An Analysis of Domestic Water Demand Structure and Water Recycling in Beijing

This study aims to obtain the knowledge necessary for constructing an urban water recycling system in Beijing City. A macro-scale water balance model was constructed for Beijing City according to statistical data, and domestic water demand structure in the city was analyzed through a survey of 124 families living in the Haidian district in 2006. Annual per capita water use in Beijing City was 220 L, and about 75% of it was used for cooking, washing, showering, and toilet flushing. The use of reclaimed wastewater for toilet flushing and room cleaning, which was estimated as 22% of domestic water demand, was deemed acceptable by most of households questioned. Finally, we estimated the effect of supplying reclaimed wastewater for municipal use by macro-scale water balance estimation based on the structure of municipal water demand. Assuming that 60% of treated sewage is reclaimed from 41% of the current total, this would result in a saving of 122 million m3 of the groundwater required. Moreover, with the useful ratio of reclaimed wastewater set to 80% and 100%, 250 million m3 and 377 million m3 of groundwater, respectively, can be saved

Address correspondence to Ryuichi Tachibana, Faculty of Regional Environment Science,

Tokyo University of Agriculture, Email: r3tachib@nodai.ac.jp

An Analysis of Domestic Water Demand Structure and Water Recycling in Beijing

Ryuichi TACHIBANA*, Hirokazu KURAHASHI**, Rong QI***, Wei AN***, Min YANG***, Koichi FUJIE****

*Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo 156-8502, Japan

**Depertment of Ecological Engineering, Toyohashi University of Technology, Aichi 441-8580, Japan

***Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing,

100085, People’s Republic of China

****Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama, Kanagawa 240-850, Japan

ABSTRACT

This study aims to obtain the knowledge necessary for constructing an urban water recycling system in Beijing City A macro-scale water balance model was constructed for Beijing City according to statistical data, and domestic water demand structure in the city was analyzed through a survey of 124 families living in the Haidian district in 2006 Annual per capita water use in Beijing City was 220 L, and about 75% of it was used for cooking, washing, showering, and toilet flushing The use of reclaimed wastewater for toilet flushing and room cleaning, which was estimated as 22% of domestic water demand, was deemed acceptable by most of households questioned Finally, we estimated the effect of supplying reclaimed wastewater for municipal use

by macro-scale water balance estimation based on the structure of municipal water demand Assuming that 60% of treated sewage is reclaimed from 41% of the current total, this would result in a saving of 122 million m 3 of the groundwater required Moreover, with the useful ratio

of reclaimed wastewater set to 80% and 100%, 250 million m 3 and 377 million m 3 of groundwater, respectively, can be saved

Keywords: reclaimed wastewater, water demand and supply, water resource

INTRODUCTION

China has various critical problems including the increase in population and lifestyle changes following a period of economic growth It is generally known that China must feed and take care of the needs of 1.3 billion inhabitants, or 22% of the world population, with only 7% of the world’s arable land and 6% of its freshwater resources

(Fischer et al., 1998)

North China has only about 20% of the country’s water resources but supports more than half of the total population (Guan and Hubacek, 2008) In this area, per capita water availability is a little more than half of the national level and 1/10 of the world

average (Yang et al., 2005; Guan and Hubacek, 2008) An increasing demand for water,

including agricultural, industrial, and municipal purposes uses across the country, has been forecasted The provinces in eastern and north-eastern China, including Beijing and Tianjin, are likely to face increasingly serious water shortage problems by 2050

(Kaneko et al., 1998) In Beijing, per capita water availability is a little more than 1/3 of the national level (Yang et al., 2005)

The city has taken steps to conserve water resources by improving water supply efficiency, adopting water-saving equipment, and other measures Furthermore, reusing reclaimed wastewater is another option to ensure a stable supply of water Until now, reclaimed wastewater has been mainly used for industrial cooling and landscaping However, it is important that reclaimed water can be supplied to households since residential water consumption generally constitutes more than half of the total municipal water use and consumption (Howe and Linaweaver, 1967; Grima, 1972) In order to estimate how much residential water can be substituted by reclaimed wastewater, it is important to understand the structure of residential water consumption

(Shan et al., 2007) Very few studies on residential water use in Beijing City have been

carried out Zhang and Brown (2005) focused on household behaviors and perceptions that affect water use and consumption in Beijing and Tianjin However, they did not consider seasonal changes Furthermore, family water use was calculated on the basis of monthly data

This study aims to obtain knowledge for constructing an urban water recycling system

in Beijing City Initially, we made macro-scale water balance estimates for Beijing City based on statistical data Next, we analyzed domestic water demand structure in Beijing through a survey on 124 families living in Haidian District in 2006 Finally, we estimated the effect of recycling water supply on the municipal use by macro-scale water balance modeling based on the structure of municipal water demand

MATERIALSAND METHODS

Macro-scale water balance estimation for Beijing City

We constructed a macro-scale water balance model for Beijing City according to statistics from the 2005 Statistical Yearbook (National Bureau of Statistics of China, 2005), the Beijing administrative area (Beijing Municipal Bureau of Statistics, 2005a) and Beijing (Beijing Municipal Bureau of Statistics, 2005b), and from reports on sewerage works in the city We used the 2005 Statistical Yearbook as the basic data for this study As discussed later, we conducted a survey of water demand in Beijing City in

2006 Therefore, the 2005 Statistical Yearbook is the latest we could use for the results

of this survey

Calculating household water use

We conducted a survey using two questionnaires to calculate residential water demand

in Beijing City The participants of this survey, which was conducted from 19 to 27 October 2006, were 124 families living in the Haidian District of Beijing City The Haidian District is located in the southern area of the city, northwest of downtown Beijing (Fig 1) The Haidian District with a population of 2.8 million people accounts for a quarter of Beijing City’s population (Beijing Municipal Bureau of Statistics, 2005a) It is assumed that households comprise three people, and that the average age in the Haidian District is around 40 These features are characteristics common to Beijing City So, the results obtained here can be thought of as being typical of Beijing City

By the end of 2003, the registered population of the district was 2.4 million, 3.4% more than in 2002 It has been predicted that this number will increase (Beijing Municipal Bureau of Statistics, 2005b) This district is also a cultural, scientific, and educational

center, and has many places of interest and famous shopping areas (Beijing Municipal Bureau of Statistics, 2005b) One of the questionnaires was answered by a target household immediately after the visit Target households were asked to provide the following information: number of members, age of members, monthly income, monthly tap water cost, frequency of water use for tooth-brushing, washing among others, as well as the awareness and behavior for water saving, and environmental attitude for reclaimed water use An average figure for monthly frequency of water use was required for showering and washing, and this had to be estimated separately for summer and winter, because the frequency of water use was clearly different in these seasons

The other questionnaire was answered by the household at the end of the six-day survey for each day of the study period The questions were read before and after each period

of water use, and the frequency and head count of water use were provided by the household Target water uses were food washing, cooking, dish washing, boiling water, face washing, tooth-brushing, using washing machine, showering, foot washing, toilet flushing, and cleaning

According to Murakawa et al (1999), water use patterns differ according to the purpose

of use Proper water use practices are determined by cultural characteristics Some specific water use practices have been observed in Beijing As regards the practice of boiling water, less than 5% of household members in the city drink tap water Most of them traditionally drink only boiled water (Zhang and Brown, 2005) To cite another example, the Chinese people generally perform “foot washing” instead of showering Zhang and Brown (2005) reported that housing typology does not significantly affect household water use and consumption Therefore, housing typology is not considered in this study

We can determine water use by the following equations:

Per capita water use based on household size d in spring and fall (L/man/day):

＋　　

d d w

w d u

u d

AWU WU

AAWU







2 1

, 10

1

,

(1)

Haidian District

The center of Beijing

Beijing City

China

Fig 1 - Location map of Beijing city and Haidian District

where

AAWU d : per capita water use based on household size d in spring and fall (L/man/day)

WU d,u : water use u with no seasonal change in all households of size d for a day (L/all

households/day)

AWU d,w : seasonal water use w in all households of size d for a day in spring and fall

(L/all households/day)

N d : number of households of size d (number)

NS d : number of people per household in size d (man/household)

d: household size class (6 classes)

u: water use with no seasonal change (10 water uses)

w: seasonal water use (2 water uses)

Per capita water use based on household size d in summer (L/man/day):

＋　　 　

d d

d

NS N

SWU WU

SAWU







2

10

where

SAWU d : per capita water use based on household size d in summer (L/man/day)

SWU d,w : seasonal water use w in all households of size d for a day in summer (L/all households/day)

Per capita water use based on household size d in winter (L/man/day):

＋　　 　

d d w

w d u

u d

NS N

WWU WU

WAWU







2 1

, 10

1

,

(3)

where

WAWU d : per capita water use based on household size d in winter (L/man/day)

WWU d,w : seasonal water use w in all households of size d for a day in winter (L/all

households/day)

Per capita annual water use based on household size d (L/man/day):

12

4

× 3

× )

2 + 3 (

×

d

WAWU SAWU

AAWU

where

CAWU d : per capita annual water use based on household size d (L/man/day)

It is assumed that spring and summer were three months (90 days) each, and fall and winter two months (60 days) and four months (120 days), respectively

Annual water use of all households in Beijing City (L/year):

×

× (

= ∑6

1

=

NB NS CAWU

where

AWUB d : annual water use of all households in Beijing City (L/year)

NB d : number of households of size d in Beijing City (number)

The composition of households in Beijing City was based on a statistical yearbook (Beijing Municipal Bureau of Statistics, 2005b)

RESULTSAND DISCUSSION

Macro-scale water balance in Beijing City

Yang and Abbaspour (2007) showed changes in water use in different sectors, as well as wastewater discharge and treatment capacity in Beijing since the 1990s Total water use has remained stable, and even declined, in recent years However, the continued over-withdrawal of water resources since the 1980s has led to the depletion of aquifers, reducing water availability on the one hand and increasing cost of water supply on the other (Yang and Abbaspour, 2007) As a result, water scarcity has increased over the years (Beijing Water Management Bureau Information, 2001)

Macro-scale water balance in Beijing City appears in Fig 2 Beijing City has two sources of water supply: surface water and groundwater The amount of surface water supplied and ground water available are 824 and 1,236 million m3, respectively Surface

Fig 2 - Macro-scale water balance in Beijing City, assuming that reclaimed wastewater

from sewerage works is supplied for municipal use and industrial use

377

2

Industrial use

Municipal use

470

Sewage works

680

824 （40%）

Surface water

Recycling

1,290

6,775

Discharge 513

reclaimed wastewater）

849 637

Total water supply

2,060 (100%)

million m 3 yr -1

626 1,236 （60%）

reclaimed wastewater）

610

144

Groundwater

(Including

well water)

260

* Reclaimed wastewater

307 Evaporation

* It is not clear using distribution of reclaimed wastewater

All reclaimed wastewater is assumed to have evaporated after use.

water is supplied for municipal and industrial use The amount of groundwater supplied

is 1,994 million m3 per year for municipal and industrial use Beijing City depends on groundwater for 60% of its total water requirements Of the total amount supplied, about 60% is for municipal use, and about 40% for industrial use Municipal water use includes domestic use and public use A large volume of water is required for industrial use However, diversion of water resources for industrial use has decreased because 90% of industrial water is recycled

Source: Statistical Yearbook of China (National Bureau of Statistics of China, 2005) and Beijing (Beijing Municipal Bureau of Statistics, 2005b), and data from sewerage plants

In 2005, wastewater treated in sewerage works amounted to 637 million m3, 41% of which (260 million m3) was reclaimed and supplied for municipal and industrial uses However, the figures for distribution of reclaimed wastewater were unclear All reclaimed wastewater is assumed to have evaporated after use The remaining 59% (377 million m3) is discharged Consequently, to lower the load of wastewater directly discharged to the environment and raise the reclaimed water supply, wastewater

treatment should be increased and treatment techniques improved

Household socioeconomic characteristics

Size of households sampled for the survey appears in Fig 3 As shown, 64% of the sampled households comprise three people (parents and a child), 19% include two people, 9% four people, 7% five people, and 1% one person There is no great difference in household size among urban households because of, in part, the government’s “one child” policy (Zhang and Brown, 2005)

Ages of the sampled household members appears in Fig 4 As shown in the figure, 34%

of household members were 40 to 49 years old, 17% were 30 to 39 years old, 14% of the members were 50 to 59 years old, 12% were 0 to 14 years old, 12% were 19 to 29 years old, and 3% of the members were 60 to 69 years old

Household monthly income appears in Fig 5 Most of the households (63% of the sample) earned 1,000 to 2,999 yuan, 12% earned 3,000 to 3,999 yuan, 12% earned

Fig 3 - Household size of sampled households

4（3%）

5（4%）

11（9%）

79（64%）

24（19%）

1（1%）

0 20 40 60 80 100 Six

Five Four Three Two One

Number of household

N=124

5,000 to 5,999 yuan, 8% earned 4,000 to 4,999 yuan, 3% earned 6,000 yuan or more, and 2% earned less than 1,000 yuan

The household water rate for each income range appears in Fig 6 The monthly water rate for households with monthly income of less than 1,000 yuan was about 16 yuan, while that for households with a monthly income of over 1,000 yuan was 20 to 30 yuan Previous investigations had shown that household income was proportional to the

amount of water use (Murakawa et al., 1999; Zhang and Brown, 2005) In this study,

the impact of income to water consumption could also be observed, although it was not

so significant Chinese society is drastically changing, so in addition to household income, the age, origin, number and educational background of a household could also possibly affect its level of water consumption

Household water uses and behavior

The annual amount of per capita water use for different water use facilities, by household size, appears in Table 1 The single-person household data of water use for

9（3%）

51（14%）

119（34%）

59（17%）

42（12%）

30（8%）

42（12%）

0 30 60 90 120 150 60-69

50-59 40-49 30-39 19-29 15-18 0-14

Number of person

N=352

Fig 5 - Monthly income of sampled households

Fig 4 - Age of sampled household members

4（3%）

15（12%）

10（8%）

15（12%）

39（32%）

38（31%）

3（2%）

0 10 20 30 40 50 6,000≦

5,000－5,999 4,000－4,999 3,000－3,999 2,000－2,999 1,000－1,999

<1,000

Number of household

N=124

showering, toilet flushing and cleaning were not available Structure of annual and seasonal per capita water demand in Beijing City appears in Fig 7 This contrasts with the structure of annual per capita water demand in Tokyo City, shown in Fig 8 Of the per capita water use, 31% was employed in the kitchen for food washing, cooking, dish washing, and boiling water, 27% for showering and foot washing, 18% for toilet flushing, and 14% for the washing machine Water use in washing and showering increased from 12 to 17% and from 16 to 25%from summer to winter, respectively Per capita water use in each water use activity was very low in households with five or six

people Generally, the Chinese bathe in groups (Murakawa et al., 1999) It is quite likely

that this factor causes the dispersal of water use for showering and foot washing

In the next survey, the domestic water demand structure of Beijing City was compared

to that of Tokyo City As reports on domestic water demand structure are rarely completed in cities around the world, we decided that it would be useful to compare these two similar Asian metropolises

Water use for cooking in Beijing (31%) is 1.3 times that of Tokyo (23%) It is assumed that water use for cooking in Beijing includes food washing, cooking, dish washing, and boiling water The use of water for bathing and showering accounts for 24% in Tokyo and 27% in Beijing, with little difference between the cities However, regarding toilet

Household

(Persons)

Number of

household

Food washing Cooking

Dish washing

Boiling water

Face washing

Tooth-brushing

Washing machine Showering

Foot washing

Flushing toilet Cleaning

Average 124 23.1 13.6 18.6 13.7 9.7 4.2 31.1 39.5 16.4 41.2 9.4

Fig 6 - Water rate for different household income ranges

The bars indicate S D

Table 1 - Annual per capita domestic water use by household size

for different water use facilities [L/man/day]

6,000≦

5,000－5,999 4,000－4,999 3,000－3,999 2,000－2,999 1,000－1,999

<1,000

Water rate (yuan / month)

flushing, the figures were 28% in Tokyo and 18% in Beijing Water use for face washing and other purposes accounted for 8% in Tokyo and 10% in Beijing Thus, there seems to be a little difference between the water demand structures of the two cities

Per capita water use in different seasons, by household size, is shown in Table 2 Per capita water use in Tokyo is given in Table 3 Annual per capita water use in the city exhibitslittle difference between one- and two-person households Therefore, from the calculated average, we can assume that the data for one- and two-person households are similar The annual per capita water use in Beijing is 220L——53L, 63L, and 51L in spring and fall, summer, and winter, respectively Thus, water demand in summer is 1.2 times that of the winter demand This seasonal tendency is consistent with the published

data in, for example, Suzhou, China (Murakawa et al., 1999) The annual per capita

water use in Tokyo is 232 L, similar to that in Beijing In Tokyo, the decrease in per capita water use is associated with an increase in the number of household members (Table 3) However, the figures for Beijing do not show a clear relationship between the number of household members and the amount of water use Thus, the annual household water use in Beijing is estimated at 980 million m3 This is about 10% higher than the published statistics for household water use

Annual

Amount of residential water use (%)

Cooking Washing machine Flushing toilet Bathing and showering Face washing and others

10.1

10.8

10.5

8.8

10.5

6.2 6.6 6.4 5.4 6.4

8.7 9.4 9.1 7.6 9.1

5.8 6.3 6.1 5.1 6.1

13.6 11.8 12.5 17.0 12.5

18.4 19.7 19.2 16.0 19.2

19.4 16.4 17.8 24.9 17.8

7.6 8.2 7.9 6.6 7.9

4.3 4.6 4.4 3.7 4.4

1.8 2.0 1.9 1.6 1.9

4.0 4.2 4.1

3.4 4.1

Annual

Winter

Fall

Summer

Spring

Amount of residential water use (%)

Food washing Cooking Dish washing Boiling water Washing machine Flushing toilet Showering Foot washing Face washing Tooth-brushing Cleaning

Fig 7 - Annual and seasonal per capita domestic water demand structure in Beijing

City

Fig 8 - Annual per capita domestic water demand structure in Tokyo City

(Bureau of Waterworks, Tokyo Metropolitan Government, 2002)

Recycling water for domestic use and effects of recycling water supply

Attitudes toward the different uses of reclaimed wastewater are shown in Fig 9 Of the sampled households, 98% answered positively for cleaning, 86% for toilet flushing, and 44% for watering plants On the other hand, over 80% households were not in favor of using reclaimed wastewater for washing machines, cleaning of pets, dish washing,

showering and cooking Lu et al (1992) also reported that over 80% of the Chinese

Table 2 - Per capita water use by household size in different seasons

Household Number of

Average amount of water use (L/man/day)

Household Amount of water use

1 9 9 16

44

86 98

100 99 91 91 84

56

14 2

Cooking

Showering

Dish washing

Cleaning a pet

Washing machine

Watering plant

Flushing toilet

Cleaning

Number of answers (%)

Available Unavailable

n=124 (Multiple answers)

Fig 9 - Attitudes toward reclaimed wastewater use for different activities

Table 3 - Per capita water use by household size in Tokyo city

(Bureau of Waterworks, Tokyo Metropolitan Government, 2006)