Joint workshop on Enhancing efficiency and sustainability of Water Supply and Sanitation presentation - Nataša Uranjek, Waste water treatment in small settlements of Slovenia

1. International Workshop
ENHANCING SUSTAINABILITY AND EFFICIENCY OF WSS
PROVISION
15. – 16. June 2021
WASTEWATER TREATMENT IN
SMALL SETTLEMENTS OF
SLOVENIA
Nataša Uranjek
Chamber of Commerce
and Industry of Slovenia
Chamber of Public
Utilities

2. Republic of Slovenia (2.094.060 Inhabitants)
Capital city: Ljubljana (270.000)
Area: 20.273 km² (46.6 km coastline)
Highest mountain: Triglav 2.864 m
Relief: The territory of Slovenia is geographically divided into four
basic types of landscape - Alpine in the north, (42.1%), Mediterranean
in the south-west (8.6%), Dinaric in the south (28.1%), and Pannonian
in the east (21.2%)
Forests: almost 58% of the Slovenia territory
No. of municipalities: 212
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3. AGGLOMERATIONS IN SLOVENIA
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AGGLOMERATION SIZE

4. AGGLOMERATIONS IN SLOVENIA
- total of 1.533 agglomerations
- 123 agglomerations with a total load ≥ 2.000 PE
- 1.410 agglomerations with a total load of < 2.000 PE
For agglomerations with a total load of < 2.000 PE:
- < 50 P.E. (IAS)
- < 500 PE (public system or IAS)
- > 500 P.E. (public system, IAS exception)
OBLIGATORY MUNICIPAL PUBLIC SERVICE:
- Public infrastructure – public service providers (public companies,
municipalities, concession)
- For IAS – inspection and sludge removal is public service
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5. BUILDINGS WITH TYPE OF COLLECTING SYSTEMS AND
TREATMENT OF MUNICIPAL WW
Source: MOP-IJSVO, cut-off date 31. December 2018
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Sewer
IAS
Septic tank no discharge
Septic tank – outflow
WW discharges (no treatment)
Unknown system
Not reported
State border

6. WASTEWATER COLLECTION AND TREATMENT
• Total WW treatment capacity ≈ 2.680.000 P.E.
• No. of public service providers: 112
• Total length of public WW network: 10.754 km
• Length of network / inhabitant connected: 8,22 m
• Number of UWWTP: 559
• Only 41 UWWTP capacity > 10.000 PE
• 430 UWWTP capacity < 2.000 PE
• 6.176 UWWTP capacity < 50 PE
• Population connected:
- 62,4% to WW sewage system
- 60,4% to WWTP
- 31,8% to individual sanitation (IAS)
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7. PROBLEMS IN SLOVENIA DEALING WITH INDIVIDUAL OR
APPROPRIATE SYSTEMS (IAS)
• Legislation:
• all WW should be treated by the end of 2021
• for existing facilities septic tanks can remain until the first
reconstruction
• Small WWTP - appropriate cleaning
Appropriate cleaning
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Parameter Unit
< 50 PE
>= 50 PE and
< 2.000 PE
COD mg O2/L 200 150
BOD5 mg O2/L (a) 30
(a) the limit value is not set
Agglomeration size
or WWTP capacity

8. PROBLEMS IN SLOVENIA DEALING WITH
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Small wastewater treatment plant ≥50 PE and < 2.000 PE
- Slovenia has extremely dispersed population (430 UWWTP capacity
< 2.000 PE)
- The versatility of the surface makes it impossible or financially
unjustified to build larger WWTPs without many pumping stations
- Problems to get WWTP with performance to fulfil legislation for big
agglomeration, especially N and P removal
- The price for such WWTP is 2-3 times higher as for secondary
treatment and demands big effort from WWTP staff to operate them

9. PROBLEMS IN SLOVENIA DEALING WITH IAS
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IAS - Small wastewater treatment plant < 50 PE (SWWTP)
- Investors are individuals (price is one of the criteria and often crucial
for the choice of SWWTP – not always the best)
- Effluent discharge on landslide area
- At the start of SWWTP operation measurements are performed (first
measurements)
- Treatment efficiency and measurements are made only at the start of
SWWTP operation – no monitoring is required
- Performance review of SWWTP operation is required every 3 years
and is one of the utility company obligations
- Performance review is defined in the legislation with the form but
based on a visual inspection and the assessment of performance is
left to the subjective decision of the individual

10. PROBLEMS IN SLOVENIA DEALING WITH IAS
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IAS - Small wastewater treatment plant < 50 PE (SWWTP)
- On the one hand, a very vague and subjective review of SWWTP
performance, without measurements (at least COD) and monitoring
is satisfying and on the other hand tertiary treatment is required (big
agglomeration) with N and P removal
- Problems to get SWWTP with performance to fulfil legislation
(especially N tot, P tot)
- And yet, for existing facilities septic tanks can remain until the first
reconstruction

11. PROBLEMS IN SLOVENIA DEALING WITH
Small WWTP ≥50 PE and < 2.000 PE and IAS
Question often asked to us, operators at utility companies:
What is the better solution for rural areas:
- good secondary treatment with carbon removal and
ammonium oxidation which we can achieve
- or almost unattainable tertiary treatment by removing
phosphorus and nitrogen to very ‘’hard-to-reach’’ values
- is the removal of carbon and phosphorus alone sufficient to
prevent eutrophication?
We were told eutrophication can be prevented by removing
one of the necessary nutrients, such as phosphorus.
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12. Thank you for you attention!
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