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Models for Sustainable Water Management in Seoul

Schuetze Thorsten1, a, Lee Pil-Ryul

2, b

1Faculty Architecture, Department Urbanism, Chair of Environmental Design,

Technical University Delft, Berlageweg 1, 2628 CR Delft, Netherlands 2 Department of Culture and Art, Korea National Open University, Seoul-Si, Korea, 110-791

a t.schuetze@tudelft.nl,

b prlee@knou.ac.kr

ABSTRACT

The degree to which the introduction of decentralized ecological water and sanitation systems can

contribute to the sustainable management of wastewater and the security of drinking water resources

in Seoul has been examined in the described research. Along with architectural, town planning and

technical feasibility in the context of renovation works on buildings, the cultural, financial and

institutional boundary conditions were considered. The results of the investigations are exemplary for

Asian metropolitan areas and are evaluated using sustainability criteria (ecological, environmental and

social). The average water consumption in private households can be reduced with minimal

investment costs, minimal operating costs and without loss of comfort, by the installation of so called

flow rate delimiters, water saving household appliances and water saving toilets. Apart from using

ecological sanitation, decentralized water systems also include the processing of sewage to service

water. In order to determine the sustainability of different technologies, three different systems for

decentralized water management were designed which differ only concerning the specific technology

for the treatment of waste water from toilets. All three systems include the retention- and infiltration of

the total precipitation (together with reclaimed waste water) with infiltration swale – and infiltration

ditch systems, the recycling of gray water from bathrooms and service water utilization (for toilet flush

and laundry). According to the findings of the investigations it may be expected, that decentralized

water systems and sewage free housing estates are not only realizable in Seoul but also in many other

international cities. They can contribute significantly to pollution control, a sustainable water resource

management and urban development and it is expected that they will be well accepted by the users.

KEYWORDS: urbanism, architecture, remodelling, apartment, sewage, water, ecological sanitation

1. INTRODUCTION

Beside the well known advantages of central water supply and waste water management systems they

also include a lot of disadvantages. The main handicaps of conventional central systems for waste

water treatment are that sewage streams with different characteristics and noxiousness are mixed and

nutrients are eliminated. Leakages in the sewage system, overflows of mixed sewers but also the

discharge of treated sewage are leading to the pollution of ground- and surface waters.[1] Sewer

systems incur high costs and the lockup of capital for long periods of time - even decades - and they

are not safe against catastrophes. Furthermore, adapting to changing demographic structures, user

behaviour, changing precipitation patterns as well as new technologies for sanitation involves high

constructive and financial effort. The central drinking water supply also bears disadvantages because

drinking water only is supplied and a complex system of mains is required. This can lead to high water

losses due to leaking pipelines and has a negative impact on the quality of the supplied water, because

of pipeline materials, leakages and long holding time.

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In opposed to the above summarized

disadvantages of centralized water systems,

decentralized systems for sewage treatment,

ecological sanitation (ecosan) and water supply

provide manifold advantages and the possibilities of

changes for the positive. They allow the separation

of waste water streams with different characteristics

(see figure 1), which allow for an efficient

treatment and high-quality utilization of nutrients

[2]. The protection of ground- and surface water is

achieved by the avoidance of waste water, the

decentralized treatment of different substances and

waste water streams. The freshwater demand can be

reduced by the reuse of recycled waste water as

service water. By saving mainly on canalization the

construction of alternative water systems only

incurs capital lockup for relatively short periods (of

less than 30 years). The systems are adaptable to

changing demographic structures, changing

precipitation patterns as well as new sustainable

technologies for sanitation, and are insusceptible to

catastrophes and malfunctions. Furthermore they have the advantage of short pipeline lengths,

minimized water losses and close water cycles. This is especially true for areas which are not equipped

with sufficient water and sanitation systems and are not connected to sewers or waste water treatment

plants. But it can be also true for already developed areas, with existing infrastructure and high

population density, e.g. in international big cities like Seoul. [3]

The potentials for the application of decentralized sustainable water and sanitation systems in

existing buildings for domestic use in Seoul, Korea are investigated and a sophisticated evaluation

Figure 1. Disposition of nutrients and

percentages of specific material flows in

relation to the total volume of domestic

waste water. The percentage is calculated

with the average water consumption of

household in Hamburg/ Germany, 117 l per

resident and day and nutrients per resident

and day. The portions of urine and faeces

are so small that they are not visible in the

right column. [3]

Figure 2. Left: Scheme of conventional central systems for waste water treatment and drinking

water supply and their disadvantages.[4] Right: Scheme of ecological sanitation (ecosan), waste

water treatment and water supply systems and their advantages.[5]

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according to social, economic and ecological criteria is conducted in the framework of the described

research. The results are compared with the common procedure of remodelling and renovation works

and with the characteristics and effects of the existing central systems for drinking water supply and

sewage treatment; the differences as well as the potential are shown. To allow the transferability of the

results of investigations, the investigated housing estate in Seoul Bang-Bae has a high inhabitant

density which is above average. It is 15.67 m² per inhabitant and 63,797 inhabitants per km². The city

area of Seoul is 608 square kilometres and comprises 10.28 million inhabitants. The average inhabitant

density is 17,000 inhabitants per square kilometre. The plot area to floor area ratio of the investigated

multi storey apartment buildings in Seoul is 2.5 before remodelling. After remodelling it is 3.2 due to

enlargement of the buildings. Compared with the average density of the city area in Seoul it is 3.2

times higher.

2. RESULTS AND DISCUSSION

2.1 Water Consumption and Use

The starting basis for the design of sustainable

water and sanitation systems in the existing housing

estate in Seoul is the minimization of the water

demand in private households. A comparably low

water consumption in households without loss of

comfort and without changing behaviour of the

users can be ensured by the application of water

saving fittings (so called flow rate delimiters),

household appliances (e.g. washing machines and

dish washers) and water saving toilets (with

cleaning flow rates of about 2 litres (for flushing

after urination) and respectively 3 litres (for

flushing after defecation). With these measures the

water consumption can be reduced in Seoul with

minimal investment costs, minimal operating costs

and without loss of comfort by approx. 38% (from

208 litres per resident and day to 129 l per resident

and day). An advanced reduction of the drinking

water consumption can be achieved by the

substitution of drinking water with so called service

water (e.g. rainwater or purified waste water) which

can and may be used for toilette flushing, laundry,

cleaning and watering purpose, according to the

legal basic conditions in Korea. The portion of the service water demand in relation to the total water

demand of these water saving households is estimated with 26% (33 litres per resident and day). It is

used for flushing toilets, laundry irrigation and cleaning. Measures for the recycling of gray water

from bathrooms and the utilization of service water can cover the service water demand in the

investigated housing estate by 100% (see below). Hence the drinking water demand compared to

standard households can be reduced by 54%, from 208 to 96 litres per resident and day.[3]

2.2 Decentralized Rainwater Management

Decentralized rainwater management is the starting basis for the realization of decentralized water

systems. It can be used for the sustainable development as well as for the redevelopment of rural and

urban human settlements.[6] Measures for rainwater utilization in both cities may not be counted as a

credit for the calculation of measures for the retention of rainwater and flood control. The service

Figure 3. Disposition of nutrients and

percentages of specific material flows in

relation to the total volume of domestic

waste water. The percentage is calculated

with the average water consumption of

household in Hamburg/ Germany, 117 l per

resident and day and nutrients per resident

and day.

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water demand is covered maximum with 25% in Seoul, due to the natural and structural basic

conditions (climate, high population density and comparable small rainwater catchment area). The

portion of collected rainwater is equivalent to only 9% of the total water demand of water saving

households. For normal households it would be even less. Rainwater catchments from greened roofs

reduce the degree of efficiency further.

Measures for extensive greening of roofs contribute substantially to the retention of rainwater and

may be counted as credit for the calculation of infiltration systems. Together with intensive greening

measures of roofs and buildings they contribute to an increase of the evaporation ratio, thus

approximating the micro climate in urban areas to natural conditions. By irrigation with reclaimed

waste water (see chapter 2.3) positive interactions can be achieved (e.g. decomposition of remaining

nutrients like Nitrogen and Phosphorous).

Measures for the infiltration of rainwater with shallow pits and infiltration ditch systems out of

plastic allow the complete retention of extreme precipitation events with a rainwater contribution

frequency of 0.01 per year, or even less. The related construction work for this purpose does not limit

the use of the real estate and the buildings in the investigated housing estate. The construction costs

are cheaper than that of rainwater utilization systems. The systems are also appropriate for the

infiltration of purified waste water. Hence they allow the total addiction of urban sewer systems.[3]

2.3 Waste Water Management Systems

In the framework of the described research the application of three different systems for waste water

management were investigated. They all are still connected to the central drinking water supply and

comprise the retention, evaporation and infiltration of rainwater and purified waste water (see chapter

2.2) as well as the recycling of grey water from bathrooms for the supply of service water. The grey

water from kitchen is first filtered in a retting container and afterwards treated either separately (in

system 1) or together with black water (in system 2) or together with brown water (in system 3).

Hence the systems differ mainly in the applied principles and technologies for the treatment of black

water, respective brown and yellow water. Collected rainwater is not utilized for the service water

supply due to the low coverage ratio (see chapter 2.2).

System 1 comprises a vacuum toilet and an anaerobic digestion facility for the fermentation of

black water (6 litres per person and day) and kitchen waste (1 litre per person and day), biogas

production and its utilization as fuel in a combined heat and power generator as well as the transport of

the fermentation residues over a distance of 20 km. In the production of biogas the fermentation of

kitchen waste has a portion of approximately 69% and the black water of 31%. A positive energy

balance of the system can only achieved if the so called product basket is also taken into account. Not

taking into account the primary energy gain through the substitution of chemical fertilizer also leads to

a negative energy balance. Summarizing the results it can be stated that the described system produces

primary energy of 0.39 kWh per inhabitant a day, while it consumes 0.3 kWh per inhabitant a day if

the fermentation of kitchen waste is not taken into account [7].

System 1 has a comparatively high space demand, especially in relation to the small volume of

the treated waste water. The facilities can only be realized outside the buildings with additional

construction effort. The construction cost compared with the systems 2 and 3 are very expensive. Also

the expenditure for the transportation of the treated residues are relatively high and are equivalent to

4.6-times that of the collected yellow water (see system 3) - but the emission of nutrients and micro

pollutants into the environment are reduced to the greatest possible degree (see also figure 4, left).

It is remarkable that the black water only has a small portion of 5% of the total waste water in the

investigated housing estate. The energy demand for the treatment of the remaining waste water is quite

similar for all three systems. Compared with the systems 2 and 3 the primary energy gain by the

fermentation of black water (without kitchen waste) is only 0.04 kWh per inhabitant and day (see also

figure 4, right). For the water saving households in Seoul with a consumption of 129 litres per

inhabitant and day, the primary energy demand for the treatment of the different fractions of waste

water and the supply with drinking water is 0.73 kWh per inhabitant per day. The required primary

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energy for the production of electric energy is calculated with a factor of 2.97. Hence the electrical end

energy demand for the service of the system is 0.25 kWh per inhabitant and day.

System 2 corresponds in general with System 1. The difference is that the black water is not fermented

together with organic kitchen waste but is treated together with grey water from kitchen in a

Membrane Bio Reactor (MBR). The main disadvantage of this system is the high content of nutrients

(see figure 4, left) and micro-pollutants in the treated sewage (compared with System 3 which is based

on the principles of ecosan). The primary energy demand for the treatment of the different fractions of

waste water and the supply with drinking water is 0.77 kWh per inhabitant and day. Hence the

electrical end energy demand for the service of the system is 0.26 kWh per inhabitant and day.

System 3 comprises the installation of urine separation toilets with yellow water collection and

storage in underground tanks. The remaining brown water is treated together with the comparably high

contaminated grey water from kitchen in a Membrane Bio Rector. The primary energy demand for the

treatment of the different fractions of waste water and the supply with drinking water corresponds with

system 2 and is 0.77 kWh per inhabitant per day. Hence the electrical end energy demand for the

service of the system is also 0.26 kWh per inhabitant and day. The energy demand for the

transportation of the urine (20 km) is so small that is has no significant influence on the balance of the

total energy demand. Under consideration of the primary energy credit through the substitution of

chemical fertilizer by the utilization of urine, the primary energy demand can be lowered by 14% to

0.67 kWh per inhabitant and day. This is equivalent to an end energy demand of 0.23 kWh per

inhabitant and day. [3]

3. CONCLUSIONS

According to the findings of the described research in Seoul alternative water systems based on

ecological sanitation are already realizable at present, with feasible constructive and technical effort as

well as low additional cost compared to conventional construction costs. They can be implemented

area-wide and allow the appropriate treatment of the specific water flows. The systems 1 and 3 do

allow the reuse of nutrients which are in conventional sewage treatment systems either discharged

with the sewage effluent or eliminated (see also figure 4, left). Due to the difficult basic conditions of

the investigated housing estate in Seoul (extreme precipitation patterns, high population density and

comparative waterproof soils) and the transferability of the single measures which have been

Figure 4. Left: Proportions of the retained and recyclable resources Nitrogen, Phosphorous,

Potassium and the Chemical Oxygen Demand (COD) for the systems 1, 2 and 3. While nutrients

are retained to a high degree in systems 1 and 3 their bigger portion is discharged in system 2.

Right: Primary energy demand in kWh per inhabitant and day in Seoul for the service of Systems

1, 2 and 3 as well as for standard households and standard water saving households. The energy

demand includes the demand for the whole water management, also for the supply with drinking

water.[3]

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described in the framework of this research, the basic conditions for a wide distribution can be

fulfilled. Hence it may be expected, that alternative water systems and sewage free housing estates are

realizable in many international cities with different natural and structural basic conditions. According

to results from surveys in Seoul [8] and experiences in Germany and Europe, also a high user

acceptance of the system may be expected.

At present admittedly, there are many barriers to realizing alternative water systems. The main

barriers are the existing infrastructure, the structure of the fees incurred by implementing the

alternative system and the institutional and legal framework. Furthermore there is the problem of the

present fees for drinking and waste water which do not cover the actual real costs in Seoul. While

decentralized rainwater management increasingly is recognized as a sustainable measure, the

acceptance of ecological sanitation of stakeholders is low, especially in urban areas, because there is

great doubt regarding its acceptance by end-users as well as its profitability and feasibility. According

to stakeholder interviews in the Republic of Korea [9], 89% of the interviewees think that

decentralized measures are not feasible yet, and 67% of them think that this will be still the case in 20

years. However decentralized environmental sound measures for waste water management are

accepted by most stakeholders; presently in particular with regard to the optimization of the efficiency

of central sewage treatment plants (regarding rainwater management). More than 50% of the

stakeholders think that the feasibility for the decentralized treatment of urine and faeces will be good

and very good in 100 years.

Scientifically supervised pilot projects and additional research regarding the integration and

service of decentralized environmental sound water and sanitation systems as well as regarding the

optimization of institutional and legal frameworks can help to dispel the doubts and to mark the

beginning of a paradigm shift in water management especially for areas which are not yet equipped

with sewer systems or waste water treatment plants.

REFERENCES

GTZ (Hrsg.), Eschborn, Deutschland, 2004. Ecosan – closing the loop. Proceedings of the 2nd

international symposium on ecological sanitation, 7th - 11th April 2003, Luebeck, Germany.

Otterpohl, R., 2004. Innovative Technologies for Decentralised Water-, Wastewater and Biowaste

Management in Urban and Peri-Urban Areas. In: Water Science & Technology, Vol 48 No 11 p:

23–32, Hamburg, Germany.

Schuetze, T, 2005. Dezentrale Wassersysteme im Wohnungsbau internationaler Grossstaedte am

Beipiel der Staedte Hamburg in Deutschland und Seoul in Sued-Korea. PhD Thesis, University

Hannover, Department Landscape and Architecture.

gtz, Deutsche Gesellschaft fuer Technische Zusammenarbeit, 2007. Shortcomings of conventional

sanitation systems. Poster and website, available at: http://www2.gtz.de/ecosan/english/

thema1.htm, Eschborn, Germany, 2007

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Germany 2007

Schuetze, T, 2006. Decentralized Rainwater management – Solution for sustainable (re)development

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163-170.

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University Hamburg Harburg, Hamburg, Germany.

Schuetze, T., 2004. Survey in private households of Korea regarding sanitary behaviour and exposure

to water. In: [3], Seoul, Republic of Korea.

Medilanski, E., Schuetze, T., 2004. The potential of introducing measures at the source (MAS) on

urban sanitation in Seoul, Korea. In: [3], Hamburg, Germany.