First-flush Rainfall Operation Strategy for the Rainwater Utilization System Design

Transcription

1 First-flush Rainfall Operation Strategy for the Rainwater Utilization System Design Shih-Chi Lee and Hsien-Te Lin * * Department of Architecture, National Cheng Kung University, No.1, University Road, Tainan City 701, Taiwan ( n @mail.ncku.edu.tw; hylaman@srdc.org.tw ) ABSTRACT Usually, the First-flush Rainfall contains more pollutant by the air pollution and silt from the automobile or the factory s discharges, especially in metropolis area or industrial region. It becomes the main influence factor for peoples do not want to use rainwater resources. A long-term rainwater quality monitors data at Hsin-Chu Science-based Industrial Park region were applied for this appraisal analysis. The result showed that approaches 85% pollutant will wash out and enter to the rainwater treatment system in front of 2mm effective rainfall. In physical property aspects of this case, the change of chromaticity and turbidity is most obvious. On the other hand, SOx quantum which by the air pollution has approaches 90% change quantity. If we can remove this rainwater volume, it will be able to reduce the funds and equipment establishment space of the rainwater treatment system in the new architectural design. This datum has bought into the country architectural design law (green building design norm) since 2007 in Taiwan. On the other hand, we also test some simply filter material (stones, charcoal ), and the treatment effective of cant cube system on sedimentation procedure. The result shows that when comparing the original water quality with the water generated from the first-level non-woven fabric flume, the elimination of SS is able to achieve around 80% of the efficiency. Moreover, the chromaticity treatment efficiency implies that given the percentage of sands exist in water is the primary critical factor, the solid suspension filtered by the first-level non-woven fabric shows that 65% of the chromaticity has already been reduced. As the result, the selecting simple filtering materials to perform rainwater filtering can greatly enhance the rainwater quality and also provides the development reference of non-energy pipe disposal system for first-flush rainfall. Finally, with the operation strategy, this study showed a practical case of rainwater utilization system of the green building project in Taiwan. KEYWORDS Green Building; First-flush Disposal System; Rainwater Interception Equipment PREFACE The average annual rainfall in Taiwan is around 2,500mm. The utilization of rain catchment has great potential. Given that the western Taiwan is a high urbanization development area and the increasing severity of having air pollution to diminish rain water quality over the past few years, the utilization of rainfall has become a mandatory category when designing water resource indexes in the green building policies currently promoted in Taiwan. In addition, the standards designed to control polluted and clean rainfalls require more precise data to be provided to designers as the selective references for treatment equipments due to the constricted space within the architectural base. As the result, the development for simple filtering materials has also become a significant research and discussion direction.

2 ESTABLISHMENT OF THE EXPERIMENTAL ZONE The average annual rainfall in Taiwan is around 2,500mm. The utilization of rain catchment has great potential. Given that the western Taiwan is a high urbanization development area and the increasing severity of having air pollution to diminish rain water quality over the past few years, the utilization of rainfall has become a mandatory category when designing water resource indexes in the green building policies currently promoted in Taiwan. In addition, the standards designed to control polluted and clean rainfalls require more precise data to be provided to designers as the selective references for treatment equipments due to the constricted space within the architectural base. As the result, the development for simple filtering materials has also become a significant research and discussion direction. Meteorological Characteristics In Experimental Zone This experimental zone locates at Hsin-chu Science-based Industrial Park Taiwan, a high technology township also often recognized as the windy city in North West of Taiwan. The location is surrounded by mountains from three sides and faces the sea in the west. the meteorological data generated over a long period of time shows that July is the month that yields the highest average temperature of whereas January yields the lowest temperature of The relative humidity shows that the annual average is 81.15(%). July yields the lowest value of 77.57(%) and March with the highest humidity of 85.67(%). The monthly average hours of sunshine concludes that February produces the lowest hours of hours and July for the maximum of hours. The vaporization volume shows that the monthly average vaporization volume over the past years yields (mm) where July has the greatest monthly average of 195.7(mm) and February has the smallest average of 62.72(mm). The related records for annual rainfall in the experimental zone are illustrated in Table 1: Table 1. Rainfall Analysis on Site Item \ Station number Hsin-Chu (1) Note Annual Rainfall Depth(mm) years Max. Potential Rainfall Depths (mm/day) 4.80 Annual Max. Daily Rainfall Depth(mm) July, 81 Average Monthly Rainfall Depths(mm) Apr. to Oct. (Rainy Season) Max. Potential Rainfall Depths (mm/day) 5.88 Apr. to Oct. (Rainy Season) Average Continuously non-rainfall days 4.44 ~ Brief Summary Of The Experimental System The experimental zone facility for the first-flush rainwater withhold was implemented in March of The primary facility functions consist of: 1. Infrared ray rainfall depth control facility: the control scope is determined at rainfall depth falls between 1 to 12mm. 2. First-flush rainwater interception flume: a 3-ton rain catchment flume with a collection area of 375 square meters and the rainfall collection scope of 1 to 12mm in depth was implemented. 3. Rain catchment flume: a 5-ton flume was put in place as a collection basin for overflow rainfalls and also as a rain source supply flume prepared in advance for follow-up treatment system. 4. Automatic gravel sand setback filtering equipment and simple filtering testing flume. 5. Setback cleansing water basin: a 5-ton catchment flume was set to instantly provide15 minutes of the water required for setback cleansing. The water source for this flume comes from city water and rains that have been filtered by the gravel sand filtering system. 6. Treatment rain catchment flume (modulation flume): a 1-ton catchment flume was implemented as the water source for setback cleansing.

3 7. Automatic control system for first-flush rainwater interception testing facility: the related operations to control all electromagnetic valves and motors. Rainfall Catchment Area (375 sq. meter) City Water Catchment Area (1 sq. meter) First-flush interception flume (3 Tons) Rain catchment flume (5 Tons) Setback cleansing water basin Infrared ray rainfall depth control facility Simple Material Filtering Testing System Automatic gravel sand setback filtering equipment Modulation flume Drain Figure 1. First-flush Rainwater Interception Testing Facility RESULTS AND DISCUSSION Brief Summary of The Experimental System The water quality of first-flush rainwater mainly depends on the air quality and degree of the collection sanitation on the day of the rainfalls. However, the number of consecutive non-rainfall days is the absolute factor impacting the degree of the collection sanitation while the unit timeframe for rainfall intensity is the key factor constituting the turbidity. This experiment started off in hen we focus on the two samples randomly selected in Table 1, the non-rainfall Effective Rainfall Depth<1mm yields the consecutive 21 days and 8 days. The table recorded that the first rainfall was great and sudden whereas the rainfall intensity for the second rainfall was more around the average value. The water quality inspection of the first-flush rainwater interception is shown in Table 2. Table 2. Inspection Record of the First-flush Rainwater Water Quality 2- Temp. Cond. ph TS TDS SS SO 4 Fe 2+ Rainfall Depth 1mm 2mm Chrom Turb. Random Sample o C us/cm - mg/l mg/l mg/l mg/l mg/l P FTU NO NO Aver NO NO Aver From the physical index viewpoints such as the conductivity, ph, TS, TDS, SS, Chromaticity and Turbidity shown in above table, the first-flush rainfall of 1mm is apparently poorer than the water quality for 2mm. An even greater difference can be seen in TS and conductivity. Chromaticity and turbidity also varies along with the volume of rainfall. Such conclusions prove that first-flush rainfall has obvious impact on the cleansing of the water collection surface. From the chemical index viewpoints, the sulfuric acid ions in air contaminants were also flushed down by the firstflush 1mm rainfall. The table above shows that sulfuric acid ions yields obvious efficiency of reducing the 1mm average value of 33mg/L to 3mg/L for 2mm. The duad iron ions also yields similar tendency. According to the preliminary analysis results mentioned above, we know that it is

4 mandatory to avoid the rainwater accrued from 1mm first-flush rain from drifting in the rain catchment system (RWCS). Each inspection result is shown in Fig 2. Physical Index 180 Conductivity units: TS,TDS,SS: mg/l ;Turbidity: FTU From left to right :TS;TDS;SS;Chromaticity;Turbidity unit: us/cm SO ph unit: mg/l Figure 2. Physical and Chemical Index Variation of the First-flush Rainwater From the planning and design of green building rain catchment system shown above, the development of first-flush rainwater interception equipment has become the firs step in the development of rainwater utilization equipment. Figure 3 illustrates a simple equipment chart of first-flush rainwater elimination. Several development and application living examples of the related equipments are already in place in Taiwan in recent years. Simple Material Filtering Testing Results Figure 3. First-flush Rainwater Interception Device In the aspect of improving the quality of rainwater collected, filtering materials such as quartz sand, coal, non-woven fabric, Chi Li rock and carbon have all been studied. Among these materials, most of the materials have low unit price except for the carbon. Quartz sand yields the best efficiency

5 when focusing on the SS efficiency that can eliminate the physical index within the rain. However, if one wishes to eliminate the bad odor and chromaticity in the water, carbon filtration is the most likely to produce optimal water quality. Of course, the best way is to select filtering materials that are both economical and easily acquired or replaced for the utilization of rainwater. Table 3. Inspection Record of Rainwater Quality Filtered By Different Filtering Materials 2- Item Temp. Cond. ph TS TDS SS SO 4 Fe 2+ Chrom Turb. Unit o C us/cm - mg/l mg/l mg/l Mg/L mg/l P FTU Rainwater Non-woven Chi-Li Rock Carbon Storage Tank Table 3 shows that one unit conducted water quality inspection by using the non-woven fabric, Chi Li rock and carbon combination. Such result tells us that when comparing the original water quality with the water generated from the first-level non-woven fabric flume, the elimination of SS is able to achieve around 80% of the efficiency. Moreover, the chromaticity treatment efficiency implies that given the percentage of sands exist in water is the primary critical factor, the solid suspension filtered by the first-level non-woven fabric shows that 65% of the chromaticity has already been reduced. However, the degree of sanitation of the Chi-Li rock materials may impact the percentage of SS in water and prompts the level of chromaticity to be slightly increased. After the carbon filtering, the chromaticity in water is at a level that is no longer determine-able. As the result, the selecting simple filtering materials to perform rainwater filtering can greatly enhance the rainwater quality. Rainwater Sedimentation Treatment Design In Large-Scale Architectural Base Foundation Space Rainwater Inflow Repair ladder First-frush space Strainer #3 (50 holes/in 2 ) Strainer #2 (25 holes/in 2 ) Repair ladder Cant Cube Tank Strainer #1 (6 holes/in 2 ) Overflow to Raft foundation storage space Over Flow to sewer Figure 4. Combined Design of First-flush Rainwater Interception and Treatment Equipment in Large-scale Architecture. Besides from the previously mentioned small-scale architectural base that collect rainwater on the rooftop, large-scale architecture often have a greater instant inflow when centralizing the collection of rainwater. Hence, rainwater utilization treatment technology is required to overcome the problems arose such as staying attentive both to the filtering velocity and sand and foreign bodies elimination, the Contra-propeller design for water flow alleviation or the Cant Cube design to enhance sedimentation efficiency. Figure 4 shows the rainwater runoff collected by large-scale architectural base in mountain area. A few techniques and functions are added to the Contrapropeller design to avoid the turbulence generated from unexpected rapid descend that may increase

6 level of treatment difficulties. The Cant Cube design also is able to strengthen the sedimentation efficiency to up to five times. CASE ILLUSTRATIONS 1. Geographic environment: National Chia-Yi Senior Commercial Vocational School locates in south west of Taiwan. The annual regional rainfall depth is averaged at 1,730mm. 88.2% of the rainfall happened in rain seasons (from April to September annually). 2. Water consumption condition: With the students numbered at 2,770 people and school holidays for periods of July to September and January to February, the rainwater collected are used to water school plants and to source the scenic pond. The volume of rainwater consumed is estimated at 70 tons weekly. 3. Application subjects: the collected rainwater is utilized to water school plants, flush toilets and mop floors. 4. Design, planning and results of rainwater utilization: Raft foundation (600 tons) used in the construction of new school buildings as the rainwater storage space (first-flush rainwater interception flume is set at 10 tons) and united with city water and well water systems to provide simple water cleansing method by using charcoal. The method not only reduces automatic carbon filtration system energy exhaustion but it also allows the system to be easily maintained. It plans to replace 100% of the water consumed to flush school toilets and provide 15% of the school plants watering. The volume of having rainwater to replace city water is estimated at 3,600 tons/year. Some designs are shown in Figure 5. CONCLUSIONS Figure 5. Design Case of Simple Rainwater Treatment System 1. In the current of the Green Building developing, Taiwan s green construct progression was depended on a series of the official process. In 2000, The Green Building Evaluation System ( EEWH ) was constituted by Architecture and Building Research Institute, Ministry of The Interior, to assist on the Taiwan green building improvement. The water index is expected to actively use the rainfall and the recycle water (find new sources) as well as adopting water-saving equipment in architectural design (water saving) in order to achieve the purpose of saving water resource. 2. According to the statistics provided in this experiment, the standard of having first-flush rainwater to eliminate 1mm is already explicitly incorporated into Taiwan s green building rainwater utilization design plan as the suggested design values. In the future, designers are required to take this design standard into account when drawing up green building rainwater utilization constructions.

7 3. Simple rainwater filter equipment research and development of low costs and more easily acquired materials such as gravel, charcoal and non-woven fabrics can efficiently reduces implementation costs and strengthen the convenience of rainwater utilization design. The case studied in this paper is an example of using first-flush rainwater interception flume and charcoal filtration to achieve outstanding rainwater cleansing effect. 4. Additional efficiency includes that the rainwater utilization system implemented in metropolitan area not only achieves the optimal water resource utilization objective stated in green building indexes, it also helps promote sustainable water resource education and reduces metropolitan rainfall peak flow. The case mentioned above can slow down the overspill downpour ran-off under the collection surface for around 107 minutes. Such efficiency dramatically eases off the burden imposed upon the metropolitan area drainage during a rainstorm and also diminishes the chance of potential floods. 5. Areas that are industrially intense may formulate acid precipitation due to the low ph value prompted by industrial pollution. Rains dropped to water collection zone may mingle with animal waste, tree branches and leafs from the area; and the materials used in water catchment flume may also influence water quality. Hence, optimal water quality not only depends on the efficient first-flush rainwater treatment, regular water quality inspections, long-term monitoring and the maintenance and arrangement of the water collection zone also are crucial. The promotion of Taiwan s green building water resource indexes are also incorporated in several related design policies. REFERENCES H.T. Lin, J.B. Hsiao, J.L. Chen (2007), Evaluation Manual for Green Buildings in Taiwan, Architecture and Building Research Institute, Taipei, Taiwan. S.C. Lee, H.T. Lin (2004), Water Resource Improvement Project for Green Buildings and Schools, Architecture and Building Research Institute Project Report, Dec., Taipei, Taiwan. H.T. Lin, S.C. Lee (2004), Introduction of Green Building Remodelling Projects for Governmental Buildings, Architecture and Building Research Institute Report, Jan., 2004, Taipei, Taiwan. S.C. Lee, M.C. Lin, W.H. Chou (2000), Rainwater Catchments System Planning and Design in Hope Engineering Project, East Asia 2000 Regional Symposium on Rainwater utilization, Taipei, Taiwan.