[ DRESDEN UNIVERSITY OF TECHNOLOGY VNU UNIVERSITY OF SCIENCE Le Quynh Dung DEVELOPMENT OF A SIMPLIFIED CONCEPT FOR PROCESS BENCHMARKING OF URBAN WASTEWATER MANAGEMENT MASTER THESIS Hanoi - 2011 [ DRESDEN UNIVERSITY OF TECHNOLOGY VNU UNIVERSITY OF SCIENCE Le Quynh Dung DEVELOPMENT OF A SIMPLIFIED CONCEPT FOR PROCESS BENCHMARKING OF URBAN WASTEWATER MANAGEMENT Major: Waste Management and Contaminated Site Treatment MASTER THESIS SUPERVISOR: PROF DR RER NAT DR H C PETER WERNER MSC-ENG PHAN HOANG MAI Hanoi - 2011 TABLE OF CONTENTS ABBREVIATIONS LIST OF FIGURES AND TABLES ACKNOWLEDGEMENTS INTRODUCTION CHAPTER I Theoretical Foundations of Urban Wastewater Management System 1.1 Characteristics of Urban Wastewater 1.1.1 What is Urban Wastewater? 1.1.2 Constituents of Wastewater 1.2 Overview of the Urban Wastewater Management System 22 1.2.1 Components of Urban Wastewater Management System 22 1.2.2 Types of Wastewater Management System 23 1.3 Sub-processes of Wastewater Management System 26 1.3.1 Collection Systems 26 1.3.2 Wastewater Treatment 28 1.3.3 Sludge Treatment and Disposal 36 1.3.4 Effluent Disposal and Reuse 37 1.4 Current situation of Urban Wastewater Management in Vietnam 37 1.4.1 The Development of the Urban Drainage System 37 1.4.2 Current Structure and Operation of Urban Drainage Systems 38 1.4.3 The Organizations of Urban Drainage Services in Vietnam 39 1.4.4 Financial Aspects of Urban Drainage Companies 40 1.4.5 Legal and Institutional Frameworks 40 1.4.6 Investment and Management of Urban Drainage System 41 CHAPTER II 42 Benchmarking in the Urban Wastewater Management Sector 42 2.1 Fundamentals of Benchmarking 42 2.1.1 Definition of benchmarking 42 2.1.2 Types and elements of benchmarking 43 2.2 International Benchmarking System in Water Industry 46 2.2.1 Benchmarking of large Municipal Wastewater Treatment Plants in Austria 46 2.2.2 Benchmarking in Canada 48 2.2.3 North European Benchmarking Co-operation 49 2.3 Process Benchmarking in Wastewater Sector 52 2.3.1 What is Process Benchmarking? 52 2.3.2 The Objectives of Process Benchmarking 52 2.3.3 Methodology in Process benchmarking 53 2.3.4 Different Process Benchmarking Concepts 53 CHAPTER III 55 Performance Indicators of Benchmarking in Wastewater Service 55 3.1 Basis of Performance Indicators 55 3.1.1 Systems of Performance Indicators 55 3.1.2 The Usage of Performance Indicators (PIs) 57 3.1.3 Performance Indicators – A component of Benchmarking 59 3.2 The System of IWA-PIs for Wastewater Services 60 3.2.1 Context Information 60 3.2.2 Performance Indicators 62 CHAPTER IV 65 Performance Assessment and Data Collection for Benchmarking in Wastewater Services of Vietnam 65 4.1 Approach of the Performance Assessment 65 4.1.1 Classification of various Undertakings 65 4.1.2 Performance Indicators 66 4.1.3 Confidence Grades 67 4.1.4 Structure of Questionnaire 67 4.2 Questionnaire of Wastewater Management System 68 4.3 Performance Indicators for Wastewater Management System 79 4.3.1 Environmental Impacts 79 4.3.2 Operation and Maintenance 80 4.3.3 Quality of services 86 4.3.4 Employees 89 4.3.5 Economic and financial aspects 90 4.4 Data Collection 92 CONCLUSIONS 93 REFERENCES 95 APPENDIX 99 ABBREVIATIONS CSOs Combined Sewer Overflows CI Context Information EWA European Water Association IWA International Water Association NEBC North European Benchmarking Co-operation No Number PIs Performance Indicators p.e Population Equivalent WWTPs Wastewater Treatment Plants LIST OF FIGURES AND TABLES Figures Figure 1.1 Representation of a Centralized Wastewater Collection and Treatment System Figure 1.2 Representation of a Decentralized Wastewater Collection and Treatment System Figure 1.3 Schematic of unit operations and processes in a wastewater treatment plant Figure 1.4 Schematic of plug flow and complete mix activated sludge process Figure 1.5 Schematic of trickling filter with rock packing and plastic packing Figure 2.1 Main steps of a benchmarking process Figure 2.2 Extended process model for wastewater treatment plants above 100,000 PE Figure 2.3 Methodology for the development of process performance indicators Figure 2.4 NEBC’s benchmarking model Figure 2.5 Procedure of process 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 flowrates from urban residential sources in the USA Table 1.5 Typical wastewater flowrates 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 Major biological treatment processes used for wastewater treatment Table 2.1 Holistic approach versus Selective approach in Process benchmarking Table 3.1 Reliability bands of collected data Table 3.2 The IWA Performance Indicators Table 4.1 Summary of Performance Indicators for Urban Wastewater Management ACKNOWLEDGEMENTS This thesis has been developed in Dresden, Germany with the support of some people to whom I would like to express my special thanks I would like to thank Prof Nguyen Thi Diem Trang - Hanoi University of Science and Prof Bernd Bilitewski - Institute of Waste Management and Contaminated Site Treatment (IAA), Dresden University of Technology (TUD) as well as DAAD because of giving me the chance to my thesis in Germany I would like to send my special thanks to Msc Phan Hoang Mai, (IAA-TUD), who gave me this topic, supervised and encouraged me to write my thesis I have learnt some things for my studying from her Also I would like to thank Dr Catalin Stefan (IAA-TUD) because of his kind help during the time I was in Dresden Thanks are also expressed to Msc Le Thi Hoang Oanh (IAA-TUD) who was always willing to help me as I need Especially, I would like to thank my family and friends, who always support and encourage me to finish my thesis INTRODUCTION Wastewater Management is one of the most concerns in any urban area An efficient management contributes to the wealth of a community, never the less a poor management leads to unpredictable hazards related to health, environmental pollution, etc In developed countries, the issues of water and sanitation are solved, floodings are well controlled However, the issues of water supply and sanitation are not solved in developing countries, poor management of floodings as well as improper operation and maintenance of sewer systems are very popular Therefore, it is an urgent requirement to improve the system of wastewater management in developing countries Benchmarking is promised to be a solution to this problem as it is always the useful tool for improvement in management Benchmarking was first time introduced by Xerox Company in the late 1970s when their peer company Fuji produced the photocopiers with better quality and lower prices Xerox was forced to critically review their products and production costs by adopting the Japanese philosophy: gaining the best of the bests by learning, adapting and improving (Parena et al., 2001) That was how benchmarking appeared In many countries experiences (Xerox model inspired) have been developed to adapt benchmarking procedures in the water context (Parena et al., 2001) Benchmarking has been conducted in many developed countries such as Australia, Canada, England, Germany etc 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 and are supposed to sustain Some systems of performance indicators have been developed with the purpose of large scale application such as the system International Water Association or Qualserve system, etc In some developing countries such as India, Vietnam, etc certain benchmarking projects regarding the issue of water and sanitation have been carried out under the support of the 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 questionnaire prepared for benchmarking in Vietnam, a representative of developing countries are adapted in this thesis based on the International Water Association (IWA) 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 urban areas of Vietnam In chapter II, fundamentals of benchmarking and process benchmarking for the water industry are discussed To make clear the tool of performance assessment presented in the thesis the performance indicators for wastewater services of IWA as well as the basis of performance indicators are given in chapter III Chapter IV explains the performance indicators selected for process benchmarking in wastewater services of Vietnam; also, the questionnaire as well as the excel file to collect data from wastewater undertakings 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 can play a significant role in the sector as a tool for institutional strengthening 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 to implement CHAPTER I 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 Vietnam 1.1 Characteristics of Urban Wastewater 1.1.1 What is Urban Wastewater? According to Tchobanoglous et al 2003, urban wastewater components may vary depending on type of collection system and may include: Domestic (sanitary) wastewater Wastewater discharged from residential areas, and from commercial, institutional and similar facilities Industrial wastewater Wastewater in which industrial wastes predominate Stormwater Runoff resulting from rainfall Infiltration/Inflow Water that enters the collection system through indirect and direct means Infiltration is extraneous water that enters the collection system through leaking joints, cracks and breaks, or porous walls Inflow is stormwater that enters the collection system from storm drain connections, roof leaders, foundation and basement drains, or through access port (manhole) covers 1.1.2 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 concerning ones are referred All wastewater treatment facilities are designed to remove these constituents completely 1.1.2.1 Physical Characteristics Solids There are many kind of solids present in wastewater, varying from coarse to colloidal ones Before any analysis of solids in wastewater the coarse material should be removed In wastewater treatment, the solids can be classified by their size and state (suspended solids & APPENDIX Table General classification of microorganisms a Group Eukaryotes Cell structure Eukaryotic Characterization Prokaryotic Prokaryotic member 10-100 µm Plants (seed extensive differentiation of cells and tissue in diameter plants, ferns, mosses); animals (vertebrates, invertebrates) coenocytic or mycelial; little or no tissue differentiation Cell chemistry Archaea Representative Multicellular with Unicellular or Eubacteria Typical size 10-100 µm Algae, fungi, in diameter protozoa 0.2-2.0 µm Most bacteria similar to eukaryotes in diameter Distinctive cell 0.2-2.0 µm Methanogens, chemistry in diameter halophiles, thermacidophil es a: From Tchobanoglous et al., 1998 99 Table General information of wastewater undertakings No Criteria Wastewater Drainage Utility General 1.1 Information 1.1.1 Utility full name 1.1.2 Utility short name or acronym 1.1.3 Province 1.1.4 City 1.1.5 Types of services provided 1.1.6 Types of assets ownership 1.1.7 Types of operations 1.2 Region Profile 1.2.1 Size of Utility’s area of Responsibility 1.2.2 Population of Utility’s area of responsibility 1.2.3 Yearly rainfall Minimum Average Maximum 1.2.4 Receiving bodies Rivers Lakes, ponds, reservoirs Wetlands Soil type of soil: 1.2.5 Total number of wastewater quality tests required by standards 1.3 System profile 1.3.1 Collection System 1.3.1.1 Daily collected sewage Unit km inhabitants mm/year mm/year mm/year km km km km # m3 / day 100 Company Company Company Company 1.3.1.2 Catchment area Total catchment area Impermeable catchment area 1.3.1.3 Physical assets of sewer networks Types of sewers (please tick on the relevant box) Combined sewer Separate sewer Mixed sewer system Total sewer length Combined sewer length Sanitary sewer length Storm sewer length Sewer materials: Clay Asbestos cement Concrete Polyethylene 1.3.1.4 Iron Other material Average age of sewer system Ancillaries of Sewer system Number of manhole chambers in the sewer system: Number of gully pots in the sewer system Number of sewer overflows 1.3.1.5 Number of storage tanks in the sewer system Total volume of storage tanks and CSOs in the 1.3.1.6 sewer system 1.3.1.7 Service connections Number of Domestic connections from residential area 101 km km km km km km % % % % % % years # # # # m3 # Number of Industrial connections from residential area: 1.3.1.8 1.3.2 1.3.2.1 1.3.2.2 1.3.2.3 Number of on-site treatment (septic tank) connections (in case of combined sewers) Number of other connections (from hospitals, commercial buildings): Number of dispensed connections Total number of service connections Number of wastewater pumping stations in the sewer system (including WWTP inlet pumping) Wastewater Treatment Plants Total number of WWTPs Total separate system WWTP (wastewater from separate sewer system) Total combined system WWTP (wastewater from combined sewer system) Total mixed system WWTP (wastewater from mixed sewer system) Number of population equivalent served by WWTPs Treatment capacity Installed Preliminary treatment capacity Installed Primary treatment capacity Installed Secondary treatment capacity 102 # # # # # # # # # # p.e p.e p.e Table Data collected for indicators of environmental impacts group No 2.1 2.1.1 2.1.2 2.2 2.2.1 2.2.2 2.2.3 Criteria Unit Wastewater Number of overflow discharge in the year Population equivalent that is served by WWTPs complying with discharge consents Solid residues Drained weight of sediments from sewers in the year Drained weigth of slugde produced from WWTPs Drained weight of sediments from septic tanks in the year 103 # / year p.e ton / year ton / year ton / year Company Company Company Company Table Data collected for indicators of operation & maintenance group No 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.1.7 3.1.8 3.2 3.3 3.3.1 3.3.2 3.3.3 3.3.4 3.3.5 3.4 3.4.1 3.4.2 3.4.3 Criteria Inspection and cleaning Length of sewer inspected in the year Length of sewer cleaned in the year Number of manhole chambers inspected Number of gully pots inspected Number of gully pots cleaned Volume of storage tanks and CSOs inspected Volume of storage tanks and CSOs cleaned Number of pumping stations inspected Energy consumed by WWTPs in the year Rehabilitation and replacement Length of defective sewers rehabilitated in the year Length of sewers replaced in the year Number of manhole chambers replaced, renewed or repaired Number of repair carried out in defective sewers and joints Number of service connections replaced or renewed Infiltration/Inflow/Exfiltration Inflow – Volume of water entering sewers from wrong / illegal connections Infiltration – Volume of water entering sewers from ground water Exfiltration – Volume of leakage from sewers into the ground 104 Unit km km # / year # / year # / year m3 / year m3 / year # / year kWh / year km km # / year # / year # / year m3 / year m3 / year m3 / year Company Company Company Company 3.4.4 No information of volume of leakage from sewers and volume of water entering sewers 3.5 Failures 3.5.1 Number of sewer blockages # / year Number of blockages that occurred in pumping 3.5.2 station in the year # / year Number of floodings that occurred from # / year 3.5.3 combined sewers Number of surface floodings (due to inadequacy # / year 3.5.4 of storm drainage system) Number of sewer collapses (not included the # / year 3.5.5 collapses in service connection) Number of hours when each pump was out of 3.5.6 order 3.6 Wastewater quality tests Number of wastewater quality tests carried out in 3.6.1 the year # / year Number of industrial discharges tests carried out 3.6.2 in the year # / year 105 hours / pump /year Table Data collected for indicators of quality of services group No 4.1 4.1.1 4.1.2 4.1.3 4.1.4 4.1.5 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.3 4.3.1 4.3.2 4.3.3 4.3.4 4.3.5 4.4 Criteria Unit Coverage degree Resident population connected to the sewer systems Resident population served by WWTPs Resident population served by septic tanks Resident population served by wastewater services Resident population whose wastewater is neither collected nor treated Wastewater discharge level Volume of wastewater treated in WWTPs in the year Volume of wastewater receiving only preliminary treatment at WWTPs Volume of wastewater receiving only primary treatment at WWTPs Volume of wastewater receiving secondary treatment at WWTPs Reply to customer requests Number of new service connections established in the year Total number of service connections repaired in the year Total time spent for repairing service connections Total number of request for emptying septic tanks or pit latrines in the year Total response time to empty septic tanks or pit latrines in the year Total number of complaints related to wastewater system in the year 106 inhabitants inhabitants inhabitants inhabitants inhabitants m3 / year m3 / year m3 / year m3 / year # / year # / year # / year # / year # / year # / year Company Company Company Company Table Data collected for indicators of employees group No 5.1 5.1.1 5.1.2 5.1.3 5.1.4 5.2 5.2.1 5.2.2 5.3 5.3.1 5.3.2 5.3.3 Criteria Unit Type of employees Permanent employees – with contract Casual / part time – contract employees Casual / part time – wages Other, please specify Full time equivalent employees in the company Number of full time equivalent employees working in sewer system Number of full time equivalent employees working in WWTPs Employee Qualification University degree employees Basic education employees Other qualification employees 107 employees employees employees employees employees Company Company Company Company Table Data collected for indicators of economic and financial aspects group No Criteria Unit 6.1 Annual revenues from wastewater drainage 6.1.1 Wastewater discharge fee The percentage of wastewater discharge fee compare to price of m3 of clean water Total revenues from wastewater discharge fee 6.1.2 Environmental protection fee The percentage of environmental protection fee compare to price of m3 of clean water (for domestic sources) From non-domestic sources 6.1.3 Total revenues from environmental protection fee Other revenues From emptying septic tanks or pit latrines Others, please specify 6.1.4 Total annual revenues 6.1.5 Adjustment of Discharge fee Is there any adjustment of discharge fee in last five years? If yes, how many percent increase? 6.2 Total Running cost 6.2.1 Internal manpower costs 6.2.2 Energy costs 6.2.3 Materials, chemicals & other consumable costs 6.2.4 External service costs 6.2.5 Other running costs 6.3 Annual interest expenses of the utility 6.4 Annual interest income of the utility 6.5 Principal source of funds for investment 108 % US$ / year % US$ / year US$ / year US$ / year US$ / year % US$ / year US$ / year US$ / year US$ / year US$ / year US$ / year US$ / year US$ / year Company Company Company Company 6.5.1 6.5.2 6.5.3 6.5.4 6.5.5 6.6 6.7 6.8 6.9 % % % % % US$/year US$ US$/year Own internal sources funding National budget Loan from ODA sources Private sector investment Other sources Annual National Budget investment Total debt servicing costs Total annual cost related to sewer system Total annual cost (including sewer system and wastewater treatment) Depreciation (refer to the book value): US$/year US$ 109 Table The value of performance indicators in wastewater undertakings No 7.1 7.1.1 7.1.2 7.1.3 7.1.4 7.1.5 7.2 7.2.1 7.2.1.1 7.2.1.2 7.2.1.3 7.2.1.4 7.2.1.5 7.2.1.6 7.2.1.7 7.2.2 7.2.2.1 7.2.2.2 7.2.2.3 7.2.2.4 7.2.3 7.2.3.1 7.2.3.2 7.2.3.4 7.2.4 7.2.4.1 Performance Indicators Environmental Impacts Wastewater treatment plant compliance with discharge consent Overflow discharge frequency Sludge production in WWTPs Sediments from sewers Sediments from septic tanks Operation and Maintenance Inspection and Maintenance Sewer inspection Sewer cleaning Manhole chamber inspection Gully pots inspection Tanks & CSOs inspection frequency Tanks & CSOs cleaning volume Pumping station inspection frequency Rehabilitation Sewer rehabilitation Sewers and joints repair Manhole chamber replacement, renewal, renovation or repair Service connection rehabilitation Infiltration/ Inflow/ Exfiltration Inflow Infiltration Exfiltration Failures Sewer blockages Unit % no./overflow device/year kg D.S/1000 p.e/year ton/km sewer/year ton/p.e./year %/year %/year %/year %/year -/year -/year -/year %/year no./100km sewer/year %/year %/year m3/km/year m3/km/year m3/km/year no./100km sewer/year 110 Company Company Company Company 7.2.4.2 7.2.4.3 7.2.4.4 7.2.4.5 7.2.4.6 7.2.5 7.2.5.1 7.2.5.2 7.3 7.3.1 7.3.1.1 7.3.1.2 7.3.1.3 7.3.1.4 7.3.2 7.3.2.1 7.3.2.2 7.3.2.3 7.3.2.4 7.3.3 7.3.3.1 7.3.3.2 7.3.4 7.4 7.4.1 7.4.2 Pumping station blockages Flooding from combined sewers Surface flooding Sewer collapses Pump failures Wastewater quality tests Wastewater quality tests carried out Industrial discharge tests carried out Quality of services Coverage degree Resident population connected to sewer system Resident population served by WWTPs Resident population served by septic tank Resident population not served Wastewater discharge level Treated wastewater in WWTPs Preliminary treatment Primary treatment Secondary treatment Reply to customer requests Service connection repair time Average response time to empty septic tanks or pits Complaints Total complaints Employees Personnel in WWT per population equivalent Personnel working on sewer per length of sewer no./pumping station/year no./100km sewer/year no./100km sewer/year no./100km sewer/year hours/pump/year -/year -/year % % % % % % % % days/repaired connection days/request no./1000 inhabitants/year no./1000 p.e no./100km sewer 111 7.4.3 7.4.3.1 7.4.3.2 7.5 7.5.1 7.5.1.1 7.5.1.2 7.5.2 7.5.3 7.5.4 Employee qualification University degree personnel Basic education personnel Economic and financial aspects Unit total cost Unit total cost per population equivalent Unit total cost per length of sewers The contribution of National Budget to total annual cost The contribution of wastewater service fee to total annual cost Total cost coverage ratio % % US$ / p.e./ year US$ / km sewer/ year % % % 112 The value of indicator is calculated automatically when data is put into groups in excel file Figure 1: Value of Performance Indicators in Wastewater Undertakings 113 [...]... Pathogens found in wastewater may be discharged by human who are suffering with diseases or who are carriers of a particular disease The pathogenic microorganisms found in wastewater can be classified into three broad categories: bacteria, parasites (protozoa and helminths) and viruses Bacteria There are many types of harmless bacteria in human intestinal track and human feces Pathogens are only found... not for waterborne protozoa or pathogenic organisms that may arise from nonhuman sources Therefore the use of new indicator bacteriophages is much more concerned (Tchobanoglous et al., 1998) 1.1.3 Flowrates and Composition of Wastewater The analysis of wastewater data involves the determination of the flowrate and mass loading variations From the standpoint of treatment processes, average flowrates and... cleaning operations Surfactants tend to 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 because of the hygienic issues but also the significance of microorganisms in water and wastewater 16 treatment In this section,... lagoons Carbonaceous BOD removal Aerobic lagoons Carbonaceous BOD removal, nitrification Maturation lagoons Maturation (tertiary) lagoons Carbonaceous BOD removal Facultative lagoons Facultative lagoons Carbonaceous BOD removal, waste stabilization Anaerobic lagoons Anaerobic lagoons a : From Tchobanoglous et al., 2003 33 Suspended growth processes In suspended growth processes, the microorganisms are... 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 as eukaryotes, eubacteria and archaea Their cell structure, typical size, characterization and representative member are illustrated in table 1 (appendix) Pathogenic Microorganisms Pathogens... infected humans feces therefore wastewater contain both pathogenic and nonpathogenic bacteria One of the most common pathogenic organisms found in domestic wastewater is the genus Salmonella The Salmonella group contains variety species causing diseases to human and animals Other bacteria isolated from raw wastewater which causes cholera is Vibrio cholerae Protozoa Because of their significant impact on... 1.8 Major biological treatment processes used for wastewater treatment a Type Common name Use Aerobic processes Activated sludge process( es) Carbonaceous BOD removal, nitrification Aerated lagoons Aerobic digestion Carbonaceous BOD removal, nitrification Stabilization, carbonaceous BOD removal Attached growth Trickling filters Rotating biological contactors Packed bed reactors Carbonaceous BOD removal,... 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 to an inert parking material The organic material and nutrients are removed from the wastewater flowing past the attached growth known as biofilm... degree of treatment and type of plant required Treated wastewater can be discharged into lakes, rivers or the ocean The reuse of treated effluent can be applied for groundwater recharge, irrigation, etc These issues will be referred later 1.2.2 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 successfully in many industrialized countries over decades However, the cost of investment and implementation of this system is a big problem for any community Decentralized wastewater systems in which wastewater are treated near the source of generation are getting more concern as a potential alternative of traditional centralized wastewater management system