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Possibilities of rainwater utilisation in densely populated areas including precipitation runoffs from traffic surfaces
Desalination 215 (2007) 1–11
Possibilities of rainwater utilisation in densely populated areas including precipitation runoffs from traffic surfaces Erwin Nolde Nolde & Partner, c/o Technical University of Berlin, Amrumer Strasse 32, D-13353 Berlin, Germany Tel. +49-3031427570; Fax +49-3031425914; email: [email protected] Received 17 August 2006; revised accepted 8 October 2006
Abstract Although Germany is not considered a water-poor country, rainwater utilisation in households became widespread since the 1980s. Today, about 50,000 professional rainwater plants are being installed every year mostly in new one-family houses. These plants collect exclusively water from the roof which is filtered, stored and primarily used for toilet flushing, garden watering and household laundry. A novel approach in Germany is the use of the more polluted rainwater draining from streets and courtyard surfaces for treatment and reuse as service water, which is the topic of this paper. Intensive investigations have shown that rainwater needs to be treated if street runoffs are diverted to the cistern. Stormwater in this case originates from roofs, courtyards and a one-way street with low traffic density. Compared to high traffic density areas, the rainwater is relatively low polluted (COD: mean 14 mg/L, max 36 mg/L; BOD7: mean 6.4 mg/L, max 45 mg/L; E. coli: median 1060/100 mL, max 43,000/100 mL). Treatment follows in a substrate filter (aerobic biological treatment) with an eventual UV disinfection of the treated rainwater. This treatment proved to be inexpensive with good effluent quality for use in toilet flushing and garden watering (COD: mean 6.8 mg/L, max 15.8 mg/L; BOD7: mean 0.9 mg/L, max 3 mg/L; E. coli: median < 4/100 mL, max 43/100 mL). This form of harvesting could be considered a viable option for densely populated urban areas. It also contributes in reducing the drinking water consumption and wastewater production as well as minimising pollutant entry into surface waters, without the need for a sewer connection. About 70% of the toilet-flush demand (about 2500 m3/a) was replaced by treated stormwater without any comfort loss. A total energy demand of only 0.88 kWh/m3 is required for treatment and distribution. Compared to the Berlin drinking water quality, the use of the much softer rainwater has also the advantage of less lime depositions on sanitary facilities. Keywords: Rainwater harvesting; Stormwater recycling; Traffic surfaces; Biological treatment; UV-disinfection; Toilet flushing; Service water
A special issue devoted to and inspired by WaT3R, MEDA WATER International Conference on Sustainable Water Management, Rational Water Use, Wastewater Treatment and Reuse, Marrakech, Morocco, 8–10 June 2006. 0011-9164/06/$ – See front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.10.033
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1. Introduction Decentralised stormwater retention and infiltration in urban areas has been used in Germany since the beginning of the 1980s as a sustainable and cost-effective alternative to combined and separate sewers. In Germany, all new developments are required by law to retain/infiltrate rainwater on site. Stormwater contains pollutants and nutrients which can endanger soils, groundwater and slowly flowing receiving water when it is discharged. Runoff from traffic areas contains higher pollutant concentrations than roof runoffs. These include abrasion from vehicle tyres and brake linings, dripping losses, emission from engines, corrosion products as well as dust and dog and bird droppings [1]. On average, the annual precipitation in Berlin amounts to about 645 mm. The natural groundwater regeneration is influenced by the high degree of sealed surfaces and therefore, water bodies are considerably burdened as a result of the direct rainwater discharges. About 15 to 20% of the rainwater outflow (80–100 Million m3) are received by separate and combined sewers. Nearly 35 Million m3 of rainwater, mostly untreated, are discharged yearly into Berlin water bodies. Added to that are diverse wastewater flows from the combined sewer which partly drain untreated wastewaters during torrential rain events [2]. On behalf of the Berlin Water Company (Berliner Wasserbetriebe) and based on studies carried out in 1989, Heinzmann concluded in 1993 that stormwater entering the rainwater sewer is occasionally highly polluted (COD: 30–1708 mg/L, BOD5: 8–120 mg/L). At annual means, concentrations in the rainwater outflows were notably higher than in the outflows from the wastewater treatment plant during dry weather [3]. In order to protect water bodies and guarantee the drinking water quality, a turning away
from the traditional rainwater disposal measures and direct rainwater discharge into surface waters towards a sustainable rainwater management is urgently required. In this context, rainwater utilisation is increasingly gaining on significance. In Germany, much research and development work has been done in the past decade on service water quality (water used in households other than drinking water) from rainwater and greywater systems. As a result, about 50,000 rainwater plants are being installed every year. In Berlin, the use of service water has been regulated in the 90s by the Berlin Senate Department of Urban Development in cooperation with the local health departments and the Technical University of Berlin [4]. In densely populated areas where more water is consumed, an important consideration would be whether a part of the urban water requirement can be covered by rainwater harvesting, and whether traffic and other surfaces, in addition to roof surfaces, can be used for rainwater catchment. In this case, rainwater need not be drained into the sewer. This will result in an upgrading of the water quality, since urban surface water bodies are increasingly negatively affected by rainwater discharges and overflows mainly from the combined sewer. In this context two questions need to be answered: (a) whether rainwater from polluted traffic and open surfaces can be easily treated to a highgrade service water and (b) whether rainwater utilisation offers financial benefits over the conventional systems. In this paper, the focus will be on the first issue. 2. Materials and methods 2.1. Sampling All samples for the physicochemical parameters were taken as quantity proportional, mainly as 24 h mixed samples, stored at 4°C and
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processed within 24 h. For microbiological parameters random samples were always taken. The influent sample was taken from the rainwater reservoir next to the influent pipe and the effluent sample from the service water tank. Sedimented samples were used for all parameters. For the microbiological samples, decimal dilution series were prepared in physiological saline (0.9%). Testing for E. coli, total coliforms, Enterococci and P. aeruginosa followed in triplicate serial dilutions and were quantified using the Most Probable Number (MPN) method.
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stripped off with synthetic air following acidification to a pH below 2. All test measurements were given as the arithmetic mean from a minimum of five consecutive measurements of a sample. 2.2.4. Chemical oxygen demand The chemical oxygen demand (COD) determination followed DIN 38409-H41. Measurements were carried out using the LASA plus photometer (Dr. Lange, Düsseldorf ). Cuvettes from Dr. Lange were used (LCK 314, 15–150 mg/L; LCK 414, 5–60 mg/L; LCK 114, 150–1000 mg/L).
2.2. Physicochemical parameters 2.2.1. UV transmission The UV transmission was determined in the sedimented sample according to DIN 38404-C3. The sample was measured in a Shimadzu UV-1201 photometer at a wavelength of 254 nm in 1 cm cuvettes against Millipore water. 2.2.2. Spectral absorption coefficient 254 nm (SAC 254nm) The spectral absorption coefficient was detected continuously with the UV-probe type LXG 139 and the device unit type LXG 144 (Dr. Lange, Düsseldorf) at 254 nm. Instead of filtration, the turbidity was compensated with a reference measurement at 550 nm. As several investigations have shown, the SAC 254nm correlates very well with TOC measurements. 2.2.3. Total organic carbon The determination of total organic carbon (TOC) followed DIN 38409-H3. Measurements were made in TOCOR 100 (Maihak, Hamburg) run in the range between 2 and 30 ppm (thermal decomposition method). Injection quantities varied between 40 and 140 µL dependent on sample concentration. The inorganic carbon portion was
2.2.5. Biological oxygen demand BOD7 was determined in the fresh sedimented sample following DIN 38409-H51 based on dilution without adding allylthiourea. The oxygen concentration was measured with a WTW Oximeter OXI 96 and the oxygen probe EOT 196 (WTW, Weilheim). Unlike the usual biological oxygen demand (BOD) measurements which follow 5 days incubation, BOD was usually determined after 7 days due to organisational reasons. For BOD7, it is expected that the value is either larger than or equal to the BOD5 for the same sample. For inoculated domestic wastewater in a moderate motion, a conversion factor of 1.17 can be used (1 mg/L BOD5 = 1.17 mg/L BOD7) [5]. 2.2.6. Electrical conductivity The electrical conductivity was measured following DIN 38 404-C8 with the electrode LF 91 (WTW, Weilheim). 2.2.7. Analysis of ions 2.2.7.1. Anions The anions fluoride, chloride, nitrite, nitrate, phosphate and sulphate were analysed in an DX 120 ion chromatograph according to EN ISO 10304-1 using a pre-column AG14 (4 mm) and
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a main column AS14 (4 mm) (Dionex) at a flow rate of 1.2 mL/min. 2.2.7.2. Cations The cations sodium, ammonium, potassium, magnesium and calcium were analysed in an ion chromatograph DX 120 (Dionex), a pre-column CG12 (4 × 50 mm) and a cation column CS12A (4 × 250 mm) at a flow rate of 1 mL/min. All samples were pre-filtered through 2 µm filters to avoid clogging of the columns. 2.2.7.3. Total phosphorous Total phosphorous concentrations were determined according to EN 1189. Since it was expected to measure very low concentrations of phosphorous in rainwater, calibration followed DIN 38 402 whereby a low concentration range (0.01–0.28 mg/L) was covered. 2.2.7.4. Total nitrogen Total nitrogen was determined according to EN ISO 11905-1:H36. Calibration followed DIN 38 402 in the range of 0.5 to 5 mg/L. 2.3. Hygienic-microbiological parameters 2.3.1. Colony forming units The determination of the number of colony forming units (CFU) followed in duplicate serial dilutions using Koch’s Pour Plate method. The DEV-nutrient agar plates were incubated for 44 ± 4 h at 20 and 37°C. Plates which showed between 30 and 300 colonies under a 8× magnification were evaluated and arithmetic means determined. 2.3.2. Escherichia coli and total coliform bacteria Detection and enumeration followed in Fluorocult-Lauryl-Sulfate broth using the MPN method. Tubes were incubated at 37°C for 48 h
and those which showed turbidity and gas formation were recorded as positive for the total coliform bacteria. For the detection of E. coli, the medium was made alkaline followed by irradiation with a longwave UV light to examine fluorescence. In the presence of a light-blue fluorescence, an additional test was made to check for the formation of indol from tryptophan using Kovac’s reagent. All tubes with turbidity, gas formation, fluorescence and indol formation were considered positive for E. coli. 2.3.3. Enterococci The detection of Enterococci followed the regulation described in the Drinking Water Decree (primary enrichment on Azide-Glucose broth, streaking on Enterococci selective agar after Slanetz-Bartley, Gram staining). Suspected colonies were further sub-cultured onto a selective broth (Brain-Heart-Infusion broth with pH 9.6 and Brain-Heart-Infusion broth with 6.5% NaCl). The test was considered positive following turbidity in both media (and if necessary Gram staining). 2.3.4. Pseudomonas aeruginosa The detection of P. aeruginosa followed DIN 38411 Part 8: liquid enrichment in MalachiteGreen broth (triple set), streaking on Cetrimide agar, oxidase test and detection of ammonia formation in Acetamide liquid media. 2.4. Investigated area and system technology Rainwater infiltration in the investigated area has been excluded from the beginning due to unfavourable soil permeability and intensive use of the scarce open space. About 11,770 m2 of sealed surface area are connected to the rainwater reservoir situated in the cellar of a new building. 63% of the collected surfaces originate from the roof, 35% from courtyards and sidewalks and
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• Roofs
First flush diversion
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Stormwater sewer
• Courtyards • Roads
Sedimentation Grit chamber 190 m³ RW-Reservoir
UV disinfection
Biological treatment Irrigation
Wastewater sewer
6 m³ storage reservoir Water pump
Toilet flushing
Receiving stream
Fig. 1. A flow diagram of the rainwater plant in Berlin-Lankwitz with first-flush diversion into the reservoir.
12% from traffic surfaces. Rainwater is first discharged into the existing rainwater sewer of the Berlin water company, and from there it drains into the rainwater reservoir until the reservoir reaches its full capacity. A flow diagram of the rainwater plant is demonstrated in Fig. 1. The 190 m3 rainwater reservoir is filled with rainwater until the water level in the reservoir reaches the sewer level. Excess water is discharged into surface water. Biological treatment of the rainwater takes place in a “planted” substrate filter which has been installed in the building (Fig. 2). About 10 m3 of rainwater are treated daily followed by disinfection with UV (28 Watt). The service water reservoir (6 m3) serves as a storage tank for the treated rainwater and acts as a system buffer during consumption peaks. The rainwater harvesting plant supplies 80 apartments and 6 small trade units (a total of 200 persons) with high-quality service water for toilet flushing and garden watering. The selected substrate filter consists of two layers each is 2.2 m long, 1.1 m wide and 0.7 m deep. The above layer consists of expanded clay particles (8–16 mm grain size) while the lower layer is filled with gravel (4–8 mm). The two layers are placed 1 m apart (Fig. 2). Rainwater percolates from above continuously and uniformly
over the whole substrate bed. The rainwater plant has been operating since 2000 without clogging or other technical problems. 3. Results 3.1. Rainwater and service water quality Rainwater entering the rainwater sewer is subject to qualitatively wide seasonal fluctuations as well as during a single storm event. Relatively high BOD7 concentrations up to 45 mg/L were measured especially after long drought periods in summer, whereby the “first-flush” was mostly polluted. Pollutants from traffic surfaces and courtyard cleaning enter the rainwater sewer besides other pollutants from air, foliage and dog faeces. These are usually partly retained by a grit chamber in the pre-treatment stage. With prolonged rain events and following treatment, clear water flows eventually in the reservoir. On 17th May 2000, a storm event took place with a duration of 4.5 h and a height of 8.1 mm. Fig. 3 shows that only after 20 min of heavy rain, an increase in the SAC and a clear drop in the conductivity could be registered. This rain event was preceded by an 18-day dry period and demonstrates the pollution load of the first-flush rainwater samples.
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80
320
70
280
60
240
50
200
40
160
30
120
20
80
10
40
0 15:30
15:40
15:50
16:00
16:10
16:20
16:30
16:40
Conductivity (µS/cm)
Stormwater flow (L /s), SAC (1/m)
Fig. 2. Rainwater plant site in Berlin-Lankwitz and substrate filter inside the building (circle).
0 16:50
Time Stormwater flow
SAC
Conductivity
Fig. 3. Results from online monitoring of the stormwater sewer for a first-flush event from 17.05.2000.
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Since highly polluted rainwater enters the reservoir following pre-treatment, a considerable environmental relief is thus achieved since these pollutants fail to enter the surface waters. Following treatment, biochemical and microbiological studies have shown that this high pollution load exerts no negative effect on the service water quality. Due to the efficient biological treatment of rainwater in the above described system, effluent from the soil filter is always pollutant-poor and clear. Due to the high oxygen content, the treated water is also suitable for storage without causing odour problems. 3.2. Physicochemical and hygienic/ microbiological parameters Table 1 summarises the measurements of the different parameters during the course of
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rainwater treatment. In the reservoir influent, a relatively low pollution load was measured. No significant reduction in the concentrations took place during residence in the reservoir (compare reservoir and substrate filter influents). The biodegradable organic components contained in rainwater are oxidised in the substrate filter (SF). The BOD7 concentration is considered an important parameter with a maximum concentration of 3 mg/L measured in the SF effluent. In most samples from SF effluent, no oxygen depletion was detected after 7 days. The Berlin requirements for BOD7 for service water [4] of less than 5 mg/L were continuously maintained under these operating conditions. These concentrations would not have been achieved with sedimentation alone without the use of the substrate filter. An overall slight rise in the ion concentrations for ammonium, nitrate and phosphate
Table 1 Results of laboratory investigations during the period between February 2000 and March 2001 for the single treatment stages (n = number of samples; reservoir influent: n = 36; substrate filter (SF) influent: n = 26; SF effluent: n = 36) [6] Parameter
Cond. (μS/cm) Trans (%) TOC BOD7 COD N-total P-total Cl NO2-N (mg/L) NO3-N PO4 SO4 Na Mg Ca NH4-N
Influent reservoir
Influent SF
Effluent SF
Max
Min
Mean
Max
Min
Mean
Max
Min
Mean
356.00 89.60 12.67 45.00 36.10 5.48 0.398 18.62 0.426 1.682 0.98 29.20 4.61 1.86 17.88 0.88
51.00 22.60 1.67 1.00 4.56 0.82 0.036 0.82 0.006 0.023 0.01 1.97 1.07 0.05 5.79 0.27
110.95 72.48 4.42 6.39 14.20 2.14 0.114 3.64 0.086 0.721 0.21 6.44 2.85 0.80 12.16 0.50
232.00 90.00 8.63 63.00 48.00 2.96 0.183 18.45 0.177 1.423 0.45 16.54 7.69 2.07 19.84 0.72
49.00 22.90 1.55 0.49 4.56 0.63 0.028 0.82 0.015 0.081 0.01 2.49 1.09 0.05 5.79 0.09
103.52 74.23 3.62 7.10 12.65 1.96 0.094 4.09 0.060 0.916 0.14 6.14 4.35 1.19 14.34 0.27
199.00 97.10 5.30 3.00 15.80 3.82 0.174 17.22 0.131 3.512 1.65 19.51 7.69 2.07 19.76 6.61
60.00 24.00 1.26 0.59 4.56 0.69 0.014 0.81 0.006 0.364 0.09 2.72 1.13 0.05 6.68 0.47
103.38 83.79 2.49 0.86 6.82 2.06 0.089 4.05 0.063 1.726 0.28 7.09 5.12 1.47 15.74 3.54
Note: BOD7 and COD were not always measured for the same samples and/or same time.
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of 0.03/mL for E. coli (based on 41 samples of which 26 were below the detection limit). Further investigations made on treated rainwater have shown that the concentrations of E. coli, total coliforms, Enterococci and Pseudomonas aeruginosa following a modification of the UV disinfection unit, remained below the detection limit of 0.03/mL [6,7]. As a general rule, the resulting service water quality is 30 to 3000-fold better than the mandatory values of the EU Directive for Bathing Water [8]. Table 2 shows the hygienic-microbiological parameters measured over a period of 1 year. The shaded cells show all values which exceeded the limits of the Berlin quality requirements for service water [4]. The concentration ranges were pooled in a log10 range. It can be clearly seen that the majority of the untreated rainwater samples, as rainwater enters the reservoir, exceeded the limit values whereas following biological treatment and subsequent UV disinfection, the limit values were safely maintained.
was observed (Table 1). However, it should be taken into consideration that the lower substrate filter has been repeatedly replanted following dieoff of the plants, thus contributing to increasing concentrations of these ions. Based on the mean concentrations of the alkaline ions and a mean Ca-concentration of about 12 mg/L, an average total hardness of only 15.71 mg/L CaCO3 was calculated for the reservoir effluent compared to that of Berlin’s drinking water which exhibits a total hardness above 143 mg/L CaCO3. This means that the treated rainwater is very soft in nature and can be used for household laundry with little or no lime deposition on sanitary fittings. Fig. 4 shows the concentrations of E. coli at the four sampling sites. Reservoir effluent concentrations were measured over a wide range with a slight reduction of E. coli during residence in the cistern. E. coli concentrations were reduced nearly one log10 following passage through the substrate filter. The median value of 0.04/mL in the service water tank lies near the detection limit
1000
E. coli (MPN/mL)
100
10
10.6 5.8
1
0.73
0.1 0.04 0.01 Sampling sites Influent reservoir
Influent SF
Effluent SF
Service water
Fig. 4. E. coli concentrations (MPN-method) at the four sampling sites in the rainwater plant including the median for the period between February 2000 and March 2001 [6].
E. Nolde / Desalination 215 (2007) 1–11
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Table 2 Frequency distribution (in %) of measured parameters at the four sampling sites in the rainwater plant [6]. The shaded cells mark the measured values which exceeded the limits of the Berlin quality requirements for service water [4]. (n = number of samples). Frequency distribution (%) Concentration range (1/mL) Influent reservoir n = 37 CFU 20°C CFU 37°C E. coli Total coliforms Enterococci P. aeruginosa Influent SF n = 29 CFU 20°C CFU 37°C E. coli Total coliforms Enterococci P. aeruginosa Effluent SF n = 41 CFU 20°C CFU 37°C E. coli Total coliforms Enterococci P. aeruginosa Service water n = 41 CFU 20°C CFU 37°C E. coli Total coliforms Enterococci P. aeruginosa
<0.1
>0.1 to <1
>1 to <10
>10 to <100
>100 to <1000
>1000 to <10,000
>10,000
0 0 0 0 2.7 64.9
0 0 16.2 10.8 13.5 24.3
0 0 35.2 29.8 37.9 10.8
0 5.6 32.4 37.8 37.8 0
13.9 24.9 16.2 21.6 8.1 0
66.7 66.7 0 0 0 0
19.4 2.8 0 0 0 0
0 0 3.5 3.5 13.8 72.4
0 0 24.1 10.3 10.3 20.6
0 0 34.5 37.9 48.3 3.5
3.6 21.4 31 37.9 20.7 3.5
25 28.6 6.9 10.4 6.9 0
57.1 46.4 0 0 0 0
14.3 3.6 0 0 0 0
0 0 19.5 12.2 43.9 95.1
0 0 31.7 26.8 24.4 4.9
0 0 39 43.9 21.9 0
0 34.1 7.3 14.6 9.8 0
82.9 61 2.5 2.5 0 0
17.1 4.9 0 0 0 0
0 0 0 0 0 0
0 0 95.1 82.9 100 97.6
0 0 4.9 4.9 0 2.4
15.4 30.8 0 12.2 0 0
48.7 51.2 0 0 0 0
33.3 15.4 0 0 0 0
2.6 2.6 0 0 0 0
0 0 0 0 0 0
4. Discussion and conclusions Rainwater utilisation in Germany is regulated by DIN 1989 which is preferentially in favour of rainwater harvesting from roof surfaces [9]. This system treats effectively rainwater from traffic surfaces beyond the German standards for rainwater harvesting systems, and shows that
these sources can be considered as viable sources in rainwater harvesting schemes. Various pollutants are commonly found in urban and suburban stormwater. Runoff from roofs, roads and parking lots can contain significant concentrations of copper, zinc and lead. Increased traffic volume results in higher concentrations of
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polyaromatic hydrocarbons commonly exceeding levels set to protect aquatic systems [10]. Other pollutants include suspended solids, organic carbon, bacteria, hydrocarbons, trace metals, pesticides, chlorides, trash and debris. Others studies investigated the scale of public health risk and environmental pollution from stormwater runoffs caused by urbanisation [11,12] and the authors came to the conclusion that stormwater management to minimise runoff and associated pollution appears to be a potentially valuable component of an integrated strategy to protect the public health at the least cost. In this study it has been shown that with simple inexpensive treatment, rainwater from more polluted surfaces, such as traffic areas, can be treated to a high quality service water for use in households for toilet flushing and laundry activities without hygienic risk and comfort loss for the user. In addition, the energy requirement of 0.88 kWh/m3 for cleaning the stormwater and distributing it for toilet flushing is low. Under certain conditions, rainwater harvesting may be realised as the only measure in areas with a high specific requirement for service water, whereby drinking water consumption and wastewater discharges are reduced as a result of rainwater harvesting. This is particularly applicable where soil conditions are unfavourable for rainwater infiltration or costs are too big. Pollutants will be also mostly retained in the reservoir, thus preventing their accumulation in the soil or infiltration into the groundwater. The pollution load on the water bodies is also reduced to almost zero, leading to an improvement of the urban surface water quality [13]. Compared to rainwater utilisation plants for single-family houses, the rainwater plant described in this paper is not more expensive (including planning and incidental costs). In this case, an optimal cost benefit is achieved when a connection to the sewer can be abandoned. In order to further reduce on costs, it would be more economical to
construct the substrate filter outdoors instead of indoors. Stormwater recycling is likely to be of significant environmental benefit through the reduction of non-point source pollutant loads and the minimisation of the requirement to build additional water supply infrastructure with increasing population densities. In this regard, stormwater management and recycling should become an essential part of every urban plan scheme. Rainwater harvesting can be considered a viable technology in an urban setting and with the increasing cost of water and wastewater services, rainwater systems are becoming more economically feasible. In a final evaluation, rainwater utilisation schemes in metropolitan areas should be also assessed on account of their environmental benefits and non-monetary aspects. Acknowledgements This project was financed by the Berlin Senate Department of Urban Development. Special thanks to Engineer Brigitte Reichmann for her dedicated project management. References [1]
[2]
[3]
[4]
[5] [6]
M. Grottker, Runoff quality from a street with medium traffic loading, Sci. Total Environ., 59 (1987) 457–466. Senatsverwaltung für Stadtentwicklung, Umweltschutz und Technologie, Stadtentwicklungsplan Ver- und Entsorgung, Berlin, 1998. B. Heinzmann, Beschaffenheit und weitgehende Aufbereitung von städtischen Regenabflüssen, Fortschritte VDI, Reihe 15: Umwelttechnik Nr. 113. Düsseldorf: VDI-Verlag, 1993. Senatsverwaltung für Bau- und Wohnungswesen, Merkblatt “Betriebswassernutzung in Gebäuden”, Senatsverwaltung für Bau- und Wohnungswesen, Württembergische Straße 6–10, 10707 Berlin, 1995. K. Imhoff, Taschenbuch der Stadtentwässerung. R. Oldenbourg Verlag München, Wien, 1990. R. Gildemeister, Regenwassernutzung im verdichteten Wohnungsbau, Diplomarbeit an der Technische
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[7]
[8]
[9]
[10]
Universität Berlin, Fakultät III: Prozesswissenschaften, AG Umwelthygiene, 2001. E. Nolde, Möglichkeiten der Regenwassernutzung im dichtbesiedelten Raum unter Einbeziehung der Niederschlagsabflüsse von Verkehrsflächen. fbrFachtagung: Regenwassernutzung und -bewirtschaftung in der Landschafts- und Freiraumplanung, am 4, November 2003, Frankfurt/Main, 2003. Council Directive 76/160/EEC of 8 December 1975 concerning the quality of bathing water, 1975. DIN 1989-1, Rainwater Harvesting Systems - Part 1: Planning, installation, operation and maintenance, German Institute for Standardisation, Berlin, 2002. J.E. Ball, R. Jenks and D. Aubourg, An assessment of the availability of pollutant constituents on
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road surfaces, Sci. Total Environ., 209 (2–3) (1998) 243–254. [11] S.J. Gaffield, R.L. Goo, L.A. Richards and R.J. Jackson, Public health effects of inadequately managed stormwater runoff, Am. J. Publ. Health, 93 (9) (2003) 1527–1533. [12] V. Meera and M.M. Ahammed, Water quality of rainwater harvesting systems: a review, Journal of Water Supply Research and Technology - Aqua, 55 (4) (2006) 257–268. [13] E. Nolde, Regenwassernutzung in Gebäuden – Ein Beitrag zur Abflussminimierung und Reduzierung des Trinkwasserverbrauchs. In Zukunft Wasser – Dokumentation zum Symposium zur Nachhaltigkeit im Wasserwesen in der Mitte Europas vom 17, bis 19, Juni 1998 in Berlin, pp. 94–97, 1998.
Possibilities of rainwater utilisation in densely populated areas including precipitation runoffs from traffic surfaces Erwin Nolde Nolde & Partner, c/o Technical University of Berlin, Amrumer Strasse 32, D-13353 Berlin, Germany Tel. +49-3031427570; Fax +49-3031425914; email: [email protected] Received 17 August 2006; revised accepted 8 October 2006
Abstract Although Germany is not considered a water-poor country, rainwater utilisation in households became widespread since the 1980s. Today, about 50,000 professional rainwater plants are being installed every year mostly in new one-family houses. These plants collect exclusively water from the roof which is filtered, stored and primarily used for toilet flushing, garden watering and household laundry. A novel approach in Germany is the use of the more polluted rainwater draining from streets and courtyard surfaces for treatment and reuse as service water, which is the topic of this paper. Intensive investigations have shown that rainwater needs to be treated if street runoffs are diverted to the cistern. Stormwater in this case originates from roofs, courtyards and a one-way street with low traffic density. Compared to high traffic density areas, the rainwater is relatively low polluted (COD: mean 14 mg/L, max 36 mg/L; BOD7: mean 6.4 mg/L, max 45 mg/L; E. coli: median 1060/100 mL, max 43,000/100 mL). Treatment follows in a substrate filter (aerobic biological treatment) with an eventual UV disinfection of the treated rainwater. This treatment proved to be inexpensive with good effluent quality for use in toilet flushing and garden watering (COD: mean 6.8 mg/L, max 15.8 mg/L; BOD7: mean 0.9 mg/L, max 3 mg/L; E. coli: median < 4/100 mL, max 43/100 mL). This form of harvesting could be considered a viable option for densely populated urban areas. It also contributes in reducing the drinking water consumption and wastewater production as well as minimising pollutant entry into surface waters, without the need for a sewer connection. About 70% of the toilet-flush demand (about 2500 m3/a) was replaced by treated stormwater without any comfort loss. A total energy demand of only 0.88 kWh/m3 is required for treatment and distribution. Compared to the Berlin drinking water quality, the use of the much softer rainwater has also the advantage of less lime depositions on sanitary facilities. Keywords: Rainwater harvesting; Stormwater recycling; Traffic surfaces; Biological treatment; UV-disinfection; Toilet flushing; Service water
A special issue devoted to and inspired by WaT3R, MEDA WATER International Conference on Sustainable Water Management, Rational Water Use, Wastewater Treatment and Reuse, Marrakech, Morocco, 8–10 June 2006. 0011-9164/06/$ – See front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.10.033
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1. Introduction Decentralised stormwater retention and infiltration in urban areas has been used in Germany since the beginning of the 1980s as a sustainable and cost-effective alternative to combined and separate sewers. In Germany, all new developments are required by law to retain/infiltrate rainwater on site. Stormwater contains pollutants and nutrients which can endanger soils, groundwater and slowly flowing receiving water when it is discharged. Runoff from traffic areas contains higher pollutant concentrations than roof runoffs. These include abrasion from vehicle tyres and brake linings, dripping losses, emission from engines, corrosion products as well as dust and dog and bird droppings [1]. On average, the annual precipitation in Berlin amounts to about 645 mm. The natural groundwater regeneration is influenced by the high degree of sealed surfaces and therefore, water bodies are considerably burdened as a result of the direct rainwater discharges. About 15 to 20% of the rainwater outflow (80–100 Million m3) are received by separate and combined sewers. Nearly 35 Million m3 of rainwater, mostly untreated, are discharged yearly into Berlin water bodies. Added to that are diverse wastewater flows from the combined sewer which partly drain untreated wastewaters during torrential rain events [2]. On behalf of the Berlin Water Company (Berliner Wasserbetriebe) and based on studies carried out in 1989, Heinzmann concluded in 1993 that stormwater entering the rainwater sewer is occasionally highly polluted (COD: 30–1708 mg/L, BOD5: 8–120 mg/L). At annual means, concentrations in the rainwater outflows were notably higher than in the outflows from the wastewater treatment plant during dry weather [3]. In order to protect water bodies and guarantee the drinking water quality, a turning away
from the traditional rainwater disposal measures and direct rainwater discharge into surface waters towards a sustainable rainwater management is urgently required. In this context, rainwater utilisation is increasingly gaining on significance. In Germany, much research and development work has been done in the past decade on service water quality (water used in households other than drinking water) from rainwater and greywater systems. As a result, about 50,000 rainwater plants are being installed every year. In Berlin, the use of service water has been regulated in the 90s by the Berlin Senate Department of Urban Development in cooperation with the local health departments and the Technical University of Berlin [4]. In densely populated areas where more water is consumed, an important consideration would be whether a part of the urban water requirement can be covered by rainwater harvesting, and whether traffic and other surfaces, in addition to roof surfaces, can be used for rainwater catchment. In this case, rainwater need not be drained into the sewer. This will result in an upgrading of the water quality, since urban surface water bodies are increasingly negatively affected by rainwater discharges and overflows mainly from the combined sewer. In this context two questions need to be answered: (a) whether rainwater from polluted traffic and open surfaces can be easily treated to a highgrade service water and (b) whether rainwater utilisation offers financial benefits over the conventional systems. In this paper, the focus will be on the first issue. 2. Materials and methods 2.1. Sampling All samples for the physicochemical parameters were taken as quantity proportional, mainly as 24 h mixed samples, stored at 4°C and
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processed within 24 h. For microbiological parameters random samples were always taken. The influent sample was taken from the rainwater reservoir next to the influent pipe and the effluent sample from the service water tank. Sedimented samples were used for all parameters. For the microbiological samples, decimal dilution series were prepared in physiological saline (0.9%). Testing for E. coli, total coliforms, Enterococci and P. aeruginosa followed in triplicate serial dilutions and were quantified using the Most Probable Number (MPN) method.
3
stripped off with synthetic air following acidification to a pH below 2. All test measurements were given as the arithmetic mean from a minimum of five consecutive measurements of a sample. 2.2.4. Chemical oxygen demand The chemical oxygen demand (COD) determination followed DIN 38409-H41. Measurements were carried out using the LASA plus photometer (Dr. Lange, Düsseldorf ). Cuvettes from Dr. Lange were used (LCK 314, 15–150 mg/L; LCK 414, 5–60 mg/L; LCK 114, 150–1000 mg/L).
2.2. Physicochemical parameters 2.2.1. UV transmission The UV transmission was determined in the sedimented sample according to DIN 38404-C3. The sample was measured in a Shimadzu UV-1201 photometer at a wavelength of 254 nm in 1 cm cuvettes against Millipore water. 2.2.2. Spectral absorption coefficient 254 nm (SAC 254nm) The spectral absorption coefficient was detected continuously with the UV-probe type LXG 139 and the device unit type LXG 144 (Dr. Lange, Düsseldorf) at 254 nm. Instead of filtration, the turbidity was compensated with a reference measurement at 550 nm. As several investigations have shown, the SAC 254nm correlates very well with TOC measurements. 2.2.3. Total organic carbon The determination of total organic carbon (TOC) followed DIN 38409-H3. Measurements were made in TOCOR 100 (Maihak, Hamburg) run in the range between 2 and 30 ppm (thermal decomposition method). Injection quantities varied between 40 and 140 µL dependent on sample concentration. The inorganic carbon portion was
2.2.5. Biological oxygen demand BOD7 was determined in the fresh sedimented sample following DIN 38409-H51 based on dilution without adding allylthiourea. The oxygen concentration was measured with a WTW Oximeter OXI 96 and the oxygen probe EOT 196 (WTW, Weilheim). Unlike the usual biological oxygen demand (BOD) measurements which follow 5 days incubation, BOD was usually determined after 7 days due to organisational reasons. For BOD7, it is expected that the value is either larger than or equal to the BOD5 for the same sample. For inoculated domestic wastewater in a moderate motion, a conversion factor of 1.17 can be used (1 mg/L BOD5 = 1.17 mg/L BOD7) [5]. 2.2.6. Electrical conductivity The electrical conductivity was measured following DIN 38 404-C8 with the electrode LF 91 (WTW, Weilheim). 2.2.7. Analysis of ions 2.2.7.1. Anions The anions fluoride, chloride, nitrite, nitrate, phosphate and sulphate were analysed in an DX 120 ion chromatograph according to EN ISO 10304-1 using a pre-column AG14 (4 mm) and
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a main column AS14 (4 mm) (Dionex) at a flow rate of 1.2 mL/min. 2.2.7.2. Cations The cations sodium, ammonium, potassium, magnesium and calcium were analysed in an ion chromatograph DX 120 (Dionex), a pre-column CG12 (4 × 50 mm) and a cation column CS12A (4 × 250 mm) at a flow rate of 1 mL/min. All samples were pre-filtered through 2 µm filters to avoid clogging of the columns. 2.2.7.3. Total phosphorous Total phosphorous concentrations were determined according to EN 1189. Since it was expected to measure very low concentrations of phosphorous in rainwater, calibration followed DIN 38 402 whereby a low concentration range (0.01–0.28 mg/L) was covered. 2.2.7.4. Total nitrogen Total nitrogen was determined according to EN ISO 11905-1:H36. Calibration followed DIN 38 402 in the range of 0.5 to 5 mg/L. 2.3. Hygienic-microbiological parameters 2.3.1. Colony forming units The determination of the number of colony forming units (CFU) followed in duplicate serial dilutions using Koch’s Pour Plate method. The DEV-nutrient agar plates were incubated for 44 ± 4 h at 20 and 37°C. Plates which showed between 30 and 300 colonies under a 8× magnification were evaluated and arithmetic means determined. 2.3.2. Escherichia coli and total coliform bacteria Detection and enumeration followed in Fluorocult-Lauryl-Sulfate broth using the MPN method. Tubes were incubated at 37°C for 48 h
and those which showed turbidity and gas formation were recorded as positive for the total coliform bacteria. For the detection of E. coli, the medium was made alkaline followed by irradiation with a longwave UV light to examine fluorescence. In the presence of a light-blue fluorescence, an additional test was made to check for the formation of indol from tryptophan using Kovac’s reagent. All tubes with turbidity, gas formation, fluorescence and indol formation were considered positive for E. coli. 2.3.3. Enterococci The detection of Enterococci followed the regulation described in the Drinking Water Decree (primary enrichment on Azide-Glucose broth, streaking on Enterococci selective agar after Slanetz-Bartley, Gram staining). Suspected colonies were further sub-cultured onto a selective broth (Brain-Heart-Infusion broth with pH 9.6 and Brain-Heart-Infusion broth with 6.5% NaCl). The test was considered positive following turbidity in both media (and if necessary Gram staining). 2.3.4. Pseudomonas aeruginosa The detection of P. aeruginosa followed DIN 38411 Part 8: liquid enrichment in MalachiteGreen broth (triple set), streaking on Cetrimide agar, oxidase test and detection of ammonia formation in Acetamide liquid media. 2.4. Investigated area and system technology Rainwater infiltration in the investigated area has been excluded from the beginning due to unfavourable soil permeability and intensive use of the scarce open space. About 11,770 m2 of sealed surface area are connected to the rainwater reservoir situated in the cellar of a new building. 63% of the collected surfaces originate from the roof, 35% from courtyards and sidewalks and
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• Roofs
First flush diversion
5
Stormwater sewer
• Courtyards • Roads
Sedimentation Grit chamber 190 m³ RW-Reservoir
UV disinfection
Biological treatment Irrigation
Wastewater sewer
6 m³ storage reservoir Water pump
Toilet flushing
Receiving stream
Fig. 1. A flow diagram of the rainwater plant in Berlin-Lankwitz with first-flush diversion into the reservoir.
12% from traffic surfaces. Rainwater is first discharged into the existing rainwater sewer of the Berlin water company, and from there it drains into the rainwater reservoir until the reservoir reaches its full capacity. A flow diagram of the rainwater plant is demonstrated in Fig. 1. The 190 m3 rainwater reservoir is filled with rainwater until the water level in the reservoir reaches the sewer level. Excess water is discharged into surface water. Biological treatment of the rainwater takes place in a “planted” substrate filter which has been installed in the building (Fig. 2). About 10 m3 of rainwater are treated daily followed by disinfection with UV (28 Watt). The service water reservoir (6 m3) serves as a storage tank for the treated rainwater and acts as a system buffer during consumption peaks. The rainwater harvesting plant supplies 80 apartments and 6 small trade units (a total of 200 persons) with high-quality service water for toilet flushing and garden watering. The selected substrate filter consists of two layers each is 2.2 m long, 1.1 m wide and 0.7 m deep. The above layer consists of expanded clay particles (8–16 mm grain size) while the lower layer is filled with gravel (4–8 mm). The two layers are placed 1 m apart (Fig. 2). Rainwater percolates from above continuously and uniformly
over the whole substrate bed. The rainwater plant has been operating since 2000 without clogging or other technical problems. 3. Results 3.1. Rainwater and service water quality Rainwater entering the rainwater sewer is subject to qualitatively wide seasonal fluctuations as well as during a single storm event. Relatively high BOD7 concentrations up to 45 mg/L were measured especially after long drought periods in summer, whereby the “first-flush” was mostly polluted. Pollutants from traffic surfaces and courtyard cleaning enter the rainwater sewer besides other pollutants from air, foliage and dog faeces. These are usually partly retained by a grit chamber in the pre-treatment stage. With prolonged rain events and following treatment, clear water flows eventually in the reservoir. On 17th May 2000, a storm event took place with a duration of 4.5 h and a height of 8.1 mm. Fig. 3 shows that only after 20 min of heavy rain, an increase in the SAC and a clear drop in the conductivity could be registered. This rain event was preceded by an 18-day dry period and demonstrates the pollution load of the first-flush rainwater samples.
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80
320
70
280
60
240
50
200
40
160
30
120
20
80
10
40
0 15:30
15:40
15:50
16:00
16:10
16:20
16:30
16:40
Conductivity (µS/cm)
Stormwater flow (L /s), SAC (1/m)
Fig. 2. Rainwater plant site in Berlin-Lankwitz and substrate filter inside the building (circle).
0 16:50
Time Stormwater flow
SAC
Conductivity
Fig. 3. Results from online monitoring of the stormwater sewer for a first-flush event from 17.05.2000.
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Since highly polluted rainwater enters the reservoir following pre-treatment, a considerable environmental relief is thus achieved since these pollutants fail to enter the surface waters. Following treatment, biochemical and microbiological studies have shown that this high pollution load exerts no negative effect on the service water quality. Due to the efficient biological treatment of rainwater in the above described system, effluent from the soil filter is always pollutant-poor and clear. Due to the high oxygen content, the treated water is also suitable for storage without causing odour problems. 3.2. Physicochemical and hygienic/ microbiological parameters Table 1 summarises the measurements of the different parameters during the course of
7
rainwater treatment. In the reservoir influent, a relatively low pollution load was measured. No significant reduction in the concentrations took place during residence in the reservoir (compare reservoir and substrate filter influents). The biodegradable organic components contained in rainwater are oxidised in the substrate filter (SF). The BOD7 concentration is considered an important parameter with a maximum concentration of 3 mg/L measured in the SF effluent. In most samples from SF effluent, no oxygen depletion was detected after 7 days. The Berlin requirements for BOD7 for service water [4] of less than 5 mg/L were continuously maintained under these operating conditions. These concentrations would not have been achieved with sedimentation alone without the use of the substrate filter. An overall slight rise in the ion concentrations for ammonium, nitrate and phosphate
Table 1 Results of laboratory investigations during the period between February 2000 and March 2001 for the single treatment stages (n = number of samples; reservoir influent: n = 36; substrate filter (SF) influent: n = 26; SF effluent: n = 36) [6] Parameter
Cond. (μS/cm) Trans (%) TOC BOD7 COD N-total P-total Cl NO2-N (mg/L) NO3-N PO4 SO4 Na Mg Ca NH4-N
Influent reservoir
Influent SF
Effluent SF
Max
Min
Mean
Max
Min
Mean
Max
Min
Mean
356.00 89.60 12.67 45.00 36.10 5.48 0.398 18.62 0.426 1.682 0.98 29.20 4.61 1.86 17.88 0.88
51.00 22.60 1.67 1.00 4.56 0.82 0.036 0.82 0.006 0.023 0.01 1.97 1.07 0.05 5.79 0.27
110.95 72.48 4.42 6.39 14.20 2.14 0.114 3.64 0.086 0.721 0.21 6.44 2.85 0.80 12.16 0.50
232.00 90.00 8.63 63.00 48.00 2.96 0.183 18.45 0.177 1.423 0.45 16.54 7.69 2.07 19.84 0.72
49.00 22.90 1.55 0.49 4.56 0.63 0.028 0.82 0.015 0.081 0.01 2.49 1.09 0.05 5.79 0.09
103.52 74.23 3.62 7.10 12.65 1.96 0.094 4.09 0.060 0.916 0.14 6.14 4.35 1.19 14.34 0.27
199.00 97.10 5.30 3.00 15.80 3.82 0.174 17.22 0.131 3.512 1.65 19.51 7.69 2.07 19.76 6.61
60.00 24.00 1.26 0.59 4.56 0.69 0.014 0.81 0.006 0.364 0.09 2.72 1.13 0.05 6.68 0.47
103.38 83.79 2.49 0.86 6.82 2.06 0.089 4.05 0.063 1.726 0.28 7.09 5.12 1.47 15.74 3.54
Note: BOD7 and COD were not always measured for the same samples and/or same time.
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of 0.03/mL for E. coli (based on 41 samples of which 26 were below the detection limit). Further investigations made on treated rainwater have shown that the concentrations of E. coli, total coliforms, Enterococci and Pseudomonas aeruginosa following a modification of the UV disinfection unit, remained below the detection limit of 0.03/mL [6,7]. As a general rule, the resulting service water quality is 30 to 3000-fold better than the mandatory values of the EU Directive for Bathing Water [8]. Table 2 shows the hygienic-microbiological parameters measured over a period of 1 year. The shaded cells show all values which exceeded the limits of the Berlin quality requirements for service water [4]. The concentration ranges were pooled in a log10 range. It can be clearly seen that the majority of the untreated rainwater samples, as rainwater enters the reservoir, exceeded the limit values whereas following biological treatment and subsequent UV disinfection, the limit values were safely maintained.
was observed (Table 1). However, it should be taken into consideration that the lower substrate filter has been repeatedly replanted following dieoff of the plants, thus contributing to increasing concentrations of these ions. Based on the mean concentrations of the alkaline ions and a mean Ca-concentration of about 12 mg/L, an average total hardness of only 15.71 mg/L CaCO3 was calculated for the reservoir effluent compared to that of Berlin’s drinking water which exhibits a total hardness above 143 mg/L CaCO3. This means that the treated rainwater is very soft in nature and can be used for household laundry with little or no lime deposition on sanitary fittings. Fig. 4 shows the concentrations of E. coli at the four sampling sites. Reservoir effluent concentrations were measured over a wide range with a slight reduction of E. coli during residence in the cistern. E. coli concentrations were reduced nearly one log10 following passage through the substrate filter. The median value of 0.04/mL in the service water tank lies near the detection limit
1000
E. coli (MPN/mL)
100
10
10.6 5.8
1
0.73
0.1 0.04 0.01 Sampling sites Influent reservoir
Influent SF
Effluent SF
Service water
Fig. 4. E. coli concentrations (MPN-method) at the four sampling sites in the rainwater plant including the median for the period between February 2000 and March 2001 [6].
E. Nolde / Desalination 215 (2007) 1–11
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Table 2 Frequency distribution (in %) of measured parameters at the four sampling sites in the rainwater plant [6]. The shaded cells mark the measured values which exceeded the limits of the Berlin quality requirements for service water [4]. (n = number of samples). Frequency distribution (%) Concentration range (1/mL) Influent reservoir n = 37 CFU 20°C CFU 37°C E. coli Total coliforms Enterococci P. aeruginosa Influent SF n = 29 CFU 20°C CFU 37°C E. coli Total coliforms Enterococci P. aeruginosa Effluent SF n = 41 CFU 20°C CFU 37°C E. coli Total coliforms Enterococci P. aeruginosa Service water n = 41 CFU 20°C CFU 37°C E. coli Total coliforms Enterococci P. aeruginosa
<0.1
>0.1 to <1
>1 to <10
>10 to <100
>100 to <1000
>1000 to <10,000
>10,000
0 0 0 0 2.7 64.9
0 0 16.2 10.8 13.5 24.3
0 0 35.2 29.8 37.9 10.8
0 5.6 32.4 37.8 37.8 0
13.9 24.9 16.2 21.6 8.1 0
66.7 66.7 0 0 0 0
19.4 2.8 0 0 0 0
0 0 3.5 3.5 13.8 72.4
0 0 24.1 10.3 10.3 20.6
0 0 34.5 37.9 48.3 3.5
3.6 21.4 31 37.9 20.7 3.5
25 28.6 6.9 10.4 6.9 0
57.1 46.4 0 0 0 0
14.3 3.6 0 0 0 0
0 0 19.5 12.2 43.9 95.1
0 0 31.7 26.8 24.4 4.9
0 0 39 43.9 21.9 0
0 34.1 7.3 14.6 9.8 0
82.9 61 2.5 2.5 0 0
17.1 4.9 0 0 0 0
0 0 0 0 0 0
0 0 95.1 82.9 100 97.6
0 0 4.9 4.9 0 2.4
15.4 30.8 0 12.2 0 0
48.7 51.2 0 0 0 0
33.3 15.4 0 0 0 0
2.6 2.6 0 0 0 0
0 0 0 0 0 0
4. Discussion and conclusions Rainwater utilisation in Germany is regulated by DIN 1989 which is preferentially in favour of rainwater harvesting from roof surfaces [9]. This system treats effectively rainwater from traffic surfaces beyond the German standards for rainwater harvesting systems, and shows that
these sources can be considered as viable sources in rainwater harvesting schemes. Various pollutants are commonly found in urban and suburban stormwater. Runoff from roofs, roads and parking lots can contain significant concentrations of copper, zinc and lead. Increased traffic volume results in higher concentrations of
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polyaromatic hydrocarbons commonly exceeding levels set to protect aquatic systems [10]. Other pollutants include suspended solids, organic carbon, bacteria, hydrocarbons, trace metals, pesticides, chlorides, trash and debris. Others studies investigated the scale of public health risk and environmental pollution from stormwater runoffs caused by urbanisation [11,12] and the authors came to the conclusion that stormwater management to minimise runoff and associated pollution appears to be a potentially valuable component of an integrated strategy to protect the public health at the least cost. In this study it has been shown that with simple inexpensive treatment, rainwater from more polluted surfaces, such as traffic areas, can be treated to a high quality service water for use in households for toilet flushing and laundry activities without hygienic risk and comfort loss for the user. In addition, the energy requirement of 0.88 kWh/m3 for cleaning the stormwater and distributing it for toilet flushing is low. Under certain conditions, rainwater harvesting may be realised as the only measure in areas with a high specific requirement for service water, whereby drinking water consumption and wastewater discharges are reduced as a result of rainwater harvesting. This is particularly applicable where soil conditions are unfavourable for rainwater infiltration or costs are too big. Pollutants will be also mostly retained in the reservoir, thus preventing their accumulation in the soil or infiltration into the groundwater. The pollution load on the water bodies is also reduced to almost zero, leading to an improvement of the urban surface water quality [13]. Compared to rainwater utilisation plants for single-family houses, the rainwater plant described in this paper is not more expensive (including planning and incidental costs). In this case, an optimal cost benefit is achieved when a connection to the sewer can be abandoned. In order to further reduce on costs, it would be more economical to
construct the substrate filter outdoors instead of indoors. Stormwater recycling is likely to be of significant environmental benefit through the reduction of non-point source pollutant loads and the minimisation of the requirement to build additional water supply infrastructure with increasing population densities. In this regard, stormwater management and recycling should become an essential part of every urban plan scheme. Rainwater harvesting can be considered a viable technology in an urban setting and with the increasing cost of water and wastewater services, rainwater systems are becoming more economically feasible. In a final evaluation, rainwater utilisation schemes in metropolitan areas should be also assessed on account of their environmental benefits and non-monetary aspects. Acknowledgements This project was financed by the Berlin Senate Department of Urban Development. Special thanks to Engineer Brigitte Reichmann for her dedicated project management. References [1]
[2]
[3]
[4]
[5] [6]
M. Grottker, Runoff quality from a street with medium traffic loading, Sci. Total Environ., 59 (1987) 457–466. Senatsverwaltung für Stadtentwicklung, Umweltschutz und Technologie, Stadtentwicklungsplan Ver- und Entsorgung, Berlin, 1998. B. Heinzmann, Beschaffenheit und weitgehende Aufbereitung von städtischen Regenabflüssen, Fortschritte VDI, Reihe 15: Umwelttechnik Nr. 113. Düsseldorf: VDI-Verlag, 1993. Senatsverwaltung für Bau- und Wohnungswesen, Merkblatt “Betriebswassernutzung in Gebäuden”, Senatsverwaltung für Bau- und Wohnungswesen, Württembergische Straße 6–10, 10707 Berlin, 1995. K. Imhoff, Taschenbuch der Stadtentwässerung. R. Oldenbourg Verlag München, Wien, 1990. R. Gildemeister, Regenwassernutzung im verdichteten Wohnungsbau, Diplomarbeit an der Technische
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[7]
[8]
[9]
[10]
Universität Berlin, Fakultät III: Prozesswissenschaften, AG Umwelthygiene, 2001. E. Nolde, Möglichkeiten der Regenwassernutzung im dichtbesiedelten Raum unter Einbeziehung der Niederschlagsabflüsse von Verkehrsflächen. fbrFachtagung: Regenwassernutzung und -bewirtschaftung in der Landschafts- und Freiraumplanung, am 4, November 2003, Frankfurt/Main, 2003. Council Directive 76/160/EEC of 8 December 1975 concerning the quality of bathing water, 1975. DIN 1989-1, Rainwater Harvesting Systems - Part 1: Planning, installation, operation and maintenance, German Institute for Standardisation, Berlin, 2002. J.E. Ball, R. Jenks and D. Aubourg, An assessment of the availability of pollutant constituents on
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road surfaces, Sci. Total Environ., 209 (2–3) (1998) 243–254. [11] S.J. Gaffield, R.L. Goo, L.A. Richards and R.J. Jackson, Public health effects of inadequately managed stormwater runoff, Am. J. Publ. Health, 93 (9) (2003) 1527–1533. [12] V. Meera and M.M. Ahammed, Water quality of rainwater harvesting systems: a review, Journal of Water Supply Research and Technology - Aqua, 55 (4) (2006) 257–268. [13] E. Nolde, Regenwassernutzung in Gebäuden – Ein Beitrag zur Abflussminimierung und Reduzierung des Trinkwasserverbrauchs. In Zukunft Wasser – Dokumentation zum Symposium zur Nachhaltigkeit im Wasserwesen in der Mitte Europas vom 17, bis 19, Juni 1998 in Berlin, pp. 94–97, 1998.