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Environmental impact and health risks associated with
greywater irrigation: a case study
A. Gross*, N. Azulai***, G. Oron*
,
**, Z. Ronen*, M. Arnold**** and A. Nejidat*
*Department of Environmental Hydrology & Microbiology, Institute for Water Sciences and Technologies,
Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus,
84990 Midreshet Ben-Gurion, Israel
** Industrial Engineering and Management and the Environmental Engineering Unit, Ben-Gurion University of
the Negev, P.O. Box 653 Beer-Sheva 84105, Israel (E-mail: amgross@bgu.ac.il; zeevrone@bgu.ac.il;
gidi@bgu.ac.il; alineji.bgu.ac.il)
*** Lockwood, Andrews and Newnam, Inc. 2925 Briarpark Drive, Houston, Texas 77042, USA
(E-mail: nzazulai@lan-inc.com)
**** Department of Horticulture, Texas A&M University, College Station, TX 77843-2133, USA
(E-mail: ma-arnold@tamu.edu)
Abstract There is an increasing trend to use greywater for irrigation in households. This is partly due to the
notion that greywater is of better quality than wastewater and therefore does not need extensive treatment
beyond addressing public health issues. The aim of the study was to evaluate the environmental impact and
health risks associated with the use of greywater for irrigation on a small private farm. Over a three-year
period, each of three plots on a farm was irrigated with either freshwater, fertilized water, or greywater.
Irrigation water and soil from the plots were analyzed for a wide range of chemical and microbial variables.
Results suggest that greywater may be of similar quality to wastewater in several parameters such as BOD
and faecal coliforms. For some other variables such as boron and surfactants, greywater may even be of
worse quality than wastewater. Long-term irrigation of arid loess soil with greywater may result in
accumulation of salts, surfactants and boron in the soil, causing changes in soil properties and toxicity to
plants. Faecal coliforms did not survive in the soil. Treating greywater before using it for irrigation is
recommended, even in places where this is not a requirement.
Keywords Greywater; environmental harm; nitrification; surfactants; faecal coliforms
Introduction
A modern lifestyle requires large quantities of potable water and generates large amounts
of wastewater. Domestic wastewater is composed of blackwater, which is effluent from
toilets, and greywater (GW), which is the remaining wastewater comprising washing,
bathing, and kitchen effluents. Some regulatory agencies separate kitchen effluents from
the rest of the GW. In recent years, there has been an increase in the use of GW for land-
scape irrigation, particularly in households. It is commonly thought that GW is of rela-
tively good quality, and consequently only minor treatment is needed before its use. This
concept is evident in several state regulations such as those in California, USA, in which
the use of GW is allowed for flood irrigation with no treatment, as long as certain barriers
are implemented to minimize the possibility of human contact with the water (California
Graywater Standards, 1995). However, using GW for landscape irrigation (in particular
for household gardening) poses two major hazards that have not been studied thoroughly.
One hazard is the harmful environmental effects and pollution caused by elevated levels
of salinity, boron and surfactants that can alter the soil properties, damage plants and
contaminate ground water (Garland et al., 2000; Abu-Zreig et al., 2003 ). The other
hazard is related to potential health risks associated with the spread of pathogenic
Water Science & Technology Vol 52 No 8 pp 161–169 Q IWA Publishing 2005
161
organisms (Dixon et al., 1999). The current study aims were to evaluate the environmen-
tal impact and health risks associated with the use of greywater for irrigation.
Materials and methods
Study area and management
The area of the study (Carmey Avdat Farm), constructed next to the bank of a small dry
streambed, is located in the Israeli Negev desert approximately 50 km south of Beer
Sheva. The location of the plots is depicted in Figure 1. The climate is arid with an aver-
age annual precipitation of 80 to 100 mm and an average of 300 dew nights that contrib-
ute annual deposits of 30 mm (Shachak, 1976; Bowman et al., 1986). The average
summer and winter temperatures are 24.5 and 13 8C respectively, and the potential evapo-
transpiration is 240 to 260 cm yr
–1
(Israeli meteorological services, Bowman et al.,
1986). The soil is native loess and rocky colluvium situated on a limestone rock for-
mation. (Bowman et al., 1986). The four plots used in the study covered 500 m
2
and
were subjected to different irrigation regimes for 3 years before the study. These were:
(a) no irrigation (control), (b) irrigation with freshwater, (c) subsurface irrigation with
raw GW and (d) freshwater irrigation with the addition of fertilizers (fertigation). The
GW was collected from a six-person family house with an extended kitchen and laundry
facility that supports nearby guesthouses. The amount of GW used was recorded with a
water meter and averaged 8.2 m
3
per week. Upon use, the GW flowed to a perforated bar-
rel that was attached to a 30 cm deep perforated pipe that passed through the middle of
the plot. The plots receiving freshwater and fertigation were irrigated for 30 weeks a year
(between March to October) at an approximate rate of 50 L per tree per week, controlled
by an irrigation computer. The liquid fertilizer used was Gopher 6:6:6 (ICL Fertilizers
Ltd.), containing 4.2%(NH
4
)
2
SO
4
–N; 1.8% KNO
3
–N, HPO
3
and micro-elements
(Fe, Mn, Zn, Cu, Mo). The fertilizer was applied with the irrigation system at an annual
rate of 375 g N, 164 g P, and 311 g K per tree.
Figure 1 Schematic map of Carmey Avdat Farm with the locations of the irrigated plots. (A-D) guesthouses.
At the time of the study there was only one active guesthouses (F) family house from which the GW was
supplied. (1) control plot, (2) fertilized plot, (3) greywater plot, and (4) freshwater plot
A. Gross et al.
162
Water analyses
Freshwater and GW samples that were used for irrigation were collected biweekly from
April to December 2001. Unless stated otherwise, samples were analyzed by standard
procedures (Standard Methods for the Examination of Water and Wastewater, 1998) for:
total suspended solids (TSS) gravimetrically; soluble reactive phosphorus (SRP) by fil-
tration on GF filter followed by the vanadomolybdate method; total phosphorus (TP) and
total nitrogen (TN) by persulfate digestion followed by a vanadomolybdate finish and UV
method respectively; total ammonia nitrogen (TAN) by the sodium salicylate method
(Krom, 1980); nitrite nitrogen (NO
2
–N) with diazo salts; nitrate nitrogen (NO
3
-N) by the
sodium salicylate method (Yang et al., 1998); electrical conductivity (EC) and pH with a
WTW oxi340-meter; anionic surfactants by the methylene blue active substances
(MBAS) method; 5-day biochemical oxygen demand (BOD
5
); chemical oxygen demand
(COD) by dichromat digestion; boron (B) by inductively coupled plasma (ICP) and faecal
coliforms (FC) by the pore plate method using TBX agar (Merck, 2000). Because GW is
expected to contain contamination originating from peoples’ bodies (mainly skin) rather
than high faecal contamination, it was tested for the pathogens Staphylococcus aureus
and Pseudomonas aeruginosa, which are related to skin flora. Analyses followed standard
methods (Merck, 2000). The load of N, P, K and trace elements in the water used for fer-
tigation were calculated based on the composition of the fertilizer and the volumes used.
Soil analyses
Five soil samples from each plot were collected twice, in August and November 2001,
and were analyzed for pH, EC, organic carbon, and total Kjeldahl nitrogen (TKN) (Soil
and Plant Analysis Council, 1999). Minerals and metals (Ca, Mg, Na, K, Fe, Mn, Cu, Al,
Zn) from the soils were extracted using 0.05N HCl and 0.025 N H
2
SO
4
as described in
the double acid extraction method (Jackson, 1958) following analysis by ICP (IRIS/AP,
Jarrell Ash) and AA (Perkin-Elmer 1100B). Anionic surfactants in the soils were deter-
mined by extraction with 0.2 N NaCl and acetone followed by the MBAS procedure
(Kornecki et al., 1997).
The impact of soil surfactants on the capillary rise of water in the soil was used to
demonstrate the possible impact of surfactant accumulation on soil hydrological proper-
ties. Sieved (1.4 mm mesh), oven-dried loess soil from the farm that was never irrigated,
was mixed with laundry detergent solution of known concentration to give 10% soil
moisture content (w/w). Concentrations of surfactants in the soil ranged from 0 to 100 mg
kg
–1
. The soil was placed in a 25 cm column (2.5 cm diameter) and covered with a fine
mesh at one end. The column was attached to a balance and its base was located on the
water surface of an open reservoir containing freshwater. The weight change due to the
capillary rise in the column was recorded every second (McGinnis, 2001). Each surfac-
tant concentration was replicated five times. Faecal coliform (FC) count was determined
in five undisturbed cores (, 6 g wet weight from depths of 5 cm) of each treatment that
were transferred into sterile tubes. Pyrophosphate buffer (10 mL) was added and the
samples were shaken for an hour. The supernatant was used for FC count on TBX agar
plates (Merck, 2000). Bacterial counts were calculated on a dry weight base. Soil nitrifi-
cation was evaluated by introducing sub-samples of 2 g of soil from each plot into Erlen-
meyer flasks containing sterile free N buffer solution (pH 8.0) enriched with 28 mg L
–1
of NH
4
Cl–N (Gross et al., 2003). One millilitre samples were withdrawn at prescribed
times from the flasks and analyzed for ammonia nitrite and nitrate as described above.
Samples from these Erlenmeyer flasks were also used to characterize the microbial popu-
lation. Total DNA was extracted using a commercial kit (UltraClean Soil DNA Isolation
Kit, MO BIO Lab. Inc., Solana Beach, CA). A DNA fragment (323 base pairs (bp)) from
A. Gross et al.
163
the 16S rDNA gene was PCR-amplified using two primers specific to the domain Bac-
teria (Jackson et al., 2001). The DNA band was carefully excised under UV from agaros
gel, extracted from the gel slices using the NucleoSpin Extract kit (Macherey-Nagel,
Duren, Germany) and cloned in plasmid pTZ57R using the InsT/ATM PCR Product
Cloning Kit (MBI Fermentas, Hanover, MD). After transformation, random clones were
selected for DNA sequencing. Sequencing was performed with an ABI Prism 377 DNA
sequencer (Perkin Elmer). Sequences were analyzed using the BLAST (www. ncbi.nlm.-
nih.gov/blast) similarity search program in order to find the most similar available data-
base sequences.
Statistical analysis
The differences in water quality and soil parameters were compared by analysis of var-
iance (ANOVA) with p , 0.05 for significance, using the Sigma Stat 2.0 package (SPSS,
1997).
Results and discussion
Characterization of water sources
A summary of the irrigation water quality is presented in Table 1. Since fertilized water
is composed of fertilizer with known composition and freshwater, and since it was
applied over a relatively short period during the irrigation, which makes interpretation of
results difficult, we did not characterize the water but calculated its expected contribution
in terms of nutrients and elements.
Faecal coliforms are used as an indication of faecal contamination and reflect the risk
of encountering pathogens in the water. The FC count in the GW averaged 106 CFU
100 mL
–1
, and did not meet current standards for unlimited irrigation, which range
between 0 to 200 CFU 100 mL
–1
in most western countries, (ANZECC, 1992; Halperin
and Aloni, 2003). As expected, FC were not found in the freshwater. Staphylococcus aur-
eus and Pseudomonas aeruginosa were not detected in any of the samples from any treat-
ments. The TSS and BOD
5
averaged 138 mg L
–1
and 270 mg L
–1
respectively, which is
similar in magnitude to domestic wastewater. The high positive correlation and the value
of 1.7 for the slope of the curve suggest that a significant fraction of the TSS was organic
(Figure 2) and degradable. The high BOD
5
is attributed to the extended kitchen and laun-
dry effluents that support the guesthouses.
Table 1 Mean ^ standard error values (n = 18) of the irrigation treatments. Concentrations are in milligrams
per litre unless stated otherwise
Irrigation water Freshwater Greywater
1
Standard
Parameter
Total suspended solids Not detected 138 ^ 21 , 10
BOD
5
0.5 ^ 0.1 270 ^ 60 10
COD Not detected 686 ^ 255
Total phosphorus 0.08 ^ 0.00 17.7 ^ 5.1
Total nitrogen 5.7 ^ 1.5 14.0 ^ 2.0
Boron 0.1 ^ 0.0 0.6 ^ 0.2
Anionic surfactants Not detected 40 ^ 4
pH 7.6 ^ 0.3 6.7 ^ 0.1 6.5-8.5
EC (dS m
–1
) 1.2 ^ 0.1 1.4 ^ 0.0
2
Average SAR 3.1 4.8
Faecal coliforms (CFU 100 mL
–1
) , 110
6
^ 10
5
, 1
1
Standard applies to the Israeli guidelines for effluent quality for use in cities (Halperin and Aloni, 2003).
2
SAR: sodium adsorption ratio (calculated).
A. Gross et al.
164
The electrical conductivity that is correlated to salinity, ranged between 1.3 to 1.5 dS
m
–1
for the GW. This was only slightly higher than that of freshwater (Table 1)
suggesting that the GW would not show negative effects due to salinity. Nitrogen and
phosphorus are essential nutrients for plants but excess amounts can alter the microbial
population in the soil as described below. In the current study the measured concentration
of P and N in the raw GW did not exceed concentrations normally found in fertilized
water (Table 1) and we could not observe negative effects of these nutrients. Detergents
and soaps are the main sources of boron (B) and surfactants found in domestic effluents
and they are more concentrated in GW because the toilet stream is excluded. As
expected, levels of B and anionic surfactants were low in the freshwater and highest in
the GW (Table 1). Boron is an essential micronutrient for plants but excessive amounts
are toxic. The recommended value for irrigation water varies between 0.3 and 1.0 mg
L
–1
for non-tolerant plants (ANZECC, 1992). The average concentration in the GW
was 0.6 and ranged between 0.1 to 1.6 mg L
–1
, suggesting the possible occurrence of
negative effects to a variety of ornamental plants. Surfactant concentrations ranged
between 29 – 60 mg L
–1
with an average of 40 mg L
–1
. Surfactants can alter soil
properties and be toxic to plants at these concentrations (Bubenheim et al., 1997;
Abu-Zreig et al., 2003). The average concentration of the metals in all water treat-
ments was similar and low except for slightly higher calculated concentrations in the
fertilized water (data not shown). The sodium adsorption ratio (SAR) of the GW ran-
ged between 2.8 and 6.0 and averaged 4.8 (Table 1). A sodium adsorption ratio of 8
was suggested as the higher limit for irrigation of non-tolerant plants (ANZECC,
1992). However, long-term irrigation using water with a SAR higher than 4 can nega-
tively alter the soil properties (i.e. a high Na concentration leads to soil dispersion).
The natural salinity and SAR of desert soils are often high, suggesting that the moder-
ately elevated SAR and salinity of the GW would not be detrimental in such areas.
The impact of the irrigation regime on the soil
Comparisons were conducted between native soil properties (not irrigated) and nearby
plots that were irrigated for 3 years with freshwater, GW, and fertilized water (Table 2).
Faecal coliforms did not survive well in the soil despite the fact that the GW contained
10
6
CFU 100 mL
–1
. The nature of GW includes a high concentration of organic matter,
some of which is poorly degraded such as some surfactants and oils. Significant accumu-
lation of nitrogen was found in the fertilized plot but not in the GW-irrigated plot. The
addition of nitrogen in fertigation is greater by at one or two orders of magnitude than in
fresh or GW respectively. As expected, the soil salinity (as measured by electrical con-
ductivity) was lowest in the plot irrigated with freshwater.
Figure 2 Correlation between TSS and BOD
5
of greywater from Carmey Avdat farm
A. Gross et al.
165
Although accumulation of salts was found in the GW plot, this was not greater than
the salinization that occurred in the fertilized plot used for agriculture purposes, and even
after three years, salinity did not reach levels that can affect most plants. Salinity does
not therefore seem to pose a major problem for the farm. It is important, however, to
take the source of salinity into account; for example the results indicated that there was
some accumulation of boron in the soil due to irrigation by GW (Table 2). High boron
concentrations exert negative effects on the soil properties and are toxic to plants (Nable
et al., 1997). Use of low B detergents would remedy such problems. Recently, new
environmental regulations in Israel have limited the amount of B permissible in deter-
gents, and B levels in cleaning agents are expected to decrease gradually. The average
SAR in the GW-irrigated plot was 1.01, followed by the dry (non-irrigated) plot (0.84),
fertilized (0.72) and freshwater (0.60) plots (Table 2). As discussed above, the increase in
SAR may negatively affect the soil properties and limit the species of plants that can be
grown. The native soil in the farm and the relatively high natural concentration of Ca in
the farm soil reduces the SAR and minimizes potential negative harm to the plants. The
concentration of metals in the soil varied between samples and between plots, but its con-
centrations were within ranges found naturally (data not shown). The pH of the soils ran-
ged from 7.86 to 8.16 with no significant differences among plots (Table 2). The
fertilized plot had slightly lower pH, presumably due to the acidity produced by higher
nitrification (Figure 3).
In the soil, ammonia is oxidized by bacteria to nitrite that can be toxic to plants, and
to nitrate, which is not toxic, in a process called nitrification (Hooper, 1989). The biologi-
cal conversion of ammonia to nitrite is carried out by ammonia-oxidizing bacteria (AOB)
and the subsequent oxidation of nitrite to nitrate by nitrite-oxidizing bacteria (NOB).
Both bacterial groups, obligate autotrophs, grow slowly (Hooper, 1989) and have differ-
ent sensitivities to environmental constraints such as salinity, light intensity and pH
(Focht and Verstraete, 1977). This may lead to imbalanced nitrification and an accumu-
lation of toxic ammonia or nitrite. Nitrification potential of the soil, which is an important
microbial process, and the soil microbial population were used as indicators of possible
differences between the plots. The ammonia fertilized plots had the highest nitrifying
potential, followed by the GW and freshwater plots, respectively (Figure 3). It is reason-
able to assume that there was a developed nitrifying bacterial population in the fertilized
plots, as they had been irrigated with ammonia for over 3 years before sampling.
Table 2 Mean ^ standard error values of soils (n = 10) from three irrigated plots (freshwater, fert ilized
water and greywater), and a dry plot (not irrigated) in Carmey Avdat farm. Soil samples were taken in August
and November 2001. Plots were irrigated similarly for three years before sampling
Parameter Soil from irrigated plots
Freshwater Fertilized water Greywater Dry
pH 8.1 ^ 0.1 7.9 ^ 0.1 8.2 ^ 0.1 8.1 ^ 0.1
EC (dS m
–1
) 0.7 ^ 0.1
b
2.2 ^ 0.4
a
2.5 ^ 0.8
a
1.6 ^ 0.7
a
Mean
3
SAR 0.6 0.7 1 0.8
2
FC (CFU g
–1
)
1
ND 1 ^ 13^ 2ND
TN (mg kg
–1
) 330 ^ 40
a
1,700 ^ 500
b
400 ^ 100
a
300 ^ 20
a
Anionic surfactants (mg kg –1) 4.3 ^ 1.8
a
5.3 ^ 2.4
a
23 ^ 4.5
b
4.5 ^ 1.9
a
Boron (mg kg
–1
) 0.4 ^ 0.1
a
1.1 ^ 0.2
ab
2.5 ^ 1.2
b
0.9 ^ 0.5
ab
4
OM (%) 0.6 ^ 0.04 0.5 ^ 0.1 0.9 ^ 0.06 0.5 ^ 0.03
1
ND, not detected
2
FC, faecal coliforms
3
SAR, sodium adsorption ratio
4
OM, organic matter; a, b indicate statistical significance ( p , 0.05).
A. Gross et al.
166
Interestingly, it seems that there was unbalanced nitrification in the freshwater plot that
led to the accumulation of nitrite. Accumulation of nitrite was also found in the GW
treatment but an increase in nitrate was also noticed from the eighth day. Unfortunately,
we did not identify the nitrifying bacterial population in any of the plots. Nitrifying bac-
teria do not tend to appear in high numbers in nature, particularly when organic matter is
abundant, as they are out-competed by heterotrophic bacteria. We could not identify
differences between the microbial groups in the plots. The main groups found were:
uncultured delta proteobacterium, Rhizobium sp., Treponema sp., Flexibacter tractuosus,
Pseudomonas sp. and Microscilla sericea. Accumulation of surfactants in soils irrigated
with GW was demonstrated (Table 2). The low surfactant concentration in the native and
freshwater irrigated soils is probably due to the presence of some native organic sub-
stances rather than an external source. The potential effects of surfactants on the capillary
rise in loess suggest that GW irrigated soils might become more hydrophobic (Figure 4).
Hydrophobic soils are not suitable for healthy plant growth. This could explain the
Figure 3 Ammonia consumption, nitrite and nitrate production over time, in a sterile ammonia (NH
4
Cl)-rich
buffer, following the introduction of soils that were irrigated with freshwater, greywater, fertilized water, and
native soils (dry)
Figure 4 Average capillary rise (measured as water weight) of freshwater in loess soils that were prewetted
(10% w/w) with laundry solution to give a known concentration of anionic surfactants in the soil
A. Gross et al.
167
observations of retarded growth in a few plants in this plot. Surfactants have also toxic
effects on many plants (Bubenheim et al., 1997), but their toxicity to grown plants was
not investigated in the current study.
Conclusions
Greywater does not meet current guidelines for unlimited irrigation, yet these guidelines
involve mainly health issues and neglect potential environmental risks such as elevated B
and surfactants. We demonstrated that using raw GW for irrigation might cause environ-
mental harm in addition to public health risks. We conclude that treating GW before its
use for irrigation is recommended, even when this is not a legal requirement.
Acknowledgements
This research was funded by the Israeli Water Commision and Texas Department of
Agriculture. We are especially grateful to Ofer Shmueli, Natasha Bundarenko and Naomi
Gordon of Ben-Gurion University of the Negev for their assistance with the chemical and
microbial analyses. Lastly, we sincerely thank Guy Reshef for his advice with the fertili-
zation practice and the Izraeli family (farm owners) who assisted us in every way.
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