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Tunisian Republic Ministry of Infrastructure and spatial planning
National Sanitation Utility
WASTEWATER TREATMENT IN TUNISIA
WASTEWATER TREATMENT IN TUNISIA
Elaborated by
- Nabiha OUERFELLIApril 2014
ONAS : PRESENTATION
ONAS:ONAS: Principal Principal Operator of Sanitation in Tunisia Operator of Sanitation in Tunisia
ONAS was established ONAS was established by Law N° 73/1974by Law N° 73/1974, this law was , this law was amended by virtue of Law N° 41/1993, ONAS was amended by virtue of Law N° 41/1993, ONAS was entrusted with the mission of management of the entrusted with the mission of management of the sanitation sectorsanitation sector
ONAS is a public institution of an industrial and ONAS is a public institution of an industrial and commercial charactercommercial character
enjoys civil status and financial autonomy enjoys civil status and financial autonomy
ONAS actions include the following fields: Studies, Works, ONAS actions include the following fields: Studies, Works, Operation and maintenance (O & M) of sanitation Operation and maintenance (O & M) of sanitation networks and facilities and Technical assistance.networks and facilities and Technical assistance.
3
Missions:Missions:
Combating the sources of water pollution under ONAS Combating the sources of water pollution under ONAS purview purview
Management, operation, maintenance, rehabilitation Management, operation, maintenance, rehabilitation and construction of all facilities intended for the and construction of all facilities intended for the sanitation of the towns assigned to ONAS by decreesanitation of the towns assigned to ONAS by decree
Promoting the sector of the sale and distribution of the Promoting the sector of the sale and distribution of the sub-products of wastewater treatment plants, such as sub-products of wastewater treatment plants, such as treated wastewater and sludgetreated wastewater and sludge
Planning and implementation of the sanitation sector Planning and implementation of the sanitation sector programmesprogrammes
Planning and implementation of integrated projects Planning and implementation of integrated projects related to the treatment of wastewater and disposal of related to the treatment of wastewater and disposal of storm water. storm water.
4
ONAS : PRESENTATION
State budgetState budget
External loans and External loans and grants 59 % grants 59 %
Sanitation feesSanitation fees 59 % 59 %
InvestmentsInvestments94 million TND94 million TND
Operating costsOperating costs264,8 Million 264,8 Million TNDTND
39 %
41%
FINANCIAL RESSOURCES OF ONAS
Other incoms Other incoms 2 % 2 %
ONAS : PRESENTATION
Principales implementationsPrincipales implementations
Major achievements have been identified from the Major achievements have been identified from the
sanitation master plans and feasibility studies. They sanitation master plans and feasibility studies. They
were concerned at the beginning to the major cities, were concerned at the beginning to the major cities,
tourist and industrial development zones.tourist and industrial development zones.
Secondly, priority was given to small and medium-sized Secondly, priority was given to small and medium-sized
cities and suburban areas.cities and suburban areas.
Finally, the districts have in turn benefited from a major Finally, the districts have in turn benefited from a major
program involving 1.5 million people spread over 1000 program involving 1.5 million people spread over 1000
districts. districts. 6
ONAS : PRESENTATION
7
Tataouine
Kébéli
Medenine
Tozeur
Gabès
Gafsa
KasserineSidi Bouzid
Sfax
Kef Béjà
Jendouba
Bizerte
Kairouan
Mahdia
Sousse
Zaghouan
NabeulThe total number of The total number of
wastewater treatment plants: wastewater treatment plants: 110110
- 101 plants treat wastewater 101 plants treat wastewater of urban origin,of urban origin,
- 2 plants treat industrial 2 plants treat industrial wastewater,wastewater,
- 7 plants treat wastewater of 7 plants treat wastewater of rural areasrural areas
Connection rate to ONAS: 90%Connection rate to ONAS: 90% For the area supported by For the area supported by
ONAS ONAS
ONAS : PRESENTATION
The capacity of these treatment plants varies from 200 The capacity of these treatment plants varies from 200 m3/d (Hammem Bourguiba) up to 78,000 m3/d m3/d (Hammem Bourguiba) up to 78,000 m3/d (Choutrana1).(Choutrana1).
Treatment plants in operation have been used to treat Treatment plants in operation have been used to treat 232 million m3 of wastewater 232 million m3 of wastewater - 41% of TWW from Greater Tunis,- 41% of TWW from Greater Tunis,-19% of TWW from northern Tunisia in which The -19% of TWW from northern Tunisia in which The region of Nabeul represents 50% of the total volumeregion of Nabeul represents 50% of the total volume-23% of the TWW from the center of Tunisia,-23% of the TWW from the center of Tunisia,-17% of TWW from southern Tunisia -17% of TWW from southern Tunisia
8% of treated wastewater is of industrial origin8% of treated wastewater is of industrial origin
ONAS : PRESENTATION
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Distribution of WWTP by type of methods of treatmentDistribution of WWTP by type of methods of treatment
84% of wastewater treatment plants are activated sludge-type 84% of wastewater treatment plants are activated sludge-type (medium and low load), the most effective method of treatment (medium and low load), the most effective method of treatment efficiency with up to 98%efficiency with up to 98%
85
14 2 7
activated sludge
lagoon
trickling
constructed wetland
ONAS : PRESENTATION
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SLUDGE MANAGEMENTSLUDGE MANAGEMENT
Issues:
Reviving the agricultural use for sustainable sludge
Avoid the impact of sludge management on the quality of treatment and environment
Meet the conditions of Land filling (specific or mixed)
Extend the value of the sludge to produce energy
Thermal recovery of sludge in the industry (cement)
In treatment
- Aerobic Stabilization:
- anaerobic Stabilization-
In drying
-Natural drying : 39 %
- Mechanical drying : 61 %
Sludge disposal
- Landfill: 24%- Storage in site of WWTP : 35%- Storage in deposit site of ONAS : 41%
Control of wastewater are carried out at the Control of wastewater are carried out at the laboratory level of WWTPs and in private laboratories. laboratory level of WWTPs and in private laboratories.
(Last year ONAS done by private 4039 analysis)(Last year ONAS done by private 4039 analysis)
Control parameters must obey to the effluent standards
For water (raw or treated): NT 106 002 (1989)
For sludge: NT 106.20 (2002)
For reuse : NT 106.003
ONAS : PRESENTATION : quality control
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Parameters for monitoring
Pollution indicators : Biological oxygen demand (5 days) BOD5 Chemical oxygen demand COD Suspended solids TSS Ionic balances (anions and cations) total nitrogen Ntot total phosphorus Ptot Nitrates, nitrites, ammonium, NO-3, NO 2, NH 4 Heavy metals (Cr tot, Cr VI, Ni, Cd, Pb, Fe, Zn, Cu, Hg) Oils and fats Bacteriology (total and fecal coliforms, Faecal streptococci, E. coli) Parasitic (helminth eggs)
In some cases, wastewater can be clean enough for In some cases, wastewater can be clean enough for reuse for particular purposes. reuse for particular purposes. ((Reuse rate : 30 %Reuse rate : 30 %))
Currently, treated wastewater from 34 WWTP are reused Currently, treated wastewater from 34 WWTP are reused in agriculture, golf courses and green spacesin agriculture, golf courses and green spacesWe have We have modest experience in the field of groundwater modest experience in the field of groundwater recharge in the region of Nabeulrecharge in the region of Nabeul
ONAS conducts additional treatment in order to remove ONAS conducts additional treatment in order to remove microbial pollution, phosphorous and nitrogen in certain microbial pollution, phosphorous and nitrogen in certain wastewater treatment plants located in the vicinity of wastewater treatment plants located in the vicinity of sensitive water mediums, as well as to prevent health-sensitive water mediums, as well as to prevent health-related hazards, according to the final destination of related hazards, according to the final destination of treated wastewater disposaltreated wastewater disposalIn Tunisia we have 17 WWTP using tertiary treatmentIn Tunisia we have 17 WWTP using tertiary treatment
the different technologies used are:the different technologies used are: Sterilisation by ultra-violet rays ; (5 WWTP)Sterilisation by ultra-violet rays ; (5 WWTP) Sand filtration (percolation) + sterilisation by ultra-violet Sand filtration (percolation) + sterilisation by ultra-violet rays ; (4 WWTP)rays ; (4 WWTP) Maturation ponds; (8 WWTP)Maturation ponds; (8 WWTP)
ONAS : PRESENTATION : Reuse and complementary treatment
14
The main axes of development focus on the following programs:The main axes of development focus on the following programs: Development and extension of sanitation infrastructure to meet Development and extension of sanitation infrastructure to meet
an urgent demandan urgent demand - Extension and rehabilitation of WWTP- Extension and rehabilitation of WWTP - Improve the processing to reach standards;- Improve the processing to reach standards; sludge Management program sludge Management program - Equipping treatment plants through technologies that improve - Equipping treatment plants through technologies that improve
the dryness of the sludge producedthe dryness of the sludge produced- Construction of sludge deposit sitesConstruction of sludge deposit sites
Energies efficiency programEnergies efficiency program- Energy optimisation of sludge : this consist in the production of Energy optimisation of sludge : this consist in the production of
Electrical and thermal energy based on biogazElectrical and thermal energy based on biogaz- Substitution of the old aeration to ameliorate the energy Substitution of the old aeration to ameliorate the energy
consumption consumption
Industrial Wastewater program (Industrial Wastewater program (Establishment of common Establishment of common treatment plant for treating industrial wastewater, treatment plant for treating industrial wastewater, separate separate WWTP between urban and industrial)WWTP between urban and industrial)
Program for the reuse of treated wastewaterProgram for the reuse of treated wastewater
ONAS : PRESENTATION :Major programs
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IMPROWARE Project
WWTP of Korba : WWTP of Korba : Korba’s wastewater treatment plant is Korba’s wastewater treatment plant is a conventional activated sludge, followed by three a conventional activated sludge, followed by three maturation ponds in series acting as a tertiary maturation ponds in series acting as a tertiary treatment (MP1, MP2, and MP3).treatment (MP1, MP2, and MP3).
Treated effluent is essentially Treated effluent is essentially used for artificial recharge of used for artificial recharge of Korba aquifer; the rest is Korba aquifer; the rest is discharged into the Korba discharged into the Korba lagoon to maintain its lagoon to maintain its ecological equilibrium ecological equilibrium
Flow : 7764 m3/dFlow : 7764 m3/d
Pollution load : 3164 kg/dPollution load : 3164 kg/d
Population equivalent : 74 898 Population equivalent : 74 898 inhabitant inhabitant
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IMPROWARE ProjectIMPROWARE Project
In the WWTP of Korba, A hydrodynamic study In the WWTP of Korba, A hydrodynamic study demonstrated the existence of short circuits and dead demonstrated the existence of short circuits and dead zones in the zones in the maturation pondsmaturation ponds, so how to improve the , so how to improve the removal efficiency of these pondsremoval efficiency of these ponds..
to reduce the short to reduce the short circuiting flow and the circuiting flow and the
dead zonedead zone
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CONCLUSIONCONCLUSION
An An appropriate engineering intervention reduces dead zone and appropriate engineering intervention reduces dead zone and dispersion, optimises the hydraulic retention time; and dispersion, optimises the hydraulic retention time; and consequently improves the bacterial removalconsequently improves the bacterial removal
Maturation ponds installed at the end of activated sludge WWTP, Maturation ponds installed at the end of activated sludge WWTP, need better hydraulic design to improve bacteriological removal need better hydraulic design to improve bacteriological removal and to reach the and to reach the guidelines of waste water reuse.guidelines of waste water reuse.
Actions are :Actions are :Improving the quality of treated wastewater Improving the quality of treated wastewater
- Filter Sand before maturation ponds - Filter Sand before maturation ponds - Buffles in the first and second ponds- Buffles in the first and second ponds
Monitoring (quality of treated waste water and aquifer)Monitoring (quality of treated waste water and aquifer)