Multi-criteria Evaluation of Wastewater Treatment Scenarios for Small Towns in Developing Countries - Case Study of Toan Thang Town in Vietnam

Selection of sustainable wastewater treatment scenarios under different local contexts is a complex process because of the inherent trade-offs among socio-economic, environmental and technical as well as functional factors. In order to fulfill conflicting yet complementary objectives, an integrated and systematic approach called the “multi-criteria analysis” (MCA) using a multi-dimensional set of criteria and life cycle assessment (LCA) tools as effective decision support mechanisms for integrated evaluation and selection of sustainable small-town wastewater treatment systems has been developed. Application of this approach was illustrated through a case study of the small Vietnamese town Toan Thang, with an estimated total population of 10,000 people. A short-list of 3 selected scenarios and a multi-dimensional set of criteria facilitated a complex decision-making process. The qualitative analysis results presented in the spider-web diagram as well as the quantitative analysis results from various impact assessments have indicated clearly that the use of waste stabilization ponds is ranked as the first priority and seems to be the most promising and sustainable choice for the town under consideration. The results obtained from this study can be used as a scientific basis and could be valuable inputs for stakeholders’ consultation and preference assessment in searching for the most suitable solution under their local context

Address correspondence to Pham Ngoc BAO, Department of Urban Engineering, The University of

Tokyo, Email: bao@env.t.u-tokyo.ac.jp

Multi-criteria Evaluation of Wastewater Treatment Scenarios for Small Towns in Developing Countries - Case Study of Toan Thang Town in Vietnam

Pham Ngoc BAO * , Toshiya ARAMAKI ** , Keisuke HANAKI *

*Department of Urban Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

**Department of Regional Development Studies, Toyo University; 2-36-5 Hakusan, Bunkyo-ku, Tokyo 112-0001, Japan

ABSTRACT

Selection of sustainable wastewater treatment scenarios under different local contexts is a complex process because of the inherent trade-offs among socio-economic, environmental and technical as well as functional factors In order to fulfill conflicting yet complementary objectives, an integrated and systematic approach called the “multi-criteria analysis” (MCA) using a multi-dimensional set of criteria and life cycle assessment (LCA) tools as effective decision support mechanisms for integrated evaluation and selection of sustainable small-town wastewater treatment systems has been developed Application of this approach was illustrated through a case study of the small Vietnamese town Toan Thang, with an estimated total population of 10,000 people A short-list of 3 selected scenarios and a multi-dimensional set of criteria facilitated a complex decision-making process The qualitative analysis results presented

in the spider-web diagram as well as the quantitative analysis results from various impact assessments have indicated clearly that the use of waste stabilization ponds is ranked as the first priority and seems to be the most promising and sustainable choice for the town under consideration The results obtained from this study can be used as a scientific basis and could be valuable inputs for stakeholders’ consultation and preference assessment in searching for the most suitable solution under their local context

Keywords: impact assessment, multi-criteria evaluation, wastewater treatment system

acceptability (Massoud et al., 2009)

So far, many sanitation projects in developing countries, particularly small-scale

projects, have tended to focus on technical solutions and mainly on developing low-cost

sanitation technologies for wastewater collection and treatment, rather than on the sustainability of those investments or on maximizing health benefits of the users

(Rosensweig et al., 2002) In providing what may be considered technically

well-functioning systems, we might risk ignoring the broader issues of sanitation, including environmental protection and human health, the important social aspects of sanitation and broader economic aspects An integrated view of sanitation planning where planners move beyond figures of initial investment, and operation and maintenance (O&M) costs are required to supply sustainable sanitation (Kvarnström and Petersens, 2004) One way of reaching beyond the provision of purely technical solutions to sanitation is to focus on what criteria should future sanitation systems comply with to be sustainable in given settings By focusing on the function of a sanitation system rather than the technology itself, more flexibility will be allowed for innovative solutions to sanitation issues (Tischner and Schmidt-Bleek, 1993) It is also necessary to emphasize that a single, best solution does not generally exist, and the sanitation planning process can be characterized as a search for acceptable compromises under local context

The framework developed in this paper proposes a procedure for integrated and criteria evaluation and selection of wastewater treatment scenarios through a case study

multi-in Toan Thang, a small town multi-in Vietnam The framework is based on multi-criteria analysis, life cycle assessment, cost and health risk analysis as decision support tools, which integrate environmental, economic, technical, functional, and societal aspects for quantification and comparison of trade-offs between the effects of newly introduced technical solutions and their related impacts

MATERIALS AND METHODS

Criteria for sanitation technologies under the sustainability concept

Global developments now focus attention on sustainability as an explicit goal (Bossel, 1999) The concept of sustainable development or sustainability is based on the observation that economy, environment and well-being can no longer be separated, and considers that all human individuals have equal rights, whether living today or in the future The concept of sustainability has to be translated into the practical dimensions of the real world to make it operational It is vital to recognize the presence or absence of sustainability, or of threats to sustainability In order to do this, proper sustainability criteria/indicators must provide this information, to indicate our progress in achieving sustainability (Bossel, 1999)

Sustainable sanitation technologies are similar to what used to be defined as appropriate technologies, i.e those compatible with or readily adaptable to the natural, economic, technical, and social environment, and offer a possibility for further development

(Balkema et al., 2002) In analyzing the sustainability of sanitation technologies in

general and wastewater treatment technologies in particular, the different dimensions of sustainability should be taken into account based on a long-term and global view It has been proved that the overall sustainability of a wastewater treatment technology is a function of economic, environmental and social dimensions, and the selection and interpretation of indicators is influenced by an area’s geographic and demographic

characteristics (Balkema et al., 2002; Muga and Mihelcic, 2008)

The end users’ needs are translated into functional criteria that must be fulfilled by the technology In order to meet those needs, technology draws from resources in its environment and affects this environment through contamination Sustainable technology is a technology that does not threaten the quantity and quality (including diversity) of the resources over a long period of time (Fig 1)

It is essential to highlight that the success and sustainability of any sanitation facility or system are dependent upon choosing the appropriate technologies, as well as the effective and feasible planning to ensure the long-term operations and maintenance requirements of the chosen technology

Development of framework based on multi-criteria analysis

Multi-criteria analysis (MCA) is often used for assessments in situations when there are competing evaluation criteria MCA identifies goals or objectives and then seeks to spot the trade-offs between them; the ultimate goal is to identify the optimal solution This approach has the advantage of incorporating both qualitative and quantitative data into

the process (Wrisberg et al., 2002)

This paper proposed an MCA-based framework as support for decision-makers and sanitation planners in searching for and identifying the most sustainable technical solution for wastewater treatment system in a local context through a two-step screening process (Fig 2) This approach is based on multi-criteria evaluation for qualitative analysis and life cycle assessment (LCA), cost analysis and health risk analysis for quantitative analysis, that integrate environmental, economic, technical, functional, and societal factors for the characterization and comparison of different technical solutions

in a complex multi-criteria problem These results can be a valuable input for the stakeholders’ preference assessment in the latter phase of the planning process

As presented in the framework, in searching for potential wastewater treatment scenarios, prior to Step 1, diverse impact factors (Fig 3) are considered because of their relevance to the sustainability of the potential systems

Fig 1 - Sanitation technology interacting with different aspects (Modified from

Balkema et al., 2002)

Factors 1 - 12 are technical, environmental, socio-cultural, institutional, and economic factors which influence the selection process of potential wastewater treatment scenarios The design flow (factor 1) and influent characteristics (factor 2) as well as the required effluent standard (factor 11) of treated wastewater significantly affect the choice of treatment methods Meanwhile, the size of site and nature of site (factor 6) are the other very basic considerations, because some treatment alternatives, e.g waste stabilization ponds, cannot be operated on small sites A site with high groundwater level is not suitable for land treatment techniques or constructing ponds Both ponds and land treatment techniques are not likely to be suitable if the site is located near residential areas

multi-Diverse Factors considered

(The most promising and sustainable solution should be identified by relevant stakeholders based on the valuable insights from analysis results of the screening process)

Criterion

Environmental Economic Technical and functional Societal

Selection of criteria/indicators per criterion Selection of method for evaluation and relative comparisons among scenarios regarding each criteria Interpretations of evaluation and comparison results

Construction Phase

Human health Ecosystem Quality Resource

Operation Phase

+ Pollutants Emission Load (BOD, COD, TSS, T-N, T-P) + Eutrophication Potential (Impact on Ecosystem) + Potential of local health damage

Factors 5 and 12 are related to O&M The more sophisticated treatment alternatives require much higher O&M costs Recently, it is not unusual in developing countries like Vietnam to have adequate budgets for construction of treatment plant; however, insufficient money is spent for O&M phase Therefore, factor 12 should be one of the most important considerations in the selection of appropriate and sustainable technology The availability of technical skills for the operation and maintenance of the plant (factor 5) is also a subjective factor The level of the treatment technology chosen must be compatible with the level of the skill of the professionals and the technicians available to run it

Obviously, water availability and climatic condition (factors 3 and 7) are also important factors especially when considering on-site sanitation alternatives and treatment processes

The cultural aspects and the use of wastewater as a nutrient source in agriculture is a very common practice (factors 8 and 9) in Vietnam since decades ago for diverse reasons, such as water scarcity, fertilizer value, and lack of an alternative source of water Thus, it is necessary to have a clear understanding of the cultural aspects and sanitation practices; also the potential for utilization of treated effluent as a nutrient source from each proposed scenario

Lastly, the final factor (factor 10) concerning the initial consultations from key stakeholders permits consideration of the most feasible alternatives before conducting a detailed analysis

These potential scenarios then go through a developed two-step screening approach (Fig 2) for comprehensive and multi-criteria assessment, which takes into accounts both the qualitative and quantitative aspects in the overall screening process

Qualitative Analysis in Step 1 (Coarse screening phase)

Based on this rough screening process, 12 potential scenarios had been proposed (Table 1); and then a short-list of the 3 most promising and feasible scenarios out of these 12 were selected from Step 1, based on a proposed set of multi-dimensional criteria and contextual factors that affect the selection or consensus on priority options These factors have been identified based on a series of questionnaire surveys conducted in the study town from August 2008 to September 2009, which included land space availability; community needs for nutrient recovery and safe reuse of treated wastewater from the proposed treatment plant; lack of access to funds for huge initial investment on sophisticated, advanced and costly treatment systems; and lack of skilled workers for effective operation and maintenance of complicated treatment systems These 3 scenarios had also been the subject of discussion with key stakeholders prior to the selection and detailed quantitative analytical process

The potential scenarios were assessed qualitatively based on a multi-dimensional set of criteria as shown in Table 2 These criteria would qualitatively describe the performance

of different small-town wastewater treatment systems, facilitating comparison of technical alternatives and providing valuable and understandable information to stakeholders during the decision-making processes The criteria were selected based on

Table 1 - Potential scenarios considered for Toan Thang case study

Technologies considered

Scenario P-0

(Business as usual) Septic tank Effluent is discharged into water bodies

Scenario P-1 Johkasou system Effluent will be discharged into irrigation canals and/or water bodies

Scenario P-2 Pour-flush toilet without septic tank Johkasou system; then effluent will be discharged into irrigation canals and/or water bodies

Scenario P-3 Septic tanks

Conventional wastewater treatment systems (Activated sludge or Trickling filter or Rotating biological contactor, RBC); then effluent will be discharged into irrigation canals and/or water bodies

Scenario P-4 Septic tanks Constructed wetlands; then effluent will be discharged into irrigation canals and/or water

bodies

Scenario P-5 Septic tanks Series of Waste Stabilization Ponds (WSPs); then effluent will be discharged into irrigation canals

and/or water bodies

Scenario P-6 Septic tanks Physico-Chemical treatment; then effluent will be discharged into water bodies

Scenario P-7 Septic tanks Sequencing batch reactor (SBR); then effluent will be discharged into irrigation canals and/or water

bodies

Scenario P-8 Septic tanks

UASB + Activated Sludge/Trickling Filter/Rotating Biological Contactor; then effluent will be discharged into irrigation canals and/or water bodies

Scenario P-9 Septic tanks UASB + Waste Stabilization Pond; then effluent will be discharged into irrigation canals and/or

water bodies

Scenario P-10 Communal baffled septic tanks Effluent will be discharged into water bodies as current situation

Scenario P-11 Baffled septic tanks Oxidization ditch; then effluent will be discharged into water bodies as current situation

Scenario P-12 Bio-toilets/ Double vault latrines/ Composting toilets/

Biogas reactors

Constructed wetland (for Greywater treatment);

then effluent will be discharged into water bodies

(i) a sound scientific basis widely acknowledged by the global scientific community; (ii)

transparency, i.e., their calculation and meaning must be clear even to non-experts; (iii)

relevance, i.e., they must cover crucial aspects of sustainable development; (iv)

quantifiability, i.e., they should be based on existing data and/or data that are easy to

gather and to update; and, (v) their finite number, in accordance to their purpose

(UNDPCSD, 1995; Muga and Mihelcic, 2008) It should be kept in mind that the

selection of a particular set of criteria may vary from community to community

depending on the local needs and stakeholders’ preferences

To compare the results and demonstrate the overall sustainability of each treatment

scenario, the individual results from each scenario were displayed in spider-web

diagram (Fig 4) This spider-web diagram enables quick and easy visual comparisons

of environmental, economic, technical and functional attributes The spider-web

diagram displays the four dimensions of wastewater sustainability covering

multi-criteria related to environmental, economic, technical and functional dimensions; the

scale of impacts from these dimensions; and a set of sustainability criteria proposed for

this study The impact values for each sustainability criteria were rated on a scale of 1

to 5, with 1 being the least preferable and situated closer to the center of plot The

Table 2 - A multi-dimensional set of criteria developed for qualitative analysis of

small-town wastewater treatment scenarios

Environmental

Land requirements

Electricity consumption

Chemical use

Biochemical oxygen demand (BOD 5 ) removal efficiency

Total suspended solid (TSS) removal efficiency

Total nitrogen and phosphorus (T-N/T-P) removal efficiency

Pathogen removal (coliforms)

Aesthetics (measured level of nuisance from odor)

Staff required to maintain the plant/facilities

Institutional requirements (efforts needed to control and enforce

the regulations and of embedding the technology in

policymaking)

Technical and functional

Complexity of construction, O&M

Flexibility of the system

Reliability of the system

m 2 /person kWh/m 3 of treated wastewater Qualitative

% removal

% removal

% removal MPN/100mL kg/person/year Qualitative Qualitative Qualitative USD/pe/year USD/pe/year Qualitative Qualitative Qualitative

Qualitative Qualitative Qualitative

results are very much context-based, and ranked after extensive literature review on the performance of different treatment technologies under the local context

Quantitative Analysis in Step 2 (Fine screening phase)

Pollutant Emission Load Comparison

Pollutant emission loads from each scenario were calculated and compared based on per capita pollutant emission load data in Vietnam (Table 3)

Life Cycle Assessment

As proposed in the research framework, not only qualitative but also quantitative aspects were taken into account in the screening process In the previous qualitative analysis step (Step 1), these indirect impacts have not been quantified clearly Thus, in the second step, the LCA method is adopted as a quantitative methodology to evaluate the unintended effects on the environment LCA is a standardized method to evaluate the environmental impacts of products or services from “cradle to grave.” It is a

structured method broadly consisting of 3 phases: (i) the goal and scope definition, (ii)

the life cycle inventory (data collection; mass and energy balances), and (iii) the impact

assessment (classification of emissions in environmental impact categories, normalization and weighing of these categories)

The main objective of LCA in this case study is to quantify the environmental impacts associated with each scenario, focusing on global warming potential (GWP) and its

public health related impacts, and eutrophication potential; and thus, provide a basis for

quantitatively comparing the results The functional unit is the environmental impact

1 2 3 4 5 6 7 8 9 10

11

12 13 14

17

Land requirement

Electricity consumption Chemical use BOD/COD removal TSS removal

T-N/T-P removal Pathogen removal

Sludge generation

Potential of nutrient recovery Energy recovery

Potential of wastewater reuse Capital cost Operation and maintenance cost Complexity of construction, O&M

Flexibility of the system systemReliability of the

Fig 4 - Spider-web diagram showing four dimensions of sustainability for qualitative

comparison among different wastewater treatment scenarios

Table 3 - Average pollutant emission loads from household wastewater in Vietnam

(MoC, 2008)

Biochemical oxygen demand (BOD 5 ) (from

effluent of household wastewater) g/pe/d 30-35

Faeces

Main constituents

Urine

Main constituents

from the wastewater generated by one person-equivalent (pe) over 1 year The total

period of comparison was set at 18 years (until 2025)

The materials used in the construction phase were considered and inventoried to last for

the whole life cycle of the treatment plant, with no replacement considered during the

operation phase The ultimate disposal site for the disassembled materials and wastes

was assumed to be a landfill The sludge generated from the treatment process, both

on-site and off-on-site, will be treated in the sludge drying bed prior to its use as soil

amendment The inventory analysis involves parameters describing resources, material and energy uses, and emissions to air, water and soil The assessment covers the entire

life cycle of the products or activities; construction; O&M; treatment; sludge disposal;

and transport Eco-indicator 99 was used to determine the impacts of treatment options

1) Global Warming Potential

Regarding the calculation of GWP, an estimated amount of CO2 and CH4 emissions during the construction, operation and disposal phase were calculated based on LCA analysis Methane (CH4) gas emission during the operation phase from each wastewater treatment scenario was calculated using the IPCC method (IPCC, 2006) Similar to other methods, the level of uncertainty depends on the equality of the data characterizing wastewater management practices In general, the theoretical CH4 yield overestimates CH4 emissions and can be considered a maximum estimate of potential gas yield, only to be used in determining complete process conversion or in determining maximum attainable yields Field test emission factors provide a lower-end estimate reflecting relatively low emission estimates, as they do not account for potential losses (El-Fadel and Massoud, 2001)

,

where:

CH 4 emissions = CH4 emissions in inventory year, kg CH4/year

TOW = total organics in wastewater in an inventory year, kg BOD/year

S = organic component removed as sludge in an inventory year, kg BOD/year

U i = fraction of population in income group i in inventory year

T i,j = degree of utilization of treatment/discharge pathway or system, j, for each income

group fraction i in an inventory year

i = income group: rural, urban high income and urban low income

j = each treatment/discharge pathway or system

EF j = emission factor, kg CH4 / kg BOD

R = amount of CH4 recovered in inventory year, kg CH4/year

2) Global Health Damage

The health damage as an impact due to greenhouse gas emissions was calculated for each scenario based on the Disability Adjusted Life Years (DALYs) methodology This

is a common public health meter now being used by the WHO, and it has been the most widely used tool which can be applied across cultures DALYs are often used to evaluate public health priorities and also to assess the disease burden associated with environmental exposures to contaminants The basic principle of the DALY approach is

to weigh each health effect for its severity from 0 (normal good health) to 1 (death as the most severe outcome with weight equal to 1) This weight is multiplied with the duration of the health effect, the time in which disease is apparent, and with the number

of people affected by the particular outcome DALYs analysis result was calculated for each proposed scenario

3) Eutrophication Potential

Eutrophication impacts caused by waterborne emissions are not considered in indicator 99, which only accounts for the eutrophication impacts caused by airborne

Eco-emissions; thus, in this study, the eutrophication potential was evaluated using the baseline method described in Guinée (2002), which is based on generic eutrophication potential (EP) factors Results are given in kg PO43- equivalent/pe.year, where P in terms of P2O5 has an EP factor of 1.34 and N has an EP factor of 0.42

Wastewater treatment and management for small towns in Vietnam

The Vietnamese government defines small towns as urban administrative units and commune as rural administrative units According to Decision No 132 HDBT (1990),

small towns in Vietnam comprise: 1) small towns (population between 4,000 and

30,000) with density averaging 60 persons/hectare (6,000/km2) or 30 persons/hectare in mountainous areas; and 2) townlets (3,000 country-wide with a minimum population of 2,000) with a density greater than 30 persons/ha (10 per ha in mountainous areas) The population residing in small towns and townlets is estimated at 15 million and account for about 22% of the national population (Staykova and Kingdom, 2006)

Small towns often fall between and do not completely fit within either the urban or rural context Small towns have more administrative capacity and more economic activity than rural communities In contrast to larger urban centers, small towns generally lack access to funds but have greater potential for meaningful community involvement The sanitation needs in small towns are different from the composition of wastewater to the cultural and educational backgrounds of the residents, to the funding options available Small towns often suffer from a lack of infrastructure and cannot ensure the minimum quality of urban life According to the authors’ survey of small towns in Vietnam, the simple and incomplete sewerage system is often used concurrently for rainwater, wastewater and livestock wastewater disposal There is typically no proper wastewater collection or treatment system in small towns Most of the town’s wastewater runs down into side drains or absorbs into rivers or soil Hygienic toilet use is still problematic and open defecation is used Existing toilets such as single vault latrines, double vault compost latrines, flush toilets and septic tanks are improperly maintained

At present, no policy dealing with the distinct issues of small towns has been developed

No single organization has clear responsibility for managing sewerage, drainage or sanitation in small towns and townlets The surveys from this study revealed that water supply and some simple, incomplete sewerage systems have been constructed in a few towns Due to the lack of synchronous investment, preliminary research and appropriate technology selection under local context, there have been ineffective investments and negative impacts to the local environment and public health Most of these systems only operated for a short time before stopping More than ever, practice of wastewater treatment and management is now becoming an urgent matter and of great concern from both public and local government Thus, equipping small towns with improved and sustainable sanitation scenarios is one of the key points toward sustainable development

of the sanitation sector in Vietnam

Toan Thang, in the Red River Delta of Vietnam (Fig 5), has been selected as a case study for the evaluation framework Toan Thang is located in the north part of Kim Dong district, Hung Yen province, Vietnam The commune is divided into 4 villages, including Truong Xa, Nghia Giang, Dong An, and An Xa The total natural land area of the community is 725.8 ha, of which 440 ha is used for rice farming The average agricultural land area per capita is 429 m2, less than half the national level Most of the

STUDY TOWN

Fig 5 - Location map of Toan Thang small town in Hung Yen province of Vietnam

(Modified from the original map of Hung Yen province on

community land area is in the lowland There are two rivers running across the commune: Kim Nguu River and Dien Bien River The main crops in the community are rice and cucumber Zucchini, pumpkin, soybeans and potato are also grown in small amounts The total population of the town is 10,236 people in 2,645 households It is expected that the population will increase to 23,000 people by 2025 (Viwase, 2007a)

The revenue of Toan Thang is mainly from agricultural sources, accounting to 45% of the total revenue of the community Main crops include: rice grown in 2 crops; 45.2 ha

of spring-summer cucumber; and 87.54 ha of other crops The number of farmer households (HHs) is 1,047 HHs, accounting to 39.6%; the remaining 60.4% is represented by non-farming households or households doing both agriculture and other occupations such as aquaculture (14 HHs); handicraft (204 HHs); construction (92 HHs); business (334 HHs); transportation services (79 HHs); and others (324 HHs) (Viwase, 2007b)

Concerning the status of water use and environmental sanitation, according to the results from field observation and a questionnaire survey, the local people in the community are now simultaneously using three sources of water (rainwater, drilled well water, and hand-dug well water) for cooking, drinking and domestic purposes However, the numbers of hand-dug wells in use are reducing gradually and mainly poor households use this source of water Regarding water quality, according to the survey’s results, drilled well water and hand-dug well water have a fishy smell, and will turn yellow and taste salty if left standing for a few minutes Concerning sanitation, the survey revealed that 58% of households are using septic tank and semi-septic tank toilets, 20% use double vault compost latrines, 18% use single vault compost latrines and the remaining use flushing toilets without septic tanks (Fig 6) According to Viwase (2007a), the estimated total amount of wastewater generated in this town will be about 1200 m3/d by the year 2025