Tài liệu Investigation of anaerobic baffled septic tank (abr) for domestic wastewater

INVESTIGATION OF ANAEROBIC BAFFLED SEPTIC TANK (ABR) FOR DOMESTIC WASTEWATER by Tran Thi Mai Hoa A research study submitted in partial fulfillment of the requirements for the degree of Master of Science Examination Committee: Dr. Thammarat Koottatep (Chairman) Dr. Nguyen Thi Kim Oanh Dr. Toshiya Aramaki Nationality: Vietnamese Previous Degree: Bachelor of Science, Hanoi Teacher University Hanoi Vietnam Scholarship Donor: AIT Fellowship Asian Institute of Technology School of Environment, Resources and Management Thailand May 2005 Acknowledgement The author wishes to express her sincere gratitude to Prof. Thammarat Kottatep for his valuable suggestions, strong support, encouragement and readiness to help through out the study period. His availability at every steps of the research work has made it possible to accomplish this work. It was a valuable experience to work under his supervision. The author expresses the heartfelt gratitude towards Dr. Nguyen Thi Kim Oanh and Dr. Toshiya Aramaki for their serving as members of the thesis committee. Their critical suggestions, encouragements and moral support are highly appreciated. The author is equally indebted her lecturers for their valuable instruction throughout her Master program. Special thanks are also given to Ms. Suchitra Piempinsest, Ms. Salaya Phunsiri, Mr. Somchai Aremsum-Ang and Mr. Zaw Win Aung for their ever-willing help in academic and laboratory work as well as their invaluable suggestions, ideas and interest through out the study. Gratitude is extended to the Asian Institute of Technology providing fellowship to this author for master program in Environmental Engineering and Technology. The author also thanks to her parents, sister, brother, nephew and relatives for their strong moral supports to complete this work. Abstract Sanitation projects in developing countries mainly focus on toilets, neglecting other aspects of liquid waste management, such as greywater. Greywater represents volumewise by far the biggest wastewater source and needs therefore to be treated and disposed or reused correctly. Main problem is the lack of appropriate systems for the treatment and management of greywater on household level. The decentralized approach is a new means of addressing wastewater management needs of sewered and unsewered areas in a comprehensive fashion. The basic idea of that is to treat the wastewater (possibly together with refuses) on-site by means of lowcost treatment systems, and make direct use the treatment products (water, compost and biogas). This alternative can meet a sustainable wastewater management requirement and has a promising future, especially for developing country of Vietnam, where the water and sanitation issues are becoming a more and more important issue and are under new period of infrastructure development. This study was conducted to determine the ability of baffled septic tank system treating greywater. For determination of the four laboratory-scale baffled septic tank units, made of acrylic plastic with dimensions of 0.25 x 0.64 x 0.64 m3 (width x length x depth). The greywater supply for the systems from AIT campus. It was found that the removal efficiencies of baffled septic tank systems in terms of COD, TS, TSS of greater than conventional septic tank. Due to Wanasen (2002) study report that performance of baffled septic tank systems at HRT 48 hours is higher tan at HRT 24 hours then, the experiments were conducted at the HRT 48 hours. Characteristics of influent wastewater, baffled septic tank performance, relationships between removal efficiency and organic loads,up -flow velocity, hydraulic retention time, ambient temperature, presence of anaerobic filter and number of baffled chambers were discussed. Further, the authors describe results from experiment on real greyewater treatment by baffled septic tank that could be most feasible option for on-site wastewater treatment in residential areas of Vietnam. The investigations of treatment performance indicated that a septic tank with three baffles was the best as compared to conventional, two –baffles, two-baffles with filter media septic tank.The data show that septic tank with 3 baffled could effectively treat greywater in Vietnamese conditions, with average COD, TS and TSS removal of 65%, 57% and 90%.The decentralized schemes of wastewater management are also proposed for medium and small cities of Vietnam. iii Abstract Sanitation projects in developing countries mainly focus on toilets, neglecting other aspects of liquid waste management, such as greywater. Greywater represents volumewise by far the biggest wastewater source and needs therefore to be treated and disposed or reused correctly. Main problem is the lack of appropriate systems for the treatment and management of greywater on household level. The decentralized approach is a new means of addressing wastewater management needs of sewered and unsewered areas in a comprehensive fashion. The basic idea of that is to treat the wastewater (possibly together with refuses) on-site by means of lowcost treatment systems, and make direct use the treatment products (water, compost and biogas). This alternative can meet a sustainable wastewater management requirement and has a promising future, especially for developing country of Vietnam, where the water and sanitation issues are becoming a more and more important issue and are under new period of infrastructure development. This study was conducted to determine the ability of baffled septic tank system treating greywater. For determination of the four laboratory-scale baffled septic tank units, made of acrylic plastic with dimensions of 0.25 x 0.64 x 0.64 m3 (width x length x depth). The greywater supply for the systems from AIT campus. It was found that the removal efficiencies of baffled septic tank systems in terms of COD, TS, TSS of greater than conventional septic tank. Due to Wanasen (2002) study report that performance of baffled septic tank systems at HRT 48 hours is higher tan at HRT 24 hours then, the experiments were conducted at the HRT 48 hours. Characteristics of influent wastewater, baffled septic tank performance, relationships between removal efficiency and organic loads,up -flow velocity, hydraulic retention time, ambient temperature, presence of anaerobic filter and number of baffled chambers were discussed. Further, the authors describe results from experiment on real greyewater treatment by baffled septic tank that could be most feasible option for on-site wastewater treatment in residential areas of Vietnam. The investigations of treatment performance indicated that a septic tank with three baffles was the best as compared to conventional, two –baffles, two-baffles with filter media septic tank.The data show that septic tank with 3 baffled could effectively treat greywater in Vietnamese conditions, with average COD, TS and TSS removal of 65%, 57% and 90%.The decentralized schemes of wastewater management are also proposed for medium and small cities of Vietnam. iv Acknowledge Nowadays there are 571 cities and towns in Vietnam. The country is under rapid urbanization and industrialization process, with positive indicators in socio-economic development. However, there is an increasing problem of water pollution. The water supply capacity has increased from 1.95 million m3/day in 1990 to nearly 3 million m3 /day in late 2001. In the same period, the urban population has raised from 12 million in late 1980 to nearly 18 million in late 1999, accounting for 23.5% of the population of the whole country. There is very low ratio of population served by adequate sanitation, especially in rural, peri-urban and poor urban areas. Urban sewerage and drainage systems are still poor and under degradation. In most of cities and towns, flood and inundation often occur in rainy season. Existing sewer networks (if any) in cities have been built for surface water drainage only. Mainly domestic wastewater from houses is directly discharged to the common sewerage network and then flows to the canals, lakes and ponds without any treatment. In consequence, self-purification capacity of receiving water bodies is overloaded and it causes surface and ground water pollution, impacting directly to the health of community, reducing the value of environment. More than ever, development of urban sewerage and drainage systems in Vietnam has become an urgent need In Vietnam, the septic tank is the most common on-site treatment facility in urban and peri-urban areas. In Hanoi, there are about 10,000 septic tanks in operation for treatment of the domestic wastewater. In urban centers the ratio of households equipped with septic tanks is nearly 0-80%. In the rest of the city the ratio is 20-30% (Hanoi PC, 1998). Dislodging of septic tanks is not often followed. There is still subsidizing form of management of public utilities including wastewater management, without or with very poor public involvement. Thus, looking for the appropriate solutions for wastewater management is becoming very hot issue and is to be paid adequate attention, especially in this period of increasing urbanization, industrialization, improvement and development of water supply and sanitation facilities. v Table of Contents Chapter Title Acknowledgement Abstract Table of Contents List of Tables List of Figures Page i ii iii iv v 1 1.1 Background 1.2 Objectives of study 1.3 Scope of study 2 3 4 5 1 1 2 Literature review 2.1 Decentralized wastewater treatment systems (DEWATS) 2.2 Septic Tank 2.3 Anaerobic baffled reactor (ABR) 2.3.1 Introduction of ABR 2.3.2. Treatment wastewater by ABR systems 2.4. Vietnam sanitation situation 3 3 6 6 7 8 Methodology 3.1 Preparation of wastewater 3.2 Experimental set up 3.2.1 Apparatus 3.2.2 Unit Installation 3.3. Start-up of the experiments 3.3.1 Operating conditions 3.3.2 Experimental investigations 13 13 14 14 16 17 17 Result and Discussion 4.1 Influent characteristics 4.2 Result of experimental units 4.2.1 COD removal 4.2.2 TS removal 4.2.3 TSS removal 4.2.4.Gas production 4.3 Discussions 19 19 19 21 22 23 24 Conclusions and Recommendations 5.1. Conclusion 5.2. Recommendation 25 25 References Appendices 26 28 iii List of Tables Table 2.1 2.2 2.3 3.1. 3.2 3.3 3.4 3.5 4.1 4.2 4.3 4.4 4.5 4.6 Title Wastewater management options for unsewered areas Urban and rural sanitation in Vietnam 2000 Vietnam sanitation and clean water for Ho Chi Minh City, Haiphong and Hanoi Characteristics of AIT wastewater Characteristics of AIT greywater and blackwater Operating conditions of experiment Parameter and analytical methods Sampling frequency Influent characteristics COD removal efficiencies of experimental units TS removal efficiencies of experimental units TSS removal efficiencies of experimental units Gas volume of experimental units Gas compositon of experimental units . iv Page 3 9 10 13 13 17 17 18 19 20 21 22 23 23 List of Figures Figure 2.1 2.2 2.3 3.1 3.2 3.3 3.4 3.5 4.1 4.2 4.3 Title Tank dimensions Conventional septic tank Anaerobic baffled reactor Conventional septic tank Septic tank with 3 baffles Septic tank with 2 baffles Septic tank with 2 baffles and an aerobic filter media Schematic diagram of laboratory–scale units Result of COD removal efficiency Result of TS removal efficiency Result of TSS removal efficiency v Page 4 5 7 14 15 15 16 16 20 21 22 Chapter Title Table of Contents List of Tables List of Figures 1 Background 1.1 Objectives of study 1.2 Scope of study 2 Literature review 2.1 Decentralized wastewater treatment systems (DEWATS) 2.2 Septic Tank 2.3 Anaerobic baffled reactor (ABR) 2.3.1 Introduction of ABR 2.3.2. Treatment wastewater by ABR systems 2.4. Vietnam sanitation situation 3 Methodology 3.1. Preparation of wastewater 3.2. Experimental set up 3.2.1 Apparatus 3.2.2 Unit Installation 3.3. Start-up of the experiments 3.3.1 Operating conditions 3.3.2 Experimental investigations 4 Result and Discussion 4.1. Influent characteristics 4.2. Result of experimental units 4.2.1 COD removal 4.2.2 TS removal 4.2.3 TSS removal 4.2.4. Gas production 5 Conclusion and Recommendation 5.1. Conclusion 5.2. Recommendation Reference vi Page i ii iii Chapter 1 Introduction 1.1 Background Environmental Sanitation Planning nowadays plays an important role in our life. As population has increased in urban area of developing countries, so has the number of people lacking access to sanitation. Since 1990, an additional 300 million individuals are making do without decent sanitation, an ominous indication that the world community if failing in its efforts to provide services where they are most needed. Many large cities are still no have central sewage systems for the millions of residents and an inadequate excreta disposal system are rarely considered a problem by the people). In the absence of sanitation systems, some communities rely on natural processes; defecation takes place in the open fields or on surface waters. In the latter option, human waste is directly disposed of into the river, canal and sea for transport and eventual dilution. In developing countries, the primary constraints to successful provision of sanitation facilities are the lack of investment, trained personnel and lack of knowledge about acceptable alternative technologies. So the selection of appropriate sanitation system for a given community is very necessary for environmental sanitation planning Decentralized wastewater treatment systems seem to be a suitable alternative, which has been proposed in both developing and developed countries. Nowadays, more than 60 millions people in the United States live in homes that are served by decentralized collection and treatment systems (Crites and Tchobanoglous, 1998). Decentralized wastewater treatment systems comprise of many type treatment facilities such as Imhoff tank, constructed wetlands, privy, septic tank, etc. Septic tank systems are widely applied in households in developing countries for treating wastewater because of its low costs in construction and maintenance systems. However, the conventional septic tank cannot provide effluent that able to meet the standards. Improper disposal of the effluent from septic tank systems threaten to the environment and human life. Then, it is required to have further treatment of the effluent by another facilities or improvement septic tank systems. This research aims at investigating anaerobic baffled reactors that could improve treatment performance of conventional septic tank systems. The septic tank was installed with the different number of baffle. All baffled septic tanks were fed with greywater, which come from AIT campus. The performance of different Anaerobic baffled reactors systems were investigated. 1.2 Objectives The research focused on specific objectives as follows: 1. To investigate the feasibility of using baffled septic tank treating greywater 2. To investigate and monitor the effects of number of baffles and anaerobic filter on the treatment performance of septic tank 1 1.3 Scope of study The experiments were conducted by using the laboratory-scale units located at the ambient laboratory of Asian Institute of Technology (AIT). The scopes of experiment were as follows: 1. AIT campus wastewater was fed into the laboratory-scale units at a constant hydraulic retention time (HRT) of 48 hours. 2. The performance and characteristics of each reactor were determined in terms of COD, TS, TSS and gas volume. 2 Chapter 2 Literature Review 2.1 Decentralized wastewater treatment systems (DEWATS) The concept of decentralized wastewater treatment systems (DEWATS) are defined as the collection, treatment, and disposal/reuse of wastewater from individual homes, clusters of homes, isolated communities, industries, or institutional facilities, as well as from portions of existing communities at or near the point of waste generation (Crites and Tchobanoglous, 1998). Decentralizes systems maintain both the solid and the liquid fractions of the wastewater near their point of original, although the liquid portion and any residual solids can be transported to a centralized point for further treatment and reuse (Polprasert, 1996). Some technologies have been applied for decentralized wastewater treatment systems that have made it possible to produce an effluent of the same quality as compared to large treatment plants. There are many DEWATS options can be used depending on operating and maintenance requirement (Crites and Tchonologous, 1998) such as: conventional septic tank, septic tank with re-circulating, trickling filters, imhoff tank, and intermittent sand filter. Table 2.1 shown the principle wastewater management options for unsewered areas. Table 2.1: Wastewater management options for unsewered areas Source of waste Individual residents: Combined wastewater, black waste water and grey wastewater, Public facilities and Commercial establishments Wastewater treatment Primary treatment : Septic tank, imhoff tank Secondary treatment: Aerobic/Anaerobic units Onsite containment: Holding tank , privy Wastewater disposal Disposal fields, Seepage beds, Shallow sand-filled, disposal trenches, mound systems, vapotranspiration, drip application, wetland, discharge to water bodies and combination of the above. DEWATS was called as “septic systems” (U.S.EPA 2000), it includes individual onsite septic systems and others wastewater treatment options such as: mound systems, recirculation sand filters, constructed wetland and ozone disinfection systems. 2.2 Septic tanks Septic tanks are mean as pretreatment for the removal of suspended solid prior to disposal by means of a sub-surface leaching field. The effluent still contains most of the organic pollutants and pathogens. The suspended solids that settle in septic tank are partially stabilized by anaerobic digestion. Biological activities reduce the mass of sewage solids in the tank; however, the septic tank still accumulates soiled over time. Typically, in Asia septic tanks are relatively small and should be cleaned every two or three years. If not, solid will pass through the septic tank and into drainage canals. The septic tank, in conjunction with its effluent disposal system, offers many of the advantages of conventional sewerage. However, septic tank systems are more expensive than most other on-site sanitation and are unlikely to be affordable by the poorer people 3 in society. They also require sufficient piped water to flush all the waste through the drains to the tanks. A tank maybe divided into two or more compartment by baffler wall. Most settlement and digestion may occur in the first compartment with some suspended materials carries forward to the second. Septic tanks with more than one compartment performed more effectively tan single – compartment tanks (Laak, 1980). Figure 2.1 Tank dimensions The construction of a septic tank usually requires the assistance and supervision of an engineer or at least an experiences construction foreman. Design of inlet and outlet is critical to the performance of the tank. Careful checking of levels is particularly important for large tanks that include complicated inlet, outlet and baffled board arrangement. During the installation of septic tanks, the following points should be considered: 1. Cast iron inlet and outlet structures should be used in disturbed soil areas where tank settling may occur. 2. The tank should be placed so that the manhole is slightly below the grade to prevent accidental entry. 3. The tank should be placed in an area with easy access to alleviate pump-out problems. (Kottatep T., 2004) It was described by Canter and Knox (1985) that the advantages of septic tank systems are shown as follows: 1. Minimal maintenance is required for the systems, with potential pump age of septage required every three to five years. While there are requirements for removal for septage, there is less sludge produced per person through use of a septic tank system than through use of a centralized mechanical plant such as an activated sludge plant. 2. The cost of individual or community septic tank systems is less than the cost of 4 central wastewater collection facilities and treatment plant. 3. The septic tank systems represent a low technology system, thus the possibility for long term operation without extensive periods of shutdown is enhanced. 4. The energy requirements of septic tank systems are low in comparison to centralized wastewater treatment facilities The disadvantages of septic tank systems are shown as follows: 1. The potential for ground water pollution depending upon the soil characteristics and density of systems in a given geographical area. 2. System overflows and pollution of adjacent water wells and surface water courses if the systems are not properly maintained. 3. Cleaners used for maintenance of septic tank systems may create difficulties in terms of ground water pollution, particularly cleaners that have organic solvent bases. Conventional septic tank Conventional septic tanks are used to receive wastewater discharged from individual residences, and other non-sewer facilities, for examples; toilet water, water used from cooking or bathing (Figure 2.1). To improve treatment performance, an in-tank baffle is used to divide the tank, and access ports are provided to permit inspection and cleaning. The benefits of two compartment tanks appears to depend more on the design of the tank than the use of tow compartment ( Matcalf and Eddy, 2003). To provide highly efficient treatment of effluent that is relatively free of oils and greases, solids and other constituents that can clog and foul collection and disposal equipment. 5 Figure 2.2: Schematic of Conventional septic tank It was suggested by Bounds (1997) that the operating requirements are shown as follows: 1. HRT should range between 24-48 hours for normal use. 2. An operating zone should be sufficient to accommodate peak inflows without causing nuisance or excessive hydraulic gradients. 3. HRT should be sufficient for allowing oils and greases, and other settle able materials to settle. HRT is based on average daily flows. 4. The space for storing sludge and scum must be big enough. 5. Septic tanks volume must be sized based on amount of wastewater to be handled ( Center et al., 1985) Polprasert (1996) investigated that the hydraulic retention time (HRT) designed for septic tank or cesspool is only about 1-3 days to remove the settle able solids and retain the scum. Watt (1984) described that there is not a steady flow of incoming sewage of septic tanks. There are surges and shock flows, which expose the tanks to wide variations in sewage flow and strength, which disturb the treatment processes. Efficiency of waste treatment therefore varies, and effluent quality varies also. Large tanks tend to smooth out these variations, but extra tank capacity has to be paid for. In order to analyze this problem of effluent quality, therefore, we need first to consider the quantity and strength of sewage inflows into septic tanks. 2.3. Anaerobic baffled reactor (ABR) 2.3.1 Introduction of ABR One option to developed septic tanks is to install baffles through out the unit, it called an Anaerobic Baffled Reactor (ABR). An ABR consists of chambers in series, in each chamber it has a vertical baffle to force wastewater to flow and over it. Baffles are used to direct the flow of wastewater in an up- flow mode through a series of sludge blanket reactors. The sludge in the reactor rises and falls with gas production and flow, but moves through the reactor at a slow rate. The last chamber could have a filter in its upper part to retain flow-over solid particles. The risk of clogging and sludge bed expansion with resulting high microbial losses is reduced and there is no need for special gas collection or biological solids separation systems (Bechmann et al., 1985). Three are three common types of the ABR (Figure 2.2) as follows: 1. ABR without media. 2. ABR with media that is known as anaerobic filter (AN/F). 3. ABR with media at the upper part of each chambers or only at the final chamber or only at the final chamber which is called as hybridized anaerobic baffled reactor (HABR) (Kemmadarong, 1992) 6 Figure 2.3: Anaerobic baffled reactor 2.3.2 Treatment wastewater by ABR systems The process of ABR was first investigated by Bachman (1983 and 1985) with strong synthetic wastewater (COD=8,000 mg/L) and was described by Sasse (1998) as a series of UASB reactors. An aerobic baffled reactor operated with a combination of several anaerobic processes. There are three basic steps involving in the over all anaerobic oxidation of waste: 1/hydrolysis, 2/ fermentation and 3/ mathenogenesis. 7 Barber and Stuckey (1999) investigated that despite losing more solids, the three – chamber reactor together with physical modifications provided a longer retention time and superior performance than the reactor with only two compartments. They also found that despite losing more solids, the three compartment reactor was more efficient at converting the trapped solids to methane. So anaerobic baffled reactor was recommended in many literatures should equip at least 3 chambers. Metcalf and Eddy, 2003 investigated the advantages for ABR process includes the following: 1/ Simplicity, i.e., no packing material, no special gas separation method, no moving parts, no mechanical mixing, and little plugging potential. 2/ Long SRT possible with low hydraulic retention time 3/ No special biomass characteristic required 4/ Wastewater with a wide variety of constituent characteristics can be treated 5/ Staged operation to improve kinetics 6/ Stable to chock loads Bechmann et al. (1985) developed the ABR and demonstrated its reliability in treating low and medium strength industrial wastewater. The ABR were operated at the constant OLR ranges from 2.5 to 36 g COD/(L.d). It was found that the COD removals of ABR operating at the OLR of 36 g COD/(L.d) were greater than the COD removals of ABR operating at the OLR of 24 g COD/(L.d). The methane productions in excess of 6 volumes per days per unit volume of reactor could be obtained at the OLR of 36 g COD/(L.d). The bacteria within ABR tend to rise and settle with gas production, but move horizontally at a relatively slow rate. The wastewater can therefore come into contact with a large active biological mass as it passes through the ABR, and the effluent is relatively free of biological solids. 2.4 Vietnam sanitation situation. Water pollution in Vietnam is caused by a combination of industrial and domestic wastewater, and waste dumped into rivers and lakes. The principal reason for the pollution is attributable to underdeveloped infrastructure for preventing water pollution, including a lack or shortage of treatment facilities. The first is about industrial wastewater because most of the factories of state-owned enterprises, the leader in the industrial sector, are not provided with wastewater treatment equipment. Moreover, industrial estates, where a large number of factories are located, are not provided with central wastewater treatment facilities as well. Secondly, domestic wastewater is mixed usually with night soil, rainwater and sometimes with industrial wastewater before being discharged into water bodies. In Hanoi and Ho Chi Minh City, the sewerage systems are old and perform almost none of their intended functions because of a prolonged lack of proper maintenance, only serving as drainage systems that collect wastewater from various sources. As a result, most of their domestic wastewater flows into rivers and other water bodies almost without any treatment, becoming a large source of water pollution. Hanoi has nearly 20 lakes and marshes; all of them are polluted by untreated domestic wastewater. The access to improved sanitation that reported by WHO is shown in Table 2.2 8 Table 2.2: Urban and rural sanitation in Vietnam 2000 (WHO/UNICEF, 2001) Sanitation Urban (%) Rural (%) - Flush toilet with septic tank 45.80 2.84 - Poor flush toilet 23.10 3.33 - Improved pit latrine 2.21 1.58 - Traditional pit latrine 10.67 24.94 Open pit 11.30 38.86 Bucket 1.41 2.30 Other 1.04 3.11 No facility/field 4.48 23.24 100 82 100 32 Total Access to improved sanitation In Vietnam septic tank is the most common on-site treatment facility in urban and periurban areas. Status use of conventional septic tanks in cities of Vietnam In Vietnam, most of septic tanks are often extremely outdated and damaged. They are not repaired and regularly overloaded, while sludge is not emptied regularly. Surveys and analyses carried out by CEETIA in the period 1998 - 2001 showed that most of septic tanks were under designed, and are operated with rather low treatment efficiency. The characteristics of effluent from surveyed septic tanks in 4 selected cities: Hanoi, Hai Duong, Vinh Yen and Thai Nguyen in northern part of Vietnam were: BOD5 = 240720 mg/l; COD = 320 - 1,200 mg/l; DO = 0.5-2.4 mg/l; TSS = 440 - 2,640 mg/l. Nitrogen ammonia and phosphorus content in most of effluents are high. All of investigated septic tanks are working without filtration chamber. In some cases suspended solids content in effluent eventually higher than in influent due to floating substances in un-emptyed septic tanks are washed out. In 1998, the Project of Water Supply, Sewerage and Environmental Sanitation for Hai Phong City, supported by FINIDA found similar values. The Situation in Hanoi The French colonial power installed the original joint sewage/drainage pipelines in Hanoi 50 years ago, but they did so for 400,000 people. There are now at least 1.6 million people living in central Hanoi and they are still using the same pipelines, which crumbling and in serious need of repair. Almost all wastewater goes into a combined system of storm water and wastewater. Infrastructure provision and maintenance in Vietnam are still centrally controlled and supply based. Government revenue is well below that of other countries with similar income levels, hence the limited provision of sanitation infrastructure and services. 9 Table 2.3: Vietnam sanitation and clean water for Ho Chi Minh City, Haiphong and Hanoi Indicator HCMC Haiphong Hanoi Total Untreated Waste Discharge (million cu/m/yr) 240-300 70 120 Population Serviced with Sewage systems (percent) 60 20-35 20-35 Sewage Treated (percent) 0 0 0 WHO Drinking Water Quality Standards Met for Piped Water yes no no Solid Waste Collected (percent) 80 70 <50 Number of Motorized Vehicles 775,000 235,000 420,000 Source: International Development Research Centre (July 1995) “Vietnam National Environmental Action Plan” Existing sanitary conditions in Hanoi Existing conditions in various parts of Hanoi can be described as follows: Village areas: In the peri-urban part of Hanoi most households have 5 rooms under a tiled roof, a kitchen and an agricultural products store attached to the front wing of the house, a water tank and a fruit/flower garden. Each plot covers a total area of 200 - 500 m2 of which the house occupies 20% - 30%. Village houses are inherited from generation to generation and are often situated next to each other, like urban terrace houses. The typical sanitary ice is a single or double vault toilet with or without urine diversion. The (partially) treated excreta are used as fertilizer on the household’s own land. In these parts of Hanoi there are no connections to sewers. Edges of village areas: Due to rapid population growth there may be up to 4 generations in one house. Over the last decades communal authorities have granted permission to cultivate and build on the edges of village areas to reduce the “overload” of traditional sources. The plots have a total area of 100 -200m2, 50 - 100m2 of which is built-up area and the rest is garden. There may also be a small shop. The typical sanitary device is a single or double-vault toilet with or without urine diversion. The (partially) treated excreta are used s fertilizer on the household’s own garden. In these parts of Hanoi there are no connections to sewers. Multi-story blocks of flats: In an attempt to meet the demand for accommodation, the State, during the period of 1970 -1990, invested in the construction of multi-story locks of flats. They were intended for State employees who did not own a house or who were living under crowded condition in town. Each block of is for 80 - 100 households. The individual flats have access via a balcony. The total area of each flat is 24, 28, 35, 41 or 55 m2. Most of the heads of households are workers or officers who are renting the flats from the State. The typical sanitary conditions in these blocks are on-site toilets or public bucket toilets. The inhabitants pay a periodic nightsoil collection fee. There are many groups of nightsoil collectors who collect from families with double-vault or bucket toilets. They collect periodically or as per request by the owners who pay them some money. The nightsoil is transported on simple vehicles such as bicycles with two baskets. Each 10