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Specifi c ch a r a ct er ist ics of m a jor con st it u en t s a r e a lso in clu ded in Ta ble V.
T h e su spen ded, colloida l a n d dissolved solids pr esen t in w a st ew a t er con t a in m a cr n u t r ien t s su ch a s (N, P, K, Ca , Mg) a n d m icr o-n u t r ieo-n t s (Cu , Fe, Zo-n , Mo-n , et c.). T h ese o-n u t r i-en t s in r ecla im ed m u n icipa l w a st ew a t er, u sed for dir ect ir r iga t ion , pr ovide fer t ilizer ben e-fi t s t o cr ops a n d la n dsca pin g gr een a r ea s. However, t h e n u t r ien t con t en t of w a st ew a t er m ay exceed t h e pla n t n eeds lea din g t o n u t r i-t ion a l im ba la n ce. Besides, i-t h ese n u i-t r ien i-t s pose a pot en t ia l sou r ce for u n der gr ou n d w a t er pollu t ion , a n d m ay ca u se pr oblem s r ela t ed t o excessive ve get a t ive gr ow t h , delayed or u n even m a t u r it y, or r edu ced qu a l-it y of t h e ir r iga t ed cr ops. N u t r ien t s occu r r in g in qu a n t it ies im por t a n t t o a gr icu lt u r e in clu de: n it r ogen , ph osph or u s, a n d occa sion -a lly pot -a ssiu m , zin c, bor on -a n d su lfu r. T h e or ga n ic m a t t er in w a st ew a t er besides it s lon g-t er m effect on t h e soil fer t ilit y ca n a lso con t r ibu t e t o t h e soil st a bilit y a n d st r u ct u r e.
Dissolved in or ga n ics con t r ibu t e t o w a st e-w a t er sa lin it y e-wh ich , if u sed for a gr icu lt u r e, a ffect s t h e cr op pr odu ct ion . Ta ble VI sh ow s h ow differ en t cr ops h ave differ en t sen sit ivi-t ies ivi-t o w a ivi-t er sa lin iivi-t y.
Wastewater treatment processes
Differ en t de gr ees of w a st ew a t er t r ea t m en t m ay be a ch ieved u sin g con ven t ion a l syst em s or n a t u r a l syst em s. Con ven t ion a l t r ea t m en t syst em s in clu de pr elim in a r y, pr im a r y, sec-on da r y, a n d som et im es a dva n ced t r ea t m en t pr ocesses a ccor din g t o t h e t r ea t m en t level of t h e w a st ew a t er t r ea t m en t pla n t . T h ey u su a lly in volve h igh r a t e biologica l t r ea t m en t . N a t -u r a l syst em s a r e lower in cost a n d less soph is-t ica is-t ed in oper a is-t ion a n d m a in is-t en a n ce. T h ey in volve low -r a t e biologica l t r ea t m en t . On e of t h e t ech n iqu es of n a t u r a l biologica l t r ea t m en t syst em s is u sin g Wa st ew a t er St a biliza -t ion Pon ds w h ich in clu de a n a er obic pon ds, fa cu lt a t ive pon ds, a n d m a t u r a t ion pon ds. Ot h er t ech n iqu es of n a t u r a l biologica l t r ea t -m en t syst e-m s a r e: La n d t r ea t -m en t t ech n iqu e; N u t r ien t fi lm t r ea t m en t t ech n iqu e; a n d Soil-a qu ifer t r eSoil-a t m en t t ech n iqu e. Follow in g is Soil-a br ief descr ipt ion of t h e con ven t ion a l t r ea t -m en t pr ocesses.
Preliminary treatment
P r elim in a r y t r ea t m en t is t h e r em ova l of la r ge solids a n d t r 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 object s. Ot h er pr elim in a r y t r ea t m en t oper a -t ion s ca n in clu de fl occu la -t ion , odor con -t r ol, ch em ica l t r ea t m en t , a n d pr e-a er a t ion (Cr ook et a l., 1992).
Table I
Agric ultural re us e in s e le c te d USA s tate s
State mgd m3/ day
California 1 5 0 5 7 0 ×1 03
Florida 9 0 3 4 0 × 1 03
Texas 2 9 0a 1 , 1 0 0 × 1 03
Note: aThis is based on the design flow of the wastewater treatment plant providing water and may exc eed ac tual use.
Source: Crook, J. (1 9 9 2 )
Table II
Wate r s upply and s anitatio n c o ve rage
Population Water supply coverage Sanitation coverage
Country (×1,000) (% of population) (% of population)
Sudan 2 4 ,6 0 0 4 7 .6 7 4 .8
Tunisia 7 ,9 0 0 9 2 .2 9 5 .3
Oman 1 ,4 6 8 5 4 .4 4 8 .2
Syria 1 2 ,1 1 3 8 4 .0 8 5 .0
Yemen 1 0 ,6 2 0 3 6 .0 6 5 .2
Source: Water supply and sanitation sec tor monitoring report 1 9 9 0 (Baseline Year), WHO, Water Supply and Sanitation Collaborative Counc il, and UNICEF
Table III
Po te ntial o f do me s tic was te wate r re us e in mo s t Middle Eas t and No rth Afric a
Potential annual
Domestic use wastewater reuse
Annual (% of annual (30% of domestic use)
Country (×109m3) withdrawals) (×109m3)
Algeria 3 .0 2 2 .0 0 .1 9 8
Egypt 5 6 .3 7 .0 1 .1 8 2 3
Bahrain 0 .2 6 0 .0 0 .0 3 6
Iraq 4 3 .9 3 .0 0 .3 9 5 1
Jordan 1 .0 2 0 .0 0 .0 6
Lebanon 0 .8 1 1 .0 0 .0 2 6 4
Libya 2 .8 1 5 .0 0 .1 2 6
M alta 0 .0 2 7 6 .0 0 .0 0 4 5 6
M orocco 1 1 .0 6 .0 0 .1 9 8
Oman 1 .3 3 .0 0 .0 1 1 7
Qatar 0 .1 5 3 6 .0 0 .0 1 6 2
Saudi Arabia 3 .6 4 5 .0 0 .4 8 6
Syria 3 .3 7 .0 0 .0 6 9 3
Tunisia 3 .0 1 3 .0 0 .1 1 7
UAE 0 .4 1 1 .0 0 .0 1 3 2
Yemen 3 .9 5 .0 0 .0 5 8 5
Total 1 3 4 .6 7 2 .9 9 8 2 6
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Primary treatment
P r im a r y t r ea t m en t is t h e r em ova l of set t lea ble or ga n ic a n d in or ga n ic solids by sedim en t a t ion , a n d t h e r em ova l of fl oa t in g m a t er ia ls by sk im m in g. T h is pr ocess a lso is effect ive for t h e r em ova l of som e or ga n ic n it r ogen , or ga n ic ph osph or u s, a n d h eavy m et a ls, bu t does lit t le for t h e r em ova l of col-loida l, dissolved con st it u en t s, biologica l species, a n d t h e level of vir u ses. Appr oxim a t ely 25 per cen t t o 50 per cen t of t h e in cooxim -in g BOD, 50 per cen t t o 70 per cen t of t h e t ot a l SS, a n d 65 per cen t of t h 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 t a t ion (FAO, 1992a ). In m a n y cou n t r ies, pr im a r y t r ea t m en t m ay be con sider ed su fficien t t r ea t -m en t if w a st ew a t er is u sed t o ir r iga t e cr ops
t h a t a r e n ot con su m ed by h u m a n s or t o ir r i-ga t e 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 t a ct is r edu ced.
Secondary treatment
Secon da r y t r ea t m en t in volves t h e r em ova l of or ga n ic m a t t er a n d in som e ca ses n it r ogen , a n d ph osph or u s u t ilizin g a n a er obic biologi-ca l t r ea t m en t pr ocess. Aer obic biologibiologi-ca l t r ea t m en t occu r s in t h e pr esen ce of oxygen wh er eby m icr oor ga n ism s oxidize t h e or ga n ic m a t t er in t h e w a st ew a t er. Sever a l t ypes of a er obic biologica l t r ea t m en t in clu de: a ct i-va t ed slu dge, t r ick lin g fi lt er s, a n d r ot a t in g biologica l con t r a ct or s (RBCs).
Table IV
Co ns titue nts o f c o nc e rn in was te wate r tre atme nt and irrigatio n with re c laime d was te wate r
Constituent M easured parameters Reason for concern
Suspended solids Suspended solids inc luding Suspended solids c an lead to the development of sludge volatile and fixed solids 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 irriga-tion systems
Biodegradable Bioc hemic al oxygen demand Composed princ ipally of proteins, c arbohydrates, and fats. organics Chemic al oxygen demand If disc harged to the environment, their biologic al dec
ompo-sition c an lead to the depletion of dissolved oxygen in rec eiving waters and to the development of septic c ondi-tions
Pathogens Indic ator organisms, total Communic able diseases c an be transmitted by the and fec al c oliform bac teria pathogens in wastewater: bac teria, virus, parasites Nutrients Nitrogen, phosphorous and Nitrogen, phosphorous, and potassium are essential
potassium nutrients for plant growth, and their presenc e normally enhanc es the value of the water for irrigation. When dis-c harges to the aquatidis-c environment, nitrogen dis-c an also lead to the pollution of groundwater
Stable (refractory) Spec ific c ompounds (e.g. These organic s tend to resist c onventional methods of organics phenols, pestic ides, wastewater treatment. Some organic c ompounds are toxic
c hlorinated hydroc arbons) in the environment, and their presenc e may limit the suit-ability of the wastewater for irrigation
Hydrogen ion activity pH 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 Heavy metals Spec ific elements (e.g. Cd, Some heavy metals ac c umulate in the environment and are Z n, Nl, Hg) toxic to plants and animals. Their presenc e may limit the
suitability of the wastewater for irrigation
Dissolved inorganics Total dissolved solids, Exc essive salinity may damage some c rops. Spec ific ations elec tric al c onduc tivity, suc h as c hloride, sodium, boron, are toxic to some c rops. spec ific elements, (e.g. Sodium may pose soil permeability problems
Na, Ca, Mg,Cl, B)
Residual chlorine Free and c ombined c hlorine Exc essive amount of free available c hlorine (>0 .0 5 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 ontamina-tion
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Tertiary/ advanced treatment
Adva n ced w a st ew a t er t r ea t m en t is u t ilized wh en h igh qu a lit y r ecla im ed w a t er is n eces-sa r y, su ch a s for ir r iga t ion of u r ba n la n d-sca pes a n d r aw edible food cr ops. Adva n ced t r ea t m en t r em oves n it r ogen , ph osph or u s, det er gen t s, w a t er soft en er s, h eavy m et a ls su ch a s Zn , Cd, N i, Fe, a n d r edu ces BOD, SS, a n d TDS. However, n it r ogen a n d ph osph or u s
a r e m a jor essen t ia l pla n t n u t r ien t s a n d t h u s t h eir pr esen ce in w a st ew a t er is a n a sset for ir r iga t ion a t cer t a in pla n t gr ow t h st a ges. P r in ciple a dva n ced w a st ew a t er t r ea t m en t pr ocesses in clu de fi lt r a t ion , n it r ifi ca t ion , den it r ifi ca t ion , biologica l or ch em ica l ph os-ph or u s r em ova l, coa gu la t ion -sedim en t a t ion , ca r bon a dsor pt ion , a m m on ia st r ippin g, br ea k poin t ch lor in a t ion , select ive ion Table V
Charac te ris tic s o f s o me was te wate r c o ns titue nts
Trace heavy metals Remarks
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 1 2 mg/ l for Sudan grass to less than 0 .0 5 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 1 0 mg/ l
Cadmium Toxic to beans, beets, and turnips at c onc entrations as low as 0 .1 mg/ l in nutrient solu-tion. 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 om-mended limit is 0 .0 7 5 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 Effec tively exc luded by plants; spec ific toleranc e levels unknown titanium
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 5 0 0 mg/ l, no detrimental effec ts are usually notic ed. Between 5 0 0 and 1 ,0 0 0 mg/ l. TDS in irrigation water c an affec t sensitive plants. At 1 ,0 0 0 to 2 ,0 0 0 mg/ l. TDS levels c an affec t many c rops and c areful management prac tic es should be followed. Above 2 ,0 0 0 mg/ l, water c an be used regularly only for tolerant plants on permeable soils
Khale d M. Abu-Z e id
Sensitive M oderately sensitive M oderately tolerant Tolerant
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br ea k poin t ch lor in a t ion , select ive ion exch a n ge, a n d r ever se osm osis.
Disinfection
Disin fect ion m ay be n eeded if gu idelin e efflu -en t qu a lit y is n ot a ch ieved. Disin fect ion is im por t a n t for t h e dest r u ct ion of m icr oor ga n -ism s. T h e m ost com m on disin fect a n t is Ch lo-r in e. Ozon e a n d Ult lo-r aviolet ligh t a lo-r e ot h elo-r
pr om in en t disin fect a n t s u sed a t w a st ew a t er t r ea t m en t pla n t s. Ch lor in e con t a ct ba sin s a r e design ed t o a llow for a con t a ct t im e of a bou t 30 m in u t es. In specifi c ir r iga t ion u ses, a con -t a c-t -t im e of 120 m in u -t es m ay be n eeded. In spit e of t h e ch lor in a t ion efficien cy in r edu cin g t h e n u m ber of ba ct er ia , it w ill leave h elm in t h s e ggs t ot a lly u n a ffect ed (FAO, 1992a ).
Table VII
Re c laime d wate r s tandards fo r re us e in irrigatio n in Kuwait, Saudi Arabia, Tunis ia, Egypt, and the USA
Kuwait Egypt USA-EPA
Irrigation of Saudi Arabia Tunisia M aximum concentration
fodder and food Irrigation M aximum cont- M aximum for reuse of different
crops not eaten food crops aminant level concentration categories of reclaimed Long Short
Parameter raw, forest land crops eaten raw for unrestricted for reuse in wastewater (see Table VIII) term term
Level of treatment Advanced Advanced irrigation agriculture Preliminary Preliminary Secondary Advanced use use
Trace heavy metals mg/ l mg/ l mg/ l mg/ l ppm ppm ppm ppm
Aluminium 5 .0 5 .0 2 0 .0
Arsenic 0 .1 0 .1 0 .1 0 .1 0 2 .0
Beryllium 0 .1 0 .1 0 0 .5
Boron 0 .5 3 5 5 5 0 .7 5 2 .0
Cadmium 0 .0 1 0 .0 1 0 .0 5 0 .0 1 0 .0 1 0 .0 1 0 .0 5
Chromium 0 .1 0 .1 0 .1 0 .1 1 .0
Cobalt 0 .0 5 0 .1 0 .0 5 0 .0 5 0 .0 5 5 .0
Copper 0 .4 0 .5 1 0 .2 0 .2 5 .0
Cyanide 0 .0 5
Fluoride 2 .0 3 1 .0 1 5 .0
Iron 5 .0 5 5 .0 5 .0 5 .0 2 0 .0
Lead 0 .1 1 1 0 5 .0 5 .0 5 .0 1 0 .0
Lithium 0 .0 7 2 .5 2 .5
M anganese 0 .2 0 .5 0 .2 0 .2 0 .2 0 .2 1 0 .0
M ercury 0 .0 0 1 0 .0 0 1
M olybdenum 0 .0 1 0 .0 5 0 .0 1 0 .0 1 0 .0 5
Nickel 0 .0 2 0 .2 0 .5 0 .5 0 .2 0 .2 2 .0
Nitrate 1 0 .0
Selenium 0 .0 2 0 .0 5 0 .0 2 0 .0 2
Tin, tungsten, titanium
Vanadium 0 .1 1 .0
Zinc 4 .0 5 2 .0 2 .0 2 .0 1 0 .0
Other parameters Rec ommended
limit
TDS(mg/ l) 2 ,5 0 0 2 ,5 0 0 2 ,5 0 0 2 ,5 0 0 5 0 0 -2 ,0 0 0
SS (mg/ l) 1 0 1 0 1 0 .0 3 0a 3 5 0 4 0 2 0
BOD(mg/ l) 1 0 1 0 1 0 .0 3 0a 3 0 0 4 0 2 0
COD(mg/ l) 4 0 4 0 9 0 6 0 0 8 0 4 0
Chloride(mg/ l) 2 8 0 2 ,0 0 0 3 5 0 3 5 0 3 5 0
Chlorine residual(mg/ l) 1 1 <1
after 12 hrs @ 20°C
pH 6 -8 .4 6 .5 -8 .5 6 .0
Coliform (count/ 100ml) 1 0 ,0 0 0 1 0 0 2 .2 1 0 ,0 0 0 1 ,0 0 0
Turbidity (NTU) 1 .0
SAR(per cent) 2 5 2 5 2 0 2 0
Oil and grease(ppm) absent 1 0 5
Phenol 0 .0 0 2
Electrical conductivity
(US/ cm) 7 ,0 0 0b
Halogenated hydrocarbons 0 .0 0 1
Intestinal nematodes (arithmetic mean no. of
eggs per liter) < 0 1 / 1 5 1 1
Note:a24 hour c omposite sample
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Wastewater reuse considerations
In a ddit ion t o ir r iga t ion su pply a n d dem a n d a n d w a t er qu a lit y r equ ir em en t s su ch a s t h ose sh ow n in Ta bles VII a n d VIII, t h er e a r e ot h er con sider a t ion s specifi c t o a gr icu lt u r a l w a t er r eu se t h a t m u st be a ddr essed. Bot h t h e u ser a n d su pplier of r ecla im ed w a t er m ay h ave t o con sider m odifi ca t ion s in cu r r en t pr a ct ice t h a t m ay be r equ ir ed t o u se r ecla im ed w a t er for a gr icu lt u r a l ir r iga t ion . T h is r equ ir es t h a t t h ose in vest iga t in g r ecla im ed w a t er
pr ogr a m s h ave a wor k in g k n ow ledge of t h e a ppr opr ia t e r e gu la t ion s, cr op r equ ir em en t s, a n d m ea n s of a pplica t ion . Im por t a n t con sid-er a t ion s in clu de:
• syst em r elia bilit y;
• sit e u se con t r ol a n d set ba ck dist a n ces for ir r iga t ion ;
• m on it or in g r equ ir em en t s; • r u n off con t r ols;
• m a r k et in g in cen t ives; a n d • ir r iga t ion equ ipm en t .
Set ba ck dist a n ces or bu ffer zon es sh ou ld be est a blish ed bet ween r eu se ir r iga t ion sit es a n d va r iou s fa cilit ies su ch a s pot a ble w a t er su pply wells, pr oper t y lin es, r esiden t ia l a r ea s, a n d r oa dw ays. Set ba ck dist a n ces va r y de pen din g on t h e qu a lit y of r ecla im ed w a t er a n d t h e m et h od of a pplica t ion . For exa m ple, Illin ois r equ ir es a 15 m set ba ck fr om t h e edge of t h e wet t ed per im et er of t h e r eu se sit e t o a
r esiden t ia l lot for a n on -spr ay a pplica t ion syst em , bu t r equ ir es a 45-m set ba ck for a spr ay ir r iga t ion syst em . For r est r ict ed a n d u n r est r ict ed u r ba n r eu se a n d ir r iga t ion of food cr ops, F lor ida r equ ir es a 23-m set ba ck t o pot a ble w a t er su pply wells; bu t for a gr icu l-t u r a l r eu se on n on -food cr ops, F lor ida r equ ir es a 150-m set ba ck t o w a t er su pply wells a n d a 30-m et er set ba ck t o pr oper t y lin es. F lor ida w ill a llow r edu ced set ba ck dist a n ces for a gr icu lt u r a l r eu se on n on -food cr ops if a ddit ion a l fa cilit y r elia bilit y a n d t r ea t m en t a r e pr ovided. Color a do r ecom -m en ds a 150--m set ba ck dist a n ce t o do-m est ic su pply wells a n d a 30m set ba ck t o a n y ir r iga -t ion well r e ga r dless of -t h e qu a li-t y of -t h e r ecla im ed w a t er (Cr ook et a l., 1992).
Or e gon a n d N eva da do n ot r equ ir e set ba ck dist a n ces wh en r ecla im ed w a t er is u sed for u n r est r ict ed u r ba n r eu se or ir r iga t ion of food cr ops du e t o t h e h igh de gr ee of t r ea t m en t r equ ir ed; h owever, set ba ck dist a n ces a r e r equ ir ed for ir r iga t ion of n on -food cr ops a n d r est r ict ed u r ba n r eu se. In N eva da , t h e qu a lit y r equ ir em en t s for r ecla im ed w a t er a r e ba sed n ot on ly on t h e t ype of r eu se, bu t a lso on t h e set ba ck dist a n ce. For exa m ple, for r est r ict ed u r ba n r eu se a n d a 30-m et er bu ffer zon e, N eva da r equ ir es t h a t t h e r ecla im ed w a t er h ave a m ea n feca l colifor m cou n t of n o m or e t h a n 23/ 100 m l a n d a t u r bidit y of n o m or e t h a n 5 N TU. However, w it h n o bu ffer zon e, t h e
Table VIII
Appe ndix o f re c laime d wate r s tandards fo r re us e in irrigatio n in Egypt
Treatment Environmental and Appropriate Suggested
Category level Permissible crops health precautions irrigation method soil type
1 Preliminary Wood trees Farms should be fenc ed Furrow Light texture Palm trees No direc t water c ontac t
No entranc e permission of non-farm employees
No entranc e for c attle Follow health prec autions
Protec ting against transmitted diseases
2 Primary Cotton As above Furrow Light texture
Flowers Filter and drip
Flax
3 Sec ondary Animal food c rops Non-milk livestoc k grazing Furrow Light texture Fields for livestoc k grazing Food should be c ooked before eaten Drip Medium texture Crops with inedible skin
Fruits not in c ontac t with water Cooked vegetables
Heat proc essed fruits
4 Advanc ed Raw c onsumed food plants None All methods All types
Crops with inedible skin exc ept sprinkler
All types of c rops and c itrus fields
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r ecla im ed w a t er m u st h ave a m ea n feca l col-ifor m cou n t of n o m or e t h a n 2.2/ 100 m l a n d a t u r bidit y of n o m or e t h a n 3 N TU.
Examples of wastewater reuse in
the Arab region
Kuwait
Wit h a popu la t ion est im a t ed a t a bou t 2,000,000, m ost of Ku w a it ca n be con sider ed u r ba n . T h e cou n t r y is a r id, w it h aver a ge a n n u a l r a in fa ll less t h a n 125 m m . Wit h n o su r fa ce sou r ces, w a t er is dr aw n fr om gr ou n d-w a t er a t t h e r a t e of a bou t 2,000 m3/ d, m a in ly for pr odu cin g bot t led w a t er. Most w a t er n eeds a r e m et by desa lin a t ion . Abou t 85 per cen t of t h e t ot a l popu la t ion is on a cen t r a l sewer a ge syst em . Ku w a it pr ovides t er t ia r y t r ea t m en t (a ct iva t ed slu dge t r ea t m en t , fi lt r a t ion , a n d ch lor in a t ion ) for r ecla m a t ion for a gr icu lt u r a l ir r iga t ion . T h eir st a n da r ds a r e sh ow n in Ta ble VII. T h r ee r ecla m a t ion pla n t s h ave a t ot a l ca pa cit y of m or e t h a n 300,000 m3/ d, w it h pla n s t o u se a ll of it for a gr icu lt u r a l a n d la n d-sca pe ir r iga t ion (Cr ook et a l., 1992).
Saudi Arabia
Sa u di Ar a bia is com m it t ed t o a policy of com -plet e r eu se. In 1978, t h e a m ou n t of r ecla im ed w a t er u sed w a s est im a t ed a t 95,000 m3/ d, a n d t h e pr oject ion for t h e yea r 2000 is a bou t 2.0 x 106m3/ d. By 2000 t h e Kin gdom expect s t o m eet a lm ost 10 per cen t of it s w a t er dem a n d t h r ou gh r eu se. Re gu la t ion s r equ ir e
secon da r y t r ea t m en t w it h t er t ia r y t r ea t m en t for u n r est r ict ed ir r iga t ion , w it h st a n da r ds sh ow n in Ta ble VII (Ka lt h em a n d J a m a a n , 1985). Of specia l in t er est a r e t h e pr oject s a t Riya dh , J edda h , a n d Mecca a n d J u ba il In du s-t r ia l Cis-t y. As-t Riya dh s-t h e s-t r ick lin g fi ls-t er fa cil-it y t r ea t s over 120,000 m3/ d. Of t h is, a bou t 15 per cen t is u sed by t h e Gen er a l Pet r oleu m a n d Min er a ls Or ga n iza t ion (Pet r om in ) for in du s-t r ia l r eu se, a n d s-t h e r ess-t is ava ila ble for a gr i-cu lt u r a l ir r iga t ion on a bou t 7,800 a cr es (3,100 h a ). A 40,000 m3/ d a ct iva t ed slu dge fa cilit y a t J edda h is design ed t o exceed WHO st a n da r ds a n d is t h e fi r st in t h e r e gion wh ich w a s design ed t o m eet t h e equ iva len t of dr in k in g w a t er st a n da r ds. Adva n ced t r ea t m en t in clu des r ever se osm osis, desa lin a t ion , fi lt r a -t ion , a n d disin fec-t ion . O-t h er pla n -t s a r e pla n n ed for J edda h a n d Mecca . In bot h cit ies t h e r ecla im ed w a t er w ill be u sed for m u n ici-pa l, in du st r ia l, a n d a gr icu lt u r a l r eu se. T h e Cit y of J u ba il is pla n n ed t o h ave a 120,000 m3/ d t r ea t m en t ca pa cit y by 1992, w it h pla n s for n on -pot a ble in du st r ia l, u r ba n la n dsca p-in g, a n d ot h er r eu ses.
In a ll, 22 w a st ew a t er t r ea t m en t pla n t s a r e in oper a t ion , 19 of wh ich a r e w a st e st a biliza t ion
pon ds. Most a r e cu r r en t ly disch a r gin g t o w a dis or t o t h e sea , a lt h ou gh pla n s a r e u n der -w ay t o in cr ea se r eu se (Ya n e z, 1989).
Sultanate of Oman
In Om a n , w a t er h a s been r eu sed a r ou n d Mu s-ca t sin ce 1987. Cu r r en t ly efflu en t fr om t wo t r ea t m en t pla n t s, a t Da r sa it a n d a t Sh a t t i a l Qu r m , is u sed m a in ly t o ir r iga t e ext en sive a m en it y pla n t in g by dr ip ir r iga t ion . Spr in -k ler ir r iga t ion is n ot u sed in r ecr ea t ion a r ea s, bu t bet ween 1a .m . a n d 6a .m . som e spr in k ler ir r iga t ion is con du ct ed in con t r olled a r ea s. P r essu r e in t h e dist r ibu t ion syst em , wh ich ext en ds t o m or e t h a n 4.0 k m is som e 2 t o 3 ba r s. E fflu en t r equ ir em en t s a r e set in t h e Re gu la t ion s for Wa st ew a t er Reu se a n d Disch a r ge. T h e Da r sa it pla n t is cu r r en t ly oper a t -in g a t ca pa cit y a n d t r ea t -in g a bou t 12,000 m3/ day of w a st ew a t er. T h is pla n t ser ves t h e loca l bu sin ess dist r ict a n d a lso r eceives sew a ge a n d w a st ew a t er pu m ped fr om h oldin g t a n k s. T h e t r ea t m en t pr ocesses in clu de scr een in g, gr it r em ova l in a er a t ed gr it ch a m ber s, pr im a r y set t in g, a ct iva t ed slu dge t r ea t -m en t by con t a ct st a biliza t ion , du a l--m edia fi lt r a t ion , a n d ch lor in a t ion . If t h e ch lor in e con cen t r a t ion s exceeds 0.2 m g/ l a ft er ch lo-r in e con t a ct , a ilo-r is a dded t o st lo-r ip ou t t h e excess ch lor in e. E fflu en t is pu m ped t o a st or -a ge t -a n k t h -a t pr ovides pr essu r e t o t h e w -a t er r eu se t r a n sm ission syst em .
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Tunisia
Alt h ou gh a ll t h e cou n t r ies of N or t h Afr ica h ave a n in t er est in w a t er r ecla m a t ion , Tu n isia h a s don e t h e m ost , m a k in g r eu se a pr ior it y in t h eir n a t ion a l w a t er r esou r ces st r a t e gy (Ba h r i, 1991; Asa n o a n d Mu jer ie go, 1982). Som e 1,500 a cr es (600 h a ) of cit r u s a n d olive t r ee or ch a r ds n ea r Tu n is h a d been ir r i-ga t ed w it h gr ou n dw a t er fr om sh a llow a qu ifer s sin ce t h e 1960s bu t , beca u se of over dr a ft a n d seaw a t er in t r u sion , secon da r y efflu -en t fr om a por t ion of Tu n is w a st ew a t er w a s u sed for ir r iga t ion sea son a lly, in spr in g a n d su m m er. T h e efflu en t is pu m ped in t o a 5,800 m3pon d a n d t h en t o a 3,800 m3r eser voir, a n d t h en fl ow s by gr avit y a bou t 8 k m t o t h e fa r m er s. Cu r r en t ly, t h e efflu en t fr om fou r t r ea t -m en t pla n t s, w it h a t ot a l fl ow of a bou t 250,000 m3/ d is u sed t o ir r iga t e a bou t 12,000 a cr es (4,500 h a ) of or ch a r ds, for a ge cr ops, cot t on , cer ea ls, golf cou r ses a n d law n s. Abou t 70 per cen t of t h e ir r iga t ed a r ea a r ou n d Tu n is w ill u se a bou t 60 per cen t of t h e ava ila ble w a st e-w a t er efflu en t .
Con sider a ble r esea r ch h a s been u n der -t a k en , pa r -t icu la r ly -t o a ssess -t h e fer -t ilizer va lu e of r ecla im ed w a t er a n d t h e sew a ge pr odu ced in t r ea t m en t . Recla im ed w a t er ir r iga t ion pr odu ced h igh er yields t h a n gr ou n dw a t er ir r iga t ion . St u dies of t h e con t a -m in a t ion of cr ops a n d gr ou n dw a t er w h en r ecla im ed w a t er is u sed r evea led lit t le sign ifi -ca n t im pa ct on soils, cr ops, or gr ou n dw a t er (Ba h r i, 1991). T h e N a t ion a l Sewer a ge a n d Sa n it a t ion Agen cy is r espon sible for t h e con -st r u ct ion a n d oper a t ion of a ll sewer a ge a n d t r ea t m en t in fr a st r u ct u r e in t h e la r ger cit ies in Tu n isia . Wh en efflu en t is t o be u sed for a gr icu lt u r a l ir r iga t ion , t h e Min ist r y of Agr i-cu lt u r e is r espon sible for exei-cu t ion of t h e pr oject s, wh ich in clu de t h e con st r u ct ion a n d oper a t ion of a ll fa cilit ies for pu m pin g, st or in g a n d dist r ibu t in g t h e r ecla im ed w a t er. Va r iou s de pa r t m en t s of t h e Min ist r y a r e r espon sible for t h e sever a l fu n ct ion s, wh ile r e gion a l de pa r t m en t s su per vise t h e Wa t er Code a n d collect ion of ch a r ges, a bou t $0.02-0.03/ m 3 . T h e Wa t er Code, en a ct ed in 1975, pr oh ibit s t h e u se of u n t r ea t ed w a st ew a t er in a gr icu l-t u r e l-t o be ea l-t en r aw. Mor e r ecen l-t le gisla l-t ion cover s t h e r e gu la t ion of con t a m in a n t s in t h e en vir on m en t , in clu din g r ecla im ed w a t er, a n d specifi es t h e r espon sibilit ies of t h e Min ist r ies of Agr icu lt u r e a n d P u blic Hea lt h , a n d t h e N a t ion a l E n vir on m en t a l P r ot ect ion Agen cy. Ta ble VII illu st r a t es t h e m a xim u m con cen t r a -t ion s for sever a l con -t a m in a n -t s in r ecla im ed w a t er t o be u sed in a gr icu lt u r e.
United Arab Emirates
E xt en sive n on pot a ble r eu se h a s been pr a c-t iced in Abu Dh a bi sin ce 1976. T h e sysc-t em , design ed for 200,000 m3/ d, in clu des a du a l dist r ibu t ion n et wor k wh ich u ses r ecla im ed w a t er for u r ba n ir r iga t ion of pu blic ga r den s, t r ees, sh r u bs a n d gr a ssed a r ea s a lon g r oa d-w ays. T h e t r ea t m en t fa cilit y pr ovides t er t ia r y t r ea t m en t w it h r a pid sa n d fi lt r a t ion a n d dis-in fect ion by ch lor dis-in a t ion a n d ozon a t ion . T h e r ecla im ed w a t er dist r ibu t ion syst em is oper -a t ed -a t lower pr essu r e t h -a n t h e pot -a ble sys-t em sys-t o r edu ce w in d spr ayin g; elem en sys-t s of sys-t h e syst em a r e m a r k ed a n d la beled t o avoid cr osscon n ect ion s. AlAin , w it h a pr oject ed popu la -t ion of 250,000 by -t h e yea r 2000, pr odu ces r ecla im ed w a t er t h a t m ay be u sed on ly for r est r ict ed ir r iga t ion . T h e r ecla im ed w a t er is pu m ped a bou t 12 k m ou t side t h e cit y wh er e it is u sed for ir r iga t ion in design a t ed a r ea s. T r ea t m en t in clu des du a l-m edia fi lt r a t ion a n d ch lor in a t ion for disin fect ion .
Egypt
T h e r eu se of m u n icipa l w a st ew a t er h a s been pr a ct iced in Ga ba l E lAsfa r sew a ge fa r m n ea r Ca ir o Cit y for m or e t h a n 60 yea r s (Ash m aw y, 1990). Fou r -t h ou sa n d a cr es of deser t la n d h a s been r ecla im ed by su r fa ce ir r iga t ion of t h is pr im a r y t r ea t ed sew a ge. Aft er t h e fi r st 20 yea r s, t h e sew a ge fl ow r ea ch in g t h e t r ea t m en t pla n t exceeded dou ble t h e ca pa cit y. T h a t is wh en en t ir ely r aw sew a ge w a s u sed for ir r i-ga t ion for t h e n ext 40 yea r s. P r odu ct ivit y of la n d in cr ea sed gr a du a lly a n d t h en dr opped du e t o cloggin g of soil r esu lt in g fr om r aw sew a ge u se. T h e t r ea t m en t pla n t is n ow bein g expa n ded, deser t r ecla m a t ion pr oject s a r e pla n n ed, a n d st a n da r ds for w a st ew a t er r eu se a r e le gisla t ed. See Ta bles VII a n d VIII for E gypt ia n St a n da r ds for w a st ew a t er r eu se in a gr icu lt u r e.
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Conclusions
Wa st ew a t er r eu se in a gr icu lt u r e is a su ccess-fu l t r en d t h a t pr ovides t h e t wo ben efi t s of developin g a n ew n on -con ven t ion a l w a t er r esou r ce, a n d u t ilizin g a low cost n a t u r a l fer t ilizer. However, t h e m ost cr it ica l r est r ic-t ion in a w a sic-t ew a ic-t er r eu se pr ogr a m is ic-t o a ssu r e t h a t pu blic h ea lt h is n ot com pr om ised. Ot h er object ives, su ch a s pr even t in g en vir on m en t a l de gr a da t ion , avoidin g pu blic discom -for t , a n d m eet in g u ser r equ ir em en t s, m u st a lso be sa t isfi ed in im plem en t in g a su ccessfu l w a st ew a t er r eu se pr ogr a m . T h e st a r t in g poin t r em a in s in t h e u se of pr oper ly t r ea t ed r ecla im ed w a t er for t h e r igh t cr op in t h e r igh t soil u sin g t h e r igh t m et h od of ir r iga t ion .
Sever a l w a st ew a t er r eu se st a n da r ds a n d gu idelin es h ave been dem on st r a t ed. It is im por t a n t t o follow w a st ew a t er r eu se gu ide-lin es a n d st a n da r ds r e ga r din g t h e de gr ee of t r ea t m en t for cu lt iva t in g differ en t cr ops, a n d t h e n ecessa r y pr eca u t ion s t h a t n eed t o be t a k en .
In gen er a l t h er e a r e cer t a in m ea su r es t h a t a r e r equ ir ed for h ea lt h pr ot ect ion . T h ey in clu de:
• trea tm en t of w a stew a ter– t o r edu ce t h e con cen t r a t ion s of pa t h ogen s in t h e r ecla im ed w a t er ;
• cr op restr iction – t o r est r ict t h e u se of t r ea t ed w a st ew a t er t o r est r ict ed cr ops; • w a stew a ter a p p lica tion – t o su pply w a st
e-w a t er via su bsu r fa ce, loca lized ir r iga t ion syst em s, a n d r ecom m en ded m et h od of ir r i-ga t ion for differ en t cr ops;
• h u m a n ex p osu re con tr ol – by lim it in g con -t a c-t , in h a la -t ion , a n d in ges-t ion of -t h e r ecla im ed w a t er ;
• con tin u ou s m on itor in g– t o a ssu r e t h e qu a l-it y of t r ea t ed w a st ew a t er, m on l-it or in g sh ou ld be m a in t a in ed on t r ea t ed w a st e-w a t er, gr ou n de-w a t er in t h e vicin it y, soils, a n d cr ops;
• a d h eren ce to w a stew a ter reu se sta n d a rd s a n d gu id elin es.
F u r t h er m or e, in vest m en t in sew a ge collec-t ion syscollec-t em s a n d w a scollec-t ew a collec-t er collec-t r ea collec-t m en collec-t pla n t s h ave a n u m ber of a dva n t a ges, espe-cia lly in cou n t r ies w it h sca r ce w a t er r esou r ces. It , n ot on ly, pr even t s t h e en vir on -m en t a l h a za r ds of i-m pr oper disposa l of w a st e-w a t er, bu t it pr ovides t h e oppor t u n it y for im plem en t in g t h e r ecen t t r en d of r eu sin g w a st ew a t er in a gr icu lt u r e.
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Table IX
Dis tributio n o f re c lamatio n s ite s
Area Wastewater reuse (1994-2020)
Site (feddans) (m3/ day)
ElBerka 3 0 ,0 0 0 7 5 0 x 1 03
ElGabal ElAsfar (1st phase) 4 5 ,0 0 0 1 ,0 8 0 x 1 03
ElGabal ElAsfar (2nd Phase) 2 5 ,0 0 0 6 0 0 x 1 03
ElGabal ElAsfar (3rd Phase) 3 0 ,0 0 0 7 5 0 x 1 03
Znein & Abu-Rawash 5 0 ,0 0 0 1 ,3 2 5 x 1 03
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Wor ld Ba n k (1995), “F r om sca r cit y t o secu r it y: aver t in g a w a t er cr isis in t h e Middle E a st a n d N or t h Afr ica ”, Wor ld Ba n k , Wa sh in gt on DC. Ya n e z, F. (1989), “Su r vey m ission on w a st ew a t er
