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
Journal of Water and Environment Technology, Vol 9, No.2, 2011 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 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 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) Address correspondence to Ryuichi Tachibana, Faculty of Regional Environment Science, Tokyo University of Agriculture, Email: r3tachib@nodai.ac.jp Received July 1, 2010, Accepted March 25, 2011 - 129 - Journal of Water and Environment Technology, Vol 9, No.2, 2011 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 - 130 - Journal of Water and Environment Technology, Vol 9, No.2, 2011 Beijing City Haidian District China The center of Beijing Fig - Location map of Beijing city and Haidian District 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): 10 AAWU d WU d ,u＋ AWU d ,w u 1 w 1 N d NS d - 131 - (1) Journal of Water and Environment Technology, Vol 9, No.2, 2011 where AAWUd: per capita water use based on household size d in spring and fall (L/man/day) WUd,u: water use u with no seasonal change in all households of size d for a day (L/all households/day) AWUd,w: seasonal water use w in all households of size d for a day in spring and fall (L/all households/day) Nd: number of households of size d (number) NSd: 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): 10 WU d ,u＋ 1 SWU d ,w u 1 w SAWU d N d NS d (2) where SAWUd: per capita water use based on household size d in summer (L/man/day) SWUd,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): 10 WU d ,u＋ 1WWU d ,w u 1 w WAWU d N d NS d (3) where WAWUd: per capita water use based on household size d in winter (L/man/day) WWUd,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): (AAWUd × (3 + 2)＋SAWUd × 3＋WAWUd × 4) CAWUd = 12 (4) where CAWUd: 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): - 132 - Journal of Water and Environment Technology, Vol 9, No.2, 2011 AWUB = (CAWU d × NS d × NBd ) ∑ (5) d =1 where AWUBd: annual water use of all households in Beijing City (L/year) NBd: 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 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 Evaporation Total water supply 2,060 (100%) 307 Municipal use Surface water 824 （40%） 680 （Not including reclaimed wastewater） 610 * Reclaimed wastewater 260 Groundwater (Including well water) 1,236 （60%） Recycling 6,205 144 626 470 1,290 513 Sewage works 377 637 Discharge 849 124 Industrial use 6,775 million m3yr-1 （Not including reclaimed wastewater） * It is not clear using distribution of reclaimed wastewater All reclaimed wastewater is assumed to have evaporated after use Fig - Macro-scale water balance in Beijing City, assuming that reclaimed wastewater from sewerage works is supplied for municipal use and industrial use - 133 - Journal of Water and Environment Technology, Vol 9, No.2, 2011 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 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 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 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 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 Persons of household One N=124 1（1%） Two 24（19%） Three 79（64%） Four 11（9%） Five 5（4%） Six 4（3%） 20 40 60 80 Number of household Fig - Household size of sampled households - 134 - 100 Journal of Water and Environment Technology, Vol 9, No.2, 2011 15-18 Age (years old) N=352 42（12%） 0-14 30（8%） 42（12%） 19-29 30-39 59（17%） 40-49 119（34%） 51（14%） 50-59 60-69 9（3%） 30 60 90 120 150 Number of person Fig - Age of sampled household members