Directory UMM :Data Elmu:jurnal:E:Environmental Management and Health:Vol09.Issue2.1998:
Recent trends and developments: reuse of
wastewater in agriculture
Khaled M . Abu-Z eid
Se nio r Wate r Re so urc e s Pro gramme Assistant, Ce ntre fo r Enviro nme nt and
De ve lo pme nt fo r the Arab Re gio n and Euro pe , Gize , Egypt
Many countries all over the
world are facing water shortages. As population
increases, water is being
perceived as a very valuable
resource. Every effort is
exerted to use water more
efficiently and to make use of
every drop of water to ensure
the well being of future generations. New trends are developed and practiced in the
area of water resources use
and water saving. These
trends vary from one country
to another according to the
degree of water scarcity,
economic situations, and
other factors. Developing
non-conventional water
resources is an example of
the recent trends in developing new water resources and
water savings. Unlike rainfall, rivers, and groundwater
which are considered conventional freshwater resources,
the non-conventional water
resources include sea water
desalination, agriculture
wastewater reuse, and municipal wastewater reuse. This
paper deals with the reuse of
agriculture, municipal, and
industrial wastewater as a
new trend in developing
additional water resources.
Special interest is given to
municipal wastewater, its
characteristics and necessary
treatment. Environmental and
human health considerations
for wastewater reuse, especially in agriculture, are also
discussed. Possible consequences of wastewater reuse
are introduced. Examples of
wastewater reuse practices in
some countries are also
mentioned.
Enviro nme ntal Manage me nt
and He alth
9 / 2 [ 1998] 7 9 –8 9
© MCB Unive rsity Pre ss
[ ISSN 0956-6163]
Introduction
Agr icu ltu r a l ir r iga tion r epr esen ts a sign ifica n t fr a ction of th e tota l dem a n d for fr esh
w a ter. Ir r iga tion is estim a ted to r epr esen t 65
per cen t of th e globa l tota l w a ter dem a n d
(Postel, 1992). In som e pla ces, su ch a s th e top
fou r sta tes in con su m in g ir r iga tion w a ter in
th e USA (Mon ta n a , Color a do, Ida h o, a n d
Ca lifor n ia ), a gr icu ltu r e ir r iga tion ca n r ea ch
90 per cen t of th e tota l w a ter dem a n d (Cr ook
et a l., 1992). In E gypt a gr icu ltu r e u ses 88 per
cen t of th e tota l w a ter dem a n d (Wor ld Ba n k ,
1995).
Reu se of a gr icu ltu r e dr a in a ge w a ter a n d
r ecla im ed m u n icipa l a n d in du str ia l w a stew a ter in a gr icu ltu r e beca m e a r ecen t tr en d in
r elievin g th e bu r den on fr esh w a ter dem a n d,
especia lly in w a ter sh or ta ge a r ea s. In E gypt,
r eu se of a gr icu ltu r e dr a in a ge w a ter in ir r iga tion pr ojects th r ou gh m ixin g w ith fr esh N ile
w a ter, a m ou n ted to 3.37 x 109 m 3/ yea r a s of
1990. Sa lin ity of dr a in a ge w a ter u sed in th ese
pr ojects r a n ges between 1090-1270 ppm a n d
w a s r edu ced to 700 ppm a fter m ixin g w ith
fr esh w a ter. Addition a l u n officia l r eu se of
a gr icu ltu r e dr a in a ge w a ter in E gypt a r e estim a ted to be 1.5 x 109 m 3/ yea r (Am er, 1992).
Cr op pr odu ctivity w a s m ediu m in com pa r ison to n a tion a l aver a ges. For r ice, pr odu ctivity w a s 1.4 ton / fedda n a s com pa r ed to 2.6
ton / fedda n . For cotton , pr odu ctivity w a s 6
k in ta r / fedda n a s com pa r ed to 8.25 k in ta r / fedda n . Abou t 0.6 x 109 m 3/ yea r of tr ea ted m u n icipa l w a stew a ter is r eu sed for a gr icu ltu r e
ir r iga tion in E gypt a s of 1993 (Abdeldayem ,
1994).
A su r vey of a gr icu ltu r a l system s, oper a tin g
in Ca lifor n ia fou n d n o in dica tion s th a t cr op,
qu a lity or qu a n tity h a d deter ior a ted a s a
r esu lt of r ecla im ed w a ter ir r iga tion . In fa ct,
sever a l of th e fa r m er s u sin g r ecla im ed w a ter
felt th a t cr op pr odu ction h a d been en h a n ced
a s a r esu lt of n u tr ien ts in th e w a ter (Boyle
E n gin eer in g Cor por a tion , 1981). In Ca lifor n ia , a gr icu ltu r a l ir r iga tion a ccou n ts for
a ppr oxim a tely 63 per cen t of th e tota l volu m e
of r ecla im ed w a ter u sed w ith in th e sta te. In
Ca lifor n ia , F lor ida , a n d Texa s, th e volu m es of
r ecla im ed w a ter, sh ow n in Ta ble I a r e bein g
u sed for a gr icu ltu r a l ir r iga tion .
Th e per cen ta ge of popu la tion ser ved w ith
w a ter su pply a n d sa n ita tion va r ies fr om on e
cou n tr y to a n oth er. See Ta ble II for selected
Ar a b Re gion cou n tr ies w a ter su pply a n d
sa n ita tion cover a ge. As m or e sa n ita tion cover a ge is pr ovided, th e poten tia l for r eu se of
tr ea ted w a stew a ter in cr ea ses. If we a ssu m e
th a t 30 per cen t of w a ter u sed for dom estic u se
ca n be r ecover ed, tr ea ted a n d r eu sed, we ca n
com e u p w ith a r eu se poten tia l of dom estic
w a stew a ter for a gr icu ltu r e of a bou t 3x109 m 3
a s sh ow n in Ta ble III. Assu m in g wh ea t’s
w a ter r equ ir em en ts is a bou t 2000 m 3/ fedda n / yea r, th is poten tia l tr ea ted w a stew a ter
m ay cu ltiva te 1.5x106 fedda n / yea r. Assu m in g
th e fedda n of wh ea t pr odu ces 2180 k g of flou r,
a n d a per son con su m es on aver a ge 365 k g of
flou r per yea r, th er efor e th e a bove m en tion ed
poten tia l tr ea ted w a stew a ter ca n feed 9 m illion people w ith th eir n eeds of wh ea t per yea r.
It h a s to be n oted th a t th e pr eviou s figu r es a r e
ver y con ser va tive sin ce dom estic w a stew a ter
ca n r ea ch u p to 80 per cen t of dom estic u se if
efficien tly collected a n d cou n tr ies a r e fu lly
cover ed w ith sew a ge fa cilities wh ich w ill
r esu lt in m or e th a n dou ble th e a bove figu r es.
Mu n icipa l w a stew a ter u sed for ir r iga tion
besides its “w a ter va lu e” h a s a lso a “fer tilizin g poten tia l”. Th e n u tr ien ts pr esen t in
w a stew a ter m ay su pply m ost of th e N, P, K
a n d oth er essen tia l m a cr o- a n d m icr o-n u tr ien ts r equ ir ed by m a n y cr ops. Th is n u tr ition a l
va lu e of w a stew a ter is im por ta n t to th e a gr icu ltu r a l econ om y of developin g cou n tr ies
wh er e fer tilizer cost is a m a jor bu r den on
fa r m er s. However, cer ta in sta n da r ds a n d
r estr iction s sh ou ld be followed in selectin g
th e type of cr op, type of ir r iga tion , a n d de gr ee
of tr ea tm en t.
Wastewater constituents of
concern
Cer ta in qu a lity pa r a m eter s of th e tr ea ted
efflu en ts, pa r ticu la r ly th ose a ffectin g en vir on m en t a n d h ea lth a spects, depen din g on
th e tr ea tm en t a ppr oa ch , sh ou ld be m on itor ed
r e gu la r ly (FAO, 1993). Th e con stitu en ts of
con cer n in w a stew a ter tr ea tm en t a n d w a stew a ter ir r iga tion a r e listed in Ta ble IV.
[ 79 ]
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Table I
Agric ultural re use in se le c te d USA state s
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
California
150
570 ×10 3
Florida
90
340 × 10 3
a
Texas
290
1, 100 × 10 3
a
Note: This is based on the design flow of the
wastewater treatment plant providing water and
may exc eed ac tual use.
Source: Crook, J. (1992)
State
mgd
m3 / day
Table II
Wate r supply and sanitatio n c o ve rage
Country
Population
( × 1,000)
Water supply coverage
(% of population)
Sudan
Tunisia
Oman
Syria
Yemen
24,600
7,900
1,468
12,113
10,620
47.6
92.2
54.4
84.0
36.0
Sanitation coverage
(% of population)
74.8
95.3
48.2
85.0
65.2
Source: Water supply and sanitation sec tor monitoring report 1990 (Baseline Year), WHO,
Water Supply and Sanitation Collaborative Counc il, and UNICEF
Specific ch a r a cter istics of m a jor con stitu en ts
a r e a lso in clu ded in Ta ble V.
Th e su spen ded, colloida l a n d dissolved
solids pr esen t in w a stew a ter con ta in m a cr on u tr ien ts su ch a s (N, P, K, Ca , Mg) a n d m icr on u tr ien ts (Cu , Fe, Zn , Mn , etc.). Th ese n u tr ien ts in r ecla im ed m u n icipa l w a stew a ter, u sed
for dir ect ir r iga tion , pr ovide fer tilizer ben efits to cr ops a n d la n dsca pin g gr een a r ea s.
However, th e n u tr ien t con ten t of w a stew a ter
m ay exceed th e pla n t n eeds lea din g to n u tr ition a l im ba la n ce. Besides, th ese n u tr ien ts
pose a poten tia l sou r ce for u n der gr ou n d
w a ter pollu tion , a n d m ay ca u se pr oblem s
r ela ted to excessive ve geta tive gr ow th ,
delayed or u n even m a tu r ity, or r edu ced qu a lity of th e ir r iga ted cr ops. N u tr ien ts occu r r in g
in qu a n tities im por ta n t to a gr icu ltu r e
in clu de: n itr ogen , ph osph or u s, a n d occa sion a lly pota ssiu m , zin c, bor on a n d su lfu r. Th e
or ga n ic m a tter in w a stew a ter besides its
lon g-ter m effect on th e soil fer tility ca n a lso
con tr ibu te to th e soil sta bility a n d str u ctu r e.
Dissolved in or ga n ics con tr ibu te to w a stew a ter sa lin ity wh ich , if u sed for a gr icu ltu r e,
a ffects th e cr op pr odu ction . Ta ble VI sh ow s
h ow differ en t cr ops h ave differ en t sen sitivities to w a ter sa lin ity.
Wastewater treatment processes
Table III
Po te ntial o f do me stic waste wate r re use in mo st Middle East and
No rth Afric a
Country
Algeria
Egypt
Bahrain
Iraq
Jordan
Lebanon
Libya
M alta
M orocco
Oman
Qatar
Saudi Arabia
Syria
Tunisia
UAE
Yemen
Total
Annual
( × 10 9 m3 )
Domestic use
(% of annual
withdrawals)
Potential annual
wastewater reuse
(30% of domestic use)
( × 10 9 m3 )
3.0
22.0
0.198
56.3
7.0
1.1823
0.2
60.0
0.036
43.9
3.0
0.3951
1.0
20.0
0.06
0.8
11.0
0.0264
2.8
15.0
0.126
0.02
76.0
11.0
6.0
0.198
0.00456
1.3
3.0
0.0117
0.15
36.0
0.0162
3.6
45.0
0.486
3.3
7.0
0.0693
3.0
13.0
0.117
0.4
11.0
0.0132
3.9
5.0
0.0585
134.67
2.99826
Source: For annual withdrawals and domestic use: “ From Sc arc ity To Sec urity: Averting a
Water Crisis in the Middle East and North Afric a” , The World Bank (1995)
[ 80 ]
Differ en t de gr ees of w a stew a ter tr ea tm en t
m ay be a ch ieved u sin g con ven tion a l system s
or n a tu r a l system s. Con ven tion a l tr ea tm en t
system s in clu de pr elim in a r y, pr im a r y, secon da r y, a n d som etim es a dva n ced tr ea tm en t
pr ocesses a ccor din g to th e tr ea tm en t level of
th e w a stew a ter tr ea tm en t pla n t. Th ey u su a lly
involve h igh -r a te biologica l tr ea tm en t. N a tu r a l system s a r e lower in cost a n d less soph istica ted in oper a tion a n d m a in ten a n ce. Th ey
involve low -r a te biologica l tr ea tm en t. On e of
th e tech n iqu es of n a tu r a l biologica l tr ea tm en t system s is u sin g Wa stew a ter Sta biliza tion Pon ds wh ich in clu de a n a er obic pon ds,
fa cu lta tive pon ds, a n d m a tu r a tion pon ds.
Oth er tech n iqu es of n a tu r a l biologica l tr ea tm en t system s a r e: La n d tr ea tm en t tech n iqu e;
N u tr ien t fi lm tr ea tm en t tech n iqu e; a n d Soila qu ifer tr ea tm en t tech n iqu e. Follow in g is a
br ief descr iption of th e con ven tion a l tr ea tm en t pr ocesses.
Preliminary treatment
P r elim in a r y tr ea tm en t is th e r em ova l of la r ge
solids a n d tr a sh . It in clu des coa r se scr een in g,
gr it (sa n d) r em ova l, a n d cr u sh in g of la r ge
objects. Oth er pr elim in a r y tr ea tm en t oper a tion s ca n in clu de floccu la tion , odor con tr ol,
ch em ica l tr ea tm en t, a n d pr e-a er a tion (Cr ook
et a l., 1992).
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Table IV
Co nstitue nts o f c o nc e rn in waste wate r tre atme nt and irrigatio n with re c laime d waste wate r
Constituent
M easured parameters
Reason for concern
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
Suspended solids
Suspended solids inc luding
volatile and fixed solids
Biodegradable
organics
Bioc hemic al oxygen demand
Chemic al oxygen demand
Pathogens
Indic ator organisms, total
and fec al c oliform bac teria
Nitrogen, phosphorous and
potassium
Suspended solids c an lead to the development of sludge
deposits and anaerobic c onditions when untreated waste
water is disc harged in the aquatic environment. Exc essive
amounts of suspended solids c an c ause plugging in irrigation systems
Composed princ ipally of proteins, c arbohydrates, and fats.
If disc harged to the environment, their biologic al dec omposition c an lead to the depletion of dissolved oxygen in
rec eiving waters and to the development of septic c onditions
Communic able diseases c an be transmitted by the
pathogens in wastewater: bac teria, virus, parasites
Nitrogen, phosphorous, and potassium are essential
nutrients for plant growth, and their presenc e normally
enhanc es the value of the water for irrigation. When disc harges to the aquatic environment, nitrogen c an also lead
to the pollution of groundwater
These organic s tend to resist c onventional methods of
wastewater treatment. Some organic c ompounds are toxic
in the environment, and their presenc e may limit the suitability of the wastewater for irrigation
The pH of wastewater affec ts metal solubility as well as
alkalinity of soils. Normal range in munic ipal wastewater is
pH 6.5 – 8.5, but industrial waste c an alter pH signific antly
Some heavy metals ac c umulate in the environment and are
toxic to plants and animals. Their presenc e may limit the
suitability of the wastewater for irrigation
Exc essive salinity may damage some c rops. Spec ific ations
suc h as c hloride, sodium, boron, are toxic to some c rops.
Sodium may pose soil permeability problems
Nutrients
Stable (refractory)
organics
Spec ific c ompounds (e.g.
phenols, pestic ides,
c hlorinated hydroc arbons)
Hydrogen ion activity pH
Heavy metals
Spec ific elements (e.g. Cd,
Z n, Nl, Hg)
Dissolved inorganics
Total dissolved solids,
elec tric al c onduc tivity,
spec ific elements, (e.g.
Na, Ca, Mg,Cl, B)
Free and c ombined c hlorine
Residual chlorine
Exc essive amount of free available c hlorine (>0.05 mg/ l
CI2 ) may c ause leaf-tip burn and damage some sensitive
c rops. However, most c hlorine in rec laimed wastewater is
in c ombined form, whic h does not c ause c rop damage.
Some c onc erns are expressed as to the toxic effec ts of
c hlorinated organic s in regard to groundwater c ontamination
Source: Pettygrove and Asano (1988)
Primary treatment
P r im a r y tr ea tm en t is th e r em ova l of
settlea ble or ga n ic a n d in or ga n ic solids by
sedim en ta tion , a n d th e r em ova l of floa tin g
m a ter ia ls by sk im m in g. Th is pr ocess a lso is
effective for th e r em ova l of som e or ga n ic
n itr ogen , or ga n ic ph osph or u s, a n d h eavy
m eta ls, bu t does little for th e r em ova l of colloida l, dissolved con stitu en ts, biologica l
species, a n d th e level of vir u ses. Appr oxim a tely 25 per cen t to 50 per cen t of th e in com in g BOD, 50 per cen t to 70 per cen t of th e tota l
SS, a n d 65 per cen t of th e oil a n d gr ea se a r e
r em oved du r in g pr im a r y sedim en ta tion
(FAO, 1992a ). In m a n y cou n tr ies, pr im a r y
tr ea tm en t m ay be con sider ed su fficien t tr ea tm en t if w a stew a ter is u sed to ir r iga te cr ops
th a t a r e n ot con su m ed by h u m a n s or to ir r iga te or ch a r ds, vin eya r ds, a n d som e pr ocessed
food cr ops, wh er eby h u m a n con ta ct is
r edu ced.
Secondary treatment
Secon da r y tr ea tm en t in volves th e r em ova l of
or ga n ic m a tter a n d in som e ca ses n itr ogen ,
a n d ph osph or u s u tilizin g a n a er obic biologica l tr ea tm en t pr ocess. Aer obic biologica l
tr ea tm en t occu r s in th e pr esen ce of oxygen
wh er eby m icr oor ga n ism s oxidize th e or ga n ic
m a tter in th e w a stew a ter. Sever a l types of
a er obic biologica l tr ea tm en t in clu de: a ctiva ted slu dge, tr ick lin g filter s, a n d r ota tin g
biologica l con tr a ctor s (RBCs).
[ 81 ]
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Table V
Charac te ristic s o f so me waste wate r c o nstitue nts
Trace heavy metals
Remarks
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
Aluminium
Can c ause non-produc tivity in ac id soils, but soils at pH 5.5 to 8.0 will prec ipitate the ion
and eliminate toxic ity
Arsenic
Toxic ity to plants varies widely, ranging from 12 mg/ l for Sudan grass to less than 0.05
mg/ l for ric e
Beryllium
Toxic ity to plants varies widely, ranging from 5 mg/ l for kale to 0.5 mg/ l for bush beans
Boron
Essential to plant growth, with optimum yields for many obtained at a few-tenths mg/ l in
nutrient solutions. Toxic to many sensitive plants (e.g. c itrus) at 1 mg/ l. Usually suffic ient
quantities in rec laimed water to c orrec t soil defic ienc ies. Most grasses relatively tolerant
at 2.0 to 10 mg/ l
Cadmium
Toxic to beans, beets, and turnips at c onc entrations as low as 0.1 mg/ l in nutrient solution. Conservative limits rec ommended
Chromium
Not generally rec ognized as essential growth element. Conservative limits rec ommended
due to lac k of knowledge on toxic ity to plants
Cobalt
Toxic to tomato plants at 0.1 mg/ l in nutrient solution. Tends to be inac tivated by neutral
and alkaline soils
Copper
Toxic to a number of plants at 0.1 to 1.0 mg/ l in nutrient solution
Fluoride
Inac tivated by neutral and alkaline soils
Iron
Not toxic to plants in aerated soils, but c an c ontribute to soil ac idific ation and loss of
essential phosphorus and molybdenum
Lead
Can inhibit plant c ell growth at very high c onc entrations
Lithium
Tolerated by most c rops at up to 5 mg/ l; mobile in soil. Toxic to c itrus at low doses rec ommended limit is 0.075 mg/ l
M anganese
Toxic to a number of c rops at a few-tenths to a few mg/ 1 in ac id soils
M olybdenum
Nontoxic to plants at normal c onc entrations in soil and water. Can be toxic to livestoc k if
forage is grown in soils with high levels of available molybdenum
Nickel
Toxic to a number of plants at 0.5 to 1.0 mg/ l; reduc ed toxic ity at neutral or alkaline pH
Selenium
Toxic to plants at low c onc entrations and to livestoc k if forage is grown in soils with low
level of added selenium
Tin, tungsten and
titanium
Effec tively exc luded by plants; spec ific toleranc e levels unknown
Vanadium
Toxic to many plants at relatively low c onc entrations
Zinc
Toxic to many plants at widely varying c onc entrations; reduc ed toxic ity at inc reased pH (6
or above) and in fine-textured or organic soils
Other parameters
pH
Most effec ts of pH on plant growth are indirec t (e.g. pH effec ts on heavy metals toxic ity
desc ribed above)
TDS
Below 500 mg/ l, no detrimental effec ts are usually notic ed. Between 500 and 1,000 mg/ l.
TDS in irrigation water c an affec t sensitive plants. At 1,000 to 2,000 mg/ l. TDS levels c an
affec t many c rops and c areful management prac tic es should be followed. Above 2,000
mg/ l, water c an be used regularly only for tolerant plants on permeable soils
Source: Adapted from EPA (1973)
Tertiary/ advanced treatment
Adva n ced w a stew a ter tr ea tm en t is u tilized
wh en h igh qu a lity r ecla im ed w a ter is n ecessa r y, su ch a s for ir r iga tion of u r ba n la n dsca pes a n d r aw edible food cr ops. Adva n ced
tr ea tm en t r em oves n itr ogen , ph osph or u s,
deter gen ts, w a ter soften er s, h eavy m eta ls
su ch a s Zn , Cd, N i, Fe, a n d r edu ces BOD, SS,
a n d TDS. However, n itr ogen a n d ph osph or u s
[ 82 ]
a r e m a jor essen tia l pla n t n u tr ien ts a n d th u s
th eir pr esen ce in w a stew a ter is a n a sset for
ir r iga tion a t cer ta in pla n t gr ow th sta ges.
P r in ciple a dva n ced w a stew a ter tr ea tm en t
pr ocesses in clu de filtr a tion , n itr ifica tion ,
den itr ifi ca tion , biologica l or ch em ica l ph osph or u s r em ova l, coa gu la tion -sedim en ta tion ,
ca r bon a dsor ption , a m m on ia str ippin g,
br ea k poin t ch lor in a tion , selective ion
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Table VI
Cro p salt to le ranc e
Sensitive
M oderately sensitive
M oderately tolerant
Tolerant
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
Bean
Paddy Ric e
Sesame
Carrot
Okra
Onion
Parsnip
Pea
Strawberry
Almond
Apple
Apric ot
Avoc ado
Blac kberry
Boysenberry
Cherimoya
Sweet Cherry
Sand Cherry
Currant
Gooseberry
Grapefruit
Lemon
Lime
Loquat
Mango
Orange
Passion Fruit
Peac h
Pear
Persimmon
Plum; Prune
Pummelo
Raspberry
Rose Apple
White Sapote
Tangerine
Broad Bean
Corn
Flax
Millet
Peanut
Sugarc ane
Sunflower
Alfalfa
Bentgrass
Angleton Bluestem
Smooth Brome
Buffelgrass
Burnet
Alsike Clover
Ladino Clover
Red Clover
Strawberry Clover
White Dutc h Clover
Corn (forage)
Cowpea (forage)
Grass dallis
Meadow Foxtail
Blue Grama
Love Grass
Cic er Milkvetc h
Tall Oat Grass
Oats (forage)
Orc hard Grass
Rye (forage)
Sesbania
Sirato
Sphaerophysa
Timothy
Big Trefoil
Common Vetc h
Broc c oli
Brussel Sprouts
Cabbage
Cauliflower
Celery
Sweet Corn
Cuc umber
Eggplant
Kale
Kohlrabi
Lettuc e
Muskmelon
Pepper
Potato
Pumpkin
Radish
Spinac h
Sc allop Squash
Sweet Potato
Tomato
Turnip
Watermelon
Castorbean
Grape
Cowpea
Kenaf
Oats
Safflower
Sorghum
Soybean
Wheat
Barley (forage)
Grass Canary
Hubam Clover
Sweet Clover
Tall Fesc ue
Meadow Fesc ue
Harding Grass
Blue Panic Grass
Rape
Resc ue Grass
Rhodes Grass
Italian Ryegrass
Perennial Ryegrass
Sundan Grass
Narrowleaf Trefoil
Broadleaf Trefoil
Wheat (forage)
Durum Wheat (forage)
Standard Crested Wheat
Grass
Intermediate Wheat Grass
Slender Wheat Grass
Beardless Wild Rye
Canadian Wild Rye
Artic hoke
Red Beet
Z uc c hini Squash
Fig
Jujube
Papaya
Pomegranate
Barley
Cotton
Guar
Rye
Sugar Beet
Tritic ale
Semi-dwarf Wheat
Durum Wheat
Alkali Grass
Nuttail Alkali
Bermuda Grass
Kallar Grass
Desert Salt Grass
Wheat Grass
Fairway Wheat
Crested Wheat
Tall Wheat Grass
Altai Wild Rye
Russian Wild Rye
Asparagus
Guayule
Jojoba
Source: Tanji (1990)
[ 83 ]
pr om in en t disin fecta n ts u sed a t w a stew a ter
tr ea tm en t pla n ts. Ch lor in e con ta ct ba sin s a r e
design ed to a llow for a con ta ct tim e of a bou t
30 m in u tes. In specific ir r iga tion u ses, a con ta ct tim e of 120 m in u tes m ay be n eeded.
In spite of th e ch lor in a tion efficien cy in
r edu cin g th e n u m ber of ba cter ia , it w ill leave
h elm in th s e ggs tota lly u n a ffected (FAO,
1992a ).
br ea k poin t ch lor in a tion , selective ion
exch a n ge, a n d r ever se osm osis.
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
Disinfection
Disin fection m ay be n eeded if gu idelin e efflu en t qu a lity is n ot a ch ieved. Disin fection is
im por ta n t for th e destr u ction of m icr oor ga n ism s. Th e m ost com m on disin fecta n t is Ch lor in e. Ozon e a n d Ultr aviolet ligh t a r e oth er
Table VII
Re c laime d wate r standards fo r re use in irrigatio n in Kuwait, Saudi Arabia, Tunisia, Egypt, and the USA
Kuwait
Irrigation of
Parameter
Level of treatment
Egypt
Saudi Arabia
Tunisia
M aximum cont- M aximum
fodder and food
Irrigation
crops not eaten
food crops
aminant level concentration
raw, forest land crops eaten raw for unrestricted for reuse in
Advanced
Advanced
irrigation
agriculture
Trace heavy metals
mg/ l
mg/ l
Aluminium
Arsenic
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Cyanide
Fluoride
Iron
Lead
Lithium
M anganese
M ercury
M olybdenum
Nickel
Nitrate
Selenium
Tin, tungsten, titanium
Vanadium
Zinc
Other parameters
TDS (mg/ l)
SS (mg/ l)
BOD (mg/ l)
COD (mg/ l)
Chloride (mg/ l)
Chlorine residual (mg/ l)
after 12 hrs @ 20°C
pH
Coliform (count/ 100ml)
Turbidity (NTU)
SAR (per cent)
Oil and grease (ppm)
Phenol
Electrical conductivity
(US/ cm)
Halogenated hydrocarbons
Intestinal nematodes
(arithmetic mean no. of
eggs per liter)
mg/ l
5.0
0.1
0.1
0.5
0.01
0.1
0.05
0.4
0.05
2.0
5.0
0.1
0.07
0.2
0.001
0.01
0.02
10.0
0.02
4.0
mg/ l
ppm
10
10
40
1
1
10,000
100
10.0
10.0
280
6-8.4
2.2
1.0
ppm
ppm
0.1
3
0.01
0.1
0.1
0.5
5
0.05
3
5
1
5
0.01
Long
term
use
Short
term
use
5.0
0.10
0.10
0.75
0.01
0.1
0.05
0.2
20.0
2.0
0.5
2.0
0.05
1.0
5.0
5.0
15.0
20.0
10.0
2.5
10.0
ppm
0.1
0.05
1
5
0.01
0.1
0.05
0.2
5.0
5.0
5.0
5.0
0.5
0.001
0.2
0.2
0.2
1.0
5.0
5.0
2.5
0.2
0.2
0.5
0.05
0.5
0.01
0.2
0.01
0.2
0.05
2.0
0.02
0.02
10
0.05
5
2.0
2,500
10
10
40
USA-EPA
M aximum concentration
for reuse of different
categories of reclaimed
wastewater (see Table VIII)
Preliminary Preliminary Secondary Advanced
30 a
30 a
90
2,000
2,500
350
300
600
350
2,500
40
40
80
350
0.1
1.0
2.0
2.0
10.0
Rec ommended
limit
2,500
500-2,000
20
20
40
350
wastewater in agriculture
Khaled M . Abu-Z eid
Se nio r Wate r Re so urc e s Pro gramme Assistant, Ce ntre fo r Enviro nme nt and
De ve lo pme nt fo r the Arab Re gio n and Euro pe , Gize , Egypt
Many countries all over the
world are facing water shortages. As population
increases, water is being
perceived as a very valuable
resource. Every effort is
exerted to use water more
efficiently and to make use of
every drop of water to ensure
the well being of future generations. New trends are developed and practiced in the
area of water resources use
and water saving. These
trends vary from one country
to another according to the
degree of water scarcity,
economic situations, and
other factors. Developing
non-conventional water
resources is an example of
the recent trends in developing new water resources and
water savings. Unlike rainfall, rivers, and groundwater
which are considered conventional freshwater resources,
the non-conventional water
resources include sea water
desalination, agriculture
wastewater reuse, and municipal wastewater reuse. This
paper deals with the reuse of
agriculture, municipal, and
industrial wastewater as a
new trend in developing
additional water resources.
Special interest is given to
municipal wastewater, its
characteristics and necessary
treatment. Environmental and
human health considerations
for wastewater reuse, especially in agriculture, are also
discussed. Possible consequences of wastewater reuse
are introduced. Examples of
wastewater reuse practices in
some countries are also
mentioned.
Enviro nme ntal Manage me nt
and He alth
9 / 2 [ 1998] 7 9 –8 9
© MCB Unive rsity Pre ss
[ ISSN 0956-6163]
Introduction
Agr icu ltu r a l ir r iga tion r epr esen ts a sign ifica n t fr a ction of th e tota l dem a n d for fr esh
w a ter. Ir r iga tion is estim a ted to r epr esen t 65
per cen t of th e globa l tota l w a ter dem a n d
(Postel, 1992). In som e pla ces, su ch a s th e top
fou r sta tes in con su m in g ir r iga tion w a ter in
th e USA (Mon ta n a , Color a do, Ida h o, a n d
Ca lifor n ia ), a gr icu ltu r e ir r iga tion ca n r ea ch
90 per cen t of th e tota l w a ter dem a n d (Cr ook
et a l., 1992). In E gypt a gr icu ltu r e u ses 88 per
cen t of th e tota l w a ter dem a n d (Wor ld Ba n k ,
1995).
Reu se of a gr icu ltu r e dr a in a ge w a ter a n d
r ecla im ed m u n icipa l a n d in du str ia l w a stew a ter in a gr icu ltu r e beca m e a r ecen t tr en d in
r elievin g th e bu r den on fr esh w a ter dem a n d,
especia lly in w a ter sh or ta ge a r ea s. In E gypt,
r eu se of a gr icu ltu r e dr a in a ge w a ter in ir r iga tion pr ojects th r ou gh m ixin g w ith fr esh N ile
w a ter, a m ou n ted to 3.37 x 109 m 3/ yea r a s of
1990. Sa lin ity of dr a in a ge w a ter u sed in th ese
pr ojects r a n ges between 1090-1270 ppm a n d
w a s r edu ced to 700 ppm a fter m ixin g w ith
fr esh w a ter. Addition a l u n officia l r eu se of
a gr icu ltu r e dr a in a ge w a ter in E gypt a r e estim a ted to be 1.5 x 109 m 3/ yea r (Am er, 1992).
Cr op pr odu ctivity w a s m ediu m in com pa r ison to n a tion a l aver a ges. For r ice, pr odu ctivity w a s 1.4 ton / fedda n a s com pa r ed to 2.6
ton / fedda n . For cotton , pr odu ctivity w a s 6
k in ta r / fedda n a s com pa r ed to 8.25 k in ta r / fedda n . Abou t 0.6 x 109 m 3/ yea r of tr ea ted m u n icipa l w a stew a ter is r eu sed for a gr icu ltu r e
ir r iga tion in E gypt a s of 1993 (Abdeldayem ,
1994).
A su r vey of a gr icu ltu r a l system s, oper a tin g
in Ca lifor n ia fou n d n o in dica tion s th a t cr op,
qu a lity or qu a n tity h a d deter ior a ted a s a
r esu lt of r ecla im ed w a ter ir r iga tion . In fa ct,
sever a l of th e fa r m er s u sin g r ecla im ed w a ter
felt th a t cr op pr odu ction h a d been en h a n ced
a s a r esu lt of n u tr ien ts in th e w a ter (Boyle
E n gin eer in g Cor por a tion , 1981). In Ca lifor n ia , a gr icu ltu r a l ir r iga tion a ccou n ts for
a ppr oxim a tely 63 per cen t of th e tota l volu m e
of r ecla im ed w a ter u sed w ith in th e sta te. In
Ca lifor n ia , F lor ida , a n d Texa s, th e volu m es of
r ecla im ed w a ter, sh ow n in Ta ble I a r e bein g
u sed for a gr icu ltu r a l ir r iga tion .
Th e per cen ta ge of popu la tion ser ved w ith
w a ter su pply a n d sa n ita tion va r ies fr om on e
cou n tr y to a n oth er. See Ta ble II for selected
Ar a b Re gion cou n tr ies w a ter su pply a n d
sa n ita tion cover a ge. As m or e sa n ita tion cover a ge is pr ovided, th e poten tia l for r eu se of
tr ea ted w a stew a ter in cr ea ses. If we a ssu m e
th a t 30 per cen t of w a ter u sed for dom estic u se
ca n be r ecover ed, tr ea ted a n d r eu sed, we ca n
com e u p w ith a r eu se poten tia l of dom estic
w a stew a ter for a gr icu ltu r e of a bou t 3x109 m 3
a s sh ow n in Ta ble III. Assu m in g wh ea t’s
w a ter r equ ir em en ts is a bou t 2000 m 3/ fedda n / yea r, th is poten tia l tr ea ted w a stew a ter
m ay cu ltiva te 1.5x106 fedda n / yea r. Assu m in g
th e fedda n of wh ea t pr odu ces 2180 k g of flou r,
a n d a per son con su m es on aver a ge 365 k g of
flou r per yea r, th er efor e th e a bove m en tion ed
poten tia l tr ea ted w a stew a ter ca n feed 9 m illion people w ith th eir n eeds of wh ea t per yea r.
It h a s to be n oted th a t th e pr eviou s figu r es a r e
ver y con ser va tive sin ce dom estic w a stew a ter
ca n r ea ch u p to 80 per cen t of dom estic u se if
efficien tly collected a n d cou n tr ies a r e fu lly
cover ed w ith sew a ge fa cilities wh ich w ill
r esu lt in m or e th a n dou ble th e a bove figu r es.
Mu n icipa l w a stew a ter u sed for ir r iga tion
besides its “w a ter va lu e” h a s a lso a “fer tilizin g poten tia l”. Th e n u tr ien ts pr esen t in
w a stew a ter m ay su pply m ost of th e N, P, K
a n d oth er essen tia l m a cr o- a n d m icr o-n u tr ien ts r equ ir ed by m a n y cr ops. Th is n u tr ition a l
va lu e of w a stew a ter is im por ta n t to th e a gr icu ltu r a l econ om y of developin g cou n tr ies
wh er e fer tilizer cost is a m a jor bu r den on
fa r m er s. However, cer ta in sta n da r ds a n d
r estr iction s sh ou ld be followed in selectin g
th e type of cr op, type of ir r iga tion , a n d de gr ee
of tr ea tm en t.
Wastewater constituents of
concern
Cer ta in qu a lity pa r a m eter s of th e tr ea ted
efflu en ts, pa r ticu la r ly th ose a ffectin g en vir on m en t a n d h ea lth a spects, depen din g on
th e tr ea tm en t a ppr oa ch , sh ou ld be m on itor ed
r e gu la r ly (FAO, 1993). Th e con stitu en ts of
con cer n in w a stew a ter tr ea tm en t a n d w a stew a ter ir r iga tion a r e listed in Ta ble IV.
[ 79 ]
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Table I
Agric ultural re use in se le c te d USA state s
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
California
150
570 ×10 3
Florida
90
340 × 10 3
a
Texas
290
1, 100 × 10 3
a
Note: This is based on the design flow of the
wastewater treatment plant providing water and
may exc eed ac tual use.
Source: Crook, J. (1992)
State
mgd
m3 / day
Table II
Wate r supply and sanitatio n c o ve rage
Country
Population
( × 1,000)
Water supply coverage
(% of population)
Sudan
Tunisia
Oman
Syria
Yemen
24,600
7,900
1,468
12,113
10,620
47.6
92.2
54.4
84.0
36.0
Sanitation coverage
(% of population)
74.8
95.3
48.2
85.0
65.2
Source: Water supply and sanitation sec tor monitoring report 1990 (Baseline Year), WHO,
Water Supply and Sanitation Collaborative Counc il, and UNICEF
Specific ch a r a cter istics of m a jor con stitu en ts
a r e a lso in clu ded in Ta ble V.
Th e su spen ded, colloida l a n d dissolved
solids pr esen t in w a stew a ter con ta in m a cr on u tr ien ts su ch a s (N, P, K, Ca , Mg) a n d m icr on u tr ien ts (Cu , Fe, Zn , Mn , etc.). Th ese n u tr ien ts in r ecla im ed m u n icipa l w a stew a ter, u sed
for dir ect ir r iga tion , pr ovide fer tilizer ben efits to cr ops a n d la n dsca pin g gr een a r ea s.
However, th e n u tr ien t con ten t of w a stew a ter
m ay exceed th e pla n t n eeds lea din g to n u tr ition a l im ba la n ce. Besides, th ese n u tr ien ts
pose a poten tia l sou r ce for u n der gr ou n d
w a ter pollu tion , a n d m ay ca u se pr oblem s
r ela ted to excessive ve geta tive gr ow th ,
delayed or u n even m a tu r ity, or r edu ced qu a lity of th e ir r iga ted cr ops. N u tr ien ts occu r r in g
in qu a n tities im por ta n t to a gr icu ltu r e
in clu de: n itr ogen , ph osph or u s, a n d occa sion a lly pota ssiu m , zin c, bor on a n d su lfu r. Th e
or ga n ic m a tter in w a stew a ter besides its
lon g-ter m effect on th e soil fer tility ca n a lso
con tr ibu te to th e soil sta bility a n d str u ctu r e.
Dissolved in or ga n ics con tr ibu te to w a stew a ter sa lin ity wh ich , if u sed for a gr icu ltu r e,
a ffects th e cr op pr odu ction . Ta ble VI sh ow s
h ow differ en t cr ops h ave differ en t sen sitivities to w a ter sa lin ity.
Wastewater treatment processes
Table III
Po te ntial o f do me stic waste wate r re use in mo st Middle East and
No rth Afric a
Country
Algeria
Egypt
Bahrain
Iraq
Jordan
Lebanon
Libya
M alta
M orocco
Oman
Qatar
Saudi Arabia
Syria
Tunisia
UAE
Yemen
Total
Annual
( × 10 9 m3 )
Domestic use
(% of annual
withdrawals)
Potential annual
wastewater reuse
(30% of domestic use)
( × 10 9 m3 )
3.0
22.0
0.198
56.3
7.0
1.1823
0.2
60.0
0.036
43.9
3.0
0.3951
1.0
20.0
0.06
0.8
11.0
0.0264
2.8
15.0
0.126
0.02
76.0
11.0
6.0
0.198
0.00456
1.3
3.0
0.0117
0.15
36.0
0.0162
3.6
45.0
0.486
3.3
7.0
0.0693
3.0
13.0
0.117
0.4
11.0
0.0132
3.9
5.0
0.0585
134.67
2.99826
Source: For annual withdrawals and domestic use: “ From Sc arc ity To Sec urity: Averting a
Water Crisis in the Middle East and North Afric a” , The World Bank (1995)
[ 80 ]
Differ en t de gr ees of w a stew a ter tr ea tm en t
m ay be a ch ieved u sin g con ven tion a l system s
or n a tu r a l system s. Con ven tion a l tr ea tm en t
system s in clu de pr elim in a r y, pr im a r y, secon da r y, a n d som etim es a dva n ced tr ea tm en t
pr ocesses a ccor din g to th e tr ea tm en t level of
th e w a stew a ter tr ea tm en t pla n t. Th ey u su a lly
involve h igh -r a te biologica l tr ea tm en t. N a tu r a l system s a r e lower in cost a n d less soph istica ted in oper a tion a n d m a in ten a n ce. Th ey
involve low -r a te biologica l tr ea tm en t. On e of
th e tech n iqu es of n a tu r a l biologica l tr ea tm en t system s is u sin g Wa stew a ter Sta biliza tion Pon ds wh ich in clu de a n a er obic pon ds,
fa cu lta tive pon ds, a n d m a tu r a tion pon ds.
Oth er tech n iqu es of n a tu r a l biologica l tr ea tm en t system s a r e: La n d tr ea tm en t tech n iqu e;
N u tr ien t fi lm tr ea tm en t tech n iqu e; a n d Soila qu ifer tr ea tm en t tech n iqu e. Follow in g is a
br ief descr iption of th e con ven tion a l tr ea tm en t pr ocesses.
Preliminary treatment
P r elim in a r y tr ea tm en t is th e r em ova l of la r ge
solids a n d tr a sh . It in clu des coa r se scr een in g,
gr it (sa n d) r em ova l, a n d cr u sh in g of la r ge
objects. Oth er pr elim in a r y tr ea tm en t oper a tion s ca n in clu de floccu la tion , odor con tr ol,
ch em ica l tr ea tm en t, a n d pr e-a er a tion (Cr ook
et a l., 1992).
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Table IV
Co nstitue nts o f c o nc e rn in waste wate r tre atme nt and irrigatio n with re c laime d waste wate r
Constituent
M easured parameters
Reason for concern
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
Suspended solids
Suspended solids inc luding
volatile and fixed solids
Biodegradable
organics
Bioc hemic al oxygen demand
Chemic al oxygen demand
Pathogens
Indic ator organisms, total
and fec al c oliform bac teria
Nitrogen, phosphorous and
potassium
Suspended solids c an lead to the development of sludge
deposits and anaerobic c onditions when untreated waste
water is disc harged in the aquatic environment. Exc essive
amounts of suspended solids c an c ause plugging in irrigation systems
Composed princ ipally of proteins, c arbohydrates, and fats.
If disc harged to the environment, their biologic al dec omposition c an lead to the depletion of dissolved oxygen in
rec eiving waters and to the development of septic c onditions
Communic able diseases c an be transmitted by the
pathogens in wastewater: bac teria, virus, parasites
Nitrogen, phosphorous, and potassium are essential
nutrients for plant growth, and their presenc e normally
enhanc es the value of the water for irrigation. When disc harges to the aquatic environment, nitrogen c an also lead
to the pollution of groundwater
These organic s tend to resist c onventional methods of
wastewater treatment. Some organic c ompounds are toxic
in the environment, and their presenc e may limit the suitability of the wastewater for irrigation
The pH of wastewater affec ts metal solubility as well as
alkalinity of soils. Normal range in munic ipal wastewater is
pH 6.5 – 8.5, but industrial waste c an alter pH signific antly
Some heavy metals ac c umulate in the environment and are
toxic to plants and animals. Their presenc e may limit the
suitability of the wastewater for irrigation
Exc essive salinity may damage some c rops. Spec ific ations
suc h as c hloride, sodium, boron, are toxic to some c rops.
Sodium may pose soil permeability problems
Nutrients
Stable (refractory)
organics
Spec ific c ompounds (e.g.
phenols, pestic ides,
c hlorinated hydroc arbons)
Hydrogen ion activity pH
Heavy metals
Spec ific elements (e.g. Cd,
Z n, Nl, Hg)
Dissolved inorganics
Total dissolved solids,
elec tric al c onduc tivity,
spec ific elements, (e.g.
Na, Ca, Mg,Cl, B)
Free and c ombined c hlorine
Residual chlorine
Exc essive amount of free available c hlorine (>0.05 mg/ l
CI2 ) may c ause leaf-tip burn and damage some sensitive
c rops. However, most c hlorine in rec laimed wastewater is
in c ombined form, whic h does not c ause c rop damage.
Some c onc erns are expressed as to the toxic effec ts of
c hlorinated organic s in regard to groundwater c ontamination
Source: Pettygrove and Asano (1988)
Primary treatment
P r im a r y tr ea tm en t is th e r em ova l of
settlea ble or ga n ic a n d in or ga n ic solids by
sedim en ta tion , a n d th e r em ova l of floa tin g
m a ter ia ls by sk im m in g. Th is pr ocess a lso is
effective for th e r em ova l of som e or ga n ic
n itr ogen , or ga n ic ph osph or u s, a n d h eavy
m eta ls, bu t does little for th e r em ova l of colloida l, dissolved con stitu en ts, biologica l
species, a n d th e level of vir u ses. Appr oxim a tely 25 per cen t to 50 per cen t of th e in com in g BOD, 50 per cen t to 70 per cen t of th e tota l
SS, a n d 65 per cen t of th e oil a n d gr ea se a r e
r em oved du r in g pr im a r y sedim en ta tion
(FAO, 1992a ). In m a n y cou n tr ies, pr im a r y
tr ea tm en t m ay be con sider ed su fficien t tr ea tm en t if w a stew a ter is u sed to ir r iga te cr ops
th a t a r e n ot con su m ed by h u m a n s or to ir r iga te or ch a r ds, vin eya r ds, a n d som e pr ocessed
food cr ops, wh er eby h u m a n con ta ct is
r edu ced.
Secondary treatment
Secon da r y tr ea tm en t in volves th e r em ova l of
or ga n ic m a tter a n d in som e ca ses n itr ogen ,
a n d ph osph or u s u tilizin g a n a er obic biologica l tr ea tm en t pr ocess. Aer obic biologica l
tr ea tm en t occu r s in th e pr esen ce of oxygen
wh er eby m icr oor ga n ism s oxidize th e or ga n ic
m a tter in th e w a stew a ter. Sever a l types of
a er obic biologica l tr ea tm en t in clu de: a ctiva ted slu dge, tr ick lin g filter s, a n d r ota tin g
biologica l con tr a ctor s (RBCs).
[ 81 ]
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Table V
Charac te ristic s o f so me waste wate r c o nstitue nts
Trace heavy metals
Remarks
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
Aluminium
Can c ause non-produc tivity in ac id soils, but soils at pH 5.5 to 8.0 will prec ipitate the ion
and eliminate toxic ity
Arsenic
Toxic ity to plants varies widely, ranging from 12 mg/ l for Sudan grass to less than 0.05
mg/ l for ric e
Beryllium
Toxic ity to plants varies widely, ranging from 5 mg/ l for kale to 0.5 mg/ l for bush beans
Boron
Essential to plant growth, with optimum yields for many obtained at a few-tenths mg/ l in
nutrient solutions. Toxic to many sensitive plants (e.g. c itrus) at 1 mg/ l. Usually suffic ient
quantities in rec laimed water to c orrec t soil defic ienc ies. Most grasses relatively tolerant
at 2.0 to 10 mg/ l
Cadmium
Toxic to beans, beets, and turnips at c onc entrations as low as 0.1 mg/ l in nutrient solution. Conservative limits rec ommended
Chromium
Not generally rec ognized as essential growth element. Conservative limits rec ommended
due to lac k of knowledge on toxic ity to plants
Cobalt
Toxic to tomato plants at 0.1 mg/ l in nutrient solution. Tends to be inac tivated by neutral
and alkaline soils
Copper
Toxic to a number of plants at 0.1 to 1.0 mg/ l in nutrient solution
Fluoride
Inac tivated by neutral and alkaline soils
Iron
Not toxic to plants in aerated soils, but c an c ontribute to soil ac idific ation and loss of
essential phosphorus and molybdenum
Lead
Can inhibit plant c ell growth at very high c onc entrations
Lithium
Tolerated by most c rops at up to 5 mg/ l; mobile in soil. Toxic to c itrus at low doses rec ommended limit is 0.075 mg/ l
M anganese
Toxic to a number of c rops at a few-tenths to a few mg/ 1 in ac id soils
M olybdenum
Nontoxic to plants at normal c onc entrations in soil and water. Can be toxic to livestoc k if
forage is grown in soils with high levels of available molybdenum
Nickel
Toxic to a number of plants at 0.5 to 1.0 mg/ l; reduc ed toxic ity at neutral or alkaline pH
Selenium
Toxic to plants at low c onc entrations and to livestoc k if forage is grown in soils with low
level of added selenium
Tin, tungsten and
titanium
Effec tively exc luded by plants; spec ific toleranc e levels unknown
Vanadium
Toxic to many plants at relatively low c onc entrations
Zinc
Toxic to many plants at widely varying c onc entrations; reduc ed toxic ity at inc reased pH (6
or above) and in fine-textured or organic soils
Other parameters
pH
Most effec ts of pH on plant growth are indirec t (e.g. pH effec ts on heavy metals toxic ity
desc ribed above)
TDS
Below 500 mg/ l, no detrimental effec ts are usually notic ed. Between 500 and 1,000 mg/ l.
TDS in irrigation water c an affec t sensitive plants. At 1,000 to 2,000 mg/ l. TDS levels c an
affec t many c rops and c areful management prac tic es should be followed. Above 2,000
mg/ l, water c an be used regularly only for tolerant plants on permeable soils
Source: Adapted from EPA (1973)
Tertiary/ advanced treatment
Adva n ced w a stew a ter tr ea tm en t is u tilized
wh en h igh qu a lity r ecla im ed w a ter is n ecessa r y, su ch a s for ir r iga tion of u r ba n la n dsca pes a n d r aw edible food cr ops. Adva n ced
tr ea tm en t r em oves n itr ogen , ph osph or u s,
deter gen ts, w a ter soften er s, h eavy m eta ls
su ch a s Zn , Cd, N i, Fe, a n d r edu ces BOD, SS,
a n d TDS. However, n itr ogen a n d ph osph or u s
[ 82 ]
a r e m a jor essen tia l pla n t n u tr ien ts a n d th u s
th eir pr esen ce in w a stew a ter is a n a sset for
ir r iga tion a t cer ta in pla n t gr ow th sta ges.
P r in ciple a dva n ced w a stew a ter tr ea tm en t
pr ocesses in clu de filtr a tion , n itr ifica tion ,
den itr ifi ca tion , biologica l or ch em ica l ph osph or u s r em ova l, coa gu la tion -sedim en ta tion ,
ca r bon a dsor ption , a m m on ia str ippin g,
br ea k poin t ch lor in a tion , selective ion
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Table VI
Cro p salt to le ranc e
Sensitive
M oderately sensitive
M oderately tolerant
Tolerant
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
Bean
Paddy Ric e
Sesame
Carrot
Okra
Onion
Parsnip
Pea
Strawberry
Almond
Apple
Apric ot
Avoc ado
Blac kberry
Boysenberry
Cherimoya
Sweet Cherry
Sand Cherry
Currant
Gooseberry
Grapefruit
Lemon
Lime
Loquat
Mango
Orange
Passion Fruit
Peac h
Pear
Persimmon
Plum; Prune
Pummelo
Raspberry
Rose Apple
White Sapote
Tangerine
Broad Bean
Corn
Flax
Millet
Peanut
Sugarc ane
Sunflower
Alfalfa
Bentgrass
Angleton Bluestem
Smooth Brome
Buffelgrass
Burnet
Alsike Clover
Ladino Clover
Red Clover
Strawberry Clover
White Dutc h Clover
Corn (forage)
Cowpea (forage)
Grass dallis
Meadow Foxtail
Blue Grama
Love Grass
Cic er Milkvetc h
Tall Oat Grass
Oats (forage)
Orc hard Grass
Rye (forage)
Sesbania
Sirato
Sphaerophysa
Timothy
Big Trefoil
Common Vetc h
Broc c oli
Brussel Sprouts
Cabbage
Cauliflower
Celery
Sweet Corn
Cuc umber
Eggplant
Kale
Kohlrabi
Lettuc e
Muskmelon
Pepper
Potato
Pumpkin
Radish
Spinac h
Sc allop Squash
Sweet Potato
Tomato
Turnip
Watermelon
Castorbean
Grape
Cowpea
Kenaf
Oats
Safflower
Sorghum
Soybean
Wheat
Barley (forage)
Grass Canary
Hubam Clover
Sweet Clover
Tall Fesc ue
Meadow Fesc ue
Harding Grass
Blue Panic Grass
Rape
Resc ue Grass
Rhodes Grass
Italian Ryegrass
Perennial Ryegrass
Sundan Grass
Narrowleaf Trefoil
Broadleaf Trefoil
Wheat (forage)
Durum Wheat (forage)
Standard Crested Wheat
Grass
Intermediate Wheat Grass
Slender Wheat Grass
Beardless Wild Rye
Canadian Wild Rye
Artic hoke
Red Beet
Z uc c hini Squash
Fig
Jujube
Papaya
Pomegranate
Barley
Cotton
Guar
Rye
Sugar Beet
Tritic ale
Semi-dwarf Wheat
Durum Wheat
Alkali Grass
Nuttail Alkali
Bermuda Grass
Kallar Grass
Desert Salt Grass
Wheat Grass
Fairway Wheat
Crested Wheat
Tall Wheat Grass
Altai Wild Rye
Russian Wild Rye
Asparagus
Guayule
Jojoba
Source: Tanji (1990)
[ 83 ]
pr om in en t disin fecta n ts u sed a t w a stew a ter
tr ea tm en t pla n ts. Ch lor in e con ta ct ba sin s a r e
design ed to a llow for a con ta ct tim e of a bou t
30 m in u tes. In specific ir r iga tion u ses, a con ta ct tim e of 120 m in u tes m ay be n eeded.
In spite of th e ch lor in a tion efficien cy in
r edu cin g th e n u m ber of ba cter ia , it w ill leave
h elm in th s e ggs tota lly u n a ffected (FAO,
1992a ).
br ea k poin t ch lor in a tion , selective ion
exch a n ge, a n d r ever se osm osis.
Khale d M. Abu-Z e id
Re c e nt tre nds and
de ve lo pme nts: re use o f
waste wate r in agric ulture
Enviro nme ntal Manage me nt
and He alth
9 / 2 [1 9 9 8 ] 7 9 –8 9
Disinfection
Disin fection m ay be n eeded if gu idelin e efflu en t qu a lity is n ot a ch ieved. Disin fection is
im por ta n t for th e destr u ction of m icr oor ga n ism s. Th e m ost com m on disin fecta n t is Ch lor in e. Ozon e a n d Ultr aviolet ligh t a r e oth er
Table VII
Re c laime d wate r standards fo r re use in irrigatio n in Kuwait, Saudi Arabia, Tunisia, Egypt, and the USA
Kuwait
Irrigation of
Parameter
Level of treatment
Egypt
Saudi Arabia
Tunisia
M aximum cont- M aximum
fodder and food
Irrigation
crops not eaten
food crops
aminant level concentration
raw, forest land crops eaten raw for unrestricted for reuse in
Advanced
Advanced
irrigation
agriculture
Trace heavy metals
mg/ l
mg/ l
Aluminium
Arsenic
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Cyanide
Fluoride
Iron
Lead
Lithium
M anganese
M ercury
M olybdenum
Nickel
Nitrate
Selenium
Tin, tungsten, titanium
Vanadium
Zinc
Other parameters
TDS (mg/ l)
SS (mg/ l)
BOD (mg/ l)
COD (mg/ l)
Chloride (mg/ l)
Chlorine residual (mg/ l)
after 12 hrs @ 20°C
pH
Coliform (count/ 100ml)
Turbidity (NTU)
SAR (per cent)
Oil and grease (ppm)
Phenol
Electrical conductivity
(US/ cm)
Halogenated hydrocarbons
Intestinal nematodes
(arithmetic mean no. of
eggs per liter)
mg/ l
5.0
0.1
0.1
0.5
0.01
0.1
0.05
0.4
0.05
2.0
5.0
0.1
0.07
0.2
0.001
0.01
0.02
10.0
0.02
4.0
mg/ l
ppm
10
10
40
1
1
10,000
100
10.0
10.0
280
6-8.4
2.2
1.0
ppm
ppm
0.1
3
0.01
0.1
0.1
0.5
5
0.05
3
5
1
5
0.01
Long
term
use
Short
term
use
5.0
0.10
0.10
0.75
0.01
0.1
0.05
0.2
20.0
2.0
0.5
2.0
0.05
1.0
5.0
5.0
15.0
20.0
10.0
2.5
10.0
ppm
0.1
0.05
1
5
0.01
0.1
0.05
0.2
5.0
5.0
5.0
5.0
0.5
0.001
0.2
0.2
0.2
1.0
5.0
5.0
2.5
0.2
0.2
0.5
0.05
0.5
0.01
0.2
0.01
0.2
0.05
2.0
0.02
0.02
10
0.05
5
2.0
2,500
10
10
40
USA-EPA
M aximum concentration
for reuse of different
categories of reclaimed
wastewater (see Table VIII)
Preliminary Preliminary Secondary Advanced
30 a
30 a
90
2,000
2,500
350
300
600
350
2,500
40
40
80
350
0.1
1.0
2.0
2.0
10.0
Rec ommended
limit
2,500
500-2,000
20
20
40
350