757
© IWA Publishing 2012 Water Science & Technology
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65.4
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2012
Potential impacts of on-site greywater reuse
in landscape irrigation
Y. Alfiya, O. Damti, A. Stoler-Katz, A. Zoubi, A. Shaviv and E. Friedler
ABSTRACT
This study investigated the effects of irrigation with different types of waters on soil, plants, and
public health. The test plant was ryegrass grown in 12 planters filled with sandy loam soil and
irrigated with three types of waters (4 planters for each type): freshwater, raw domestic light
greywater (GW), and treated domestic light GW. The sodium adsorption ratio (SAR), EC, pH and
alkalinity of the three types of irrigation waters did not differ significantly, suggesting that raw or
treated light GW should not exhibit negative effects. Concentrations of anionic and cationic
surfactants in the freshwater and the treated GW were about the same, while their concentrations in
the raw GW were higher. Surfactant levels in the three drainage water types were low. Some
accumulation of surfactants occurred in planters irrigated with raw and treated GW. The COD of the
drainage water of planters irrigated with raw GW was higher than the COD of other two drainage
water types. Although raw and treated GW contained faecal coliforms, they were hardly detected in
the drainage waters. All plants did not show any signs of stress. This may be due to the fact that the
GW originated mainly from showers and washbasins.
Key words
| greywater, landscape irrigation, microbial quality, on-site, ryegrass, SAR, soil
Y. Alfiya
A. Shaviv
E. Friedler (corresponding author)
Faculty of Civil and Environmental Eng.,
Technion – Israel Institute of Technology,
Haifa 32000,
Israel
E-mail: [email protected]
O. Damti
GES ltd.,
Akko Industrial Park,
Israel
A. Stoler-Katz
Ha’Emek St,
Nofit 36001,
Israel
A. Zoubi
Tahal Consulting Engineers ltd.,
154 Begin Rd.,
Tel-Aviv 64921,
Israel
INTRODUCTION
With growing demand for freshwater, greywater (GW)
reuse for non-potable consumption becomes an attractive
alternative water source. GW can be reused for toilet
flushing (Nolde ; Friedler et al. ), laundry and
car washing, fire protection, air conditioning (Lu &
Leung ; Pidou et al. ) and for garden and landscape irrigation (Weil-Shafran et al. , ). GW
reuse for landscape irrigation has the highest water
saving potential in rural areas. In addition, garden farming
with GW effluent may lead to poverty alleviation in poor
peri-urban/rural neighbourhoods. GW constitutes 60–70%
of the volume of domestic wastewater and only 2–3% and
22% of the ammonia and TSS, respectively (Almeida et al.
). Thus, it is considered to be less polluted than domestic wastewater. Nevertheless, GW contains elevated
levels of COD, surfactants, salts and in some cases also
boron (Friedler ; Weil-Shafran et al. ). GW
further contains up to 105 cfu/100 mL and 107 cfu/mL
faecal coliforms (FC) and heterotrophic plate count
doi: 10.2166/wst.2012.903
(HPC), respectively (Casanova et al. ; Friedler et al.
; Gilboa & Friedler ). Pathogen bacteria
may also be present in GW, such as Pseudomonas aeruginosa sp. (P.a. – mucous tissues pathogen), Staphylococcus
aureus sp. (S.a. – skin pathogen) and Clostridium prefringes sp. (C.p. – faecal pathogen). Therefore, GW reuse
may pose a public health hazard, and specifically, GW
reuse for landscape irrigation may lead to accumulation
and growth of pathogenic bacteria in the irrigated soils
(Ottoson & Stenström ). Introducing high loads of
organic matter, surfactants and salts by GW irrigation
can negatively affect soil properties and harm the environment, especially when practiced above sensitive
groundwater. This study endeavours to investigate and
quantify the effects of irrigation with raw/treated domestic
light GW (originating mainly from, showers and washbasins) on soil properties, on plants growth, and their
potential public health and environmental implications
in a comparative manner.
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MATERIALS AND METHODS
Experimental set-up
Twelve rounded planters (soil depth 30 cm, diameter 24 cm
(top), 22 cm (bottom)) were filled with 13 L of red loam
sand (Hamra) with the following characteristics: porosity
40%, field capacity 20%, clay 3.75%, silt 2.50%, sand
93.75%; CaCO3 2.1%; density 1.3 g/cm3; organic matter content 0.4%, cation exchange capacity 3.0 meq/100 g; pH in
water 6.7 (1:2 ratio 1 portion soil and 2 portions distilled
water). Ryegrass (Lolium perenne) was selected as the
model plant due to its high growth rate, high water and nutrients uptake and the possibility to perform multiple harvests
(Hall ). Each planter was seeded with 15–20 seeds of ryegrass. Planters were placed outdoors on benches in a random
order, in order to avoid location bias. They were irrigated with
three types of water: freshwater (four planters), raw domestic
light GW (four planters), and RBC (Rotating Biological Contactor) treated light GW effluent (four planters). The GW was
collected from 14 flats in a house accommodating married
students (some with young children), within the Technion
Campus. The collected greywater was treated in a pilotscale treatment plant situated in the basement of the building
and consisting of an equalisation basin, RBC (rotating biological contactor), followed by sedimentation basin. A detailed
description of the raw GW, the treatment system and the treated GW can be found in Friedler et al. () and in Gilboa &
Friedler (). The raw and treated GW were transported to
experiment site on the date of irrigation. The time elapsed
between collection of the two types of GW and commencing
irrigation was very short (not more than 30 min).
The plants were irrigated for 144 d from 27/4/06 to 18/
9/06 (spring–summer). During this period, no precipitation
Figure 1
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The schedule of irrigation, washing and harvesting as implemented.
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occurred. They were irrigated by drip irrigation, each planter
by two drippers of 2 L/h, which were placed very close to
the soil surface. Irrigation was performed every 3 days on
average, with increasing volumes following plant growth
(Figure 1). Each planter was connected to a flexible drainage
hose. About every fortnight (days 25, 39, 52, 70, 83 and 96,
after planting) the planters were irrigated with excess water
in order to wash the soils of accumulated substances (3.5–
6 l, Figure 1). On these occasions the whole volume of the
drainage water from each planter was collected in a vessel
and analyzed in the laboratory. Soluble fertilizer solution
was added to the three types of irrigation water, with the following concentrations: 2 mg-P/L potassium phosphate
dibasic, 30 mg-N/L ammonium sulfate, and 50 mg-K/L potassium sulfate. Two weeks before each harvest the dose of
ammonium sulfate was doubled, in order to meet the
higher demand of the plants. Plants were harvested four
times during the experiment (days 43, 68, 89 and 111 after
planting). During the harvest, the biomass of the plants was
cut from 5 cm above the soil surface, collected from each
planter separately, and weighed (wet weight) within 1–2 h.
Analysis methods
The three types of irrigation water and the drainage water
from each planter were analyzed according to the Standard
Methods (APHA et al. ) for the following parameters:
total suspended solids (TSS), volatile suspended solids
(VSS), chemical oxygen demand (COD), total ammonium
nitrogen (TAN), anionic surfactants as methylene blue
active substances (MBAS). Cationic surfactants (CS) were
measured by extraction with bromophenol blue and chloroform (Kornecki et al. ). Alkalinity was measured with
Gran titration (Stumm & Morgan ). Turbidity was
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Potential impacts of on-site greywater reuse
measured with Lamotte 2020e nephlometer (method
2310B). Nitrate (NO3), nitrite (NO2), phosphate (PO43)
and sulfate (SO42) were measured using Ion Chromatograph DIONEX AS4. Total organic carbon (TOC) and
total nitrogen (TN) were measured with Multi N/C 2000
analyzer (Analytik-Jena). Na, K, Ca and Mg were measured
by ICP (Perkin-Elmer, Optima 3000 DV). Bacterial quality
was characterized by Heterotrophic Plate Count (HPC)
(method 9215C), Faecal Coliforms (FC) (method 9213D),
Pseudomonas aeruginosa sp. (P.a.) (method 9215E) and
Staphylococcus aureus sp. (S.a.) (method 9215E). The
latter two bacteria species are pathogens that are commonly
found in light GW (Gilboa & Friedler ).
RESULTS AND DISCUSSION
Irrigation water characteristics
Raw GW quality exhibited high variability especially in key
parameters, such as TSS, VSS, Turbidity, COD and TOC
(Table 1). Treated GW quality was more stable, but still
showed some variability. Nevertheless, both the raw
and treated (un-disinfected) GW exhibited high variability,
as expressed by the large standard deviations. This
high variability is common and reported in the literature
(Friedler et al. ; Gilboa & Friedler ). The variability
exhibited in the freshwater quality, that as expected was
much lower, resulted from the fact that the source of
water of Haifa varies from surface water to groundwater
and vice-versa.
pH, EC, Na2þ Ca2þ and Mg2þ concentrations did not
exhibit large differences between the three types of water.
Consequently, the sodium adsorption ratio (SAR) did not
differ significantly, rising from 2.88 in freshwater to 3.23
(12% rise) in raw GW and 3.12 in treated GW (8% rise).
Thus, in regard to SAR, irrigation with either raw or treated
light GW is not expected to harm the soil structure. Alkalinity of the freshwater was the highest while in the raw
GW and treated GW it was somewhat lower. As the GW
stream did not contain laundry and dishwasher streams,
no alkalinity addition occurred during water use within
the households. In addition, some of the household products
which may enter this type of GW are acidifying (e.g. hydrochloric acid, boric acid). The difference between the
alkalinity of the raw and treated GW was not found to be significantly different (p 0.7624).
Minor differences between anionic and cationic surfactant concentrations in the freshwater and the treated GW
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were noticed, but as expected, their concentrations in the
raw GW were higher. The RBC efficiently removed both cationic and anionic surfactants. This is an important point, as
accumulation of surfactants in soils may lead to hyrophobicity (Gross et al. ). The loads of anionic surfactants in
the raw and treated GW were 113 and 0.43 μg/(kgsoil d),
respectively. Sodium and sulfate concentrations in the raw
and treated GW were higher than in freshwater (∼10%
and 70% higher for sodium and sulfate, respectively). The
RBC did not remove phosphorus and nitrogen compounds,
but succeeded to transform some of the TAN to nitrate. The
overall N:P:K contribution of the irrigation waters
(expressed as mg-N/L:mg-P/L:mg-K/L), including contribution of fertilizers, of the freshwater, treated GW and raw
GW were 48:7:88, 55:7:98 and 51:6:96 respectively. These
differences between the irrigation waters were marginal (±
10%).
Generally, the microbial quality of all three types of irrigation waters were within the range reported in the
literature (Table 1). As expected, no FC were found in the
freshwater. In the raw GW, FC concentrations were 3
orders higher than in the treated GW. HPC concentration
in the raw GW was the highest (∼3 orders of magnitude
higher than in freshwater), but, in the treated GW, HPC
was only about 0.5 order of magnitude lower than in the
raw GW. This is due to the fact that residual organic
matter in the treated GW enabled bacterial growth. In
60% of the freshwater samples P.a. was found. Pathogen
bacteria should not be present in tap water, especially
when indicator bacteria like FC are not found. Thus, the
presence of P.a. could be artificial (i.e. owing to contamination of the samples). In the raw GW, P.a. was in the
order of 104 cfu/100 mL, while the treated GW contained
two orders less. S.a. was found only in one third of the
raw GW samples, while in the other two types of irrigation
waters it was not found. Following these findings, it can be
postulated that raw light GW and even the treated GW
may pose a health risk, especially if irrigated by sprinklers,
due to possible body contact. This stresses the need for
proper disinfection prior to reuse. Finally, it should be
noted that the microbial quality of the irrigation and drainage waters were sampled for two bacterial indicators and
two bacterial pathogens, while other pathogens could potentially be present (e.g. viruses).
Quality of the drainage water
The EC of the three types of irrigation waters was around
1 mS/cm, while the EC of the drainage waters was, as
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760
Table 1
Irrigation water characteristics (n ¼ 6)
Parameter
Fresh-water
Raw GW
GW
Parameter
water
Raw GW
GW
0.987
0.232
1.044
0.220
1.081
0.142
TAN (mg-N/L)
AVG range
SD
0.07
0.08
3.46 (1–75)
3.27
6.95
12.9
pH
AVG range
SD
7.74
0.28
7.24 (6.4–10)
0.37
7.64
0.56
NO3 (mg-N/L)
AVG range
SD
1.97
1.54
1.21 (0.1–17)
1.48
4.53
2.54
Alkalinity
(mgCaCO3/L)
AVG range
SD
160
80
112
39
122
21
NO2 (mg-N/L)
AVG range
SD
1.2
0.6
4.9 (0.04–0.4)
7.2
2.1
1.6
TSS (mg/L)
AVG range
SD
8
1
52 (2–1,070)
28
19
8
TN (mg/L)
AVG range
SD
2.2
1.1
10.5 (0.1–128)
7.5
11.2
14.3
VSS (mg/L)
AVG range
SD
<8b
45 (6–413)
22
18
7
PO43 (mg-PO4/L)
AVG range
SD
0.6
0.9
1.9 (0.1–49)
1.0
2.1
1.0
Turbidity (NTU)
AVG range
SD
1.0
0.38
28 (20–279)
19
1.7
0.53
SO42 (mg-SO4/L)
AVG range
SD
89
51
157 (0.5–72)
146
149
147
COD (mg-O2/L)
AVG range
SD
40
15
174 (7–2,570)
30
74
27
Naþ (mg/L)
AVG range
SD
114
6.8
125 (7.4–480)
4.3
123
6.8
TOC (mg-C/L)
AVG range
SD
2.94
0.61
27 (73–93)
7.7
5.8
1.0
Kþ (mg/L)
AVG range
SD
13.8
12.7
18.7 (0.2–24)
17.1
21.1
19.0
Cationic
surfactants
(mg/L)
AVG range
SD
0.10
0.11
0.64 (NA)
0.30
0.14
0.11
Ca2þ (mg/L)
AVG range
SD
64
14.7
57 (3.5–58)
7.3
61
6.9
Anionic
surfactant
(mgMBAS/L)
AVG range
SD
0.07
0.07
2.87 (1.4–56)
2.20
0.08
0.07
Mg2þ (mg/L)
AVG range
SD
34
3.2
33 (1.1–34)
2.6
34
2.9
SAR
AVG range
2.88
3.23 (3–7)
3.12
SD
0.43
0.25
0.28
P.a. (cfu/100 mL)
AVG range
2.9 × 101
3.1 × 102
SD
%0
3.4 × 101
40
3.0 × 104
(3 × 103–3 × 104)
3.9 × 104
33
AVG range
0
SD
%0
0
100
FC (cfu/100 mL)
HPC (cfu/mL)
AVG range
B.D.b
SD
%0c
0
100
AVG range
3.9 × 104
SD
%0
2.9 × 104
17
3.0 × 105 (2 × 102 6 × 106)
3.8 × 105
0
8.8 × 106
(8 × 106 3 × 107)
7.9 × 106
0
1.7 × 102
2.3 × 102
0
1.7 × 106
2.5 × 106
0
1.2 × 104
(2 × 103 1 × 104)
1.8 × 104
67
0
0
100
Range reported in the literature (Compilation of: Fox et al. 2002; Ottoson & Stenström 2003; Friedler 2004; Jefferson et al. 2004; Gross et al. 2005; Palmquist & Hanaeus 2005; Friedler et al. 2006; Vinnerås et al. 2006; Briks & Hills 2007;
b
2012
Below detection.
%0 – Proportion of samples in which concentrations were below the detection limit.
|
c
65.4
Ghunmi et al. 2008; Gilboa & Friedler 2008; Jamrah et al. 2008; Winward et al. 2008; Meinzinger & Oldenburg 2009).
|
a
S.a. (cfu/100 mL)
5.4 × 102
60
Water Science & Technology
AVG range
SD
Potential impacts of on-site greywater reuse
EC (mS/cm)
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a
RBC
treated
Fresh-
Y. Alfiya et al.
RBC treated
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Potential impacts of on-site greywater reuse
expected, significantly higher (Figure 2(a)). The excess irrigation water washed salts that accumulated in the soil
during normal irrigation. The EC of the drainage water of
planters irrigated with raw GW was higher than that of planters irrigated with treated GW and with freshwater.
Furthermore, large variability was observed in the EC
values of the drainage water between the four planters that
were irrigated with raw GW.
The pH of the drainage water at the beginning of the
experiment was low: 6.19, 6.00 and 6.68 for planters irrigated with freshwater, treated GW and raw GW
respectively (Figure 2(b)). The pH values rose during the
experiment, reaching their final values after 60–70 days, at
the end of the experiment the pH values were 7.20, 7.11
and 7.19 (freshwater, treated GW and raw GW, respectively). Travis et al. () observed the same pattern of
rising pH after irrigation with freshwater treated GW and
raw GW. Differences in pH values between the drainage
waters of different irrigation treatments were marginal. At
the beginning of the experiment the alkalinity of the drainage waters was lower than that of the irrigation waters
(Figure 2(c)), with values of 74, 21 and 45 mg-CaCO3/L in
the drainage water of the planters irrigated with freshwater,
treated GW and raw GW respectively. It should be noted
that the alkalinity of 21–45 mg-CaCO3/L is very low and
under these conditions the soil may suffer from pH instability. During the experiment, the alkalinity gradually
increased, generally reaching the values of the irrigation
Figure 2
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waters towards the end of the experiment. This may explain
the changes in the pH. Differences between the alkalinity
values of the drainage waters of the different irrigation treatments were not significant. Alkalinity expresses the buffer
capacity of liquids. Therefore, irrigation had a positive
effect on the buffer capacity of the soil.
The COD of the drainage water of the planters irrigated
with raw GW was higher than the COD of the other two
drainage water types, with concentrations generally equaling the values in the irrigation waters (Figure 2(d)). The
difference in the COD of the drainage water of the planters
irrigated with freshwater and treated GW was marginal.
TOC in the drainage waters exhibited the same general
trend (data not shown), lying in the range of 15–30 mg-C/L.
COD leaching from fields irrigated with GW can contaminate surface water and groundwater, and promote growth
of pathogen bacteria. Anionic and cationic surfactant
concentrations in the drainage water of all types of irrigation
water were low and decreased during the experiments to
close-to or below the detection limits of the analytical
methods used (Figure 2(e)–(f)). This can result from gradual
development of the microbial community in the soil that
can degrade the surfactants added by the irrigation waters.
Nevertheless, minor (statistically significant) accumulation
of surfactants was observed in the soil, 0.35 and 0.73 μg/
(kgsoil d), anionic surfactants in planters irrigated with treated
and raw GW, respectively, and 9.5 μg/(kgsoil d) cationic
surfactants in planters irrigated with raw GW. Considering
EC (a), pH (b), alkalinity (c), COD (d), anionic surfactants (e) and cationic surfactants (f) in irrigation and drainage waters.
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the above accumulation, the loads of surfactants exerted by
raw GW (see irrigation quality characteristics, above), and
the amounts lost by drainage, the calculated degradation of
surfactants was 99 and 46% respectively for anionic and cationic surfactants in the soil of the planters irrigated with raw
GW.
As expected, in most of the samples of drainage water of
the planters irrigated with freshwater, FC were not detected
(Figure 3(a)), while only on one occasion was low FC level
detected in one planter (out of four replicates). Thus, it
can be assumed that the sample was contaminated. The treated GW contained FC (1.7 · 102 ± 2.3 · 102 cfu/100 mL),
while only in three samples (at days 39, 109 and 144) from
the same planter drainage (out of four replicates), FC were
detected at concentrations lower than 10 cfu/100 mL
(Figure 3(b)). This was probably, due to the wall effect.
Although the raw GW exerted a high load of FC on the planters (3 · 105 ± 3.8 · 105 cfu/100 mL), only on two occasions
were FC detected in the planters’ drainage water: on day
52 in planter 12 drainage (1 · 101 cfu/100 mL) and on day
69 in planter 10 drainage (2 · 103 cfu/100 mL). The fact that
hardly any FC leached out of the planters may be due to
the fact that the environment in the root zone (represented
by the soil in the planters) is hostile to FC and thus they do
not proliferate. This finding is supported by Gross et al.
() who found that FC did not survive in soil irrigated
with raw greywater. Nevertheless, if the load of FC were
high enough they could get to the leachate as well.
HPC concentrations both in the irrigation and drainage
waters were much higher (6–7 orders of magnitude) than
Figure 3
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those of FC for all irrigation water types (Figure 3(d)–(f)),
and HPC were present in all samples. HPC concentrations
in the drainage waters were in the range of 106 cfu/mL,
regardless of the type of irrigation water. In planters irrigated with freshwater HPC, concentrations in the drainage
water were higher than in the irrigation water, in planters
irrigated with treated GW it was about the same, while in
planters irrigated with raw GW, HPC concentration in the
drainage water was somewhat lower than in the irrigation
water. Thus, it can be postulated that HPC present in the drainage water are not necessarily the ones that were introduced
to the soil by the irrigation water and may originate from a
population that developed in the soil within the planters.
S.a. was found only in two samples (33%) of raw GW.
Consequently, its concentration in all drainage waters
was always below its detection limit (<1/100 mL). Although
P.a. is widely known as an opportunistic pathogen for
humans and animals, it can be found ubiquitously in
nature from sources as diverse as water, soil and plants
(Alonso et al. ). Thus, although it was present in the irrigation waters, it was not possible to study its fate and
transport in this experiment.
Influence of the irrigation on plant growth
All plants, including the ones irrigated with raw GW, did
not show any signs of disease or phytotoxicity throughout
the experimental period (144 d). This is contrary to the
findings of Eriksson et al. () who reported that bathroom GW was toxic to algae, and kitchen and laundry
Geometric means of FC (a–c), HPC (d–f) concentrations in the irrigation and drainage waters. NM – Not measured; %zero – proportion of samples where bacteria were below
detection limit; vertical lines (HPC) indicate one SD.
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Irrigation water effects on plant growth – average weight of harvested biomass (a); plant growth rate (b).
GW were toxic to algae and willow cuttings. Weil-Shafran
et al. () observed chlorosis of lettuce leaves following
irrigation with laundry GW. The GW in this study originated mainly from showers and washbasins and hardly
contained laundry GW. This could explain why no phytotoxicity was observed. Nevertheless, irrigation with treated
GW resulted in biomass yield higher than the other two
types of irrigation water (statistically significant two-tailed
t-test; p 0.001 over freshwater, p 0.0023 over raw GW;
(Figure 4(a)). The difference between yields of plants irrigated with freshwater and those irrigated with raw GW
was very small and not proven to be statistically significant.
No obvious reason for this difference was found. Pinto
et al. () reported that no detrimental effects of irrigating
Silver-beet plants (a common garden plant) with raw GW
were observed, although there was a slight reduction in biomass. Growth rate of all plants slightly increased with time
(Figure 4(b)), with growth rate of plants irrigated with treated GW being higher (statistically significant) than the ones
of plants irrigated with freshwater and raw GW. The higher
yield of plants irrigated with treated GW may be related to
higher levels of nutrients, although nutrient levels in the
three types of irrigation water were about the same, with
slightly higher levels in the raw and treated GW (although
differences between nutrient levels were not found to be
statistically different, see irrigation water characteristics,
above). The lower growth rate of the plants irrigated with
raw GW may be attributed to compounds present in raw
GW that can inhibit the plants' growth (and degraded
during treatment). However, no evidence was found to support this hypothesis.
CONCLUSIONS
This study investigated the effects of irrigation with raw/treated domestic light GW (originating predominantly from,
showers and washbasins) on soil properties, plant growth,
and public health. The SAR, EC, pH and alkalinity of the
three types of irrigation water did not exhibit large differences, suggesting that regarding these parameters irrigation
with raw or treated light GW is not expected to harm soil
structure or have detrimental effects on plants. Anionic and
cationic surfactant concentrations in freshwater and treated
GW were about the same, being higher in the raw GW (as
expected). Surfactant concentrations in the three drainage
water types were low, nevertheless, minor accumulation
was observed in planters irrigated with treated GW and
raw GW. This may lead to some increase of soil hydrophobicity. The COD of the drainage water of planters irrigated with
raw GW was higher than the COD of the other two drainage
water types. This higher leaching can contaminate surface
and groundwater and promote growth of pathogen bacteria.
Although raw and treated GW contained FC, they were
hardly detected in the respective drainage waters. This
could possibly indicate that the health risk associated with
contamination of groundwater due to irrigation with GW
may be minimal, however, should pathogen loads in the
GW used for irrigation be high enough, they may leach
from the root zone. As HPC concentrations in the drainage
waters did not correlate with their concentration in the
respective irrigation waters, it seems that HPC in the drainage waters is not a good indicator of the microbial quality
of the drainage waters. All plants, including the ones irrigated
with raw GW, did not show any signs of disease or phytotoxicity. This may be due to the fact that the GW in this
study originated mainly from showers and washbasins,
which are the less polluted GW streams. Irrigation with treated GW resulted in statistically significant higher biomass
yield. The difference between yields of plants irrigated with
freshwater and ones irrigated with raw GW was very small.
No obvious reason for this difference was found, however,
slightly higher nutrient levels in the treated greywater may
supply an explanation for this observation.
764
Y. Alfiya et al.
|
Potential impacts of on-site greywater reuse
ACKNOWLEDGEMENTS
The study was supported by the Grand Water Research Inst.
(Technion) and by IL Water Authority.
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First received 19 July 2011; accepted in revised form 10 October 2011