Experimental investigation on water saving by the reuse of washbasin grey waters for WC flushing

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1 11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 Experimental investigation on water saving by the reuse of washbasin grey waters for WC flushing A. Campisano 1 *, C. Modica 1 1 Department of Civil and Environmental Engineering, University of Catania, Viale A. Doria 6, Catania, Italy *Corresponding author, acampisa@dica.unict.it ABSTRACT In the recent years, several studies on methodologies for domestic water saving have concerned the reuse of grey waters for WC flushing operations; in particular, some available literature studies show that water volumes used in domestic bath washbasins and for toilet flushing operations result comparable, suggesting possible significant benefits deriving from the direct hydraulic connection of the two sanitary devices. Anyway, only general indications can be derived from available results since they are commonly obtained starting from experimental data at large time-scales (monthly or quarterly). Instead, the availability of short time-scale chronological series of water consumptions from both washbasins and WCs can enable more accurate evaluations of water saving, taking into account also the characteristics of the adopted grey water reuse installation. In this paper the results of an experimental investigation aimed at determining chronological series of contemporaneous water consumptions of washbasins and WCs (at event scale) in domestic baths is presented; six households characterised by different kind and number of users were selected for the experiments. On the basis of simulated water balances at event scale, the acquired data series allowed to derive indications on the significant water saving that can be performed by the adoption of a simple grey water reuse scheme. KEYWORDS Water saving; grey water; reuse scheme; washbasin; WC INTRODUCTION As it is largely recognised, today high-quality waters should be primarily used for drinking and sanitary purposes, while for other civil uses, waters with less valuable quality characteristics, such as grey waters, should be taken into account. Since the beginning of the sixties, various schemes and systems for domestic grey water reuse have been proposed by many authors (Call, 1963; Toms, 198; McDonald et al., 1993; Aylward et al., 26). Anyway, these schemes have not found large development for the high costs due to the need of reconstructing the pre-existing house hydraulic piping systems (Jefferson et al., 1999; Nolde, 1999; Brennan and Patterson, 24); in fact, a large part of these schemes requires to build specific separate piping networks for collecting grey waters coming from showers, washbasins and other house water facilities, sometimes adding also rain water from the roofs; these systems need also to be equipped with high-capacity tanks for the grey water storage with the additional problems related to the large overall size and to the elevate grey water detention times within the tank (Dixon et al., 1999; Eriksson, 22). Campisano et al. 1

2 11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 During the recent years, different studies (AA.VV., 1997; AA.VV., 22; Eriksson, 22; Failla and Stante, 24) were specifically addressed to the investigation of the main uses of water in households and to the evaluation test of new water saving technologies based on the reuse of grey and rain waters. Results of these investigations evidenced that the prompt reuse of domestic grey waters should be addressed to the flushing of WCs. In particular, available literature data show that a significant part (close to 3%) of water in houses is actually used for WC flushing and that values between 1% and 2% of the domestic total consumption are related to the use of bath washbasins for the personal hygiene, then suggesting possible significant benefits deriving from the direct hydraulic connection of the two sanitary devices. Anyway, these results are derived from water consumption data (of washbasins and WCs) which are characterised by large temporal scales (monthly or quarterly). Instead, very scarce is the availability of data at short time-scale (at event scale), notwithstanding the important information that these data can provide; in fact, the availability of detailed chronological series of washbasin and WC water consumptions can enable accurate evaluations of saving from grey water reuse, taking into account also the structural constrains of the adopted reuse installation (i.e. WC flushing box capacity, grey water tank capacity, etc.). In this paper the results of an experimental investigation aimed at acquiring chronological series of contemporaneous water consumptions of washbasins and WCs (at event scale) in domestic baths are presented. For the experimental campaign six households characterised by different type and number of users were chosen. On the basis of water balances at event scale, the acquired data series were used to derive indications about the water saving that can be obtained with a simple grey water reuse scheme; in particular, this scheme is based on the reuse of water volumes consumed at the washbasin for the supply of the WC flushing box, in order to reduce the consumption of potable water (supplied by the aqueduct) for toilet flushing operations. DESCRIPTION OF THE EXPERIMENTAL ACTIVITIES Experimental set-up The acquisition of water consumption data from washbasin and WC for each selected household was carried out using measuring devices which were specifically set-up for this experimental investigation; in particular, two simple sensors respectively connected to the washbasin tap and to the WC flushing box push-button were adopted for the measurements, the two sensors being equipped with a data acquisition system (logger Series HOBO U-11). The datalogger is provided with data recording channels for the contemporaneous acquisition of signals coming from both the washbasin and the WC sensors; in particular, for each household (bath), the device allowed to record the opening/closure time instants of the washbasin tap and the initial instant of the WC flushing operations. The described measuring system was initially tested for a time period of ten consecutive in order to determine eventual malfunctionings of the devices. selection and recorded data Six households characterised by different number of users largely heterogeneous for customs and consumptions, were selected for the experiments. Moreover, the households were chosen among different Sicilian places within the Provinces of Catania and Messina. For each one household a two-weeks long measuring campaign was launched, this time length resulting sufficient for determining the household water consumption patterns (i.e. used water volumes, consumption modalities, customs, etc.). Main characteristics of the 6 selected households are summarized in Table 1. 2 Water saving by the reuse of washbasin grey waters for WC flushing

11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 Table 1. Main characteristics of the 6 households selected for the experiments.

3 11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 Table 1. Main characteristics of the 6 households selected for the experiments Type Aggregation Family Family Family Family Family Number of users Typology of users 5 students 2 retirees 1 student 1 employee 1 housewife 2 retirees 1 student 4 employees 1 housewife 3 employees 3 children 1 student Users in week- Users in week-end Measuring starting time 27 march 6 hour 23: 27 march 6 hour 6: 15 april 6 hour 7: 16 april 6 hour 21:4 1 may 6 hour 19:3 3 may 6 hour 14:3 Measuring end 1 april 6 hour 23: 1 april 6 hour 6: 29 april 6 hour 7: 3 april 6 hour 21:4 15 may 6 hour 19:3 Notes * ** *** none none **** * No one at home during the week-end 1/2 april 26 ** No one at home Thursday 6 april 26 *** 4 people during the period april 26 **** In the bathroom there are two washbasins, both monitored. 17 may 6 hour 14:3 After the experimental campaign, the recorded information were analysed separately for each one monitored household. Acquired data consisted of the chronological series of changes of state recorded by the two sensors (mounted at the washbasin and at the WC box of each bath). As an example, information recorded during the experiments for one of the 6 bathrooms is reported in Figure 1; in particular, the figure shows the successive changes of state of the washbasin sensor (opening 1, - closure,) and the cumulated number of flushing events concerning the WC sensor. In addition, date and time instant for each one change of state of the two sensors are reported. Figure 1. Acquired information for one of the households during the experiments. Campisano et al. 3

4 11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 RESULTS AND DISCUSSION Preliminary evaluation of grey water volumes for water saving purposes Acquired chronological series were firstly elaborated in order to determine the time length of each event (use of washbasins). Then, the obtained results were used for deriving chronological series of water consumptions at washbasins and WC; in particular this was done, adopting a value of.12 l/s for the washbasin tap flow discharge and a value of 9 l for the WC flushing box capacity, being these values typical of the sanitary devices. The obtained results allowed to perform a preliminary evaluation of water saving obtainable when reusing washbasin grey-waters for the WC flushing. In particular, in Figure 2, for the 6 monitored households, the cumulated curves (per capita) of water consumptions at washbasins and WCs for the entire experimental time length are reported; clearly, consumptions are referred to users effectively at home during the various of the two weeks of experiments., (l/capita), (l/capita), (l/capita) /3 28/3 15/4 16/4 29/3 3/3 31/3 1/4 2/4 3/4 4/4 5/4 6/4 7/4 8/4 9/4 1/4 Figure 2. Cumulated per capita consumptions at washbasin and WC for the 6 households /4 18/4 19/4 2/4 21/4 22/4 23/4 24/4 25/4 26/4 27/4 28/4 29/4 2/5 3/5 4/5 5/5 6/5 7/5 8/5 9/5 1/5 11/5 12/5 13/5 14/5 15/ /3 28/3 29/3 3/3 31/3 1/4 2/ /4 18/4 19/4 2/4 21/4 22/4 23/4 24/4 3/4 4/4 5/4 25/4 6/4 7/4 8/4 26/4 27/4 28/4 9/4 1/4 29/4 3/4 3/5 4/5 5/5 6/5 7/5 8/5 9/5 1/5 11/5 12/5 13/5 14/5 15/5 16/5 17/5 18/5 1/5 4 Water saving by the reuse of washbasin grey waters for WC flushing

5 11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 Globally, for each one household, quasi-linear trends were found for the cumulated curves with comparable values of per capita water consumptions at washbasin and WC devices; in particular, flushed (per capita) volumes at the WCs during the two weeks resulted higher (of about 15% on average for the 6 analysed households) than consumed (per capita) volumes at the washbasins, indicating the possibility of reusing, for the WC flushing, a maximum of about 85% (on average) of washbasin grey waters. Water balance simulations at event scale The previous evaluations did not take into account the technical constrains of the reuse scheme; in fact, the grey water volumes that could be effectively reused for the flushing of the WC can vary significantly as function of characteristics of the reuse system such as, for instance, the WC flushing box and the grey water tank capacities. In order to take into account these characteristics for an improved evaluation of water saving benefits, further elaborations were carried out by means of water balance simulations at event scale based on the acquired experimental data; in particular, a simple reuse system collecting washbasin waters into a grey water tank and then into the WC flushing box was considered. From an operational point of view, the reuse scheme requires to store the washbasin grey waters within the grey water tank and their prompt pumping on the WC flushing box, as soon as the stored volume (in the grey water tank) results at least equal to the WC flushing box capacity. For the toilet flushing, this scheme requires primarily the use of grey waters into the tank and, only in case the stored grey waters result not sufficient, the recourse to the acqueduct waters. Volumes overflowing the grey water tank capacity were considered to be lost. Adequate chlorination in the tank is to be considered in order to avoid problems of grey water quality decay. An international pending patent describes the technological aspects for the practical set up of the proposed reuse system. Simulations of water balances were carried out separately for each household considering typical commercial values of the WC flushing box capacity C WC (6, 7, 8, 9 litres) and different values of the grey water tank storage capacity C S (ranging from 1 to 1 litres). For each simulated case obtainable water saving and lost overflow volumes were determined. The water saving was evaluated as: V = 1 A WS 1 (1) V F where V A is the water volume (per capita) used for flushing operations and externally supplied by the acqueduct. Instead, overflow water losses were computed as: VS WL = 1 (2) V W where V S is the water volume (per capita) overflowed from the grey water tank. Results of the simulations are reported in the graphs of Figures 3 and 4; in particular, the two figures respectively reports the values of WS and WL as function of the grey water tank capacity C S and for different WC flushing box capacities C WC. Globally, as expected, the graphs of Figure 3 show improved performances of the system (increasing values of WS) as the grey water tank capacity C S grows; in particular, the trend of the curves points out that larger benefits in increasing C S are obtained for the lower values of Campisano et al. 5

6 11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 the tank capacity (the curves shows higher slopes). Moreover the figure shows increasing values of WS as the capacity C WC of the WC flushing box decreases; according to the adopted reuse scheme, in fact, smaller WC boxes allow an increased number of flushing operations with grey waters. WS (%) WS (%) WS (%) Cassetta C WC = da 6 l Cassetta C WC = da 7 l Cassetta C WC = da 8 l Cassetta C WC = da 9 l C S (litri) Figure 3. Water saving WS as function of grey water tank and of WC flushing box capacities. The graphs of Figure 4 shows, instead, decreasing water losses as the grey water tank capacity C S grows; the graphs also show that values of WL are not significantly affected by variations of the capacity C WC. However, the general analysis of the graphs shows that a tank with a capacity C S of about 3-4 litres results adequate to determine quite high values of WS and sufficiently reduced values 6 Water saving by the reuse of washbasin grey waters for WC flushing

7 11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 of WL; in fact, a capacity of 3 litres can lead to water saving values close to 75% for C WC = 6 litres and to 55% for C WC = 9 litres (average values for the 6 households). Correspondently, the average overflow losses result close to 4% for C WC = 6 litres and to 35% for C WC = 9 litres. Moreover, such a capacity C S allows to limit both the size of the reuse system (and the occupied space within the bathroom) and the grey water detention times within the tank. Globally, the obtained results allow to estimate that, considering a daily water supply volume of 25 litres/capita/day, such a kind of reuse scheme could allow to achieve an average water saving value of about 1%. WL (%) WL (%) WL (%) Cassetta C WC = da 6 l Cassetta C WC = da 7 l Cassetta C WC = da 8 l Cassetta C WC = da 9 l Figure 4. Water losses WL (overflows) as function of grey water tank and of WC flushing box capacities. Campisano et al. 7

8 11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 28 CONCLUSIONS The paper reports the results of an experimental investigation on the evaluation of water saving from the reuse of washbasin grey waters for WC flushing operations in domestic bathrooms. The experiments allowed to acquire, for various users, the chronological series of simultaneous water consumptions at the two sanitary devices. On the basis of water balance simulations at event scale and on acquired data of water consumptions, water saving provided by a simple grey water reuse scheme were evaluated; the scheme provides that water volumes used at the washbasin are reused for the WC flushing box feeding in order to reduce, for this particular use, the consumption of high-quality water coming from the aqueduct. In particular, obtained results show significant water saving values, also in the case of systems with relatively small reservoirs, clearly suitable for their reduced size and for the limited grey water detention times. Further investigations should concern cost-benefit evaluations for the reuse system realisation taking into account, not only monetary savings, but also important environmental and social aspects of the system. REFERENCES AA.VV. (1997), Sustainable Housing in Europe. Sustainable Building, Independent Journal on Building and the Environment. Special issue, Europe, October, 8-41 AA.VV. (22), Acqua. Sistemi e dispositivi per il risparmio e il riuso. Edicom Edizioni, Milano. Aylward, P.G., Casali, J.A., Porter, B.D. and Perjins, R.G (26), Grey water reclamation system and method for providing and operating same. U.S. Pat. N 7,121,292. Brennan, M.J. and Patterson, R.A. (24): Economic analysis of grey water recycling. In: Proceedings of 1 st International Conference on Onsite Wastewater Treatment and Recycling, Perth, February 24, pp Call, R.G. (1963), Water conservation system. U.S. Pat. N 3,112,497. Dixon, A., Butler, D., Fewkes, A. and Robinson M. (1999), Measurement and modelling of quality changes in stored untreated grey water. Urban Water, Elsevier, 1, Eriksson, E. H. (22), Potential and problems related to reuse of water in households. PhD. Thesis, Environmental & Resources DTU, Technical University of Denmark. Failla, B. and Stante, L. (24), Progetto Aquasave. Sistema sperimentale di risparmio dell acqua nelle abitazioni, ENEA Report, EU Life Environmental Program, Bologna. Jefferson, B., Laine, A., Parsons, S., Stephenson, T. and Judd S. (1999), Technologies for domestic wastewater recycling, Urban Water, Elsevier, 1, McDonald, J.R., Henry, M. and Steele, R.J. (1993), Grey water recycle system. U.S. Pat. N 5,243,719. Nolde, E. (1999), Greywater reuse systems for toilet flushing in multi-storey buildings over ten years experience in Berlin, Urban Water, Elsevier, 1, Toms, Ed P. (198), Water recycling with solids and foam removal. U.S. Pat. N 4,197, Water saving by the reuse of washbasin grey waters for WC flushing

G3) Implications of grey water re-use on solid transport in building drainage systems.

G3) Implications of grey water re-use on solid transport in building drainage systems. M.Gormley and S.K.Dickenson Drainage Research Group The School of the built Environment Heriot-Watt University Edinburgh