients are attached fo an inert parking material The organic material

and nuitients are removed from the wastewater owing past the altached growth known as

biofilm ‘here is a wide range of packing materials used in attached grawth processes

34

inelnding: rock, gravel, slag redwood, plastios and other synthetic materials Attached growth processes can be operated in aerobic ar anaerobic conditions ‘Ihe packing materials can be submerged completely in liquid or nen-submerged with aix or gas space above the biofilm liquid layer

The most common cerobic attached growth process used is trickling filter (see figure

13 in which water is distributed over the lop dieu of a coluwm containing packing saterials Rock wag the most commonly used in trickling filters, with typical depths ranging ftom 1.25

to 2m, Most modem trickling filters vary in height ttom 5 to 10 m and are filled with plastic packing mnaterials for biofibn alachment Air circulation in the void space between packing materials provides aerobic condition for microorganisms growing as an attached biofilm Influent wastewater is distributed over the packing materials and flows as a non-uniform liquid film over the attached biofilm Excess biomass sloughs from the attached growth periodically and clarification is required for liquid/solids separation to provide an efiluent with

an aeceplable suspended solids concentration The solids are collected at the bottom of the clarifier and removed for studge processing

Vigure 1.5 Schematic of trickling filter with (a) rock packing and (b) plastic packing

(Source: Tchobanoglous et al., 2003)

calcium, potassium, sulfate, nitrate, and phosphate or highly complex synthetic organic compounds (Izhobanoglous et al,, 2003}

The need for advanced wastewater treatment is based on the consideration of one or more of following factors: (1) the removal of organic matter and total suspended solids that can’t be accomplished by conventional secondary treatment processes to meet the stringent discharge and rouse viandards, (2) the removal of residual total suspended solids to condition the treated wastewater for more effective disinfection, (3) the removal of nutrients of treated effluent fiom convention secondary treatment to limit eutrophication of sensitive water bodies, (4) the ued to remove specific inorganic (eg heavy melals) and organic constiluents (e.g

MTB) to meet the stringent discharge and reuse requirements, (5) the need to remove

specific inorganic and organic constituents for industrial reuse (0.9 cooling water, process water, etc.)

Filtrahon, adsorption, gas stripping, ion exchange, advanced oxidation processes, distillation axe some of common processes used in wastewater treatment

1.3.3 Shudge Treatment and Disposal

In wastewater treatment sludge comes ftom preliminary, primary and secondary steps These sludges contain 95-99% water and probably pathogens fiom raw sewage The disposal

of sludge into sea has been forbidden and required treatment before any disposal in case of plants which have size more than 2000 people equivalents //Forsfer, 2003)

As referred above, sludge comes trom both preliminary and primary treatment steps such ay sercentings, gril romovel, primary sedimentation ay well a sevoudary Lreabnent such as activated sludge process, secondary sedimentation ‘The types of solids are different from various sources It should be noted that sludge also comes from processes used for thickening, digesting, conditioniug and Gilling (TcHobanoglous, 1979)

‘Yo treat and dispose of sludges prodnced from wastewater treatment plants, it is very necossary to know the physical, chemical as well as thermal characteristics of them The characteristics vary depending on the origin af sludge, the amount of aging that has carried out, and the processing type to which they have been subjected (Tchobemaglous, 1979)

Certain options which are now availible for sludge teatneu! indude: thickating, stabilization (chemical processes, heat treatment, aerobic digestion, anaerobic digestion),

36

dewatering, composting and for the disposal can he: landfill or utilization for agricultural land (Forster, 2003; Tchobanogious, 1979)

1.3.4 Effluent Disposal and Reuse

A treatment plant is designed to accomplish as much removal of pollutants as probably required Treated effinents which meet quality criteria will be disposed of or reused

The basic principle of the effluent disposal and the regulation of pollution is to make the treubuent plans do part of the work and Lo let ngiare complete il If this badunce is used improperly the receiving water will be polluted ‘Therefore the standard is set to ensure the safe disposal of treated effluents into the receiving water Depending on the local regulations there are different fimdamneutal considerations applicable for selling standard bul the basic oues we (1) degradable organic matter, (2) bacterial content, (3) conservative pollutants, (1) nutrients and (5) temperature Appropriate treated cfiluents can be disposed into lakes, rivers, estuaries and the ocean (Tehohanoglous, 1979}

A wide range of options for water reuse exists, including: (1) agricultural irrigation, (2) landscape inigution, (3) industiisl reuse, (4) recreational impoundinents, ($) groundwater recharge, (6) habitat wetlands, (7) miscellaneous uses, (x) augmentation of potable supplies

‘Also the reuse of effluents needs standard to ensure the safety (Tchobanoglous et al., 1998}

1.4 Current situation of Urban Wastewater Management in Vietnam

1A} The Development of the Urban Drainage System

In the period of 1858-1945, Vieluau started to build urban drainage syslems Drainage systems were built by bricks and collected both wastewater and stormwater Collected wastewater was discharged into lakes, canals or rivers (Trinh, 2007)

During the period of 1945-1975, sewerage systems in urban areas were expanded bul without planning Sewers are mainly made of precast concrete and bricks and the covers are broken because of no maintenance or destruction by bombs in the war (Trinh, 2007;

In the next fifteen years from 1975 to 1990, all concem was ahout the unification of the South and the North (hus, the gavernment did not pay much attention on sewerage system After 1990, as the renovation started, the authorities were more interested in urban dhainaye eyelem though as compare to waler supply il received less priority From the carly of

37

the 21" centnry the authorities have become more aware of significance af sewerages ax a part

of urban infrastructure systems,

1.4.2 Current Strncture and Operation of Urbun Drainage Systems

In this soction, the current situation of urban drainage systems in Vietnam inckuding collection systems and treatment systems will be disenssed

Collection of wastewater

Existing sewer networks in towns of class IV and higher are combined sysiems, including precast concrete pipes, brick canals with concrete panel covers, open channels ponds aud stabilization pond systems Sewerage system was constmucted in the past without a master plan of urban development; thus many sewers have smaller capacity (ham as reguired and without proper maintenance Mast af sewers and canals were not designed to have self- cleaning properties or not included ventilation to prevent odour in dry scazon (Trinh, 2007)

At present, there is no complete drainage system for collection of stormwater and wastewater nor wastewater treatment plants in towns of class V (Trinh, 2007) The rate of houschold with hygicne latrines is very low and the use of bucket Loilets and open defecation

is very popular Double vault composting latrines are also operated but generally maintained improperly Some households have septic tanks but do not connect to public sewerage system; thus wastewaler is discharged 1o small dilches or seeps inlo soil nearby People oflen throw

rubbish directly to sewers, canals and ditches leading to blockages in sewers and flooding in

rain season

‘The coverage of drainage services in urban arrours lias not been investigated Howev

according to estimation of experts from the Wepariment of Urban Infrastructure — ‘The

Ministry of Construction and Vietnam Dramage and Water Supply Association, the coverage

of drainage service is lower than (hal of water supply service The average coverage is

approximately 10-50% (from 1-2% in towns of class V to 70% in large towns) (Trinh, 2007)

The ratio of length in big towns is 0.2-0.5 m/person, but only 0.05-0.08 m/parson in small towns (Status Report, Water Secior Review Project, 2008) Many households served by septic tanks but not connected to public sewerage systems, thns wastewater flows over ta open ditches or sceps into the ground, Sume houscholds which have water pour toilets discharge

wastewater directly into the publie sewerage aystems withont any preliminary treatment (7'rinh,

2087)

38